JP4095878B2 - Battery management system, battery pack, and charge state measuring method thereof - Google Patents

Description

【０１０６】
その他の基準充電状態、例えば満充電状態100％、10％、及び完全放電状態0％についても、同様な表がメモリ6aにより記憶される。表1のように、基準充電状態に対応する電池電圧、放電電流、及び電池温度の組を示す表を、以下、放電特性表という。
表1に示される放電特性表では、一つの基準充電状態に対し、放電電流Iと電池温度Tとのそれぞれの所定範囲ごとに、セル当たりの電池電圧Vの基準値が一つずつ設定される。
【０１０７】
図2は、二次電池ブロック1の放電期間中、電池管理システム2により測定された電池電圧Vと充電状態とのそれぞれについて、放電電気量の増大に伴う変化を示すグラフである。図2の(a)は二次電池ブロック1での電池電圧Vと放電電気量との関係（すなわち放電曲線）を示す。図2の(b)は充電状態の測定値と放電電気量との関係を示す。
図2では、二次電池ブロック1の放電期間中、放電電流Iと電池温度Tとが過大な変動を示さず、比較的安定しているときを想定する。電池電圧Vはそのとき、図2の(a)に示されるように、放電電気量の増大に伴いほぼ単調に低下する。
【０１０８】
図2の(a)では、二次電池ブロック1の放電曲線が、初期（充放電サイクル数＝0サイクル）では破線で、充放電サイクル数＝250サイクルでは実線で、それぞれ示される。ここで、両方の放電曲線では放電期間中の放電電流と電池温度との変動が実質的に一致する、と想定される。
以下、説明の簡明化を目的として、放電が満充電状態100％から完全放電状態0％まで連続に実行されるときを想定する。更に、基準充電状態としては、第一の基準充電状態（満充電状態）100％、第二の基準充電状態10％、及び第三の基準充電状態（完全放電状態）0％だけを考慮する。
【０１０９】
充電状態修正部6eは、二次電池ブロック1の放電開始時、電池状態監視部6bを通し、電池電圧V、放電電流I、及び電池温度Tを計測する。それにより、それらの測定値の組（V，I，T）が第一の基準充電状態100％に対応する放電特性表中の基準値の組のいずれかと一致するか否か、を確認する。具体的には例えば、それらの基準値の組の中から放電電流と電池温度との測定値を含む組（VA，I，T）を探し、その組に含まれる電池電圧の基準値（第一の基準電圧値）VAと電池電圧の測定値Vとを比較する。それらが実質的に一致するとき、充電状態修正部6eは二次電池ブロック1の充電状態Sを第一の基準充電状態100％に設定する。図2に示されるこの設定時点Aを、以下、第一の確定点という。
充電状態修正部6eは更に、二次電池ブロック1の放電容量を第一の確定点Aでの残存容量として設定する。ここで、メモリ6aには、二次電池ブロック1の放電容量として製造時での値（初期値）が予め記憶される。
【０１１０】
第一の基準充電状態は満充電状態100％より低い値に設定されても良い。そのとき、第一の確定点での残存容量が放電容量と第一の基準充電状態との積に設定され、充電状態の計測が満充電状態100％より低い値から開始される。
【０１１１】
充電状態計測部6dは第一の確定点A以降、第一の確定点Aでの残存容量と、電池電流積算部6cにより計測される放電電気量との差から充電状態Sを計測する。
初期の二次電池ブロック1では放電電気量の増大に伴い、電池電圧の測定値Vが図2の(a)に示される破線に沿って降下する。一方、充電状態の測定値Sが図2の(b)に示されるように、第一の確定点Aから直線的に減少する。
【０１１２】
充電状態修正部6eは、第一の確定点A以降、電池状態監視部6bを通し、電池電圧V、放電電流I、及び、電池温度Tを監視する。更に、それらの測定値の組（V，I，T）が第二の基準充電状態10％に対応する放電特性表中の基準値の組のいずれかと一致するか否か、を確認する。具体的には例えば、それらの基準値の組の中から放電電流と電池温度との測定値を含む組（VB，I，T）を探し、その組に含まれる電池電圧の基準値（第二の基準電圧値）VBと電池電圧の測定値Vとを比較する。それらが実質的に一致するとき、充電状態修正部6eは充電状態の測定値Sを第二の基準充電状態10％で置換する。この置換時点を、以下、第二の確定点という。図2では点Bが、初期の二次電池ブロック1の放電での第二の確定点を表す。この置換により、充電状態の測定値Sの誤差が修正される。
【０１１３】
充電状態修正部6eは更に、放電容量と第二の基準充電状態10％との積を第二の確定点Bでの残存容量として設定する。充電状態計測部6dは第二の確定点B以降、第二の確定点Bでの残存容量と放電電気量との差から充電状態Sを計測する。
第二の確定点B以降、電池電圧V、放電電流I、及び電池温度Tの測定値の組（V，I，T）が第三の基準充電状態（完全放電状態）0％に対応する放電特性表中の基準値の組のいずれかと一致するか否か、を充電状態修正部6eは確認する。具体的には例えば、それらの基準値の組の中から放電電流と電池温度との測定値を含む組（VC，I，T）を探し、その組に含まれる電池電圧の基準値（放電終止電圧値）VCと電池電圧の測定値Vとを比較する。それらが実質的に一致するとき、充電状態修正部6eは充電状態の測定値Sを完全放電状態0％で置換し、二次電池ブロック1の放電を停止する。この時点を以下、第三の確定点という。図2では点Cが初期の二次電池ブロック1の放電での第三の確定点を表す。この置換により、充電状態の完全放電状態への到達時点が正確に検知される。
【０１１４】
例えば充放電サイクル数が増大するとき、又は、特にリチウムイオン二次電池では高温下で高充電状態に長期間維持されるとき、二次電池は劣化する。劣化した二次電池では、放電容量が初期値より低減し、放電曲線の形状が初期のものから大きくずれる。
例えば充放電サイクル数＝250サイクルの放電曲線（図2の(a)の実線）では、初期の放電曲線（図2の(a)の破線）より、放電の開始（第一の確定点A）から終止（電池電圧V＝放電終止電圧VC）までの放電期間全体での放電電気量が低減する。すなわち、初期の二次電池ブロック1の第三の確定点Cまでの放電電気量をQ4とし、劣化した二次電池ブロック1の第三の確定点CPまでの放電電気量をQ2とするとき、Q2＜Q4。更に、放電開始時からの一定の放電電気量に対する電池電圧が降下する。その上、放電開始時では電池電圧の降下が急激になり、放電終止時では逆に電池電圧の降下が緩やかになる。その結果、劣化した二次電池ブロック1では、図2の(a)に示されるように、第二の確定点は点BPまで、第三の確定点は点CPまでそれぞれ早まり、それぞれの確定点までの放電電気量が低減する。すなわち、初期の二次電池ブロック1の第二の確定点Bまでの放電電気量をQ3とし、劣化した二次電池ブロック1の第二の確定点BPまでの放電電気量をQ1とするとき、Q1＜Q3である。更に、第二の確定点までの放電電気量の差（点B−点BP間の距離＝Q3−Q1）は第三の確定点までの差（点C−点CP間の距離＝Q4−Q2）より大きい。従って、劣化した二次電池ブロック1の放電では、特に第二の確定点BPでの実際の充電状態が第二の基準充電状態10％から増大する。
【０１１５】
放電特性表補正部6gは二次電池ブロック1の放電ごとに、第一の確定点Aから第二の確定点BPまでの放電期間での放電電気量Q1と、第一の確定点Aから第三の確定点CPまでの放電期間での放電電気量Q2とを記憶する。更に、それらの放電電気量Q1とQ2とに基づき、放電特性表を次のように補正する。以下、放電特性表の補正及びその効果の説明を目的として、劣化した二次電池ブロック1に対し、放電容量の初期値と初期の放電特性表とで充電状態を計測しかつ修正する場合を想定する。
【０１１６】
充電状態計測部6dは二次電池ブロック1の放電容量を初期値に設定し、充電状態を計測する。従って、充電状態の測定値Sは放電開始から第二の確定点までの期間では、図2の(b)に太い実線で示されるように直線A−Bに沿って減少する。
図2の(a)に示されるように、放電開始時、劣化した二次電池ブロック1では電池電圧V（実線）が初期での電池電圧（破線）より急速に降下する。従って、第二の確定点BPが初期でのものBより早い。その結果、容量跳びが、図2の(b)の点B1−点B2間で示されるように生じる。
【０１１７】
図2の(b)に示されるように、第三の確定点CPより前に、充電状態の測定値Sが第三の基準充電状態の値0％まで降下する。そのとき、充電状態修正部6eは充電状態の測定値Sを第三の基準充電状態0％よりわずかに高い値（例えば1％）に固定する。充電状態修正部6eは第三の確定点CPを検出したとき、充電状態の測定値Sを完全放電状態0％とする。そのとき、制御部6は第一のスイッチ7aをオフし、放電電流を遮断する。
【０１１８】
第一の確定点Aから第三の確定点CPまでの放電期間で、放電容量計測部6fは放電電気量の総量Q2を算定する。更に、その総量Q2で放電容量を更新する。次の放電では、充電状態計測部6dがその更新された放電容量に基づき充電状態を計測する。
この放電容量の学習により、図2の(b)の例では、充電状態の測定値Sを示す太い実線の傾き（すなわち直線A−Cの傾き）が、次の放電では一点鎖線で示される傾き（すなわち直線A−CPの傾き）に修正される。それにより、例えば第二の確定点BPでの容量跳び（図2の(b)の点B1a−点B2間参照）が低減する。
【０１１９】
放電特性表補正部6gは、第一の確定点Aから第二の確定点BPまでの放電期間中での放電電気量Q1（以下、第一の放電電気量という）と、第一の確定点Aから第三の確定点CPまでの放電期間中での放電電気量Q2（以下、第二の放電電気量という）とを記憶する。更に、第一の放電電気量Q1と第二の放電電気量Q2とに基づき放電特性表を次のように補正する。
【０１２０】
第一の放電電気量Q1を第一の基準充電状態100％から第二の基準充電状態10％までの間での放電電気量とみなし、放電容量（すなわち満充電状態100％から完全放電状態0％までの間の放電電気量）を次式で換算する：QA＝Q1／(100−10)×100。この換算された放電容量QAを第一の換算放電容量という。
同様に、第二の放電電気量Q2に基づき、第二の換算放電容量QBを次式で定義する：QB＝Q2／(100−0)×100（＝Q2)。
【０１２１】
放電特性表が実際の放電曲線を良く近似するとき、第一の換算放電容量QAと第二の換算放電容量QBとは実質的に一致する。すなわち、第一の換算放電容量QAと第二の換算放電容量QBとの差は放電特性表の実際の放電曲線からのずれを表す。
放電特性表補正部6gは第一の換算放電容量QAと第二の換算放電容量QBとの差に基づき放電特性表を補正する。例えば、第一の換算放電容量QAが第二の換算放電容量QBより大きいとき（QA＞QB)、第二の基準電圧VBを所定の補正量だけ上げ、逆のとき（QA＜QB）は下げる。
【０１２２】
図2の(b)では、第一の換算放電容量QAは直線A−B2と横軸との交点で定まる放電電気量に等しく、第二の換算放電容量QBは直線A−CPと横軸との交点で定まる放電電気量Q2に等しい。従って、第一の換算放電容量QAは第二の換算放電容量QBより小さい（QA＜QB)。そのとき、放電特性表補正部6gは放電特性表中の第二の基準電圧VBを、例えば1mVだけ下げる。この補正された基準電圧を、以下、修正基準電圧VB1という：VB1＝VB−1mV。
次回の放電で放電電流と電池温度とが前回の放電と同様な変動を示すとき、電池電圧Vが第一の基準電圧VAから第二の基準電圧VBを超え、修正基準電圧VB1まで降下するとき、充電状態修正部6eは第二の確定点BQを検出する。すなわち、第二の確定点が図2の(a)の点BPから点BQまで遅れる。それにより、容量跳び（図2の(b)の点B3−点B4間の距離）が前回の放電での容量跳び（点B1−点B2間の距離）より低減する。
こうして、制御部6は放電容量の学習及び換算放電容量に基づく放電特性表の補正により、充電状態の測定精度を向上できる。
【０１２３】
上記の説明では、充放電サイクル数＝250サイクルの二次電池ブロック1に対し放電容量の初期値と初期の放電特性表とで充電状態を計測しかつ修正する場合が想定される。放電容量の学習と放電特性表の補正とを250サイクルより小さい充放電サイクル数から開始するとき、二次電池ブロック1の劣化による放電曲線のずれが図2の(a)に示されるものよりかなり小さいので、充電状態の測定精度は高い。特に、容量跳びは図2の(b)に示されるものよりかなり小さく抑えられる。
更に、上記の説明では、基準充電状態が三つだけ設定される。基準充電状態を更に多く設定することにより、充電状態の測定精度を更に向上できる。
【０１２４】
前回の放電終了時から次回の放電開始時までの期間が長いとき、又は放電がその終了前に長期間中断するとき、二次電池ブロック1は一般に劣化する。特にリチウムイオン二次電池では、高温下で高充電状態に長期間維持されるとき劣化が著しく進行する。その結果、二次電池ブロック1の放電特性が比較的大きく変化し、前回の放電で学習された放電容量及び放電特性表による充電状態の測定精度が比較的大きく低下する。
【０１２５】
放電容量計測部6fは放電特性のそのような比較的大きな変化に関わらず、放電容量の学習精度を次のように高く維持する。
図3は、二次電池ブロック1の放電容量と放電特性とが学習されたものから比較的大きくずれるとき、放電電気量の増大に伴う充電状態の測定値Sの変化を示すグラフである。図3の(a)は二次電池ブロック1について、劣化前の放電曲線を実線で、劣化後の放電曲線を破線で、それぞれ示す。図3の(b)は充電状態の測定値Sと放電電気量との関係を示す。図3では、二次電池ブロック1の放電期間中、放電電流Iと電池温度Tとが過大な変動を示さず、電池電圧Vが放電電気量の増大に伴いほぼ単調に低下するときを想定する。更に、放電期間中の放電電流と電池温度との変動が劣化前後の放電の間で実質的に一致する、と想定される。
【０１２６】
図3の(a)に実線で示される劣化前の放電曲線に基づき、放電容量と放電特性表とが学習される。その放電特性表は、第一の基準充電状態100％、第二の基準充電状態10％、第三の基準充電状態5％、第四の基準充電状態2％、及び第五の基準充電状態0％のそれぞれに対する確定点A〜Eでの電池状態、特に第一の基準電圧VA、第二の基準電圧VB、第三の基準電圧VC、第四の基準電圧VD、及び第五の基準電圧（放電終止電圧）VEをそれぞれ含む。
【０１２７】
前回の放電から次回の放電までの間に長時間が経過し、その間に二次電池ブロック1の劣化が進行するとき、次回の放電では電池電圧Vは図3の(a)に破線で示される放電曲線に沿って降下する。その結果、電池電圧Vが第一の基準電圧VAから第二の基準電圧VBまで早く降下し、第二の確定点が早まる（図3の(a)の点B−点BR間参照)。それにより、充電状態の測定値Sには、図3の(b)の点B1−点B2間に示されるような容量跳びが生じる。
それ以後、電池電圧Vが第三の基準電圧VCまで降下し、第三の確定点CRが検出される前に、充電状態の測定値Sが第三の基準充電状態の値5％まで低下する（図3の(b)の点C1)。従って、第三の確定点CRまで充電状態の測定値Sが第三の基準充電状態の値5％に固定される（図3の(b)の点C1−点C2間参照)。同様に、充電状態の測定値Sは、図3の(b)の点D1−点D2間では第四の基準充電状態の値2％に、点E1−点E2間では第五の基準充電状態の値0％よりわずかに高い値1％に、それぞれ固定される。
【０１２８】
放電容量計測部6fは電池電流積算部6cによる放電電流Iの積算を、充電状態の測定値Sの固定期間（例えば図3の(b)の点C1−点C2間、点D1−点D2間、及び点E1−点E2間）でも継続させる。
電池電圧Vが放電終止電圧VEまで降下するとき、又は放電から充電への切替がホストHから通知されるとき、放電容量計測部6fは電池電流積算部6cによる放電電流Iの積算を停止する。更に、その停止時までの放電電流Iの積算値（放電電気量）とその停止時での充電状態の測定値Sとに基づき放電容量を換算し、その換算値で放電容量を更新する。
【０１２９】
例えば、図3の(b)で、充電状態の測定値Sが第四の基準充電状態の値2％に固定される期間（点D1−点D2間）中に放電が充電に切り替えられるとき（点M)、放電開始時から充電への切替時までの放電電気量と、その充電への切替時での充電状態の測定値Sすなわち第四の基準充電状態の値2％とで、放電容量が換算される。その換算値は図3の(b)で直線A−Mと横軸との交点Nに相当する。
充電への切替時点Mでは充電状態の測定値Sは第四の基準充電状態の値2％に固定され、その正確な値は不明である。しかし、図3の(b)から明らかなように、その換算値Nは実際の放電容量E2を良く近似する。特に、第三の基準充電状態5％に対する確定点C2での放電電気量と第三の基準充電状態5％とに基づき放電容量を換算するときより、換算値の誤差が小さい。
こうして、前回の放電から次回の放電までの間に長時間が経過し、その間に二次電池ブロック1の劣化が進行するときでも、放電容量計測部6fは放電容量の学習精度を高く維持できる。
【０１３０】
上記の制御部6による充電状態の計測の具体的な手順は、例えば以下の通りである。図4は、制御部6による充電状態の計測を示すフローチャートである。
以下、説明の簡明化を目的として、放電特性表が、第一の基準充電状態（満充電状態）SR(0)＝100％、第二の基準充電状態SR(1)＝10％、及び第三の基準充電状態（完全放電状態）SR(2)＝0％の三つの基準充電状態に対し、第一の基準電圧VA、第二の基準電圧VB、及び第三の基準電圧（放電終止電圧）VCをそれぞれ含むときを想定する。
【０１３１】
＜ステップS1＞
放電開始時、二次電池ブロック1が満充電状態であることを、制御部6はセンサ群3〜5を通し確認する。その確認は具体的には例えば次のように行われる。
図5は、制御部6による満充電状態の確認を示すフローチャートである。
＜ステップS21＞
センサ群3〜5により、二次電池ブロック1に対し、電池電圧V、放電電流I、及び電池温度Tが検出される。
＜ステップS22＞
放電電流の測定値Iと電池電圧の測定値Tとを含む満充電状態100％に対応する基準値の組（VA，I，T）が、放電特性表から読み出される。
＜ステップS23＞
電池電圧Vと第一の基準電圧VAとが比較される。電池電圧Vが第一の基準電圧VAを含む所定の範囲を超えて高いとき（V≫VA)、処理はステップS24へ分岐する。電池電圧Vが第一の基準電圧VAと実質的に等しいとき（V＝VA)、すなわち上記の所定の範囲内に収まるとき、処理はステップS26へ分岐する。電池電圧Vが上記の所定の範囲より低いとき（V≪VA)、処理はステップS28へ分岐する。
【０１３２】
＜ステップS24＞
電池電圧Vが第一の基準電圧VAより異常に高いので、制御部6は放電電流Iを遮断し、放電を中止させる。
＜ステップS25＞
電池電圧Vが異常に高いことを制御部6はホストHへ通知し、充電状態の計測を中止する。
＜ステップS26＞
電池電圧Vが第一の基準電圧VAと実質的に等しいとき（V＝VA)、充電状態の測定値Sは満充電状態100％に設定される。
＜ステップS27＞
二次電池ブロック1の残存容量QRは所定の放電容量QFに設定される。
＜ステップS28＞
電池電圧Vが第一の基準電圧VAより極端に低いとき（V≪VA)、正確な充電状態は不明である。従って、充電状態の測定値Sは仮に、第二の基準充電状態SR(1)＝10％に設定される。
＜ステップS29＞
二次電池ブロック1の残存容量QRは放電容量QFと第二の基準充電状態SR(1)＝10％との積に設定される：QR＝QF×SR(1)＝QF×0.10。
ステップS26とS27又はステップS28とS29により充電状態の測定値Sと残存容量QRとが設定され、満充電状態の確認のステップS1が終了する。以下、処理は図4のフローチャートへ戻る。
【０１３３】
＜ステップS2＞
整数値変数iが1に初期化される。
＜ステップS3＞
放電電気量Qが0に初期化され、次の修正目標の基準充電状態SRが第(i＋1)の基準充電状態SR(i)に設定される。
＜ステップS4＞
第iの基準充電状態SR(i−1)から第(i＋1)の基準充電状態SR(i)までの範囲で、充電状態の計測が次のように行われる。
図6は、ステップS4による充電状態の計測を示すフローチャートである。
＜ステップS41＞
放電電流Iが流れているか否かがチェックされる。放電電流Iが流れていないときは処理がステップS42へ分岐する。放電電流Iが流れているときは処理がステップS43へ分岐する。
＜ステップS42＞
電池電流が充電の向きに流れているか否か、又は放電から充電への切替がホストHから通知されるか否か、がそれぞれチェックされる。それにより充電への切替が検知されるとき、ステップS4が終了し、図4のフローチャートのステップS5へ処理が分岐する。それ以外のとき、処理がステップS41へ戻る。
【０１３４】
＜ステップS43＞
センサ群3〜5により、電池電圧V、放電電流I、及び電池温度Tが検出される。
＜ステップS44＞
放電電流のサンプルIとサンプリングの時間間隔Δt（＝約2秒）との積が放電電気量Qに加算される：Q＝Q＋I×Δt。
＜ステップS45＞
残存容量QR、放電電気量Q、及び放電容量QFから充電状態の候補値S1が換算される：S1＝(QR−Q)／QF。
＜ステップS46＞
放電電流の測定値Iと電池電圧の測定値Tとを含む修正目標の基準充電状態SRに対応する基準値の組（VR，I，T）が、放電特性表から読み出される。
＜ステップS47＞
電池電圧Vが修正目標の基準電圧VRと比較される。電池電圧Vが基準電圧VRより大きいとき（V＞VR)、処理がステップS48へ分岐する。それ以外のとき、処理がステップS51へ分岐する。
【０１３５】
＜ステップS48＞
充電状態の候補値S1が修正目標の基準充電状態SRと比較される。
＜ステップS49＞
充電状態の候補値S1が修正目標の基準充電状態SRより大きいとき（S1＞SR)、充電状態の測定値Sとして充電状態の候補値S1が選択される（ステップS49A)。
それ以外のとき、充電状態の測定値Sとして修正目標の基準充電状態SRが選択される（ステップS49B)。それにより、電池電圧Vが修正目標の基準電圧VRまで降下する前に充電状態の候補値S1が修正目標の基準充電状態の値SRまで低下するとき、充電状態の測定値Sがその基準充電状態の値SRに固定される。
＜ステップS50＞
電池電圧V、放電電流I、電池温度T、及び充電状態の測定値Sを含む電池状態がホストHへ通知される。
以下、処理はステップS41へ戻る。
＜ステップS51＞
電池電圧Vが修正目標の基準電圧VRまで降下し、すなわち放電時間が修正目標の基準充電状態SRに対する確定点に達する。そのとき、充電状態の測定値Sが修正目標の基準充電状態SRで置換される：S＝SR。
＜ステップS52＞
電池電圧V、放電電流I、電池温度T、及び充電状態の測定値Sを含む電池状態がホストHへ通知され、ステップS4が終了する。
以下、処理は図4のフローチャートへ戻る。
【０１３６】
＜ステップS5＞
放電開始時から前回の修正目標の基準充電状態すなわち第iの基準充電状態SR(i−1)に対する確定点（第iの確定点）までの期間で積算された放電電気量（第(i−1)の放電電気量）をQ(i−1)とする。その第(i−1)の放電電気量Q(i−1)にステップS4終了時の放電電気量Qを加算し、放電開始時から第(i＋1)の基準充電状態SR(i)に対する確定点（第(i＋1)の確定点）までの期間で積算された放電電気量（第iの放電電気量）Q(i)とみなす：Q(i)＝Q(i−1)＋Q。ここで、i＝1のとき、Q(0)＝0とする。
＜ステップS6＞
修正目標の基準充電状態SRが完全放電状態0％であるか否か、又は、放電から充電への切替が検知されたか否か、がチェックされる。それらの判断のいずれかが肯定的であるとき、処理はステップS9へ分岐する。それ以外のとき、処理はステップS7へ分岐する。
＜ステップS7＞
放電容量QFと修正目標の基準充電状態SRとの積を第(i＋1)の確定点での残存容量QRとして設定する：QR＝QF×SR。
＜ステップS8＞
整数値変数iを1だけ増やし、処理をステップS3へ戻す。
【０１３７】
＜ステップS9＞
制御部6は放電電流Iを遮断し、放電を停止する。
＜ステップS10＞
放電停止時の整数値変数iについて、第iの放電電気量Q(i)を新たな放電容量として設定する。
＜ステップS11＞
第一の換算放電容量QAと第二の換算放電容量QBとをそれぞれ次式で算定する：QA＝Q(1)／(SR(0)−SR(1))、QB＝Q(2)／(SR(0)−SR(2))。
＜ステップS12＞
第一の換算放電容量QAと第二の換算放電容量QBとを比較する。
＜ステップS13＞
第一の換算放電容量QAが第二の換算放電容量QBより大きいとき（QA＞QB)、第二の基準電圧VBを1mVだけ下げる：VB＝VB−1mV（ステップS13A)。逆に、第一の換算放電容量QAが第二の換算放電容量QBより小さいとき（QA＜QB)、第二の基準電圧VBを1mVだけ上げる：VB＝VB＋1mV（ステップS13B)。第一の換算放電容量QAが第二の換算放電容量QBと実質的に等しいとき（QA＝QB)、第二の基準電圧VBをそのまま維持する：VB＝VB（ステップS13C)。
こうして、放電容量の学習（ステップS10）と放電特性表の補正（ステップS11〜13）とを経て、充電状態の計測が終了する。
【０１３８】
図4のフローチャートでは三つの基準充電状態が設定される。その他に、四つ以上の基準充電状態が設定されても良い。そのとき、ステップS11〜13による放電特性表の補正は、好ましくは、満充電状態100％、完全放電状態0％、及びそれらの間のいずれか一つの基準充電状態について行われる。その他に、特に放電深度が浅いときは、完全放電状態0％以外の三つの基準充電状態の組合せについて行われても良い。いずれの場合も、真ん中の基準充電状態に対応する基準電圧が補正される。
更に、全ての基準充電状態について換算放電容量をそれぞれ求め、それらの平均値に対するそれぞれの換算放電容量のずれからそれぞれの基準電圧の補正量を決定しても良い。
【０１３９】
（参考例１）
図７は、参考例１による電池パック１０Ａを示すブロック図である。図７では、実施例１による電池パック１０と同様な構成要素に対し、図１と同じ符号を付す。更に、それらの同様な構成要素の説明は実施例１でのものを援用する。
【０１４０】
制御部6Aは例えばメモリ6aに記憶されたファームウェアを実行し、実施例１と同様な電池状態監視部6b、電池電流積算部6c、及び放電容量計測部6fとしての機能に加え、充電状態計測部6j、内部抵抗計測部6h、及び内部抵抗補正部6iとしての機能を発揮する。
【０１４１】
放電容量計測部6fは実施例１と同様、放電開始時から終了時までの放電電気量の総量を算定する。更に、その総量から放電終了時での充電状態の測定値に基づき、放電容量を換算し、その換算値と初期値との比を求める。その比は、後述の内部抵抗補正部6iによる内部抵抗値の補正で、二次電池ブロック1の劣化状態の評価に対し利用される。
【０１４２】
図8は、二次電池ブロック1の充電状態が満充電状態に等しい時点から二次電池ブロック1が放電を開始するとき、その放電開始時近傍での二次電池ブロック1全体の両端電圧と放電時間との関係を示すグラフである。図8に示される実線と破線とはそれぞれ充放電サイクル数＝0サイクルと250サイクルとでの関係を示す。ここで、放電電流の上限は一定に設定され、電池温度は一定の範囲内に維持される。
【０１４３】
図8に示されるように、電池電圧は放電開始直後、一旦急激に降下する。放電開始時点から約20秒以後、電池電圧の降下速度は比較的低い値で安定する。
放電開始時、放電電流がごく小さい間での電池電圧の初期値V_INは二次電池ブロック1の開路電圧V_OCと実質的に等しい。放電電流の急速な増大に伴い、二次電池ブロック1内では内部抵抗による電圧降下が急速に増大する。それにより、電池電圧は初期値V_INから急激に降下する。放電電流が一定値まで増大し、安定すると共に、電池電圧の降下が緩み、安定する。
このように、電池電圧の放電開始直後での急激な降下は主に二次電池の内部抵抗に起因する。それ故、この急激な降下はＩＲドロップと呼ばれる。
【０１４４】
内部抵抗計測部6hは電池状態監視部6bを通し、放電開始時の電池電圧と放電電流とを監視する。それにより、例えばＩＲドロップでの電圧降下量と放電電流の平均値とを計測し、それらの比を二次電池の内部抵抗とみなす。又は、ＩＲドロップの期間中、所定の時間間隔で電圧降下量と放電電流とをサンプリングし、それぞれのサンプルごとの比を内部抵抗のサンプルとし、それらのサンプルの平均を内部抵抗とみなしても良い。
【０１４５】
図8に示される実線（充放電サイクル数＝0サイクル）と破線（250サイクル）との比較から明らかなように、充放電サイクル数が大きいほど、ＩＲドロップによる電圧降下は増大する。その主な原因は、充放電サイクル数の増大に伴い二次電池が劣化し、内部抵抗が増大するからである、と考えられる。
図9は、内部抵抗と充放電サイクル数との関係を示すグラフである。このように、充放電サイクル数の増大に伴い、内部抵抗は増大する。
内部抵抗計測部6hは二次電池ブロック1の放電ごとに内部抵抗を計測する。それにより、二次電池ブロック1の劣化に伴う内部抵抗の変化を学習し、内部抵抗の測定精度を高く維持する。
【０１４６】
内部抵抗計測部6hは更に、上記の内部抵抗の学習ごとに、その新たな内部抵抗値と初期の二次電池ブロック1での内部抵抗値（以下、内部抵抗の初期値という）との比を求める。その比は、後述の内部抵抗補正部6iによる内部抵抗値の補正で、二次電池ブロック1の劣化状態の評価に対し利用される。
【０１４７】
内部抵抗の測定値が所定の閾値を超えるとき、内部抵抗計測部6hはホストHへ電池電流の低減を要求するための信号を送出しても良い。
内部抵抗の異常な増大は放電電流によるジュール熱を過大にするので、二次電池ブロック1で過熱が生じやすい。内部抵抗に対する上記の閾値は好ましくは、二次電池ブロック1の安定性が失われ、例えば熱暴走が生じ得る温度より電池温度が十分に低く維持されるように設定される。それにより、過熱による二次電池ブロック1の劣化又は熱暴走が生じる前に、ホストHは放電電流を十分に低減できる。特に、過熱の発生時での放電電流の強制的な遮断が回避されるので、ホストHの突然のシャットダウンが防止される。
【０１４８】
メモリ6aは、二次電池ブロック1について開路電圧と充電状態との関係を示す開路電圧特性表を記憶する。図10はその関係を示すグラフである。
二次電池の開路電圧は電池電圧と内部抵抗による電圧降下量との和であり、二次電池の起電力と実質的に等しい。従って、開路電圧は充電状態で実質的に決まる。特に、一定の充電状態での開路電圧は二次電池の劣化に依らず実質的に一定である。
【０１４９】
電池状態監視部6bは、二次電池ブロック1の放電期間中、電池電圧V、放電電流I、及び電池温度Tを所定の時間間隔でサンプリングする。充電状態計測部6jはそれらのサンプルと、内部抵抗計測部6hにより放電開始時に計測された内部抵抗とから、それぞれのサンプリング時点での開路電圧を算定する。更に、開路電圧特性表を参照し、算定された開路電圧に対応する充電状態を決定する。こうして、二次電池ブロック1の放電期間中、充電状態が計測される。
開路電圧特性表は二次電池ブロック1の劣化に関わらず実質的に不変であるので、充電状態計測部6jによる充電状態の測定精度は二次電池の劣化に依らず、高く維持される。
【０１５０】
内部抵抗計測部6hによる内部抵抗の計測は放電開始時に行われる。しかし、内部抵抗は厳密には充電状態に依存する。
図11は、二次電池ブロック1の内部抵抗と充電状態との関係を示すグラフである。図11に示される実線と破線とはそれぞれ、充放電サイクル数＝0サイクルと300サイクルとでの関係を示す。ここで、放電電流と電池温度とはそれぞれ一定に維持される。
図11に実線で示されるように、充放電サイクル数が十分に小さいとき、内部抵抗の充電状態による変化は十分に小さく、内部抵抗は実質的に一定である。しかし、図11に破線で示されるように、充放電サイクル数が増大するとき、内部抵抗は充電状態の低下と共に増大する。このような充放電サイクル数の増大に伴う内部抵抗と充電状態との関係の変化は、二次電池の劣化によるものと考えられる。
【０１５１】
内部抵抗補正部6iは以下のように、二次電池ブロック1の劣化状態に応じ、内部抵抗計測部6hにより計測された内部抵抗を補正する。その補正は特に、充電状態の小さい領域で内部抵抗を増大させる。
内部抵抗補正部6iは放電容量計測部6fから、学習された放電容量の初期値に対する比（以下、学習放電容量比という）を入力する。二次電池ブロック1の劣化が進むほど、学習放電容量比は小さい。その他に、内部抵抗補正部6iは内部抵抗計測部6hから、学習された内部抵抗値の初期値に対する比（以下、学習内部抵抗比という）を入力する。二次電池ブロック1の劣化が進むほど、学習内部抵抗比は大きい。
【０１５２】
内部抵抗補正部6iは学習放電容量比又は学習内部抵抗比に応じ、例えば所定の低い充電状態の領域に対し、内部抵抗値を一律に増大させる。
具体的には例えば、20％以下の充電状態に対し、学習放電容量比が95％以上、80〜95％、及び60〜80％のそれぞれの範囲内に含まれるとき、内部抵抗値の補正率をそれぞれ、1.00、1.20、及び1.40と設定する。
学習内部抵抗比については、20％以下の充電状態に対し、学習内部抵抗比が105％以下、105〜120％、及び120〜140％のそれぞれの範囲内に含まれるとき、内部抵抗値の補正率をそれぞれ、1.00、1.20、及び1.40と設定する。
【０１５３】
充電状態が20％以下であることが予測されるとき、充電状態計測部6jは上記の補正率と内部抵抗値との積を改めて内部抵抗値とみなし、開路電圧を算定する。こうして、劣化した二次電池ブロック1での充電状態の低下に伴う内部抵抗の増大が充電状態の計測に反映される。その結果、開路電圧の計算誤差が低減し、充電状態の測定精度が向上する。
【０１５４】
制御部6Aによる充電状態の計測の具体的な手順は例えば以下の通りである。 図12は、制御部6Aによる充電状態の計測を示すフローチャートである。
ここで、二次電池ブロック1は一旦満充電状態まで充電され、その充電完了から十分に時間が経過した後、放電が開始されるときを想定する。特に、放電開始時では二次電池ブロック1は満充電状態に安定に維持される。
＜ステップS61＞
放電開始時、ＩＲドロップの検出を通し、内部抵抗IRが計測される。
内部抵抗IRの計測は具体的には、次の二つの方法のいずれかで行われる。
【０１５５】
図13は、内部抵抗IRの第一の計測方法を示すフローチャートである。
＜ステップS71＞
放電開始直後の電池電圧の初期値V_INを計測し、記録する。
＜ステップS72＞
センサ群3〜5により、二次電池ブロック1に対し、電池電圧V、放電電流I、及び電池温度Tが検出される。
＜ステップS73＞
放電電流Iが所定の閾値I_TH（例えば約300mA）を超えるまで増大したか否か、をチェックする。放電電流Iが閾値I_THを超えない間は、内部抵抗IRによる電圧降下量が計測に対し過小だからである。放電電流Iが閾値I_THを超えないとき（I＞I_TH)処理はステップS74へ分岐する。逆に、放電電流Iが閾値I_THを超えるとき（I＜I_TH)処理はステップS75へ分岐する。
＜ステップS74＞
放電開始から所定時間（例えば約16秒）が経過したか否かをチェックする。正常な放電ではＩＲドロップがその所定時間内に終了する。従って、放電電流Iが閾値I_THを超えない内にその所定時間が経過したとき、何らかの異常が発生したものとみなせる。そのとき、制御部6は内部抵抗の計測を終了する。それ以外のときは、処理がステップS72へ戻る。
【０１５６】
＜ステップS75＞
ステップS72で計測された電池電圧Vと放電電流Iとが記録される。
＜ステップS76＞
放電開始から所定時間（例えば約16秒）が経過したか否かをチェックする。その所定時間が経過するまで、処理はステップS72〜76のループを所定の時間間隔で反復する。それにより、電池電圧Vと放電電流Iとの対が複数記録される。
上記の所定時間が経過したとき、処理はステップS77へ分岐する。
＜ステップS77＞
放電開始後、約10秒が経過した時点から約16秒が経過した時点までの間、電池電圧Vと放電電流Iとの記録が反復される。記録されたサンプル全体で、電池電圧Vと放電電流Iとがそれぞれ平均され、平均値V_AVとI_AVとが算定される。
＜ステップS78＞
電池電圧の初期値V_IN、電池電圧の平均値V_AV、及び放電電流の平均値I_AVに基づき内部抵抗IRが次式で算定される：IR＝(V_IN−V_AV)／I_AV。
【０１５７】
図14は、内部抵抗IRの第二の計測方法を示すフローチャートである。図14では第一の計測方法と同様なステップには図13と同じ符号を付し、それら同様なステップの説明は第一の計測方法でのものを援用する。
＜ステップS81＞
電池電圧Vが所定の閾値V_THより高く維持されるか否か、をチェックする。放電開始直後、二次電池ブロック1は実質的に満充電状態に維持されるはずである。従って、電池電圧Vは十分に高く維持されるべきである。もし、放電開始からあまり時間が経過しない内に電池電圧Vが上記の閾値V_THより降下すれば、何らかの異常が生じたものとみなせる。それ故、電池電圧Vが上記の閾値V_TH以下であるとき（V＜V_TH)、内部抵抗の計測は終了する。それ以外のとき、処理はステップS73へ分岐する。
【０１５８】
＜ステップS82＞
放電開始から所定の時間間隔（例えば約2秒間隔）で、電池電圧Vと放電電流Iとが計測され、記録される。その記録はn回（正整数nは好ましくは2以上である）続けて反復される。
＜ステップS83＞
ステップS82で記録されたn個の放電電流のサンプルI(1)、I(2)、…、I(n)について、それぞれが所定の閾値I_THを超えたか否か、をチェックする。それらのサンプルI(1)、I(2)、…、I(n)が全て所定の閾値I_THを超えるまで、処理はステップS72、S81、S73、及びS82から成るループを反復する。
ステップS82で記録されたn個の放電電流のサンプルI(1)、I(2)、…、I(n)が全て閾値I_THを超えたとき、処理はステップS84へ分岐する。
＜ステップS84＞
電池電圧の初期値V_IN、及びステップS82で記録された電池電圧Vと放電電流Iとのn対のサンプル（V(1)，I(1))、（V(2)，I(2))、…、（V(n)，I(n)）のそれぞれに基づき、n個の内部抵抗値IR(1)、IR(2)、…、IR(n)が次式で算定される：IR(k)＝(V_IN−V(k))／I(k) (k＝1、2、…、n)。更に、それらの平均値が内部抵抗IRとして決定される：IR＝(IR(1)＋IR(2)＋…＋IR(n))／n。
【０１５９】
＜ステップS62＞
センサ群3〜5により、二次電池ブロック1に対し、電池電圧V、放電電流I、及び電池温度Tが検出される。
＜ステップS63＞
電池電圧V、放電電流I、及び内部抵抗IRに基づき、開路電圧V_OCが次式で算定される：V_OC＝V＋I×IR。ここで、好ましくは、電池温度Tに基づき、内部抵抗IRの温度変動による抵抗値の変化が補正される。更に、学習放電容量比又は学習内部抵抗比に基づき、上記の内部抵抗値の補正が行われる。
＜ステップS64＞
開路電圧特性表を参照し、開路電圧V_OCに対応する充電状態Sが決定される。
【０１６０】
参考例１では充電状態の計測が開路電圧のみに基づき行われる。その他に、充電状態の計測を、通常は実施例１のように放電容量と放電電流の積算値とに基づいて行い、特定の電池状態（例えば電池電圧）については参考例１のように開路電圧に基づいて行っても良い。すなわち、特定の電池状態が検出されるとき、充電状態の測定値が開路電圧に対応する値で置換され、修正される。そのとき、充電状態の測定精度を高く維持し、かつ開路電圧特性表のデータ量を低減できる。
【０１６１】
《実施例２》
図１５は、本発明の実施例２による電池パック１０Ｂを示すブロック図である。図１５では、実施例１による電池パック１０及び参考例１による電池パック１０Ａと同様な構成要素に対し、図１及び図７と同じ符号を付す。更に、それらの同様な構成要素の説明は実施例１又は参考例１でのものを援用する。
【０１６２】
制御部6Bは例えばメモリ6aに記憶されたファームウェアを実行し、電池状態監視部6b、電池電流積算部6c、充電状態計測部6d、充電状態修正部6e、放電容量計測部6f、内部抵抗計測部6h、及び内部抵抗補正部6iとしての機能に加え、放電特性表補正部6kとしての機能を発揮する。
【０１６３】
二次電池は例えば充放電サイクル数の増大に伴い劣化するので、その放電特性が放電ごとに変化する。一方、内部抵抗は二次電池の劣化に伴い増大するので、劣化状態は放電ごとの内部抵抗の変化から評価される。
放電特性表補正部6kは、内部抵抗計測部6hによる内部抵抗の学習に基づき、放電特性表中の数値を放電ごとに、次のように補正する。
二次電池ブロック1の開路電圧は電池電圧と内部抵抗による電圧降下量との和である。従って、一定の基準充電状態SRに対応する開路電圧V_OCは、その基準充電状態SRに対応する放電特性表中の電池電圧VR₁、放電電流I、及び電池温度Tの一組と、内部抵抗計測部6hによる内部抵抗の測定値IR₁とで次式(1)を満足する：
【０１６４】
V_OC＝VR₁＋I×(IR₁×α₁)。 (1)
【０１６５】
ここで、係数α₁（以下、第一の温度補正係数という）は、内部抵抗の測定値IR₁を電池温度Tでの値に補正するためのものである。
仮に、二次電池ブロック1の新たな放電の開始時、内部抵抗計測部6hが内部抵抗を元の値IR₁から別の値IR₂へ更新した、と想定する。上記の基準充電状態SRに対応する開路電圧V_OCは二次電池ブロック1の劣化に依らず実質的に一定である。従って、放電電流Iと電池温度Tとをそれぞれ上記の値に維持するとき、開路電圧V_OC、放電電流I、電池温度T、及び新たな内部抵抗IR₂に対応する電池電圧、すなわち修正電池電圧VR₂は、次式(2)を満足すべきである：
【０１６６】
V_OC＝VR₂＋I×(IR₂×α₂)。 (2)
【０１６７】
ここで、係数α₂（以下、第二の温度補正係数という）は、新たな内部抵抗の測定値IR₂を電池温度Tでの値に補正するためのものである。
上記の式(1)と(2)とから放電電流Iを消去するとき、修正電池電圧VR₂は次式(3)により求まる：
【０１６８】
VR₂＝V_OC−(V_OC−VR₁)×{(IR₂／IR₁)×(α₂／α₁)}。 (3)
【０１６９】
以下、内部抵抗値の比と温度補正係数の比とで決まる係数K＝{(IR₂／IR₁)×(α₂／α₁)}を劣化係数という。
放電特性表補正部6kは基準充電状態ごとに、対応する開路電圧を記憶する。更に、初期の二次電池ブロック1の放電特性表、内部抵抗値、及びその温度特性を示す表（以下、温度特性表という）を記憶する。ここで、温度特性表は例えば、放電特性表中の電池温度ごとに、所定温度（例えば25℃）での内部抵抗値に対する比を含む。
【０１７０】
放電特性表補正部6kは式(3)中の元の内部抵抗値IR₁へ内部抵抗の初期値を代入する。次に、基準充電状態SRを一つ選択し、それに対応する開路電圧を式(3)中の開路電圧V_OCへ代入する。
放電特性表補正部6kは続いて電池温度Tを一つ選択し、劣化係数Kを、内部抵抗の初期値IR₁に対する更新値IR₂の比と電池温度Tとに基づき算定する。ここで、第一の温度補正係数α₁は、電池温度Tと内部抵抗の初期値IR₁の計測時の電池温度とのそれぞれに対応する温度特性表中の数値から算定される。第二の温度補正係数α₂は、電池温度Tと内部抵抗の更新値IR₂の計測時の電池温度とのそれぞれに対応する温度特性表中の数値から算定される。
放電特性表補正部6kは更に放電電流Iを一つ選択し、基準充電状態SR、電池温度T、及び放電電流Iに対応する初期の放電特性表中の電池電圧を、式(3)中の元の電池電圧VR₁へ代入する。
【０１７１】
放電特性表補正部6kは以上の設定の下で式(3)を計算し、修正電池電圧VR₂を決定する。放電特性表中の基準充電状態SR、放電電流I、及び電池温度Tに対応する電池電圧は修正電池電圧VR₂に書き換えられる。
放電特性表補正部6kは以上のような電池電圧の書き換えを、放電特性表中の基準充電状態SR、放電電流I、及び電池温度Tのそれぞれについて繰り返す。
こうして、二次電池ブロック1の劣化による内部抵抗の変化に応じ放電特性表が補正され、その放電特性の近似の精度が高く維持される。
充電状態の修正はこの補正された放電特性表に基づき、実施例１と同様に行われる。従って、二次電池の劣化が放電特性を変化させるときでも、充電状態の測定精度が高く維持される。
【０１７２】
制御部６Ｂによる充電状態の計測の具体的な手順は例えば以下の通りである。図１６は、制御部６Ｂによる充電状態の計測を示すフローチャートである。図１６では実施例１又は参考例１と同様なステップに対し、図４又は図１２と同じ符号を付す。更に、それらの同様なステップについての説明は実施例１又は参考例１のものを援用する。
図１６に示されるように、実施例２による充電状態の計測は主に、放電開始時に内部抵抗ＩＲを計測し（ステップＳ６１）、その内部抵抗ＩＲに基づき放電特性表を補正する（ステップＳ９０）ことで、実施例１による計測と異なる（図４参照）。更に、ステップＳ６１による内部抵抗ＩＲの計測は参考例１と同様に行われる。
【０１７３】
＜ステップS90＞
内部抵抗の学習に基づく放電特性表の補正は、具体的には例えば次のように行われる。
図17は、制御部6Bによる放電特性表の補正を示すフローチャートである。
＜ステップS91＞
基準充電状態SRが一つ選択される。ここで、選択すべき基準充電状態が残されていないときは、ステップS90を終了し、処理が図16のフローチャートへ戻る。
＜ステップS92＞
基準充電状態SRに対応する開路電圧V_OCが読み出される。
＜ステップS93＞
放電特性表に含まれる電池温度Tを一つ選択する。ここで、選択すべき電池温度が残されていないときはステップS90を終了し、処理が図16のフローチャートへ戻る。
【０１７４】
＜ステップＳ９４＞
劣化係数Ｋを上記の通り計算する。ここで、好ましくは、内部抵抗の更新値ＩＲ２は参考例１と同様に、学習放電容量比又は学習内部抵抗比に基づき補正される。それにより、劣化した二次電池ブロック１での充電状態の低下に伴う内部抵抗の増大が放電特性表の補正に反映される。
＜ステップＳ９５＞
放電特性表中に含まれる放電電流Ｉを一つ選択する。ここで、選択すべき放電電流が残されていないときは、処理がステップＳ９３へ戻る。
＜ステップＳ９６＞
初期状態での放電特性表から基準充電状態ＳＲ、放電電流Ｉ、及び電池温度Ｔに対応する電池電圧ＶＲ１が読み出される。
＜ステップＳ９７＞
修正電池電圧ＶＲ２が式（３）に従い算定される。更に、放電特性表中の基準充電状態ＳＲ、放電電流Ｉ、及び電池温度Ｔに対応する電池電圧は修正電池電圧ＶＲ２に書き換えられる。
【０１７５】
（参考例２）
図１８は、参考例２による電池パック１０Ｃの内、温度検出部３Ａ近傍を示すブロック図である。その他の部分については、実施例１による電池パック１０又は参考例１による電池パック１０Ａと同様であるので、図１又は図７を参照する。更に、図１８では、実施例１による電池パック１０及び参考例１による電池パック１０Ａと同様な構成要素に対し、図１及び図７と同じ符号を付す。それらの同様な構成要素の説明は実施例１又は参考例１でのものを援用する。
【０１７６】
二次電池ブロック1は、n個のセル（整数nは1以上である）1a、1b、…、1nを含む。温度検出部3Aは、固定抵抗器30、二次電池ブロック1のセルと同数、すなわちn個のセル温度検出用サーミスタ31、32、…、3n、回路素子温度検出用サーミスタ3m、電圧源3b、及び(n＋3)個の温度検出端子3A0、3A1、3A2、…、3An、3A(n＋1)、3A(n＋2)を含む。
【０１７７】
固定抵抗器30は実質的に一定の抵抗値R0を持つ。特に、抵抗値R0の温度変動は十分に小さい。
n個のセル温度検出用サーミスタ31、32、…、3nはいずれも同種のサーミスタである。それらの抵抗値R1、R2、…、Rnは所定の温度変化を示す。セル温度検出用サーミスタ31、32、…、3nはそれぞれ二次電池ブロック1のセル1a、1b、…、1nに近接する。それにより、それぞれの抵抗値R1、R2、…、Rnは、セル1a、1b、…、1nのそれぞれの温度で決まる。
回路素子温度検出用サーミスタ3mはサーミスタであり、その抵抗値Rmは所定の温度変化を示す。回路素子温度検出用サーミスタ3mは、例えば電池電流検出抵抗器5aに近接する。その他に、第一のスイッチ7a又は第二のスイッチ7b等、電池電流による発熱を伴う回路素子のそれぞれに近接しても良い。それにより、その抵抗値Rmは、例えば電池電流検出抵抗器5a等、近接した回路素子の温度で決まる。
固定抵抗器30と(n＋1)個のサーミスタ31、32、…、3n、3mとは直列に接続される。その直列回路Lの一端は温度検出部3A内の電圧源3bへ、他端は二次電池ブロック1の負極へ、それぞれ接続される。
【０１７８】
(n＋3)個の温度検出端子3A0、3A1、3A2、…、3An、3A(n＋1)、3A(n＋2)は順に直列回路L内の固定抵抗器30、(n＋1)個のサーミスタ31、32、…、3n、3mのそれぞれの両端へ接続される。すなわち、第一の温度検出端子3A0は電圧源3bと固定抵抗器30との接続点へ接続され、第二の温度検出端子3A1は固定抵抗器30と第一のサーミスタ31との接続点へ接続され、第三の温度検出端子3A2は第一のサーミスタ31と第二のサーミスタ32との接続点へ接続され、……、第(n＋2)の温度検出端子3A(n＋1)は第nのサーミスタ3nと回路素子温度検出用サーミスタ3mとの接続点へ接続され、第(n＋3)の温度検出端子3A(n＋2)は回路素子温度検出用サーミスタ3mと二次電池ブロック1の負極との接続点へ接続される。
【０１７９】
電圧源3bは電位Vccに維持される。ここで、電圧源3bの電位は目標値Vccから所定範囲内で変動（特に降下）しても良い。温度検出部3Aは以下の通り、電圧源3bのそのような電位の変動に関わらず、セル温度及び回路素子温度を高精度に計測する。
温度検出部3Aは(n＋3)個の温度検出端子3A0、3A1、3A2、…、3An、3A(n＋1)、3A(n＋2)について、互いに隣り合うものの間の電圧V0、V1、V2、…、Vn、Vmを測る。それらは固定抵抗器30及び(n＋1)個のサーミスタ31、32、…、3n、3mのそれぞれでの電圧降下量に等しい。
固定抵抗器30及び(n＋1)個のサーミスタ31、32、…、3n、3mは直列回路Lを成すので、それらを流れる電流は共通である。従って、温度検出部3Aにより計測される（n＋2)個の電圧降下量の間の比V0：V1：V2：…：Vn：Vmは固定抵抗器30と(n＋1)個のサーミスタ31、32、…、3n、3mとの間の抵抗値の比R0：R1：R2：…：Rn：Rmに実質的に等しい。
【０１８０】
固定抵抗器30の抵抗値R0は電池温度及び回路素子温度に依らず、実質的に一定に保たれる。従って、上記の電圧降下量間の比V0：V1：V2：…：Vn：Vmと固定抵抗器30の抵抗値R0とに基づき、(n＋1)個のサーミスタ31、32、…、3n、3mのそれぞれの抵抗値R1、R2、…、Rn、Rmが算定される：R1＝(V1／V0)R0、R2＝(V2／V0)R0、…、Rn＝(Vn／V0)R0、Rm＝(Vm／V0)R0。
サーミスタの温度特性から、n個のセル温度検出用サーミスタ31、32、…、3nのそれぞれに近接するセル1a、1b、…、1nの電池温度T1、T2、…、Tnが決定し、回路素子温度検出用サーミスタ3mに近接する電池電流検出抵抗器5aの温度Tmが決定する。
【０１８１】
温度検出部3Aによる抵抗計測は直列回路L全体の正確な電圧を要しない。従って、電圧源3bの電位Vccが大きく変動するときでも、(n＋1)個のサーミスタ31、32、…、3n、3mの抵抗値R1、R2、…、Rn、Rmがそれぞれ、高精度に決定される。それ故、セル1a、1b、…、1nの電池温度T1、T2、…、Tn、及び電池電流検出抵抗器5aの温度Tmがそれぞれ、高精度に計測される。
【０１８２】
好ましくは、実施例１及び２、並びに参考例１のそれぞれと同様な電池管理システムが、参考例２の温度検出部３Ａを有する。それにより、充電状態の測定精度が更に向上する。
【０１８３】
【発明の効果】
本発明の一つの観点による電池管理システムは、所定の放電容量と放電電流の積算値（放電電気量）との差に基づき二次電池の充電状態を計測する。充電状態の測定値は所定の放電特性表に基づき、特定の基準充電状態に対する確定点ごとにその基準充電状態で置換され、その放電特性表により示される二次電池の放電特性と対応するように修正される。
この電池管理システムは、二つの異なる基準充電状態について、それぞれに対応する二つの確定点間での放電電気量から放電容量を換算する。更に、様々な基準充電状態の対について換算された放電容量（換算放電容量）を一致させるように、放電特性表中の数値を放電ごとに補正する。それにより、放電特性表は実際の放電特性を良く近似する。
こうして、この電池管理システムは放電特性表の補正を通し、充電状態の修正に対し二次電池の劣化による放電特性の変化を反映させる。その結果、充電状態の測定精度が二次電池の劣化に関わらず高く維持される。
【０１８５】
本発明の更に別な観点による電池管理システムは、所定の放電容量と放電電流の積算値（放電電気量）との差に基づき二次電池の充電状態を計測する。充電状態の測定値は所定の放電特性表に基づき、特定の基準充電状態に対する確定点ごとにその基準充電状態で置換され、その放電特性表により示される二次電池の放電特性と対応するように修正される。
この電池管理システムは更に、二次電池の内部抵抗を放電ごとに学習し、学習された内部抵抗の変化に基づき放電特性表中の数値を放電ごとに補正する。それにより、二次電池の劣化による放電特性の変化に応じ放電特性表が補正される。こうして、二次電池の劣化が放電特性を変化させるときでも、充電状態の修正が高精度に維持される。その結果、充電状態の測定精度が高く維持される。
【０１８６】
上記の電池管理システムは、放電容量又は内部抵抗の学習を通し二次電池の劣化状態を評価し、その劣化状態と充電状態の測定値とに応じ、内部抵抗の測定値を補正しても良い。特に、放電末期で内部抵抗の測定値を増大させる。更に、その増大の割合を劣化した二次電池ほど増大させる。こうして、開路電圧の計算誤差が低減し、充電状態の測定精度が更に向上する。
【図面の簡単な説明】
【図１】 本発明の実施例１による電池パック１０を示すブロック図である。
【図２】 本発明の実施例１の電池管理システム２により、二次電池ブロック１の放電期間中に測定された電池電圧Ｖと充電状態Ｓとのそれぞれについて、放電電気量の増大に伴う変化を示すグラフである。（ａ）は二次電池ブロック１での電池電圧Ｖと放電電気量との関係（放電曲線）を示す。（ｂ）は充電状態の測定値Ｓと放電電気量との関係を示す。
【図３】 本発明の実施例１による電池管理システム２について、二次電池ブロック１の放電容量と放電特性とが学習されたものから比較的大きくずれるとき、放電電気量の増大に伴う充電状態の測定値Ｓの変化を示すグラフである。（ａ）は二次電池ブロック１について、劣化前の放電曲線を実線で、劣化後の放電曲線を破線で、それぞれ示す。（ｂ）は充電状態の測定値Ｓと放電電気量との関係を示す。
【図４】 本発明の実施例１の制御部６による充電状態の計測を示すフローチャートである。
【図５】 本発明の実施例１の制御部６による満充電状態の確認を示すフローチャートである。
【図６】 本発明の実施例１について、ステップＳ４による充電状態の計測を示すフローチャートである。
【図７】 参考例１による電池パック１０Ａを示すブロック図である。
【図８】 二次電池ブロック１の充電状態が満充電状態に等しい時点から二次電池ブロック１が放電を開始するとき、その放電開始時近傍での二次電池ブロック１全体の両端電圧と放電時間との関係を示すグラフである。
【図９】 二次電池ブロック１について、内部抵抗と充放電サイクル数との関係を示すグラフである。
【図１０】 二次電池ブロック１について、開路電圧と充電状態との関係を示すグラフである。
【図１１】 二次電池ブロック１の内部抵抗と充電状態との関係を示すグラフである。
【図１２】 参考例１の制御部６Ａによる充電状態の計測を示すフローチャートである。
【図１３】 参考例１による内部抵抗ＩＲの第一の計測方法を示すフローチャートである。
【図１４】 参考例１による内部抵抗ＩＲの第二の計測方法を示すフローチャートである。
【図１５】 本発明の実施例２による電池パック１０Ｂを示すブロック図である。
【図１６】 本発明の実施例２の制御部６Ｂによる充電状態の計測を示すフローチャートである。
【図１７】 本発明の実施例２の制御部６Ｂによる放電特性表の補正を示すフローチャートである。
【図１８】 参考例２による電池パック１０Ｃの内、温度検出部３Ａ近傍を示すブロック図である。
【図１９】 二次電池の放電期間中、従来の電池管理システムにより測定される電池電圧及び充電状態について、放電電気量の増大に伴う変化の一例を示すグラフである。（ａ）は電池電圧と放電電気量との関係を表すグラフ（放電曲線）を示す。（ｂ）は、充電状態の測定値と放電電気量との関係を表すグラフを実線で示し、充電状態の真値と放電電気量との関係を示すグラフを破線で示す。
【図２０】 劣化した二次電池の放電期間中、従来の電池管理システムによる電池電圧及び充電状態の測定値の放電電気量の増大に伴う変化の一例を示すグラフである。（ａ）は、放電期間中、放電電流と電池温度とが実質的に同一の変動を示すとき、初期の二次電池の放電曲線を破線で、劣化した二次電池の放電曲線を実線で、それぞれ示す。（ｂ）は、充電状態の測定値と放電電気量との関係を表すグラフを実線で、劣化した二次電池の充電状態の真値と放電電気量との関係を表すグラフを破線で、初期の二次電池の充電状態の真値と放電電気量との関係を表すグラフを一点鎖線で、それぞれ示す。
【符号の説明】
１０ 電池パック
１ 二次電池ブロック
１ａ、１ｂ セル
２ 電池管理システム
３ａ サーミスタ
５ａ 電池電流検出抵抗
７ａ 第一のスイッチ
７ｂ 第二のスイッチ
８ａ 二次電池ブロック１の正極
８ｂ 二次電池ブロック１の負極
９ ホストＨとの通信用端子
Ｔ 電池温度の測定値
Ｖ 電池電圧の測定値
Ｉ 電池電流の測定値[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery management system for monitoring and controlling the state of a secondary battery such as a nickel-cadmium storage battery, a nickel-hydrogen storage battery, and a lithium ion secondary battery, or notifying the outside, and More particularly, the present invention relates to a method for measuring the state of charge of a secondary battery by the battery management system.
[0002]
[Prior art]
In recent years, battery-driven electric devices such as notebook personal computers and mobile phones use mainly secondary batteries as their drive sources. These devices are further equipped with a charger and charge the secondary battery when connected to an external power source. Thereby, the frequency of battery replacement is reduced.
[0003]
In order to make maximum use of the capacity of the secondary battery, it is desirable to charge to near the upper limit of the capacity and to discharge deeply to near the lower limit of the capacity. On the other hand, it is necessary to prevent overcharge, overdischarge, overvoltage, overcurrent, or overheating, to ensure safety against them, and to suppress deterioration of the secondary battery due to them. Therefore, the use of the secondary battery requires highly accurate charge / discharge control, and in particular, strict monitoring of the battery state is required.
[0004]
A secondary battery is usually housed in a battery pack dedicated to each electric device (hereinafter referred to as a host) that uses the secondary battery as a drive source.
Recent battery packs are equipped with a battery management system together with a secondary battery.
The battery management system monitors the battery voltage, battery current, and battery temperature of the secondary battery, and measures the discharge capacity and the state of charge. Further, the measurement value is notified to the host as the battery state of the secondary battery. The host performs charge / discharge control for the secondary battery based on the battery state. In particular, when the secondary battery is discharged, the control unit or user of the host can plan the use of the host based on the state of charge notified from the battery management system, and can avoid a failure due to sudden battery exhaustion.
[0005]
The battery management system includes a sensor, a protection circuit, and a control circuit.
The sensor detects battery voltage, battery current, and battery temperature for the secondary battery.
The protection circuit cuts off the battery current for the purpose of preventing overcharge, overdischarge, overvoltage, overcurrent, and overheating of the secondary battery.
The control circuit includes a CPU and a memory, and controls the sensor and the protection circuit. For example, battery voltage, battery current, and battery temperature are detected by a sensor, and information indicating the state of the secondary battery including those measured values (hereinafter referred to as battery state) is managed. In particular, the battery status is notified to the host. Furthermore, the protection circuit is activated in accordance with the battery status and the instruction from the host to prevent the secondary battery from being destroyed due to overcharge or the like.
[0006]
The battery state managed by the battery management system includes the remaining capacity or charge state of the secondary battery. Here, in the present application, the “remaining capacity” and “charged state” of a secondary battery at a certain point in time are referred to as the former meaning “amount of electricity that can be discharged from that point in time”, and the latter is “full”. The term “representing the ratio of the remaining capacity at that time to the remaining capacity (that is, the discharge capacity) in the state of charge (also referred to as full charge)” is used separately.
The battery management system integrates the battery current when the secondary battery is charged or discharged, and calculates the amount of charge or discharge of the secondary battery. Furthermore, the remaining capacity or state of charge of the secondary battery is determined based on the amount of charged electricity or the amount of discharged electricity. At that time, the discharge capacity of the secondary battery, the self-discharge, the deterioration state, and the power consumption of the battery management system itself are taken into consideration, and the remaining capacity or the charged state is measured with high accuracy. The measured value of the remaining capacity or the charged state is notified to the host as a part of the battery state.
[0007]
The conventional battery management system measures the remaining capacity or the charged state as follows, for example, when the secondary battery is discharged (see Patent Document 1).
FIG. 19 is a graph showing an example of a change accompanying an increase in the amount of discharged electricity with respect to a battery voltage and a charge state measured by a conventional battery management system during a discharge period of the secondary battery. FIG. 19 (a) is a graph showing the relationship between the battery voltage and the amount of discharge electricity (hereinafter referred to as a discharge curve). (B) of FIG. 19 shows a graph showing the relationship between the measured value of the charge state and the discharge electricity amount by a solid line, and shows a graph showing the relationship between the true value of the charge state and the discharge electricity amount by a broken line.
[0008]
Even when the secondary battery starts discharging from a certain state of charge, the change in the battery voltage during the discharge period is not determined only by the amount of discharge electricity, but the discharge current and battery temperature at each time point during the discharge period. Depends on. In a general discharge of a secondary battery, the discharge current and the battery temperature vary during the discharge period. Therefore, the detailed shape of the discharge curve varies from discharge to discharge.
In the example of FIG. 19, the discharge current and the battery temperature do not show excessive fluctuations and are relatively stable during the discharge period of the secondary battery for the purpose of simplifying the description about the measurement of the following state of charge. Assume the time. At that time, as shown in (a) of FIG. 19, the battery voltage decreases almost monotonously as the amount of discharge electricity increases.
[0009]
The battery management system generally determines a plurality of reference value charging states (hereinafter referred to as reference charging states). Furthermore, a set of the battery voltage, the battery current (discharge current), and the battery temperature in each reference charge state is determined based on the discharge characteristics of the secondary battery, and stored in correspondence with each reference charge state. Thus, the correspondence table between the reference charge state and the battery voltage stored by the battery management system is hereinafter referred to as a discharge characteristic table.
Here, the discharge characteristics of the secondary battery refer to the relationship between the battery voltage and the amount of discharge electricity under the condition that the discharge current and the battery temperature are maintained substantially constant during the discharge period. The discharge characteristics of the secondary battery are determined experimentally, for example, with respect to the initial secondary battery immediately after manufacture. That is, the discharge characteristics table represents the discharge characteristics of the initial secondary battery.
The discharge characteristics table shows, for example, the batteries corresponding to the four reference charge states of 100% (A), 70% (B), 10% (C), and 0% (D) of the fully discharged state. It includes a set of reference values for voltage, discharge current, and battery temperature.
[0010]
Hereinafter, it is assumed that discharging is continuously performed from 100% fully charged state to 0% fully discharged state. Here, the complete discharge state refers to a state when the battery voltage drops to the discharge end voltage (fourth reference voltage VD).
The battery management system measures the battery voltage, the discharge current, and the battery temperature at the start of discharging the secondary battery. When the measured value set substantially matches the set of reference values in the discharge characteristics table corresponding to the first reference charge state 100%, the battery management system sets the charge state of the secondary battery to the first Set the standard charge state to 100%. This time point is hereinafter referred to as the first definite point. In FIG. 19, point A represents the first definite point. In particular, at the first definite point A, the battery voltage is equal to the first reference voltage value VA.
The battery management system further sets the discharge capacity of the secondary battery as the remaining capacity at the first definite point A. Here, the battery management system stores in advance a value at the time of manufacture (hereinafter referred to as an initial value) as the discharge capacity of the secondary battery.
[0011]
The battery management system samples the discharge current at regular time intervals and integrates these samples. The integrated value is substantially equal to the amount of discharge electricity during the integration period. The battery management system determines the state of charge of the secondary battery at each sampling point based on the discharge capacity of the secondary battery and the integrated value (discharged electric quantity) of the discharge current. That is, the difference between the discharge capacity and the amount of discharge electricity is regarded as the remaining capacity, and the ratio between the remaining capacity and the discharge capacity is calculated as the state of charge.
In FIG. 19 (b), the solid line represents the measured value of the state of charge. On the other hand, the broken line represents the true value of the state of charge. The measured value of the state of charge by the battery management system (solid line in FIG. 19B) generally deviates from the true value (broken line in FIG. 19B). The cause of the deviation includes, for example, temperature variation of the resistance value at the battery current detection resistor, accumulation of measurement error due to integration of the discharge current, deviation from the initial value of the discharge capacity, and the like.
[0012]
The battery management system corrects the error in the measured value of the state of charge as follows based on the discharge characteristic table.
The battery management system measures the battery voltage and the battery temperature together with the sampling of the discharge current. In addition, referring to the discharge characteristics table for each sampling, check whether the set of measured values matches one of the set of reference values in the discharge characteristics table corresponding to the second reference charge state 70%. To do. Specifically, for example, a set including the measured values of the discharge current and the battery temperature is searched from the set of reference values, and the reference value of the battery voltage included in the set is compared with the measured value of the battery voltage. .
When the set of battery voltage, discharge current, and battery temperature measurements substantially match the set of reference values in the discharge characteristics table, the battery management system converts the charge state measurements to the second reference charge state 70. Replace with%. Hereinafter, this time of replacement is referred to as a second definite point. In FIG. 19, point B represents the second definite point. At the second definite point B, the battery voltage is equal to the second reference voltage value VB. By this replacement, the deviation between the measured value of the state of charge and the true value is corrected.
[0013]
Here, for example, as indicated by a point B1 in FIG. 19 (b), the measured value (solid line) of the charged state may drop to the second reference charged state 70% before the true value (broken line). That is, when the time when the measured value of the charge state matches one of the reference charge states is referred to as the reference charge state detection point, the second reference charge state detection point B1 can be earlier than the second definite point B. In that case, the battery management system temporarily fixes the measured value of the state of charge to the second reference state of charge 70%, and restarts the update of the measured value from the second definite point B (point (b) in FIG. 19). (See between B1 and point B). Thus, it is avoided that the measured value of the charging state suddenly increases due to the replacement with the reference charging state, and the battery control of the host or the user of the host is prevented from being confused.
[0014]
After the second definite point B, the battery management system continues to measure the state of charge based on the discharge capacity and the integrated value of the discharge current. Thereby, as shown in FIG. 19B, the measured value of the state of charge falls again from the point B.
On the other hand, the battery voltage, discharge current, and battery temperature are continuously monitored, and whether or not the set of those measured values matches any of the set of reference values in the discharge characteristic table corresponding to the third reference charge state 10%. To check. When the set of measured values substantially matches the set of reference values, the battery management system replaces the measured state of charge with a third reference state of charge 10%. Hereinafter, the time of this replacement is referred to as a third definite point. In FIG. 19, the point C represents the third definite point. At the third definite point C, the battery voltage is equal to the third reference voltage value VC. By this replacement, the deviation between the measured value of the state of charge and the true value is corrected.
For example, as indicated by point C1 in FIG. 19 (b), the measured value (solid line) of the charge state falls to the third reference charge state 10% before the true value (broken line), and the third reference charge The state detection point C1 can be earlier than the third determination point C. In that case, the battery management system temporarily fixes the measured value of the state of charge to the third reference state of charge 10%, and restarts the update of the measured value from the third definite point C (point (b) in FIG. 19). (See between C1 and point C).
[0015]
The battery management system continues to measure the state of charge based on the discharge capacity and the integrated value of the discharge current after the third definite point C. Thereby, as shown in FIG. 19 (b), the measured value of the state of charge falls again from the point C.
Meanwhile, the battery voltage, the discharge current, and the battery temperature are continuously monitored, and any of the reference value sets in the discharge characteristics table corresponding to 0% of the fourth reference charge state (complete discharge state) is a set of those measured values. To see if they match. When the set of measured values substantially matches the set of reference values, the battery management system replaces the measured state of charge with a fourth reference state of charge 0%. Hereinafter, the time of this replacement is referred to as a fourth definite point. In FIG. 19, point D represents the fourth definite point. In particular, at the fourth definite point D, the battery voltage is equal to the fourth reference voltage value (discharge end voltage) VD. Therefore, the battery management system stops discharging the secondary battery at the fourth fixed point D.
For example, as indicated by point D1 in FIG. 19 (b), the measured value (solid line) of the charge state falls to 0% of the fourth reference charge state before the true value (broken line), and the fourth reference charge The state detection point D1 can be earlier than the fourth definite point D. In that case, the battery management system temporarily returns the measurement value of the state of charge to a predetermined value (for example, 1%) slightly higher than 0% of the fourth reference state of charge, and fixes it (point D1− in FIG. 19B). See between points D). Further, the measured value of the state of charge at the fourth definite point D is set to 0%.
[0016]
The above measurement of the state of charge by the battery management system uses a discharge characteristic table (hereinafter referred to as an initial discharge characteristic table) representing the discharge characteristics of the initial secondary battery. For example, when the number of charge / discharge cycles is sufficiently small, the discharge characteristics of the secondary battery are well approximated by the initial discharge characteristics table, and thus the above measurement is realized with high accuracy.
In the example of FIG. 19, the detection point is earlier than the fixed point for each of the second to fourth reference charging states. However, in general, the deterministic point may be earlier than the detection point due to the measurement error of the state of charge based on the discharge capacity and the amount of discharge electricity. The replacement of the measured state of charge with the reference state of charge is then visible to the host or its user as an instantaneous drop of state of charge. Hereinafter, such an instantaneous drop in the measured value of the state of charge is referred to as “capacity jump”. When the discharge characteristics of the secondary battery are well approximated in the initial discharge characteristics table, the capacity jump is generally small.
[0017]
When the number of charge / discharge cycles increases, the secondary battery generally deteriorates. In particular, even when the number of charge / discharge cycles is small, the lithium ion secondary battery is remarkably deteriorated when shallow charge / discharge is repeated at a high temperature or maintained in a high charge state for a long time.
The discharge characteristics of the deteriorated secondary battery greatly deviate from the initial discharge characteristics. That is, the discharge capacity is reduced, and the battery voltage for a certain amount of discharge electricity is lowered. In addition, the battery voltage drop is abrupt at the start of discharge, and conversely, the battery voltage drop is moderate at the end of discharge.
[0018]
For a deteriorated secondary battery, a conventional battery management system measures the state of charge as follows.
FIG. 20 is a graph showing an example of a change in the measured value of the battery voltage and the state of charge by the conventional battery management system with an increase in the amount of discharge electricity during the discharge period of the deteriorated secondary battery. (A) of FIG. 20 shows the discharge curve of the initial secondary battery with a broken line and the discharge curve of the deteriorated secondary battery when the discharge current and the battery temperature show substantially the same fluctuation during the discharge period. Each is indicated by a solid line. Here, in FIG. 20, as in FIG. 19, it is assumed that the fluctuations of the discharge current and the battery temperature are not excessive. (B) of FIG. 20 is a solid line showing a relationship between the measured value of the charged state and the discharge electric quantity, and a broken line showing a graph showing the relation between the true value of the charged state of the deteriorated secondary battery and the discharged electric quantity. Then, the graph showing the relationship between the true value of the charge state of the initial secondary battery and the amount of discharged electricity is shown by a one-dot chain line.
[0019]
Hereinafter, it is assumed that discharging is continuously performed from 100% fully charged state to 0% fully discharged state.
When the secondary battery starts discharging, the battery management system detects the first definite point, and sets the secondary battery charge state to 100% of the first reference charge state (see point A in FIG. 20). The battery management system further sets the initial discharge capacity (initial value) of the secondary battery as the remaining capacity of the secondary battery at the first definite point A.
[0020]
As shown in FIG. 20 (a), the discharge capacity of the deteriorated secondary battery is smaller than the initial value. Accordingly, as shown in FIG. 20 (b), the true value of the state of charge of the deteriorated secondary battery decreases faster than that of the initial secondary battery.
After the first definite point A, the battery management system determines the state of charge based on the initial value of the discharge capacity and the integrated value of the discharge current (see the solid line in FIG. 20 (b)). Therefore, as shown in FIG. 20 (b), the rate of decrease in the measured value of the charged state relative to the amount of discharged electricity (the slope of the solid line) is the rate of decrease in the true value of the charged state in the initial secondary battery (one point). It is close to the slope of the chain line. Therefore, the measured value of the state of charge is larger than the true value (broken line) for a while from the first definite point A.
[0021]
On the other hand, as shown in FIG. 20 (a), the battery voltage (solid line) of the deteriorated secondary battery drops more rapidly than the battery voltage (broken line) of the initial secondary battery. Accordingly, the second deterministic point for the second reference charge state 70% is earlier in the deteriorated secondary battery than in the initial secondary battery (see point BR and point B in FIG. 20 (a)). That is, the amount of discharge electricity when the battery voltage is equal to the second reference voltage VB, the first discharge electricity amount Q1 for the deteriorated secondary battery, the second discharge electricity amount Q2 for the initial secondary battery Then, the first discharge electricity quantity Q1 is smaller than the second discharge electricity quantity Q2 (Q1 <Q2).
Therefore, in the discharge of a deteriorated secondary battery, the battery management system detects the second definite point BR during the period when the measured value of the charged state is greater than 70% of the second reference charged state, and the measured value of the charged state is Replace with 70% of second reference charge state. As a result, a relatively large capacity jump occurs (see the point B2 to the point B3 in FIG. 20B).
[0022]
A capacity jump similar to the capacity jump at the second deterministic point can occur at other deterministic points.
In the example of FIG. 20, the third deterministic point for the third reference charging state 10% is earlier in the deteriorated secondary battery than the initial secondary battery (the points CR and C in FIG. reference). Therefore, the battery management system detects the third deterministic point CR during the period when the measured state of charge is greater than the third reference state of charge 10%, and the measured value of state of charge is the third reference state of charge 10%. Replace. As a result, a relatively large capacity jump occurs (see the point C2 to the point C3 in FIG. 20B).
[0023]
In general, at the end of discharge of a deteriorated secondary battery, the rate of decrease in battery voltage with respect to the amount of discharged electricity is smaller than that of the initial secondary battery (the solid line between point CR and point DR in FIG. (See the dashed line between points D). Therefore, for example, for a low reference charging state of less than 10%, the detection point tends to be earlier than the fixed point.
In FIG. 20, the measured value of the charge state drops to the fourth reference charge state 0% before the fourth definite point DR for the fourth reference charge state 0%. That is, the detection point D2 of the fourth reference charging state 0% is earlier than the fourth definite point DR. At that time, the battery management system temporarily returns the measurement value of the state of charge to a predetermined value (for example, 1%) slightly higher than the fourth reference state of charge 0% (for example, point D2− in FIG. 20B). See between points DR). Further, the measured value of the state of charge is set to 0% at the fourth fixed point DR, and the discharge of the secondary battery is stopped.
[0024]
In the measurement of the state of charge by the battery management system, an initial value is used as the discharge capacity. Further, a definite point with respect to the reference charge state is detected based on the initial discharge characteristic table. Therefore, the measurement error of the state of charge increases with the discharge of the deteriorated secondary battery. In addition, large capacity jumps can occur. When the capacity jump is excessive, the control unit of the host and the user of the host must suddenly change the schedule set based on the measured value of the state of charge, for example, which is not preferable.
[0025]
The conventional battery management system learns the discharge capacity for each discharge, for example (see Patent Documents 2 and 3). Thereby, when the deterioration of the secondary battery decreases the discharge capacity, an increase in the measurement error of the charged state is suppressed over the entire discharge period.
For example, the battery management system disclosed in Patent Document 2 calculates the total amount of discharge electricity for each complete discharge (discharge from the fully charged state to the fully discharged state), and the total amount is used as the discharge capacity for the next discharge. Set as. When the number of charge / discharge cycles increases, the total amount of discharge electricity in the previous complete discharge is closer to the true value than the initial value of the discharge capacity. Therefore, the measurement accuracy of the state of charge is improved.
In the example of (b) of FIG. 20, by learning the discharge capacity, the slope of the solid line indicating the measured value of the state of charge is corrected so as to match the slope of the broken line indicating the true value. Thereby, for example, the difference between the measured value of the charged state and the true value is reduced between the point B3 corresponding to the second determined point BR and the point C2 corresponding to the third determined point CR.
[0026]
The battery management system disclosed in Patent Document 3 stores in advance the relationship between the number of charge / discharge cycles and the discharge capacity (charge / discharge cycle characteristics). The battery management system continues to count the number of charge / discharge cycles from the time of manufacturing the secondary battery, and corrects the discharge capacity in each charge / discharge cycle according to the number of charge / discharge cycles at that time. Thereby, when the deterioration of the secondary battery decreases the discharge capacity, an increase in the measurement error of the charged state is suppressed.
Here, the number of charge / discharge cycles is weighted according to the depth of discharge in each charge / discharge cycle. For example, in a charge / discharge cycle with a discharge depth of 20%, the number of charge / discharge cycles is counted as 1/5. Specifically, the amount of charge electricity is integrated, and when the total amount exceeds, for example, 90% of the discharge capacity at that time, the charge / discharge cycle is increased by one. Therefore, even when shallow charging / discharging is repeated, a reduction in discharge capacity due to deterioration of the secondary battery can be estimated based on charging / discharging cycle characteristics.
Thus, the measurement accuracy of the state of charge is improved without substantially depending on the depth of discharge in each charge / discharge cycle.
[0027]
Among conventional battery management systems, there is known one that estimates a discharge current larger than a measured value in accordance with, for example, a reduction rate of a discharge capacity (see Patent Document 2). The battery management system reduces the magnitude of capacity jump as follows by estimating the discharge current largely.
The battery management system stores, for example, the total amount of discharge electricity (that is, the learned discharge capacity) in the last two complete discharges. When the ratio of the previous total amount to the previous total amount is greater than 1, the battery management system multiplies the measured value of the discharge current by the ratio and integrates the multiplication results. The integrated value is regarded as the amount of discharged electricity and is used for measuring the state of charge. Since the amount of discharged electricity is larger than the integrated value of the measured value of the discharge current itself, the measured value of the charging state based on the former drops more rapidly than that based on the latter. As a result, the magnitude of the capacity jump is reduced.
[0028]
In the deteriorated secondary battery, the battery voltage drop is moderate in the vicinity of the end-of-discharge voltage compared to the initial secondary battery. Therefore, when the definite point with respect to the reference charge state is detected based on the initial discharge characteristic table, the true value of the charge state at the definite point at the end of discharge is higher than the reference charge state. That is, the true value of the remaining capacity at the determined point is larger than the remaining capacity converted from the reference charging state.
For example, in (a) of FIG. 20, the measured value of the charging state is replaced with the third reference charging state 10% at the third definite point CR. However, in FIG. 20 (a), it can be understood by comparing the ratio of the distance between point CR and point DR to the distance between point A and point DR with the ratio of the distance between point C and point D to the distance between point A and point D. As shown, the actual state of charge at the definite point CR is clearly higher than the value “10%” of the third reference state of charge.
The conventional battery management system learns, for each discharge, the amount of discharge electricity from the definite point to the specific reference charge state at the end of discharge until the end of discharge. Further, the battery management system corrects the reference value of the battery voltage corresponding to the specific reference charging state to be low so that the amount of discharged electricity becomes equal to a predetermined value, for example (see Patent Document 4). Thereby, in the next discharge, since the definite point with respect to the specific reference charging state is delayed, the actual charging state is close to the reference charging state. Thus, the measurement accuracy of the state of charge at the end of discharge is improved.
[0029]
In the example of FIG. 20 (a), the amount of discharge electricity within the period in which the battery voltage drops from the third reference voltage VC to the fourth reference voltage VD is calculated for each discharge. That is, in the initial discharge curve (broken line) of the secondary battery, the amount of discharge electricity QI = Q6−Q5 between the third definite point C and the fourth definite point D is calculated. On the other hand, in the discharge curve (solid line) of the deteriorated secondary battery, the amount of discharge electricity QJ = Q4−Q3 between the third definite point CR and the fourth definite point DR is calculated. In the vicinity of the end-of-discharge voltage VD, the discharge curve (solid line) of the deteriorated secondary battery is gentler than the discharge curve (broken line) of the initial secondary battery. Accordingly, the amount of discharge electricity QJ between point CR and point DR is larger than the amount of discharge electricity QI between point C and point D (QJ> QI). The battery management system then reduces the third reference voltage VC. Thereby, the discharge electricity quantity QJ between the point CR and the point DR is made substantially equal to the discharge electricity quantity QI between the point C and the point D. As a result, since the third deterministic point CR is delayed, the magnitude of the capacity jump between the point C2 and the point C3 in (b) of FIG. 20 is reduced.
[0030]
The conventional battery management system as described above integrates the battery current and measures the state of charge of the secondary battery. The battery current is measured from, for example, a voltage drop at a predetermined resistance. Therefore, accurate measurement of the state of charge requires an accurate temperature of the resistance.
Further, as described above, these battery management systems detect a definite point with respect to a predetermined reference charging state based on the discharge characteristics of the secondary battery, and measure the measured value of the charging state at each definite point to the corresponding reference charging state. Replace and correct. In order to correct the state of charge accurately, it is necessary to accurately detect the definite point. Therefore, the battery temperature must be accurately measured.
As described above, the battery management system must accurately measure and manage the temperature of a circuit element that generates heat, such as a battery current detection resistor or a battery current cutoff switch, or the environment temperature.
[0031]
A conventional battery management system measures a circuit element or a battery temperature using, for example, a thermistor (see Patent Documents 4 and 5).
In the battery management system disclosed in Patent Document 4, one thermistor is close to the secondary battery, and the battery temperature detection circuit is connected to the thermistor. The battery temperature detection circuit measures the resistance value of the thermistor and calculates the battery temperature.
In the battery management system disclosed in Patent Document 5, the same number of thermistors as the cells in the secondary battery are close to each of those cells, and the battery temperature detection circuit is connected in parallel with each thermistor. The battery temperature detection circuit measures the resistance value of each thermistor and calculates the battery temperature of each cell.
[0032]
In addition to the purpose of measuring the temperature of the circuit element or the battery temperature as described above, the temperature monitoring by the conventional battery management system is accompanied by heat generation of, for example, a battery current detection resistor or a battery current cutoff switch. A device for detecting an excessive temperature rise in a circuit element or a cell in a secondary battery is known (see Patent Document 6). Through this detection, overheating of those circuit elements, overcharge, overdischarge, or overheating in any of the cells in the secondary battery is quickly detected. At that time, for example, the battery management system notifies the host of the occurrence of those abnormalities or immediately cuts off the battery current. Thus, the battery management system functions as a protection circuit for the secondary battery and ensures safety against the use of the secondary battery.
[0033]
In the battery management system disclosed in Patent Document 6, each cell in the secondary battery includes a thermal fuse or a PTC (Positive Thermal Coefficient) element as a thermal element. These thermal elements are connected in series with each other. Furthermore, one end of the series circuit of the thermal elements is connected to the safety control circuit. When overheating occurs in any of the cells in the secondary battery, the thermal fuse of that cell is blown, or the resistance value of the PTC element increases rapidly. The safety control circuit monitors the current flowing in the series circuit of the heat sensitive elements, and detects the occurrence of overheating in any of the cells from the sudden decrease in the current.
[0034]
[Patent Document 1]
Japanese Patent Laid-Open No. 05-87896
[Patent Document 2]
JP 09-308113 A
[Patent Document 3]
JP 2001-283929 A
[Patent Document 4]
JP-A-10-213638
[Patent Document 5]
JP 2001-231178 A
[Patent Document 6]
Japanese Patent Laid-Open No. 10-214613
[0035]
[Problems to be solved by the invention]
As described above, the measurement of the state of charge by the conventional battery management system regards the difference between the predetermined discharge capacity and the integrated value of the discharge current (the amount of discharge electricity) as the remaining capacity, and calculates the ratio between the remaining capacity and the discharge capacity. Calculate as the state of charge. However, for example, the measurement error of the discharge electric quantity increases due to the accumulation of the measurement error of the discharge current, and the measurement error of the charged state increases. The battery management system detects a definite point with respect to a predetermined reference charging state based on the discharge characteristic table of the initial secondary battery, and replaces the measured value of the charging state with the corresponding reference charging state at the definite point. Thereby, the deviation between the measured value of the state of charge and the true value is removed (see Patent Document 1).
However, since the battery management system disclosed in Patent Document 1 fixes the discharge capacity to the initial value, when the deterioration of the secondary battery decreases the discharge capacity, the measurement error of the state of charge increases. A large capacity jump occurs particularly in a deteriorated secondary battery.
[0036]
The battery management system disclosed in Patent Document 2 learns the discharge capacity for each discharge as described above. Thereby, when the deterioration of the secondary battery decreases the discharge capacity, an increase in the measurement error of the charged state is suppressed.
As described above, the battery management system disclosed in Patent Document 3 counts the number of charge / discharge cycles according to the depth of discharge in each charge / discharge cycle, and sets a predetermined discharge capacity corresponding to the number of charge / discharge cycles. . Thereby, when the deterioration of the secondary battery decreases the discharge capacity, an increase in the measurement error of the charged state is suppressed regardless of the depth of discharge.
However, in those battery management systems, since the reference value of the battery voltage corresponding to the reference charge state is fixed to the value in the initial secondary battery, the battery voltage corresponding to the reference charge state is reduced by the deterioration of the secondary battery. When lowered, the measurement error of the state of charge increased.
[0037]
In the example of FIG. 20, when the discharge capacity is learned for each discharge, the rate of decrease in the measured value of the state of charge (the slope of the solid line) with respect to the amount of discharged electricity is a true rate of decrease (broken line) than that shown in FIG. Approach the slope). Therefore, for example, the measured value of the state of charge immediately before the second fixed point is closer to the true value than that shown in FIG. 20 (see point B2 in FIG. 20B). On the other hand, since the second reference voltage VB is fixed, the true value of the charged state at the second fixed point is greatly different from the second reference charged state 70%. As a result, an excessive capacity jump (between point B2 and point B3) occurs. The same applies to the third reference voltage VC.
[0038]
As described above, the battery management system disclosed in Patent Document 4 reduces the reference value (hereinafter referred to as a reference voltage) of the battery voltage corresponding to the reference charge state, particularly at the end of discharge. Thereby, since the definite point with respect to the reference | standard charge state is overdue, the measurement accuracy of the charge state in the last stage of discharge improves.
However, since the new reference voltage does not correspond to the original reference charge state, a new reference charge state corresponding to the new reference voltage has to be determined based on the discharge capacity at that time. Therefore, it is not preferable because the reference charge state greatly depends on the measurement error of the discharge capacity.
Furthermore, the improvement in the measurement accuracy of the state of charge is limited to the end of discharge, and is difficult throughout the discharge period.
[0039]
In the measurement of the state of charge, a definite point with respect to the reference state of charge must be detected accurately. That is, each of the reference voltage, the discharge current, and the battery temperature must be measured with high accuracy.
The battery management system disclosed in Patent Document 4 measures the temperature of the entire secondary battery with one thermistor. However, when the secondary battery includes a plurality of cells, the battery temperature of each cell is generally different. Therefore, the definite point for a certain reference charge state generally differs from cell to cell. Since the battery management system described above cannot individually measure the battery temperature of each cell, it cannot distinguish the difference between such definite points for each cell. Therefore, it has been difficult to improve the detection accuracy of the definite point.
[0040]
The battery management system disclosed in Patent Document 5 calculates the battery temperature for each cell. However, since the same number of thermistors as the cells are connected in parallel to the battery temperature detection circuit, the total amount of current supplied from the battery temperature detection circuit to the thermistor is large. At that time, the power consumption generally increases, which is not preferable.
[0041]
The battery management system disclosed in Patent Document 6 detects the occurrence of overheating in any of the cells in the secondary battery, that is, an excess of a predetermined threshold value due to the battery temperature. However, no cell that caused overheating was identified. Furthermore, it is difficult to measure the battery temperature value of each cell with high accuracy.
[0042]
The present invention allows accurate learning of the discharge characteristics including the discharge capacity of the secondary battery, maintains high measurement accuracy of the charged state even when the deterioration of the secondary battery changes the discharge characteristics, and particularly reduces capacity jump. An object is to provide a battery management system and a charging state measurement method thereof.
[0043]
[Means for Solving the Problems]
  A battery management system according to one aspect of the present invention includes (A) a secondary battery, (a) a voltage detection unit for measuring battery voltage, (b) a current detection unit for measuring battery current, and (c A battery state monitoring unit for managing a battery state including a temperature detection unit for measuring the battery temperature and including a set of measurement values by the detection unit;
(B) a battery current integrating unit for integrating the measured values of the battery current by the battery state monitoring unit;
(C) From the time when the charging state of the secondary battery is equal to a reference value (hereinafter referred to as a reference charging state), the amount of discharged electricity of the secondary battery is measured by the battery current integrating unit, the amount of discharged electricity, A charge state measuring unit for determining a charge state of the secondary battery based on a discharge capacity of the secondary battery and the reference charge state;
(D) (a) As the reference charging state, first, second, and third reference charging states are determined in order of value, and the battery voltage, battery current, and battery temperature in each reference charging state are determined. A discharge characteristic table indicating a set; and (b) from a point in time when the battery state includes one set in the discharge characteristic table corresponding to the first reference charge state (hereinafter referred to as a first definite point). When the battery state includes a set in the discharge characteristic table corresponding to the second reference charge state (hereinafter referred to as a second definite point), the second battery is discharged. In the reference charge state, the battery state includes a set in the discharge characteristic table corresponding to the third reference charge state (hereinafter referred to as a third definite point), in the third reference charge state, Replacing the measured value of the state of charge by the state of charge measuring unit, Charging state modification of; and,
(E) The discharge amount of the secondary battery between the first to second fixed points is the reference charge state between the first and secondBattery voltage determined by battery temperature and discharge current atThe value divided by the difference between the first and third definite points of discharge energy of the secondary battery between the first and third fixed points of the reference charge state of the first and thirdAbove battery voltageA discharge characteristic table correction unit for correcting a set of battery voltage, battery current, and battery temperature in the discharge characteristic table so as to coincide with a value divided by the difference;
Have
[0044]
Here, the battery state refers to information indicating the state of the secondary battery, and particularly includes a set of measured values of battery voltage, battery current, and battery temperature. In addition, the remaining capacity of the secondary battery, the state of charge, the discharge capacity, or the number of charge / discharge cycles may be included.
The remaining capacity of the secondary battery at a certain point in time refers to “the amount of electricity that can be discharged from that point in time”, and in particular, the “remaining capacity in a fully charged state (also referred to as full charge)” is referred to as a discharge capacity. The state of charge of the secondary battery at a certain point refers to “the ratio of the remaining capacity at that point to the discharge capacity”.
[0045]
Said battery management system measures the charge condition of the secondary battery at the time of discharge of a secondary battery as follows, for example.
The charging state correction unit measures the battery voltage, battery current, and battery temperature of the secondary battery by the battery state monitoring unit at the start of discharging the secondary battery, and the set of those measured values corresponds to the first reference charging state. Confirm that it matches one set in the discharge characteristics table.
Here, the first reference charge state is preferably a full charge state. When the measurement of the charged state is started from a charged state lower than the fully charged state, the first reference charged state may be a charged state at the start of the measurement.
[0046]
The charge state measurement unit sets the product of the predetermined discharge capacity and the first reference charge state as the remaining capacity at the start of measurement of the charge state. Here, the first reference charging state is preferably 100% fully charged. For example, when the first reference charging state is 100%, the remaining capacity at the start of measurement is equal to a predetermined value of the discharging capacity.
The discharge capacity is preferably learned for each discharge. That is, the battery current integration unit calculates an integrated value of the discharge current (battery current during discharge) over the entire discharge period, and the integrated value is regarded as the discharge capacity. In addition, the discharge capacity may be set according to the battery state detected at the start of discharge from the correspondence table between the discharge capacity and the battery state at the start of discharge.
[0047]
The battery current integration unit samples the measured value of the discharge current, for example, at a predetermined time interval from the start of measurement of the state of charge (that is, the first definite point), and integrates the samples.
The charge state measurement unit subtracts the integrated value of the discharge current sample (that is, the amount of discharge electricity) from the remaining capacity at the start of measurement of the charge state, and calculates the remaining capacity of the secondary battery at each time point of the discharge current sampling. . Furthermore, the ratio between the remaining capacity and the discharge capacity is determined as the state of charge of the secondary battery.
[0048]
Since the measured value of the charge state by the charge state measurement unit is based on the integration of the discharge current, the measurement error includes the accumulation of the measurement error of the discharge current. In addition, for example, fluctuations in discharge current or battery temperature during the discharge period give an error to the measured value of the state of charge.
The charging state correction unit monitors the battery voltage, the battery current, and the battery temperature of the secondary battery through the battery state monitoring unit during the discharging period of the secondary battery. Thereby, as described above, the measured value of the charging state is replaced with the second reference charging state at the second definite point and the third reference charging state at the third deterministic point. Thus, the measured value of the state of charge is corrected so as to correspond to the discharge characteristic of the secondary battery indicated by the discharge characteristic table.
Here, the above-described correction by the charge state correction unit may be performed in the same manner for the reference charge states different from those in addition to the second and third reference charge states.
[0049]
The numerical value in the discharge characteristic table is set based on, for example, the discharge characteristic of the initial secondary battery. However, the secondary battery deteriorates, for example, due to repeated charge / discharge cycles. In particular, even when the number of charge / discharge cycles is small, the lithium ion secondary battery is remarkably deteriorated when shallow charge / discharge is repeated at a high temperature or maintained in a high charge state for a long time. The discharge characteristics of the secondary battery change with each discharge due to deterioration and deviate from the initial one.
In the battery management system, the discharge characteristic table correction unit corrects the numerical value in the discharge characteristic table for each discharge as described above. Here, the value obtained by dividing the amount of discharge electricity between two definite points by the difference between the two reference charge states corresponding to each deterministic point is the discharge capacity converted from the amount of discharge electricity (hereinafter referred to as the converted discharge capacity). Equivalent to Therefore, it can be considered that the smaller the variation of the converted discharge capacity between the various pairs of the reference charge states, the better the actual discharge characteristics in the discharge characteristic table. Therefore, the above correction by the discharge characteristic table correction unit maintains high accuracy of approximation of the discharge characteristic by the discharge characteristic table.
Thus, the battery management system corrects the discharge characteristic table according to the change of the discharge characteristic due to the deterioration of the secondary battery, and maintains the correction of the charge state with high accuracy. As a result, the measurement accuracy of the state of charge is maintained high.
[0050]
Specifically, the above-described correction of the discharge characteristic table is performed as follows, for example.
The value obtained by dividing the amount of discharge electricity between the first to second fixed points by the difference between the reference charge states of the first and second (hereinafter referred to as the first converted discharge capacity) is the first to third Corresponds to the second reference charge state when the amount of discharged electricity between the determined points up to is larger than the value divided by the difference between the first and third reference charge states (hereinafter referred to as the second equivalent discharge capacity) Increase the battery voltage value in the discharge characteristics table by a fixed amount. Conversely, when the first converted discharge capacity is smaller than the second converted discharge capacity, the battery voltage value in the discharge characteristic table corresponding to the second reference charge state is decreased by a certain correction amount. Thereby, the position of the second fixed point with respect to the first and third fixed points changes, and the difference between the first converted discharge capacity and the second converted discharge capacity is reduced.
[0051]
Preferably, the first reference charge state is set to a full charge state, and the third reference charge state is set to a complete discharge state. Here, the completely discharged state refers to a charged state when the battery voltage drops to the discharge end voltage. Usually, a set of battery voltage, battery current, and battery temperature corresponding to each of a fully charged state and a fully discharged state is defined. Therefore, the above correction is effective.
[0052]
In addition, the first to third reference charge states may be set to different values for each discharge. In particular, when the discharge is shallow, the third reference charge state may be set higher than the complete discharge state. Thereby, the discharge characteristic table is corrected regardless of the depth of discharge, so that the measurement accuracy of the state of charge is maintained high irrespective of the deterioration of the secondary battery.
In particular, since lithium ion secondary batteries are remarkably deteriorated by repeated shallow charge and discharge at high temperatures, the setting for each discharge as described above is effective for measuring the state of charge of a lithium ion secondary battery.
[0059]
A battery management system according to still another aspect of the present invention includes
(A) For a secondary battery, (a) a voltage detector for measuring battery voltage, (b) a current detector for measuring battery current, and (c) a temperature detector for measuring battery temperature. A battery state monitoring unit for managing a battery state including a set of measurement values by the detection unit;
(B) a battery current integrating unit for integrating the measured values of the battery current by the battery state monitoring unit;
(C) The secondary battery discharge state is measured by the battery current integrating unit from the time when the charge state of the secondary battery is equal to the reference charge state, and based on the discharge capacity, reference charge state, and discharge amount of the secondary battery. A charging state measuring unit for determining a charging state of the secondary battery;
(D) (a) A discharge characteristic table indicating a set of battery voltage, battery current, and battery temperature in each reference charge state is stored, and (b) when the secondary battery is discharged, the battery state is the reference charge state. A charge state correction unit for replacing the measured value of the charge state by the charge state measurement unit with the reference charge state every time a set in the discharge characteristic table corresponding to is included;
(E) An internal resistance measurement unit for detecting a sudden drop in battery voltage by the battery state monitoring unit at the start of secondary battery discharge and determining the internal resistance of the secondary battery based on the change in the battery state at that time; and ,
(F) The internal resistance of the secondary battery is measured by the internal resistance measurement unit every time the secondary battery starts discharging, and the battery voltage and battery current in the discharge characteristics table are based on the change in the internal resistance for each secondary battery discharge. , And a discharge characteristic table correction unit for correcting a set of battery temperatures;
Have
[0060]
The numerical value in the discharge characteristic table is set based on, for example, the discharge characteristic of the initial secondary battery. However, the secondary battery deteriorates, for example, due to repeated charge / discharge cycles. In particular, even when the number of charge / discharge cycles is small, the lithium ion secondary battery is remarkably deteriorated when shallow charge / discharge is repeated at a high temperature or maintained in a high charge state for a long time. The discharge characteristics of the secondary battery change with each discharge due to deterioration and deviate from the initial one.
Since the internal resistance increases with the deterioration of the secondary battery, the deterioration state is evaluated from the change of the internal resistance for each discharge. In the battery management system, the discharge characteristic table correction unit corrects the numerical value in the discharge characteristic table for each discharge based on the learned change in internal resistance as described above. Thereby, the discharge characteristic table is corrected according to the change of the discharge characteristic due to the deterioration of the secondary battery. Thus, even when the deterioration of the secondary battery changes the discharge characteristics, the state of charge is corrected with high accuracy. As a result, the measurement accuracy of the state of charge is maintained high.
[0061]
Specifically, the correction of the discharge characteristic table based on the learning of the internal resistance is performed as follows, for example.
The open circuit voltage of the secondary battery is the sum of the battery voltage and the voltage drop due to the internal resistance. Therefore, the open circuit voltage corresponding to a specific reference charge state has a constant relational expression between a set of battery voltage, discharge current, and battery temperature in the discharge characteristics table corresponding to the reference charge state and the internal resistance. Make it. Here, the battery temperature is used when the internal resistance is converted into a value at the battery temperature.
The open circuit voltage is substantially constant regardless of the deterioration of the secondary battery in a constant charge state. Therefore, when the internal resistance changes due to deterioration of the secondary battery under a constant discharge current and battery temperature, the amount of change in battery voltage can be obtained from the above relational expression.
For example, the discharge characteristic table correction unit stores an open circuit voltage corresponding to each reference charging state. Based on these open circuit voltages and the above relational expression, the respective change amounts of the battery voltage in the discharge characteristic table corresponding to the learned change in internal resistance are obtained, and the respective battery voltages are corrected by the change amount.
[0062]
The above battery management system
(A) a discharge capacity measuring unit for determining a discharge capacity for each discharge of the secondary battery based on a measured value of the amount of discharged electricity by the battery current integrating unit and a measured value of the charged state by the charged state measuring unit; and ,
(B) An internal resistance correction unit for correcting the measurement value of the internal resistance used by the charge state measurement unit based on the change of the discharge capacity for each discharge and the measurement value of the charge state by the charge state measurement unit;
May be further included.
Other,
Measure the internal resistance used by the charge state measurement unit based on the change in the measured value of the internal resistance by the internal resistance measurement unit for each discharge of the secondary battery and the measured value of the charge state by the charge state measurement unit Internal resistance correction part for correcting the value;
May be further included.
[0063]
Strictly speaking, when the secondary battery is discharged, the internal resistance increases as the state of charge decreases. The rate of increase is quite small in the early secondary batteries. However, the increase rate increases with the deterioration of the secondary battery. That is, in the deteriorated secondary battery, the internal resistance obviously increases with the passage of discharge time.
The battery management system evaluates the deterioration state of the secondary battery through learning of the discharge capacity or the internal resistance, and corrects the measurement value of the internal resistance according to the deterioration state and the measurement value of the charge state. In particular, the measured value of internal resistance is increased at the end of discharge. Furthermore, the rate of increase is increased for a degraded secondary battery. Thus, the calculation error of the open circuit voltage is reduced, and the measurement accuracy of the state of charge is further improved.
[0064]
Specifically, the measured value of the internal resistance is corrected as follows, for example.
When the discharge capacity of the deteriorated secondary battery is reduced beyond a predetermined ratio with respect to the initial value, or the internal resistance value of the deteriorated secondary battery is the predetermined ratio of the internal resistance value of the initial secondary battery. When the value increases beyond, the measured value of the internal resistance used to calculate the open circuit voltage is corrected so as to increase by a predetermined coefficient, particularly at the end of the discharge.
[0066]
In a deteriorated secondary battery, the drop in battery voltage becomes slow especially at the end of discharge. As a result, generally at the end of discharge, the measured value of the charge state falls to the value of the reference charge state before the definite point for the reference charge state. The battery management system then fixes the measured value of the state of charge to a value of the reference state of charge or a value higher than the value by a predetermined width (for example, 1%). As a result, the substantial drop in the measured value of the charged state is delayed, so that the measurement error of the charged state is generally reduced, and in particular, the closer to the fully discharged state, the smaller.
The battery management system further continues to measure the amount of discharged electricity during the period in which the measured value of the charging state is fixed to a value near the reference charging state as described above. Thereby, the discharge capacity is converted from the measured value of the amount of discharged electricity from the start of discharge to the time of switching to charging and the measured value of the state of charge at the time of switching to charging. In particular, when switching from discharging to charging occurs during the fixed period of the measured value of the charged state, the amount of discharge electricity during the fixed period is taken into account for the conversion of the discharge capacity. Therefore, the measurement error of the discharge capacity is generally suppressed to be small.
[0067]
In the above battery management system, when the measured value of the battery temperature by the temperature detecting unit exceeds a predetermined threshold value, or when the measured value of the internal resistance by the internal resistance measuring unit exceeds the predetermined threshold value, the battery state monitoring unit is Alternatively, a signal for requesting a reduction in battery current may be transmitted.
Here, the threshold value for the battery temperature is preferably sufficiently lower than a temperature at which the stability of the secondary battery is lost, for example, thermal runaway may occur.
[0068]
An abnormal increase in internal resistance causes excessive Joule heat due to the discharge current, so overheating is likely to occur in the secondary battery. The threshold value of the internal resistance is preferably set so that the stability of the secondary battery is lost, and the battery temperature is maintained sufficiently lower than the temperature at which, for example, thermal runaway may occur.
By setting these threshold values, the host can sufficiently reduce the discharge current before secondary battery deterioration or thermal runaway due to overheating occurs. Thus, the battery management system described above can avoid deterioration of the secondary battery and sufficiently ensure safety. Furthermore, since the forced interruption of the discharge current when overheating occurs can be avoided, the sudden shutdown of the host is prevented, and the reliability of the battery pack can be improved.
[0071]
The battery pack according to the present invention includes any of the battery management systems described above together with a secondary battery. The battery pack notifies the device driven by the internal secondary battery with high accuracy, in particular, the state of charge of the secondary battery regardless of the deterioration of the secondary battery.
[0072]
  The secondary battery charge state measurement method according to one aspect of the present invention includes: (A) as the reference charge state of the secondary battery, the first, second, and third reference charge states are determined in order of magnitude; Setting a discharge characteristic table showing a set of battery voltage, battery current, and battery temperature in each reference charging state;
(B) monitoring the battery state including a set of battery voltage, battery current, and battery temperature for the secondary battery;
(C) Accumulating the discharge current of the secondary battery from a point in time when the battery state includes a set in the discharge characteristic table corresponding to the first reference charge state (hereinafter referred to as a first definite point). Measuring the amount of discharged electricity and determining the state of charge of the secondary battery based on the amount of discharged electricity, the discharge capacity of the secondary battery, and the first reference state of charge;
(D) At the time when the battery state includes one set in the discharge characteristic table corresponding to the second reference charge state (hereinafter referred to as a second definite point), the charge in the second reference charge state Replacing the state measurements;
(E) integrating the discharge current of the secondary battery from the second deterministic point and measuring the amount of discharge electricity, and based on the amount of discharge electricity, the discharge capacity, and the second reference charge state, Determining the state of charge of the secondary battery;
(F) When the battery state of the secondary battery includes a set in the discharge characteristic table corresponding to the third reference charge state (hereinafter referred to as a third definite point), the third reference charge Replacing the state-of-charge measurement with a state; and
(G) A reference charge state between the first and the second is the discharge electric quantity between the first to second fixed points.Battery voltage determined by battery temperature and discharge current atThe value divided by the difference between the first and third fixed points of the first to third fixed charge states of the first and thirdAbove battery voltageCorrecting the set of battery voltage, battery current, and battery temperature in the discharge characteristics table to match the value divided by the difference;
Have
[0073]
In the step of determining the charge state based on the first reference charge state, first, for example, the product of a predetermined discharge capacity and the first reference charge state is set as the remaining capacity at the start of measurement of the charge state. Here, the first reference charge state is preferably a full charge state.
The discharge capacity is preferably learned for each discharge. That is, the integrated value of the discharge current over the entire discharge period is calculated for each discharge, and the integrated value is regarded as the discharge capacity. In addition, the discharge capacity may be set according to the battery state detected at the start of discharge from the correspondence table between the discharge capacity and the battery state at the start of discharge.
[0074]
Next, the measured value of the discharge current is sampled, for example, at predetermined time intervals from the start of measurement of the state of charge (that is, the first definite point), and the samples are integrated.
Further, the remaining capacity of the secondary battery is calculated at each time point of sampling of the discharge current from the difference between the remaining capacity at the start of measurement of the charge state and the integrated value of the discharge current sample (ie, the amount of discharge electricity). Furthermore, the ratio between the remaining capacity and the discharge capacity is determined as the state of charge of the secondary battery.
The same applies to the step of determining the state of charge based on the second reference state of charge.
[0075]
Since the measured value of the state of charge is based on the integration of the discharge current, the accumulated measurement error of the discharge current is included as a measurement error. In addition, for example, fluctuations in discharge current or battery temperature during the discharge period give an error to the measured value of the state of charge.
However, due to the step of replacing the measured value of the state of charge in the second or third reference state of charge, the measured value of the state of charge is the second reference state of charge at the second deterministic point and at the third definite point. In the third reference charging state, each is replaced. As a result, the measured value of the state of charge is corrected so as to correspond to the discharge characteristic of the secondary battery indicated by the discharge characteristic table.
Here, in addition to the second and third reference charge states, the above replacement may be performed in the same manner for other reference charge states.
[0076]
The numerical value in the discharge characteristic table is set based on, for example, the discharge characteristic of the initial secondary battery. However, the secondary battery deteriorates, for example, due to repeated charge / discharge cycles. In particular, even when the number of charge / discharge cycles is small, the lithium ion secondary battery is remarkably deteriorated when shallow charge / discharge is repeated at a high temperature or maintained in a high charge state for a long time. The discharge characteristics of the secondary battery change with each discharge due to deterioration and deviate from the initial one.
In the step of correcting the discharge characteristic table, as described above, the battery voltage and the like in the discharge characteristic table are corrected for each discharge. Here, the value obtained by dividing the amount of discharge electricity between two definite points by the difference between the two reference charge states corresponding to the respective definite points corresponds to the converted discharge capacity by the amount of discharge electricity. Therefore, it can be considered that the smaller the variation of the converted discharge capacity between the various pairs of the reference charge states, the better the actual discharge characteristics in the discharge characteristic table. Therefore, the correction of the discharge characteristic table maintains a high accuracy of the approximation of the discharge characteristic according to the discharge characteristic table.
Thus, in the above-described charging state measurement method, the discharging characteristic table is corrected in accordance with the change in discharging characteristics due to deterioration of the secondary battery, and the above-described correction of the charging state is maintained with high accuracy. As a result, the measurement accuracy of the state of charge is maintained high.
[0077]
Specifically, the above-described correction of the discharge characteristic table is performed as follows, for example.
The value obtained by dividing the amount of discharge electricity between the first to second fixed points by the difference between the reference charge states of the first and second (hereinafter referred to as the first converted discharge capacity) is the first to third Corresponds to the second reference charge state when the amount of discharged electricity between the determined points up to is larger than the value divided by the difference between the first and third reference charge states (hereinafter referred to as the second equivalent discharge capacity) Increase the battery voltage value in the discharge characteristics table by a fixed amount. Conversely, when the first converted discharge capacity is smaller than the second converted discharge capacity, the battery voltage value in the discharge characteristic table corresponding to the second reference charge state is decreased by a certain correction amount. Thereby, the position of the second fixed point with respect to the first and third fixed points changes, and the difference between the first converted discharge capacity and the second converted discharge capacity is reduced.
[0078]
Preferably, the first reference charge state is set to a full charge state, and the third reference charge state is set to a complete discharge state. Usually, a set of battery voltage, battery current, and battery temperature corresponding to each of a fully charged state and a fully discharged state is defined. Therefore, the above correction is effective.
In addition, the first to third reference charge states may be set to different values for each discharge. In particular, when the discharge is shallow, the third reference charge state may be set higher than the complete discharge state. Thereby, the discharge characteristic table is corrected regardless of the depth of discharge, so that the measurement accuracy of the state of charge is maintained high irrespective of the deterioration of the secondary battery.
In particular, since lithium ion secondary batteries are remarkably deteriorated by repeated shallow charge and discharge at high temperatures, the setting for each discharge as described above is effective for measuring the state of charge of a lithium ion secondary battery.
[0085]
The charging state measuring method according to a further different aspect of the present invention is as follows.
(A) A step of setting a discharge characteristic table indicating a set of a battery voltage, a battery current, and a battery temperature in a reference charging state for the secondary battery;
(B) for a secondary battery, monitoring battery status including a set of battery voltage, battery current, and battery temperature;
(C) detecting a sudden drop in battery voltage at the start of secondary battery discharge, and determining an internal resistance of the secondary battery based on a change in battery state at that time;
(D) The secondary battery is charged from the time when the charge state of the secondary battery is equal to the reference charge state, and the discharge current of the secondary battery is measured by integrating the discharge current of the secondary battery. And determining a charge state of the secondary battery based on the reference charge state;
(E) replacing the measured value of the charge state with the reference charge state each time the battery state includes a set in the discharge characteristic table corresponding to the reference charge state; and
(F) correcting a set of battery voltage, battery current, and battery temperature in the discharge characteristics table based on a change in internal resistance for each discharge of the secondary battery;
Have
[0086]
The numerical value in the discharge characteristic table is set based on, for example, the discharge characteristic of the initial secondary battery. However, the secondary battery deteriorates, for example, due to repeated charge / discharge cycles. In particular, even when the number of charge / discharge cycles is small, the lithium ion secondary battery is remarkably deteriorated when shallow charge / discharge is repeated at a high temperature or maintained in a high charge state for a long time. The discharge characteristics of the secondary battery change with each discharge due to deterioration and deviate from the initial one.
Since the internal resistance increases with the deterioration of the secondary battery, the deterioration state is evaluated from the change of the internal resistance for each discharge. In the above charging state measurement method, the battery voltage and the like in the discharge characteristics table are corrected for each discharge based on the learned change in internal resistance. Thereby, the discharge characteristic table is corrected according to the change of the discharge characteristic due to the deterioration of the secondary battery. Thus, even when the deterioration of the secondary battery changes the discharge characteristics, the state of charge is corrected with high accuracy. As a result, the measurement accuracy of the state of charge is maintained high.
[0087]
The open circuit voltage of the secondary battery is the sum of the battery voltage and the voltage drop due to the internal resistance. Therefore, the open circuit voltage corresponding to a specific reference charge state has a constant relational expression between a set of battery voltage, discharge current, and battery temperature in the discharge characteristics table corresponding to the reference charge state and the internal resistance. Make it. Here, the battery temperature is used when the internal resistance is converted into a value at the battery temperature.
The open circuit voltage is substantially constant regardless of the deterioration of the secondary battery in a constant charge state. Therefore, when the internal resistance changes due to deterioration of the secondary battery under a constant discharge current and battery temperature, the amount of change in battery voltage can be obtained from the above relational expression.
In the step of correcting the battery voltage or the like in the discharge characteristic table, for example, an open circuit voltage corresponding to each reference charging state is stored. Based on these open circuit voltages and the above relational expression, the respective changes in the battery voltage in the discharge characteristics table corresponding to the learned change in internal resistance are obtained, and each battery voltage is corrected by the change. The
[0088]
The charge state measurement method above is
(A) integrating the discharge current for each discharge of the secondary battery, measuring the amount of discharge electricity, and determining the discharge capacity based on the amount of discharge electricity and the measured value of the state of charge; and
(B) Based on the change in discharge capacity for each discharge and the measured value of the charge state, the measured value of internal resistance used in the step of correcting the set of battery voltage, battery current, and battery temperature in the discharge characteristics table is corrected. Step to do;
May be further included.
Other,
In the step of obtaining the measured value of the internal resistance for each discharge of the secondary battery and correcting the set of the battery voltage, the battery current, and the battery temperature in the discharge characteristics table based on the change and the measured value of the charging state. Correcting the measurement of the internal resistance used;
May be further included.
[0089]
Strictly speaking, when the secondary battery is discharged, the internal resistance increases as the state of charge decreases. The rate of increase is quite small in the early secondary batteries. However, the increase rate increases with the deterioration of the secondary battery. That is, in the deteriorated secondary battery, the internal resistance obviously increases with the passage of discharge time.
In the above charging state measuring method, the deterioration state of the secondary battery is evaluated through learning of the discharge capacity or the internal resistance, and the measured value of the internal resistance is corrected according to the deterioration state and the measured value of the charged state. In particular, the measured value of internal resistance increases at the end of discharge. Furthermore, the rate of increase is greater for degraded secondary batteries. Thus, the calculation error of the open circuit voltage is reduced, and the measurement accuracy of the state of charge is further improved.
[0090]
Specifically, the measured value of the internal resistance is corrected as follows, for example.
When the discharge capacity of the deteriorated secondary battery is reduced beyond a predetermined ratio with respect to the initial value, or the internal resistance value of the deteriorated secondary battery is the predetermined ratio of the internal resistance value of the initial secondary battery. When the value increases beyond, the measured value of the internal resistance used to calculate the open circuit voltage is corrected so as to increase by a predetermined coefficient, particularly at the end of the discharge.
[0094]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, taking preferred examples.
[0095]
Example 1
FIG. 1 is a block diagram showing a battery pack 10 according to Embodiment 1 of the present invention.
The battery pack 10 includes a secondary battery block 1 and a battery management system 2.
The secondary battery block 1 includes a plurality of cells 1a, 1b,. Each cell is preferably a lithium ion secondary battery. In addition, a nickel-cadmium secondary battery or a nickel-hydrogen secondary battery may be used. The positive electrode 8a and the negative electrode 8b of the secondary battery block 1 are connected to the host H, respectively, and output power to the host H during discharging, and input power from a charger in the host H during charging.
[0096]
The battery management system 2 includes sensor groups 3 to 5 and a control unit 6 for secondary batteries.
The sensor group includes a temperature detection unit 3, a voltage detection unit 4, and a current detection unit 5.
The temperature detection unit 3 measures the temperature T of the secondary battery block 1 through a thermistor 3a installed in the vicinity of the secondary battery block 1.
The voltage detection unit 4 measures the voltage V for each cell in the secondary battery block 1.
The current detection unit 5 measures a voltage drop at the resistor 5a connected in series with the secondary battery block 1. Since the resistor 5a has a predetermined resistance value, the battery current I is detected from the voltage drop amount.
[0097]
The control unit 6 includes a CPU and a memory 6a. The memory 6a is preferably a flash memory. In addition to the memory 6a, a DRAM may be included as a working memory for the CPU or a buffer for communication with the host H.
For example, the control unit 6 executes firmware stored in the memory 6a, a battery state monitoring unit 6b, a battery current integration unit 6c, a charge state measurement unit 6d, a charge state correction unit 6e, a discharge capacity measurement unit 6f, and a discharge, which will be described later It functions as a characteristic table correction unit 6g.
[0098]
The battery state monitoring unit 6b receives a command from the host H through the communication terminal 9, controls the sensor groups 3 to 5 according to the command, and monitors the battery voltage V, the battery current I, and the battery temperature T. Further, information indicating the state of the secondary battery including those measured values, that is, the battery state is managed, and is notified to the host H through the communication terminal 9 in particular. The host H performs charge / discharge control of the secondary battery based on the battery state.
[0099]
The battery state monitoring unit 6b further functions as a protection circuit for the secondary battery. That is, the battery current is interrupted according to the battery state, and the secondary battery is prevented from being deteriorated and destroyed due to overcharge, overdischarge, overvoltage, overcurrent, and overheating.
For example, when the voltage exceeds a predetermined threshold in any cell in the secondary battery block 1, an abnormal increase in the voltage is notified to the host H. At that time, the host H sends a command to the control unit 6 to instruct to cut off the discharge current. In accordance with the command, the control unit 6 turns off the first switch 7a during discharging and the second switch 7b during charging to cut off the battery current.
[0100]
On the other hand, when the measured value of the battery temperature exceeds a predetermined threshold, the battery state monitoring unit 6b may send a signal for requesting a reduction in battery current to the host H.
Here, each threshold value of the battery temperature is preferably sufficiently lower than a temperature at which the stability of the secondary battery block 1 is lost, for example, thermal runaway may occur. Thereby, before the deterioration or thermal runaway of the secondary battery block 1 due to overheating occurs, the host H can sufficiently reduce the discharge current. In particular, since the forced interruption of the discharge current at the occurrence of overheating is avoided, the host H is prevented from being shut down suddenly.
[0101]
The battery current integration unit 6c samples the discharge current I from the predetermined time point at a constant time interval (for example, about 2 seconds) by the current detection unit 5, and integrates these samples. The integrated value is substantially equal to the amount of electricity discharged by the secondary battery block 1 during the integration period.
[0102]
The charging state measuring unit 6d measures the charging state of the secondary battery as follows. First, the discharge current I is integrated from the start of discharge by the battery current integration unit 6c. Next, based on the predetermined discharge capacity of the secondary battery block 1 and the integrated value of the discharge current I (that is, the amount of discharge electricity), the state of charge of the secondary battery block 1 at each sampling time is determined. That is, the difference between the discharge capacity and the amount of discharge electricity is regarded as the remaining capacity, and the ratio between the remaining capacity and the discharge capacity is calculated as the state of charge. The measured value of the charging state is notified to the host H as a part of the battery state.
[0103]
The measured value of the state of charge based on the integration of the discharge current I generally includes many errors. The charged state correcting unit 6e corrects the measured value of the charged state based on the discharge characteristics of the secondary battery block 1 stored in the memory 6a as follows.
In the correction, the variation of the discharge characteristics due to the deterioration of each cell in the secondary battery block 1 is further reflected as follows. As a result, the measurement of the state of charge is maintained with high accuracy regardless of the deterioration of the secondary battery.
[0104]
The charge state correcting unit 6e stores the discharge characteristics of the secondary battery block 1 as follows.
First, a plurality of reference value charging states (that is, reference charging states) are determined. For example, the fully charged state (100%), 70%, 10%, 5%, 2%, and the fully discharged state (0%) are set as the reference charged state. Here, some of these may not be included, and other charge states may be included.
Next, a set of the battery voltage V, the discharge current I, and the battery temperature T corresponding to each of the reference charge states is determined based on, for example, the discharge characteristics (that is, the initial discharge characteristics) of the secondary battery block 1 immediately after manufacture. This is stored in the memory 6a.
Table 1 is a table showing a set of the battery voltage V, the discharge current I, and the battery temperature T per cell corresponding to the reference charge state of 5%, which is determined based on the initial discharge characteristics.
[0105]
[Table 1]

[0106]
Similar tables are stored in the memory 6a for other reference charging states, for example, 100%, 10% fully charged, and 0% fully discharged. As shown in Table 1, a table showing a set of the battery voltage, the discharge current, and the battery temperature corresponding to the reference charge state is hereinafter referred to as a discharge characteristic table.
In the discharge characteristic table shown in Table 1, one reference value of the battery voltage V per cell is set for each predetermined range of the discharge current I and the battery temperature T for one reference charge state. .
[0107]
FIG. 2 is a graph showing changes in the amount of discharged electricity with respect to each of the battery voltage V and the state of charge measured by the battery management system 2 during the discharge period of the secondary battery block 1. FIG. 2 (a) shows the relationship between the battery voltage V and the amount of discharge electricity (that is, the discharge curve) in the secondary battery block 1. FIG. 2 (b) shows the relationship between the measured value of the state of charge and the amount of discharged electricity.
In FIG. 2, it is assumed that during the discharge period of the secondary battery block 1, the discharge current I and the battery temperature T do not show excessive fluctuations and are relatively stable. At that time, as shown in FIG. 2 (a), the battery voltage V decreases almost monotonously as the amount of discharge electricity increases.
[0108]
In (a) of FIG. 2, the discharge curve of the secondary battery block 1 is indicated by a broken line at the initial stage (number of charge / discharge cycles = 0), and by a solid line at the number of charge / discharge cycles = 250 cycles. Here, in both discharge curves, it is assumed that the fluctuations in the discharge current and the battery temperature during the discharge period substantially coincide.
Hereinafter, for the purpose of simplifying the explanation, it is assumed that discharging is continuously performed from a fully charged state 100% to a fully discharged state 0%. Furthermore, only the first reference charge state (full charge state) 100%, the second reference charge state 10%, and the third reference charge state (complete discharge state) 0% are considered as the reference charge state.
[0109]
The charging state correction unit 6e measures the battery voltage V, the discharging current I, and the battery temperature T through the battery state monitoring unit 6b when the secondary battery block 1 starts discharging. Thereby, it is confirmed whether or not the set (V, I, T) of those measured values matches any of the set of reference values in the discharge characteristic table corresponding to the first reference charge state 100%. Specifically, for example, a set (VA, I, T) including measured values of the discharge current and the battery temperature is searched from the set of reference values, and the reference value (first value) of the battery voltage included in the set is searched. The reference voltage value) VA is compared with the measured value V of the battery voltage. When they substantially match, the charging state correction unit 6e sets the charging state S of the secondary battery block 1 to the first reference charging state 100%. This setting time point A shown in FIG. 2 is hereinafter referred to as a first fixed point.
The charging state correction unit 6e further sets the discharge capacity of the secondary battery block 1 as the remaining capacity at the first definite point A. Here, a value (initial value) at the time of manufacture is stored in advance as the discharge capacity of the secondary battery block 1 in the memory 6a.
[0110]
The first reference charge state may be set to a value lower than 100% of the full charge state. At that time, the remaining capacity at the first definite point is set to the product of the discharge capacity and the first reference charge state, and the measurement of the charge state is started from a value lower than 100% of the full charge state.
[0111]
The charging state measuring unit 6d measures the charging state S from the difference between the remaining capacity at the first determined point A and the amount of discharged electricity measured by the battery current integrating unit 6c after the first determined point A.
In the initial secondary battery block 1, the measured value V of the battery voltage drops along the broken line shown in FIG. On the other hand, the measured value S of the state of charge decreases linearly from the first definite point A as shown in FIG.
[0112]
The charging state correcting unit 6e monitors the battery voltage V, the discharging current I, and the battery temperature T through the battery state monitoring unit 6b after the first definite point A. Further, it is confirmed whether or not the set of measured values (V, I, T) matches one of the set of reference values in the discharge characteristic table corresponding to the second reference charge state 10%. Specifically, for example, a set (VB, I, T) including measured values of the discharge current and the battery temperature is searched from the set of reference values, and the reference value of the battery voltage included in the set (second) The reference voltage value) VB is compared with the measured value V of the battery voltage. When they substantially match, the charging state correction unit 6e replaces the measured value S of the charging state with the second reference charging state 10%. Hereinafter, this replacement time point is referred to as a second fixed point. In FIG. 2, the point B represents the second definite point in the initial discharge of the secondary battery block 1. This replacement corrects the error in the measured value S of the state of charge.
[0113]
The charging state correcting unit 6e further sets the product of the discharge capacity and the second reference charging state 10% as the remaining capacity at the second definite point B. The charging state measurement unit 6d measures the charging state S from the difference between the remaining capacity at the second fixed point B and the amount of discharged electricity after the second fixed point B.
After the second definite point B, the set of measured values of battery voltage V, discharge current I, and battery temperature T (V, I, T) corresponds to the third reference charge state (complete discharge state) 0% discharge The charge state correction unit 6e checks whether or not it matches any of the reference value pairs in the characteristic table. Specifically, for example, a set (VC, I, T) including measured values of the discharge current and the battery temperature is searched from the set of reference values, and the reference value of the battery voltage (discharge end) included in the set is searched. Voltage value) VC and measured value V of battery voltage are compared. When they substantially coincide with each other, the charging state correcting unit 6e replaces the measured value S of the charging state with 0% of the complete discharging state, and stops discharging the secondary battery block 1. This point is hereinafter referred to as the third definite point. In FIG. 2, the point C represents the third definite point in the initial discharge of the secondary battery block 1. By this replacement, the time when the charged state reaches the fully discharged state is accurately detected.
[0114]
For example, when the number of charge / discharge cycles increases, or particularly in a lithium ion secondary battery, when the battery is kept in a high charge state at a high temperature for a long time, the secondary battery deteriorates. In the deteriorated secondary battery, the discharge capacity is reduced from the initial value, and the shape of the discharge curve is greatly deviated from the initial one.
For example, in the discharge curve of charge / discharge cycles = 250 cycles (solid line in Fig. 2 (a)), the start of discharge (first definite point A) from the initial discharge curve (dashed line in Fig. 2 (a)) The amount of discharge electricity in the entire discharge period from the battery to the end (battery voltage V = discharge end voltage VC) is reduced. That is, when the amount of discharge electricity to the third fixed point C of the initial secondary battery block 1 is Q4, and the amount of discharged electricity to the third fixed point CP of the deteriorated secondary battery block 1 is Q2, Q2 <Q4. Furthermore, the battery voltage with respect to a certain amount of discharge electricity from the start of discharge decreases. In addition, the battery voltage drop is abrupt at the start of discharge, and conversely, the battery voltage drop is moderate at the end of discharge. As a result, in the deteriorated secondary battery block 1, as shown in FIG. 2 (a), the second definite point is advanced to the point BP and the third definite point is accelerated to the point CP. The amount of electricity discharged is reduced. That is, when the amount of discharge electricity to the second fixed point B of the initial secondary battery block 1 is Q3, and the amount of discharged electricity to the second fixed point BP of the deteriorated secondary battery block 1 is Q1, Q1 <Q3. Furthermore, the difference in the amount of electric discharge to the second fixed point (distance between point B and point BP = Q3-Q1) is the difference to the third fixed point (distance between point C and point CP = Q4-Q2). Larger) Therefore, in the discharge of the deteriorated secondary battery block 1, the actual charge state particularly at the second definite point BP increases from the second reference charge state 10%.
[0115]
For each discharge of the secondary battery block 1, the discharge characteristic table correction unit 6g discharges electric energy Q1 during the discharge period from the first definite point A to the second deterministic point BP and The amount of discharge electricity Q2 during the discharge period up to the third definite point CP is stored. Further, the discharge characteristic table is corrected as follows based on the discharge electric quantities Q1 and Q2. In the following, for the purpose of correcting the discharge characteristics table and explaining the effects, it is assumed that the state of charge of the deteriorated secondary battery block 1 is measured and corrected using the initial value of the discharge capacity and the initial discharge characteristics table. To do.
[0116]
The charge state measuring unit 6d sets the discharge capacity of the secondary battery block 1 to an initial value and measures the charge state. Therefore, the measured value S of the state of charge decreases along the line AB as shown by the thick solid line in FIG. 2B during the period from the start of discharge to the second definite point.
As shown in FIG. 2 (a), at the start of discharge, in the deteriorated secondary battery block 1, the battery voltage V (solid line) drops more rapidly than the initial battery voltage (broken line). Therefore, the second definite point BP is earlier than the initial one B. As a result, the capacity jump occurs as shown between the points B1 and B2 in FIG.
[0117]
As shown in FIG. 2 (b), the measured value S of the charge state falls to the value 0% of the third reference charge state before the third definite point CP. At that time, the charging state correcting unit 6e fixes the measured value S of the charging state to a value (for example, 1%) slightly higher than 0% of the third reference charging state. When the charging state correcting unit 6e detects the third definite point CP, the charging state measurement value S is set to 0% of the complete discharging state. At that time, the controller 6 turns off the first switch 7a to cut off the discharge current.
[0118]
In the discharge period from the first definite point A to the third definite point CP, the discharge capacity measuring unit 6f calculates the total amount Q2 of discharge electricity. Further, the discharge capacity is updated with the total amount Q2. In the next discharge, the charge state measurement unit 6d measures the charge state based on the updated discharge capacity.
By learning this discharge capacity, in the example of FIG. 2 (b), the slope of the thick solid line indicating the measured value S of the state of charge (that is, the slope of the straight line AC) is the slope indicated by the one-dot chain line in the next discharge. (Ie, the slope of the straight line A-CP). Thereby, for example, the capacity jump at the second definite point BP (see the point B1a-point B2 in FIG. 2B) is reduced.
[0119]
The discharge characteristic table correction unit 6g includes a discharge electricity amount Q1 (hereinafter referred to as a first discharge electricity amount) during a discharge period from the first decision point A to the second decision point BP, and a first decision point. The amount of discharge electricity Q2 (hereinafter referred to as the second amount of discharge electricity) during the discharge period from A to the third definite point CP is stored. Further, the discharge characteristic table is corrected as follows based on the first discharge electricity quantity Q1 and the second discharge electricity quantity Q2.
[0120]
The first discharge electricity amount Q1 is regarded as the discharge electricity amount between the first reference charge state 100% and the second reference charge state 10%, and the discharge capacity (ie, the fully charged state 100% to the complete discharge state 0) % Of discharge electricity) is converted by the following formula: QA = Q1 / (100−10) × 100. This converted discharge capacity QA is referred to as a first converted discharge capacity.
Similarly, the second converted discharge capacity QB is defined by the following formula based on the second discharge electricity quantity Q2: QB = Q2 / (100−0) × 100 (= Q2).
[0121]
When the discharge characteristic table closely approximates the actual discharge curve, the first converted discharge capacity QA and the second converted discharge capacity QB substantially match. That is, the difference between the first converted discharge capacity QA and the second converted discharge capacity QB represents a deviation from the actual discharge curve in the discharge characteristic table.
The discharge characteristic table correction unit 6g corrects the discharge characteristic table based on the difference between the first converted discharge capacity QA and the second converted discharge capacity QB. For example, when the first converted discharge capacity QA is larger than the second converted discharge capacity QB (QA> QB), the second reference voltage VB is increased by a predetermined correction amount, and when it is reversed (QA <QB) .
[0122]
In FIG. 2 (b), the first converted discharge capacity QA is equal to the amount of discharge electricity determined at the intersection of the straight line A-B2 and the horizontal axis, and the second converted discharge capacity QB is the straight line A-CP and the horizontal axis. It is equal to the amount of discharge electricity Q2 determined by the intersection of. Accordingly, the first converted discharge capacity QA is smaller than the second converted discharge capacity QB (QA <QB). At that time, the discharge characteristic table correction unit 6g lowers the second reference voltage VB in the discharge characteristic table by, for example, 1 mV. This corrected reference voltage is hereinafter referred to as a corrected reference voltage VB1: VB1 = VB−1 mV.
When the discharge current and battery temperature show the same fluctuation as the previous discharge in the next discharge, when the battery voltage V exceeds the second reference voltage VB from the first reference voltage VA and drops to the corrected reference voltage VB1 The charging state correction unit 6e detects the second fixed point BQ. That is, the second definite point is delayed from point BP to point BQ in FIG. Thereby, the capacity jump (distance between point B3 and point B4 in FIG. 2B) is reduced more than the capacity jump in the previous discharge (distance between point B1 and point B2).
Thus, the control unit 6 can improve the measurement accuracy of the state of charge by learning the discharge capacity and correcting the discharge characteristic table based on the converted discharge capacity.
[0123]
In the above description, it is assumed that the charge state is measured and corrected for the secondary battery block 1 with the number of charge / discharge cycles = 250 cycles using the initial value of the discharge capacity and the initial discharge characteristic table. When starting the learning of the discharge capacity and the correction of the discharge characteristic table from the number of charge / discharge cycles smaller than 250 cycles, the deviation of the discharge curve due to the deterioration of the secondary battery block 1 is considerably larger than that shown in (a) of FIG. Since it is small, the measurement accuracy of the charge state is high. In particular, the capacity jump is much smaller than that shown in FIG.
Furthermore, in the above description, only three reference charging states are set. By setting more reference charge states, the measurement accuracy of the charge state can be further improved.
[0124]
When the period from the end of the previous discharge to the start of the next discharge is long, or when the discharge is interrupted for a long time before the end of the discharge, the secondary battery block 1 generally deteriorates. In particular, in a lithium ion secondary battery, when the battery is kept in a high charge state at a high temperature for a long time, the deterioration proceeds remarkably. As a result, the discharge characteristics of the secondary battery block 1 change relatively greatly, and the measurement accuracy of the state of charge according to the discharge capacity and the discharge characteristics table learned in the previous discharge is relatively greatly reduced.
[0125]
The discharge capacity measuring unit 6f maintains the learning accuracy of the discharge capacity as follows, regardless of such a relatively large change in discharge characteristics.
FIG. 3 is a graph showing a change in the measured value S of the state of charge accompanying an increase in the amount of discharged electricity when the discharge capacity and discharge characteristics of the secondary battery block 1 deviate relatively from those learned. FIG. 3 (a) shows, for the secondary battery block 1, a discharge curve before deterioration as a solid line and a discharge curve after deterioration as a broken line. FIG. 3B shows the relationship between the measured value S of the state of charge and the amount of discharged electricity. In FIG. 3, it is assumed that during the discharge period of the secondary battery block 1, the discharge current I and the battery temperature T do not show excessive fluctuations, and the battery voltage V decreases almost monotonously as the amount of discharge electricity increases. . Furthermore, it is assumed that the fluctuations in the discharge current and the battery temperature during the discharge period substantially match between the discharges before and after the deterioration.
[0126]
Based on the discharge curve before deterioration indicated by the solid line in FIG. 3 (a), the discharge capacity and the discharge characteristic table are learned. The discharge characteristic table shows that the first reference charge state is 100%, the second reference charge state is 10%, the third reference charge state is 5%, the fourth reference charge state is 2%, and the fifth reference charge state is 0%. The battery state at the definite points A to E for each of the%, in particular the first reference voltage VA, the second reference voltage VB, the third reference voltage VC, the fourth reference voltage VD, and the fifth reference voltage ( Including discharge end voltage (VE).
[0127]
When a long time elapses from the previous discharge to the next discharge and the deterioration of the secondary battery block 1 proceeds during that time, the battery voltage V is indicated by a broken line in FIG. It descends along the discharge curve. As a result, the battery voltage V drops quickly from the first reference voltage VA to the second reference voltage VB, and the second definite point is advanced (see between point B and point BR in FIG. 3A). As a result, a capacity jump as shown between the points B1 and B2 in FIG.
Thereafter, the battery voltage V drops to the third reference voltage VC, and the measured value S of the charging state decreases to the value of the third reference charging state 5% before the third deterministic point CR is detected. (Point C1 in FIG. 3 (b)). Therefore, the measured value S of the state of charge is fixed to the value 5% of the third reference state of charge until the third definite point CR (see between point C1 and point C2 in FIG. 3B). Similarly, the measured value S of the charge state is 2% of the fourth reference charge state between the points D1 and D2 in FIG. 3B, and the fifth reference charge state between the points E1 and E2. The value of 1% is slightly higher than the value of 0%.
[0128]
The discharge capacity measuring unit 6f calculates the integration of the discharge current I by the battery current integrating unit 6c, for a fixed period of the measured value S of the state of charge (for example, between point C1 and point C2 in FIG. 3B, between point D1 and point D2 , And between point E1 and point E2).
When the battery voltage V drops to the end-of-discharge voltage VE, or when switching from discharging to charging is notified from the host H, the discharge capacity measuring unit 6f stops the accumulation of the discharge current I by the battery current integrating unit 6c. Further, the discharge capacity is converted based on the integrated value (discharged electric quantity) of the discharge current I until the stop and the measured value S of the charge state at the stop, and the discharge capacity is updated with the converted value.
[0129]
For example, in (b) of FIG. 3, when discharging is switched to charging during a period (between points D1 and D2) in which the measured value S of the charging state is fixed to the value 2% of the fourth reference charging state ( Point M), the discharge capacity from the start of discharge to the time of switching to charging, and the measured value S of the charging state at the time of switching to charging, that is, the value of 2% of the fourth reference charging state, the discharge capacity Is converted. The converted value corresponds to the intersection N between the straight line A-M and the horizontal axis in FIG.
At the time M when switching to charging, the measured value S of the state of charge is fixed at 2% of the value of the fourth reference state of charge, and the exact value is unknown. However, as is apparent from FIG. 3B, the converted value N closely approximates the actual discharge capacity E2. In particular, the error in the converted value is smaller than when the discharge capacity is converted based on the amount of discharged electricity at the definite point C2 with respect to the third reference charge state 5% and the third reference charge state 5%.
In this way, even when a long time elapses from the previous discharge to the next discharge and the deterioration of the secondary battery block 1 proceeds during that time, the discharge capacity measuring unit 6f can maintain high learning accuracy of the discharge capacity.
[0130]
A specific procedure for measuring the state of charge by the control unit 6 is as follows, for example. FIG. 4 is a flowchart showing the measurement of the state of charge by the control unit 6.
Hereinafter, for the purpose of simplifying the explanation, the discharge characteristic table includes the first reference charge state (full charge state) SR (0) = 100%, the second reference charge state SR (1) = 10%, Three reference charge states (complete discharge state) SR (2) = 0% for three reference charge states, first reference voltage VA, second reference voltage VB, and third reference voltage (discharge end voltage) ) Assume that each VC is included.
[0131]
<Step S1>
At the start of discharge, the control unit 6 confirms that the secondary battery block 1 is fully charged through the sensor groups 3 to 5. Specifically, the confirmation is performed as follows, for example.
FIG. 5 is a flowchart showing confirmation of the fully charged state by the control unit 6.
<Step S21>
The sensor groups 3 to 5 detect the battery voltage V, the discharge current I, and the battery temperature T with respect to the secondary battery block 1.
<Step S22>
A set of reference values (VA, I, T) corresponding to the fully charged state 100% including the measured value I of the discharge current and the measured value T of the battery voltage is read from the discharge characteristic table.
<Step S23>
The battery voltage V is compared with the first reference voltage VA. When the battery voltage V is higher than a predetermined range including the first reference voltage VA (V >> VA), the process branches to step S24. When the battery voltage V is substantially equal to the first reference voltage VA (V = VA), that is, when it falls within the predetermined range, the process branches to step S26. When the battery voltage V is lower than the predetermined range (V << VA), the process branches to step S28.
[0132]
<Step S24>
Since the battery voltage V is abnormally higher than the first reference voltage VA, the control unit 6 cuts off the discharge current I and stops the discharge.
<Step S25>
The control unit 6 notifies the host H that the battery voltage V is abnormally high, and stops measuring the state of charge.
<Step S26>
When the battery voltage V is substantially equal to the first reference voltage VA (V = VA), the measured value S of the charged state is set to 100% of the fully charged state.
<Step S27>
The remaining capacity QR of the secondary battery block 1 is set to a predetermined discharge capacity QF.
<Step S28>
When the battery voltage V is extremely lower than the first reference voltage VA (V << VA), the exact state of charge is unknown. Accordingly, the measured value S of the state of charge is temporarily set to the second reference state of charge SR (1) = 10%.
<Step S29>
The remaining capacity QR of the secondary battery block 1 is set to the product of the discharge capacity QF and the second reference charge state SR (1) = 10%: QR = QF × SR (1) = QF × 0.10.
In step S26 and S27 or steps S28 and S29, the measured value S and the remaining capacity QR of the charged state are set, and the step S1 for checking the fully charged state is completed. Hereinafter, the processing returns to the flowchart of FIG.
[0133]
<Step S2>
The integer value variable i is initialized to 1.
<Step S3>
The amount of discharged electricity Q is initialized to 0, and the reference charge state SR of the next correction target is set to the (i + 1) th reference charge state SR (i).
<Step S4>
In the range from the i-th reference charge state SR (i−1) to the (i + 1) th reference charge state SR (i), the charge state is measured as follows.
FIG. 6 is a flowchart showing measurement of the state of charge in step S4.
<Step S41>
It is checked whether the discharge current I is flowing. When the discharge current I is not flowing, the process branches to step S42. When the discharge current I is flowing, the process branches to step S43.
<Step S42>
It is checked whether or not the battery current is flowing in the charging direction or whether or not the host H notifies the switching from discharging to charging. Thus, when switching to charging is detected, step S4 ends, and the process branches to step S5 in the flowchart of FIG. In other cases, the process returns to step S41.
[0134]
<Step S43>
The sensor groups 3 to 5 detect the battery voltage V, the discharge current I, and the battery temperature T.
<Step S44>
The product of the discharge current sample I and the sampling time interval Δt (= about 2 seconds) is added to the discharge electricity quantity Q: Q = Q + I × Δt.
<Step S45>
The candidate value S1 of the state of charge is converted from the remaining capacity QR, the amount of discharged electricity Q, and the discharge capacity QF: S1 = (QR−Q) / QF.
<Step S46>
A set of reference values (VR, I, T) corresponding to the reference charge state SR of the correction target including the measured value I of the discharge current and the measured value T of the battery voltage is read from the discharge characteristic table.
<Step S47>
The battery voltage V is compared with the corrected reference voltage VR. When the battery voltage V is higher than the reference voltage VR (V> VR), the process branches to step S48. Otherwise, the process branches to step S51.
[0135]
<Step S48>
The charge state candidate value S1 is compared with the reference charge state SR of the correction target.
<Step S49>
When the charge state candidate value S1 is larger than the correction target reference charge state SR (S1> SR), the charge state candidate value S1 is selected as the measurement value S of the charge state (step S49A).
Otherwise, the correction target reference charging state SR is selected as the measured value S of the charging state (step S49B). Thus, when the charge state candidate value S1 drops to the correction target reference charge state value SR before the battery voltage V drops to the correction target reference voltage VR, the charge state measurement value S is the reference charge state. The value is fixed to SR.
<Step S50>
The host H is notified of the battery state including the battery voltage V, the discharge current I, the battery temperature T, and the measured value S of the state of charge.
Hereinafter, the process returns to step S41.
<Step S51>
The battery voltage V drops to the correction target reference voltage VR, that is, the discharge time reaches a definite point with respect to the correction target reference charge state SR. At that time, the measured value S of the state of charge is replaced with the reference charge state SR of the correction target: S = SR.
<Step S52>
The battery state including the battery voltage V, the discharge current I, the battery temperature T, and the measured value S of the state of charge is notified to the host H, and Step S4 ends.
Hereinafter, the processing returns to the flowchart of FIG.
[0136]
<Step S5>
Discharge electric quantity accumulated in the period from the start of discharge until the definite point (i-th definite point) with respect to the reference charge state of the previous correction target, i.e., the i-th standard charge state SR (i−1) Let Q (i−1) be the amount of electricity discharged in 1). Add the discharge electricity quantity Q at the end of step S4 to the (i-1) th discharge electricity quantity Q (i-1), and the definite point for the (i + 1) th reference charge state SR (i) from the beginning of the discharge Q (i) = Q (i−1) + Q, which is regarded as the discharge electric energy (i-th discharge electric energy) Q (i) accumulated in the period up to (the (i + 1) definite point). Here, when i = 1, Q (0) = 0.
<Step S6>
It is checked whether or not the reference charge state SR of the correction target is the complete discharge state 0%, or whether or not switching from discharge to charge is detected. When any of these determinations is affirmative, the process branches to step S9. Otherwise, the process branches to step S7.
<Step S7>
The product of the discharge capacity QF and the corrected target reference charge state SR is set as the remaining capacity QR at the (i + 1) th definite point: QR = QF × SR.
<Step S8>
The integer value variable i is incremented by 1, and the process returns to step S3.
[0137]
<Step S9>
The control unit 6 cuts off the discharge current I and stops the discharge.
<Step S10>
For the integer value variable i when the discharge is stopped, the i-th discharge electric quantity Q (i) is set as a new discharge capacity.
<Step S11>
First converted discharge capacity QA and second converted discharge capacity QB are calculated by the following formulas: QA = Q (1) / (SR (0) −SR (1)), QB = Q (2) / (SR (0) −SR (2)).
<Step S12>
The first converted discharge capacity QA and the second converted discharge capacity QB are compared.
<Step S13>
When the first converted discharge capacity QA is larger than the second converted discharge capacity QB (QA> QB), the second reference voltage VB is lowered by 1 mV: VB = VB−1 mV (step S13A). Conversely, when the first converted discharge capacity QA is smaller than the second converted discharge capacity QB (QA <QB), the second reference voltage VB is increased by 1 mV: VB = VB + 1 mV (step S13B). When the first converted discharge capacity QA is substantially equal to the second converted discharge capacity QB (QA = QB), the second reference voltage VB is maintained as it is: VB = VB (step S13C).
Thus, the measurement of the charge state is completed through the learning of the discharge capacity (step S10) and the correction of the discharge characteristic table (steps S11 to S13).
[0138]
In the flowchart of FIG. 4, three reference charging states are set. In addition, four or more reference charge states may be set. At that time, the correction of the discharge characteristics table in steps S11 to S13 is preferably performed for the fully charged state 100%, the fully discharged state 0%, and any one reference charge state therebetween. In addition, when the depth of discharge is shallow, the combination of three reference charge states other than the complete discharge state 0% may be performed. In either case, the reference voltage corresponding to the middle reference charging state is corrected.
Further, the converted discharge capacities may be obtained for all the reference charge states, and the correction amounts of the respective reference voltages may be determined from the deviations of the respective converted discharge capacities with respect to their average values.
[0139]
  (Reference Example 1)
  FIG.Reference example 1It is a block diagram which shows the battery pack 10A by. In FIG. 7, the same reference numerals as those in FIG. 1 are assigned to the same components as those of the battery pack 10 according to the first embodiment. Furthermore, the description of those similar components is the same as in Example 1.
[0140]
For example, the control unit 6A executes firmware stored in the memory 6a, and in addition to the functions as the battery state monitoring unit 6b, the battery current integration unit 6c, and the discharge capacity measurement unit 6f similar to those in the first embodiment, the charge state measurement unit 6j, functions as an internal resistance measurement unit 6h, and an internal resistance correction unit 6i.
[0141]
As in the first embodiment, the discharge capacity measuring unit 6f calculates the total amount of discharge electricity from the start to the end of discharge. Further, the discharge capacity is converted from the total amount based on the measured value of the state of charge at the end of discharge, and the ratio between the converted value and the initial value is obtained. The ratio is used to evaluate the deterioration state of the secondary battery block 1 by correcting the internal resistance value by an internal resistance correction unit 6i described later.
[0142]
FIG. 8 shows that when the secondary battery block 1 starts discharging from the time when the charging state of the secondary battery block 1 is equal to the fully charged state, the voltage across both ends of the secondary battery block 1 and the discharge in the vicinity of the start of discharging. It is a graph which shows the relationship with time. The solid line and the broken line shown in FIG. 8 indicate the relationship between the number of charge / discharge cycles = 0 and 250 cycles, respectively. Here, the upper limit of the discharge current is set constant, and the battery temperature is maintained within a certain range.
[0143]
As shown in FIG. 8, the battery voltage once suddenly drops immediately after the start of discharge. After about 20 seconds from the start of discharge, the battery voltage drop rate stabilizes at a relatively low value.
Initial value V of battery voltage when discharge current is very small at the start of discharge_INIs the open circuit voltage V of the secondary battery block 1_OCIs substantially equal. As the discharge current rapidly increases, the voltage drop due to the internal resistance rapidly increases in the secondary battery block 1. Thereby, the battery voltage is the initial value V_INDescent suddenly. The discharge current increases to a constant value and stabilizes, and the battery voltage drop is relaxed and stabilized.
Thus, the rapid drop immediately after the start of discharge of the battery voltage is mainly caused by the internal resistance of the secondary battery. This sudden drop is therefore called IR drop.
[0144]
The internal resistance measurement unit 6h monitors the battery voltage and discharge current at the start of discharge through the battery state monitoring unit 6b. Thereby, for example, the amount of voltage drop due to IR drop and the average value of the discharge current are measured, and the ratio thereof is regarded as the internal resistance of the secondary battery. Alternatively, during the IR drop period, the voltage drop amount and the discharge current may be sampled at a predetermined time interval, and the ratio of each sample may be regarded as the internal resistance sample, and the average of those samples may be regarded as the internal resistance. .
[0145]
As is clear from the comparison between the solid line (number of charge / discharge cycles = 0 cycle) and the broken line (250 cycles) shown in FIG. 8, the voltage drop due to IR drop increases as the number of charge / discharge cycles increases. The main cause is considered to be that the secondary battery deteriorates and the internal resistance increases as the number of charge / discharge cycles increases.
FIG. 9 is a graph showing the relationship between the internal resistance and the number of charge / discharge cycles. Thus, the internal resistance increases as the number of charge / discharge cycles increases.
The internal resistance measuring unit 6h measures the internal resistance every time the secondary battery block 1 is discharged. Thereby, the change of the internal resistance accompanying the deterioration of the secondary battery block 1 is learned, and the measurement accuracy of the internal resistance is kept high.
[0146]
The internal resistance measuring unit 6h further calculates the ratio between the new internal resistance value and the initial internal resistance value in the secondary battery block 1 (hereinafter referred to as the initial value of the internal resistance) for each learning of the internal resistance. Ask. The ratio is used to evaluate the deterioration state of the secondary battery block 1 by correcting the internal resistance value by an internal resistance correction unit 6i described later.
[0147]
When the measured value of the internal resistance exceeds a predetermined threshold, the internal resistance measuring unit 6h may send a signal for requesting the host H to reduce the battery current.
An abnormal increase in internal resistance causes excessive Joule heat due to the discharge current, and therefore, overheating is likely to occur in the secondary battery block 1. The above threshold value for the internal resistance is preferably set so that the stability of the secondary battery block 1 is lost, for example, the battery temperature is maintained sufficiently lower than the temperature at which thermal runaway may occur. Thereby, before the deterioration or thermal runaway of the secondary battery block 1 due to overheating occurs, the host H can sufficiently reduce the discharge current. In particular, since the forced interruption of the discharge current at the occurrence of overheating is avoided, the host H is prevented from being shut down suddenly.
[0148]
The memory 6a stores an open circuit voltage characteristic table showing the relationship between the open circuit voltage and the state of charge for the secondary battery block 1. FIG. 10 is a graph showing the relationship.
The open circuit voltage of the secondary battery is the sum of the battery voltage and the amount of voltage drop due to the internal resistance, and is substantially equal to the electromotive force of the secondary battery. Therefore, the open circuit voltage is substantially determined by the state of charge. In particular, the open circuit voltage in a fixed state of charge is substantially constant regardless of the deterioration of the secondary battery.
[0149]
The battery state monitoring unit 6b samples the battery voltage V, the discharge current I, and the battery temperature T at predetermined time intervals during the discharge period of the secondary battery block 1. The charge state measurement unit 6j calculates the open circuit voltage at each sampling time from those samples and the internal resistance measured at the start of discharge by the internal resistance measurement unit 6h. Further, the state of charge corresponding to the calculated open circuit voltage is determined with reference to the open circuit voltage characteristic table. Thus, during the discharging period of the secondary battery block 1, the state of charge is measured.
Since the open circuit voltage characteristic table is substantially unchanged regardless of the deterioration of the secondary battery block 1, the measurement accuracy of the charging state by the charging state measuring unit 6j is maintained high regardless of the deterioration of the secondary battery.
[0150]
The internal resistance measurement by the internal resistance measurement unit 6h is performed at the start of discharge. However, strictly speaking, the internal resistance depends on the state of charge.
FIG. 11 is a graph showing the relationship between the internal resistance of the secondary battery block 1 and the state of charge. The solid line and the broken line shown in FIG. 11 indicate the relationship between the number of charge / discharge cycles = 0 and 300 cycles, respectively. Here, the discharge current and the battery temperature are maintained constant.
As shown by the solid line in FIG. 11, when the number of charge / discharge cycles is sufficiently small, the change in the internal resistance depending on the state of charge is sufficiently small, and the internal resistance is substantially constant. However, as indicated by a broken line in FIG. 11, when the number of charge / discharge cycles increases, the internal resistance increases as the state of charge decreases. Such a change in the relationship between the internal resistance and the state of charge accompanying an increase in the number of charge / discharge cycles is considered to be due to deterioration of the secondary battery.
[0151]
The internal resistance correction unit 6i corrects the internal resistance measured by the internal resistance measurement unit 6h according to the deterioration state of the secondary battery block 1 as follows. The correction increases the internal resistance especially in a small charged state region.
The internal resistance correction unit 6i inputs a ratio of the learned discharge capacity to the initial value (hereinafter referred to as a learned discharge capacity ratio) from the discharge capacity measurement unit 6f. As the deterioration of the secondary battery block 1 progresses, the learning discharge capacity ratio becomes smaller. In addition, the internal resistance correction unit 6i inputs a ratio of the learned internal resistance value to the initial value (hereinafter referred to as a learned internal resistance ratio) from the internal resistance measurement unit 6h. The learning internal resistance ratio increases as the secondary battery block 1 deteriorates.
[0152]
The internal resistance correction unit 6i uniformly increases the internal resistance value, for example, for a predetermined low charge state region according to the learning discharge capacity ratio or the learning internal resistance ratio.
Specifically, for example, when the learning discharge capacity ratio is included in the respective ranges of 95% or more, 80 to 95%, and 60 to 80% for a charging state of 20% or less, the correction rate of the internal resistance value Are set to 1.00, 1.20, and 1.40, respectively.
Regarding the learning internal resistance ratio, when the learning internal resistance ratio is included in the respective ranges of 105% or less, 105 to 120%, and 120 to 140% for a charging state of 20% or less, the internal resistance value is corrected. The rates are set as 1.00, 1.20, and 1.40, respectively.
[0153]
When the state of charge is predicted to be 20% or less, the state-of-charge measuring unit 6j again considers the product of the correction factor and the internal resistance value as the internal resistance value, and calculates the open circuit voltage. In this way, an increase in internal resistance accompanying a decrease in the state of charge in the deteriorated secondary battery block 1 is reflected in the measurement of the state of charge. As a result, the calculation error of the open circuit voltage is reduced, and the measurement accuracy of the charged state is improved.
[0154]
A specific procedure for measuring the state of charge by the control unit 6A is, for example, as follows. FIG. 12 is a flowchart showing measurement of the state of charge by the control unit 6A.
Here, it is assumed that the secondary battery block 1 is once charged to a fully charged state, and discharge is started after a sufficient time has elapsed since the completion of the charging. In particular, the secondary battery block 1 is stably maintained in a fully charged state at the start of discharge.
<Step S61>
At the start of discharge, the internal resistance IR is measured through IR drop detection.
Specifically, the internal resistance IR is measured by one of the following two methods.
[0155]
FIG. 13 is a flowchart showing a first measuring method of the internal resistance IR.
<Step S71>
Initial value of battery voltage V immediately after starting discharge_INMeasure and record
<Step S72>
The sensor groups 3 to 5 detect the battery voltage V, the discharge current I, and the battery temperature T with respect to the secondary battery block 1.
<Step S73>
The discharge current I is a predetermined threshold I_THCheck to see if it has increased to above (eg about 300 mA). Discharge current I is threshold I_THThis is because the voltage drop due to the internal resistance IR is too small for the measurement while the value does not exceed. Discharge current I is threshold I_THWhen not exceeding (I> I_TH) The process branches to step S74. Conversely, the discharge current I is the threshold I_TH(I <I_TH) The process branches to step S75.
<Step S74>
It is checked whether a predetermined time (for example, about 16 seconds) has elapsed since the start of discharge. In normal discharge, the IR drop ends within the predetermined time. Therefore, the discharge current I is the threshold I_THWhen the predetermined time elapses without exceeding, it can be considered that some abnormality has occurred. At that time, the control unit 6 ends the measurement of the internal resistance. In other cases, the process returns to step S72.
[0156]
<Step S75>
The battery voltage V and the discharge current I measured in step S72 are recorded.
<Step S76>
It is checked whether a predetermined time (for example, about 16 seconds) has elapsed since the start of discharge. Until the predetermined time elapses, the process repeats the loop of steps S72 to S76 at predetermined time intervals. Thereby, a plurality of pairs of the battery voltage V and the discharge current I are recorded.
When the predetermined time has elapsed, the process branches to step S77.
<Step S77>
The recording of the battery voltage V and the discharge current I is repeated from about 10 seconds after the start of discharge until about 16 seconds have passed. The battery voltage V and the discharge current I are averaged over the entire recorded sample, and the average value V_AVAnd I_AVIs calculated.
<Step S78>
Initial value of battery voltage V_IN, Average battery voltage V_AV, And average discharge current I_AVThe internal resistance IR is calculated by the following formula: IR = (V_IN−V_AV) / I_AV.
[0157]
FIG. 14 is a flowchart showing a second measuring method of the internal resistance IR. In FIG. 14, the same steps as those in the first measurement method are denoted by the same reference numerals as those in FIG. 13, and the description of those steps is the same as that in the first measurement method.
<Step S81>
Battery voltage V is a predetermined threshold V_THCheck if it is kept higher. Immediately after the start of discharge, the secondary battery block 1 should be substantially fully charged. Therefore, the battery voltage V should be kept high enough. If the battery voltage V falls within the above threshold value V within a short period of time since the start of discharge_THIf it descends further, it can be considered that some abnormality has occurred. Therefore, the battery voltage V is the above threshold V_THWhen V <V_TH), Measurement of internal resistance ends. Otherwise, the process branches to step S73.
[0158]
<Step S82>
The battery voltage V and the discharge current I are measured and recorded at a predetermined time interval (for example, approximately every 2 seconds) from the start of discharge. The recording is repeated n times (a positive integer n is preferably 2 or more).
<Step S83>
Each of the n discharge current samples I (1), I (2),..., I (n) recorded in step S82 has a predetermined threshold value I._THCheck whether or not Those samples I (1), I (2),..., I (n) are all predetermined threshold values I_THThe process repeats the loop consisting of steps S72, S81, S73, and S82.
Samples I (1), I (2), ..., I (n) of n discharge currents recorded in step S82 are all threshold I_THIf it exceeds, the process branches to step S84.
<Step S84>
Initial value of battery voltage V_IN, And n pairs of samples (V (1), I (1)), (V (2), I (2)), (V (1) of the battery voltage V and the discharge current I recorded in step S82. n), I (n)), n internal resistance values IR (1), IR (2),..., IR (n) are calculated as follows: IR (k) = (V_IN−V (k)) / I (k) (k = 1, 2,..., N). Furthermore, their average value is determined as the internal resistance IR: IR = (IR (1) + IR (2) +... + IR (n)) / n.
[0159]
<Step S62>
The sensor groups 3 to 5 detect the battery voltage V, the discharge current I, and the battery temperature T with respect to the secondary battery block 1.
<Step S63>
Open circuit voltage V based on battery voltage V, discharge current I, and internal resistance IR_OCIs calculated by the following formula: V_OC= V + I x IR. Here, preferably, based on the battery temperature T, the change in the resistance value due to the temperature variation of the internal resistance IR is corrected. Further, the internal resistance value is corrected based on the learning discharge capacity ratio or the learning internal resistance ratio.
<Step S64>
Open circuit voltage V with reference to open circuit voltage characteristics table_OCThe charging state S corresponding to is determined.
[0160]
  Reference example 1Then, the state of charge is measured based only on the open circuit voltage. In addition, the measurement of the state of charge is usually performed based on the discharge capacity and the integrated value of the discharge current as in Example 1, and for a specific battery state (for example, battery voltage)Reference example 1It may be performed based on the open circuit voltage. That is, when a specific battery state is detected, the measured value of the state of charge is replaced with a value corresponding to the open circuit voltage and corrected. At that time, the measurement accuracy of the state of charge can be maintained high, and the data amount of the open circuit voltage characteristic table can be reduced.
[0161]
<ImplementationExample 2>>
  FIG. 15 illustrates the implementation of the invention.Example 2It is a block diagram which shows the battery pack 10B by. In FIG. 15, the battery pack 10 according to Example 1 andReference example 1Constituent elements similar to those of the battery pack 10A are attached with the same reference numerals as in FIGS. Furthermore, descriptions of those similar components are given in Example 1 orReference example 1Incorporate the thing in.
[0162]
The controller 6B executes, for example, firmware stored in the memory 6a, a battery state monitoring unit 6b, a battery current integration unit 6c, a charge state measurement unit 6d, a charge state correction unit 6e, a discharge capacity measurement unit 6f, an internal resistance measurement unit In addition to the function as 6h and the internal resistance correction unit 6i, the function as the discharge characteristic table correction unit 6k is exhibited.
[0163]
Since the secondary battery deteriorates, for example, with an increase in the number of charge / discharge cycles, its discharge characteristics change with each discharge. On the other hand, since the internal resistance increases with the deterioration of the secondary battery, the deterioration state is evaluated from the change in the internal resistance for each discharge.
The discharge characteristic table correction unit 6k corrects the numerical value in the discharge characteristic table for each discharge as follows based on learning of the internal resistance by the internal resistance measurement unit 6h.
The open circuit voltage of the secondary battery block 1 is the sum of the battery voltage and the voltage drop due to the internal resistance. Therefore, the open circuit voltage V corresponding to a certain reference charge state SR_OCIs the battery voltage VR in the discharge characteristics table corresponding to the reference charge state SR.₁, Discharge current I and battery temperature T, and internal resistance measurement value IR by internal resistance measurement unit 6h₁And satisfies the following equation (1):
[0164]
V_OC= VR₁+ I × (IR₁× α₁). (1)
[0165]
Where the coefficient α₁(Hereinafter referred to as the first temperature correction factor) is the measured value of internal resistance IR₁Is corrected to a value at the battery temperature T.
If the secondary battery block 1 starts a new discharge, the internal resistance measurement unit 6h converts the internal resistance to the original value IR.₁From another value IR₂It is assumed that it has been updated. Open circuit voltage V corresponding to the above reference charge state SR_OCIs substantially constant regardless of the deterioration of the secondary battery block 1. Therefore, when maintaining the discharge current I and the battery temperature T at the above values, the open circuit voltage V_OC, Discharge current I, battery temperature T, and new internal resistance IR₂Battery voltage corresponding to₂Should satisfy the following equation (2):
[0166]
V_OC= VR₂+ I × (IR₂× α₂). (2)
[0167]
Where the coefficient α₂(Hereinafter referred to as the second temperature correction factor) is the new measured value of internal resistance IR₂Is corrected to a value at the battery temperature T.
When erasing the discharge current I from the above equations (1) and (2), the corrected battery voltage VR₂Is obtained by the following equation (3):
[0168]
VR₂= V_OC− (V_OC−VR₁) × {(IR₂/ IR₁) × (α₂/ Α₁)}. (3)
[0169]
Hereinafter, the coefficient K = {(IR determined by the ratio of the internal resistance value and the ratio of the temperature correction coefficient₂/ IR₁) × (α₂/ Α₁)} Is called the degradation coefficient.
The discharge characteristic table correction unit 6k stores a corresponding open circuit voltage for each reference charging state. Furthermore, a discharge characteristic table of the initial secondary battery block 1, an internal resistance value, and a table indicating the temperature characteristic (hereinafter referred to as a temperature characteristic table) are stored. Here, the temperature characteristic table includes, for example, a ratio to the internal resistance value at a predetermined temperature (for example, 25 ° C.) for each battery temperature in the discharge characteristic table.
[0170]
Discharge characteristic table correction unit 6k is the original internal resistance value IR in equation (3)₁Substitute the initial value of the internal resistance into. Next, one reference charging state SR is selected, and the corresponding open circuit voltage is set to the open circuit voltage V in equation (3)._OCAssign to.
Next, the discharge characteristic table correction unit 6k selects one battery temperature T and sets the deterioration coefficient K to the initial value IR of the internal resistance.₁Update value for IR₂The ratio is calculated based on the battery temperature T. Where the first temperature correction coefficient α₁Is the initial value IR of the battery temperature T and internal resistance₁It is calculated from the numerical values in the temperature characteristic table corresponding to each of the battery temperatures at the time of measurement. Second temperature correction factor α₂Is the battery temperature T and the internal resistance update value IR₂It is calculated from the numerical values in the temperature characteristic table corresponding to each of the battery temperatures at the time of measurement.
The discharge characteristic table correction unit 6k further selects one discharge current I, and calculates the battery voltage in the initial discharge characteristic table corresponding to the reference charge state SR, the battery temperature T, and the discharge current I in the equation (3). Original battery voltage VR₁Assign to.
[0171]
The discharge characteristic table correction unit 6k calculates Equation (3) under the above settings, and the corrected battery voltage VR.₂To decide. The battery voltage corresponding to the reference charge state SR, discharge current I, and battery temperature T in the discharge characteristics table is the corrected battery voltage VR.₂To be rewritten.
The discharge characteristic table correction unit 6k repeats the rewriting of the battery voltage as described above for each of the reference charge state SR, the discharge current I, and the battery temperature T in the discharge characteristic table.
In this way, the discharge characteristic table is corrected in accordance with the change in internal resistance due to deterioration of the secondary battery block 1, and the approximation accuracy of the discharge characteristic is maintained high.
The charge state is corrected in the same manner as in the first embodiment based on the corrected discharge characteristic table. Therefore, even when the deterioration of the secondary battery changes the discharge characteristics, the measurement accuracy of the state of charge is maintained high.
[0172]
  A specific procedure for measuring the state of charge by the control unit 6B is, for example, as follows. FIG. 16 is a flowchart showing measurement of the state of charge by the control unit 6B. In FIG. 16, Example 1 orReference example 1The same reference numerals as those in FIG. 4 or FIG. Further, a description of those similar steps can be found in Example 1 orReference example 1The thing of the thing is used.
  As shown in FIG.Example 2The measurement of the state of charge mainly differs from the measurement by Example 1 by measuring the internal resistance IR at the start of discharging (step S61) and correcting the discharge characteristic table based on the internal resistance IR (step S90) ( (See FIG. 4). Furthermore, the measurement of the internal resistance IR in step S61 isReference example 1Done in the same way.
[0173]
<Step S90>
Specifically, the correction of the discharge characteristic table based on the learning of the internal resistance is performed as follows, for example.
FIG. 17 is a flowchart showing correction of the discharge characteristic table by the control unit 6B.
<Step S91>
One reference charge state SR is selected. Here, when the reference charging state to be selected does not remain, step S90 is ended, and the process returns to the flowchart of FIG.
<Step S92>
Open circuit voltage V corresponding to the reference charge state SR_OCIs read out.
<Step S93>
One battery temperature T included in the discharge characteristics table is selected. Here, when the battery temperature to be selected does not remain, step S90 is ended, and the process returns to the flowchart of FIG.
[0174]
<Step S94>
  The deterioration coefficient K is calculated as described above. Here, preferably, the updated value IR2 of the internal resistance isReference example 1Similarly, the correction is made based on the learning discharge capacity ratio or the learning internal resistance ratio. As a result, an increase in internal resistance due to a decrease in the state of charge in the deteriorated secondary battery block 1 is reflected in the correction of the discharge characteristic table.
<Step S95>
One discharge current I included in the discharge characteristic table is selected. Here, when there is no remaining discharge current to be selected, the process returns to step S93.
<Step S96>
The battery voltage VR1 corresponding to the reference charge state SR, the discharge current I, and the battery temperature T is read from the discharge characteristic table in the initial state.
<Step S97>
The corrected battery voltage VR2 is calculated according to equation (3). Further, the battery voltage corresponding to the reference charge state SR, the discharge current I, and the battery temperature T in the discharge characteristic table is rewritten to the corrected battery voltage VR2.
[0175]
(Reference Example 2)
  FIG.Reference example 2It is a block diagram which shows the temperature detection part 3A vicinity among the battery packs 10C by. For the other parts, the battery pack 10 according to Example 1 orReference example 11 is similar to the battery pack 10A according to FIG. Further, in FIG. 18, the battery pack 10 according to Example 1 andReference example 1Constituent elements similar to those of the battery pack 10A are attached with the same reference numerals as in FIGS. The description of those similar components is given in Example 1 orReference example 1Incorporate the thing in.
[0176]
The secondary battery block 1 includes n cells (the integer n is 1 or more) 1a, 1b, ..., 1n. The temperature detector 3A has the same number of fixed resistors 30, cells of the secondary battery block 1, that is, n cell temperature detecting thermistors 31, 32,..., 3n, circuit element temperature detecting thermistor 3m, voltage source 3b, And (n + 3) temperature detection terminals 3A0, 3A1, 3A2,..., 3An, 3A (n + 1), 3A (n + 2).
[0177]
The fixed resistor 30 has a substantially constant resistance value R0. In particular, the temperature fluctuation of the resistance value R0 is sufficiently small.
The n cell temperature detection thermistors 31, 32,..., 3n are all thermistors of the same type. The resistance values R1, R2,..., Rn indicate a predetermined temperature change. The cell temperature detection thermistors 31, 32, ..., 3n are close to the cells 1a, 1b, ..., 1n of the secondary battery block 1, respectively. Accordingly, the respective resistance values R1, R2,..., Rn are determined by the respective temperatures of the cells 1a, 1b,.
The circuit element temperature detecting thermistor 3m is a thermistor, and its resistance value Rm indicates a predetermined temperature change. The circuit element temperature detection thermistor 3m is, for example, close to the battery current detection resistor 5a. In addition, the first switch 7a, the second switch 7b, and the like may be close to each circuit element that generates heat due to the battery current. Accordingly, the resistance value Rm is determined by the temperature of adjacent circuit elements such as the battery current detection resistor 5a.
The fixed resistor 30 and (n + 1) thermistors 31, 32, ..., 3n, 3m are connected in series. One end of the series circuit L is connected to the voltage source 3b in the temperature detector 3A, and the other end is connected to the negative electrode of the secondary battery block 1.
[0178]
(n + 3) temperature detection terminals 3A0, 3A1, 3A2,..., 3An, 3A (n + 1), 3A (n + 2) are fixed resistor 30 in series circuit L, (n + 1) thermistors 31, 32,. , 3n, and 3m. That is, the first temperature detection terminal 3A0 is connected to the connection point between the voltage source 3b and the fixed resistor 30, and the second temperature detection terminal 3A1 is connected to the connection point between the fixed resistor 30 and the first thermistor 31. The third temperature detection terminal 3A2 is connected to the connection point between the first thermistor 31 and the second thermistor 32, and the (n + 2) th temperature detection terminal 3A (n + 1) is the nth thermistor 3n. Is connected to the connection point between the circuit element temperature detection thermistor 3m and the (n + 3) th temperature detection terminal 3A (n + 2) is connected to the connection point between the circuit element temperature detection thermistor 3m and the negative electrode of the secondary battery block 1 Is done.
[0179]
The voltage source 3b is maintained at the potential Vcc. Here, the potential of the voltage source 3b may vary (particularly drop) within a predetermined range from the target value Vcc. As described below, the temperature detection unit 3A measures the cell temperature and the circuit element temperature with high accuracy regardless of such potential fluctuation of the voltage source 3b.
The temperature detection unit 3A has (n + 3) temperature detection terminals 3A0, 3A1, 3A2,..., 3An, 3A (n + 1), 3A (n + 2), voltages V0, V1, V2,. Measure Vm. They are equal to the amount of voltage drop across the fixed resistor 30 and (n + 1) thermistors 31, 32,..., 3n, 3m.
Since the fixed resistor 30 and the (n + 1) thermistors 31, 32, ..., 3n, 3m form a series circuit L, the currents flowing through them are common. Therefore, the ratio V0: V1: V2: ...: Vn: Vm between the (n + 1) voltage drop amounts measured by the temperature detector 3A is the fixed resistor 30 and the (n + 1) thermistors 31, 32, ... , 3n, 3m, the ratio of the resistance values is substantially equal to R0: R1: R2: ...: Rn: Rm.
[0180]
The resistance value R0 of the fixed resistor 30 is kept substantially constant regardless of the battery temperature and the circuit element temperature. Therefore, based on the ratio V0: V1: V2: ...: Vn: Vm and the resistance value R0 of the fixed resistor 30, the (n + 1) thermistors 31, 32, ..., 3n, 3m The respective resistance values R1, R2,..., Rn, Rm are calculated: R1 = (V1 / V0) R0, R2 = (V2 / V0) R0, ..., Rn = (Vn / V0) R0, Rm = ( Vm / V0) R0.
The cell temperatures T1, T2, ..., Tn of the cells 1a, 1b, ..., 1n adjacent to each of the n cell temperature detection thermistors 31, 32, ..., 3n are determined from the temperature characteristics of the thermistors, and circuit elements The temperature Tm of the battery current detection resistor 5a adjacent to the temperature detection thermistor 3m is determined.
[0181]
The resistance measurement by the temperature detector 3A does not require an accurate voltage of the entire series circuit L. Therefore, even when the potential Vcc of the voltage source 3b varies greatly, the resistance values R1, R2,..., Rn, Rm of (n + 1) thermistors 31, 32,. The Therefore, the battery temperatures T1, T2,..., Tn of the cells 1a, 1b,..., 1n and the temperature Tm of the battery current detection resistor 5a are measured with high accuracy.
[0182]
  Preferably, Example 1And 2, and Reference Example 1A battery management system similar to each of theReference example 2Temperature detection unit 3A. Thereby, the measurement accuracy of the state of charge is further improved.
[0183]
【The invention's effect】
A battery management system according to one aspect of the present invention measures the state of charge of a secondary battery based on a difference between a predetermined discharge capacity and an integrated value of discharge current (amount of discharge electricity). The measured value of the charge state is replaced with the reference charge state at each definite point for a specific reference charge state based on a predetermined discharge characteristic table, and corresponds to the discharge characteristic of the secondary battery indicated by the discharge characteristic table. Will be corrected.
This battery management system converts the discharge capacity from the amount of electricity discharged between two definite points corresponding to two different reference charge states. Furthermore, the numerical values in the discharge characteristic table are corrected for each discharge so that the discharge capacities (converted discharge capacities) converted for various pairs of reference charge states are matched. Thereby, the discharge characteristics table closely approximates the actual discharge characteristics.
Thus, this battery management system reflects the change in the discharge characteristics due to the deterioration of the secondary battery in the correction of the state of charge through the correction of the discharge characteristics table. As a result, the measurement accuracy of the state of charge is maintained high regardless of the deterioration of the secondary battery.
[0185]
A battery management system according to still another aspect of the present invention measures a state of charge of a secondary battery based on a difference between a predetermined discharge capacity and an integrated value of discharge current (amount of discharge electricity). The measured value of the charge state is replaced with the reference charge state at each definite point for a specific reference charge state based on a predetermined discharge characteristic table, and corresponds to the discharge characteristic of the secondary battery indicated by the discharge characteristic table. Will be corrected.
The battery management system further learns the internal resistance of the secondary battery for each discharge, and corrects the numerical value in the discharge characteristic table for each discharge based on the learned change in the internal resistance. Thereby, the discharge characteristic table is corrected according to the change of the discharge characteristic due to the deterioration of the secondary battery. Thus, even when the deterioration of the secondary battery changes the discharge characteristics, the state of charge is corrected with high accuracy. As a result, the measurement accuracy of the state of charge is maintained high.
[0186]
The battery management system may evaluate the deterioration state of the secondary battery through learning of the discharge capacity or internal resistance, and correct the measurement value of the internal resistance according to the deterioration state and the measurement value of the charge state. . In particular, the measured value of internal resistance is increased at the end of discharge. Furthermore, the rate of increase is increased for a degraded secondary battery. Thus, the calculation error of the open circuit voltage is reduced, and the measurement accuracy of the state of charge is further improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a battery pack 10 according to a first embodiment of the invention.
FIG. 2 shows the battery voltage V and the charge state S measured during the discharge period of the secondary battery block 1 by the battery management system 2 according to the first embodiment of the present invention. It is a graph which shows. (A) shows the relationship (discharge curve) between the battery voltage V and the amount of discharge electricity in the secondary battery block 1. (B) shows the relationship between the measured value S of the state of charge and the amount of electricity discharged.
FIG. 3 shows a state of charge associated with an increase in the amount of discharge electricity when the discharge capacity and discharge characteristics of the secondary battery block 1 are relatively largely different from those learned in the battery management system 2 according to the first embodiment of the present invention. It is a graph which shows the change of measured value S. (A) About the secondary battery block 1, the discharge curve before deterioration is shown with a continuous line, and the discharge curve after deterioration is shown with a broken line, respectively. (B) shows the relationship between the measured value S of the state of charge and the amount of electricity discharged.
FIG. 4 is a flowchart illustrating measurement of a state of charge by a control unit 6 according to the first embodiment of the present invention.
FIG. 5 is a flowchart showing confirmation of a fully charged state by the control unit 6 according to the first embodiment of the present invention.
FIG. 6 is a flowchart showing the measurement of the state of charge in step S4 in the first embodiment of the present invention.
[Fig. 7]Reference example 1It is a block diagram which shows the battery pack 10A by.
FIG. 8 shows that when the secondary battery block 1 starts discharging from the time when the charging state of the secondary battery block 1 is equal to the fully charged state, the voltage across both ends of the secondary battery block 1 and the discharge in the vicinity of the start of discharging. It is a graph which shows the relationship with time.
FIG. 9 is a graph showing the relationship between the internal resistance and the number of charge / discharge cycles for the secondary battery block 1;
FIG. 10 is a graph showing the relationship between the open circuit voltage and the state of charge for the secondary battery block 1;
11 is a graph showing the relationship between the internal resistance of the secondary battery block 1 and the state of charge. FIG.
FIG.Reference example 1It is a flowchart which shows the measurement of the charge condition by 6A of control parts.
FIG. 13Reference example 15 is a flowchart showing a first measuring method of internal resistance IR by the method.
FIG. 14Reference example 15 is a flowchart showing a second measuring method of the internal resistance IR according to FIG.
FIG. 15 shows the implementation of the present invention.Example 2It is a block diagram which shows the battery pack 10B by.
FIG. 16: Implementation of the present inventionExample 2It is a flowchart which shows the measurement of the charge condition by the control part 6B.
FIG. 17 shows the implementation of the present invention.Example 2It is a flowchart which shows correction | amendment of the discharge characteristic table | surface by the control part 6B.
FIG. 18Reference example 2It is a block diagram which shows the temperature detection part 3A vicinity among the battery packs 10C by.
FIG. 19 is a graph showing an example of a change accompanying an increase in the amount of discharge electricity, with respect to a battery voltage and a charge state measured by a conventional battery management system during a discharge period of a secondary battery. (A) shows the graph (discharge curve) showing the relationship between a battery voltage and the amount of discharge electricity. (B) shows the graph which shows the relationship between the measured value of a charge condition, and the amount of discharge electricity with a continuous line, and shows the graph which shows the relationship between the true value of a charge state, and the amount of discharge electricity with a broken line.
FIG. 20 is a graph showing an example of a change in a measured value of a battery voltage and a state of charge according to a conventional battery management system with an increase in discharge electricity during a discharge period of a deteriorated secondary battery. (A), during the discharge period, when the discharge current and the battery temperature show substantially the same fluctuation, the discharge curve of the initial secondary battery is a broken line, the discharge curve of the deteriorated secondary battery is a solid line, Each is shown. (B) is a graph showing the relationship between the measured value of the charged state and the amount of discharged electricity with a solid line, and a graph showing the relationship between the true value of the charged state of a deteriorated secondary battery and the amount of discharged electricity with a broken line, Each of the graphs showing the relationship between the true value of the state of charge of the secondary battery and the amount of discharged electricity is indicated by a one-dot chain line.
[Explanation of symbols]
10 Battery pack
1 Secondary battery block
1a, 1b cell
2 Battery management system
3a thermistor
5a Battery current detection resistor
7a First switch
7b Second switch
8a Positive electrode of secondary battery block 1
8b Negative electrode of secondary battery block 1
9 Terminal for communication with host H
Measured value of battery temperature
V Battery voltage measurement
I Battery current measurement

Claims (11)

(A) For a secondary battery, (a) a voltage detector for measuring battery voltage, (b) a current detector for measuring battery current, and (c) a temperature detector for measuring battery temperature, A battery state monitoring unit for managing a battery state including a set of measurement values by the detection unit;
(B) a battery current integrating unit for integrating the measured values of the battery current by the battery state monitoring unit;
(C) From the time when the charging state of the secondary battery is equal to a reference value (hereinafter referred to as a reference charging state), the amount of discharged electricity of the secondary battery is measured by the battery current integrating unit, the amount of discharged electricity, A charge state measuring unit for determining a charge state of the secondary battery based on a discharge capacity of the secondary battery and the reference charge state;
(D) (a) As the reference charging state, first, second, and third reference charging states are determined in order of value, and the battery voltage, battery current, and battery temperature in each reference charging state are determined. A discharge characteristic table indicating a set; and (b) from a point in time when the battery state includes one set in the discharge characteristic table corresponding to the first reference charge state (hereinafter referred to as a first definite point). When the battery state includes a set in the discharge characteristic table corresponding to the second reference charge state (hereinafter referred to as a second definite point), the second battery is discharged. In the reference charge state, the battery state includes a set in the discharge characteristic table corresponding to the third reference charge state (hereinafter referred to as a third definite point), in the third reference charge state, Replacing the measured value of the state of charge by the state of charge measuring unit, Charging state modification of; and,
(E) The difference in battery voltage determined by the battery temperature and the discharge current in the reference charge state between the first and second, the amount of discharge electricity of the secondary battery between the first to second fixed points The value divided by the value obtained by dividing the amount of discharge electricity of the secondary battery between the first to third fixed points by the difference between the battery voltages in the first and third reference charge states. A discharge characteristic table correction unit for correcting a set of battery voltage, battery current, and battery temperature in the discharge characteristic table so as to match;
A battery management system. (A) Regarding secondary batteries, (a) A voltage detector for measuring battery voltage, (b) A current detector for measuring battery current, and (c) A battery state monitoring unit for managing a battery state including a temperature detection unit for measuring a battery temperature and including a set of measurement values by the detection unit;
(B) A battery current integrating unit for integrating the measured values of the battery current by the battery state monitoring unit;
(C) The secondary battery discharge state is measured by the battery current integrating unit from the time when the secondary battery charge state is equal to the reference charge state, the secondary battery discharge capacity, the reference charge state, and the discharge electricity A state-of-charge measuring unit for determining a state of charge of the secondary battery based on the amount;
(D) (A) Storing a discharge characteristic table indicating a set of a battery voltage, a battery current, and a battery temperature in each of the reference charge states; and (b) When the secondary battery is discharged, each time the battery state includes a set in the discharge characteristic table corresponding to the reference charge state, the charge state measurement value by the charge state measurement unit is measured in the reference charge state. A state-of-charge correcting unit for replacing;
(E) An internal resistance measuring unit for detecting a sudden drop in battery voltage by the battery state monitoring unit at the start of discharging the secondary battery and determining an internal resistance of the secondary battery based on a change in the battery state at that time; And
(F) The internal resistance of the secondary battery is measured by the internal resistance measurement unit every time the secondary battery starts discharging, and based on the change of the internal resistance for each discharge, the battery voltage, the battery current in the discharge characteristics table, and Discharge characteristic table correction unit for correcting a set of battery temperatures;
A battery management system. (A) A discharge capacity measuring unit for determining a discharge capacity for each discharge of the secondary battery based on a measured value of the amount of discharged electricity by the battery current integrating unit and a measured value of the charged state by the charged state measuring unit; And
(B) The measured value of the internal resistance used by the charge state measurement unit is corrected based on the change of the discharge capacity for each discharge and the measured value of the charge state by the charge state measurement unit. Internal resistance correction unit for
The battery management system according to claim 2, further comprising: A change for each discharge of the secondary battery is obtained for the measurement value of the internal resistance by the internal resistance measurement unit, and based on the change and the measurement value of the charge state by the charge state measurement unit, the charge state measurement unit An internal resistance correction unit for correcting the measured value of the internal resistance used;
The battery management system according to claim 2, further comprising: The battery status monitoring unit sends a signal for requesting a reduction in the battery current to the host when the measured value of the battery temperature by the temperature detection unit exceeds a predetermined threshold. The battery management system described in 1. The battery state monitoring unit sends a signal for requesting a reduction in the battery current to the host when the measured value of the internal resistance by the internal resistance measurement unit exceeds a predetermined threshold. Battery management system. A battery pack comprising the secondary battery and the battery management system according to claim 1. (A) As the reference charge state of the secondary battery, the first, second, and third reference charge states are determined in order of value, and the set of battery voltage, battery current, and battery temperature in each reference charge state is shown. Setting the discharge characteristics table;
(B) Monitoring battery status including a set of battery voltage, battery current, and battery temperature for the secondary battery;
(C) From the point in time when the battery state includes a set in the discharge characteristic table corresponding to the first reference charge state (hereinafter referred to as the first definite point), the discharge current of the secondary battery is integrated and the discharge electricity is obtained. Measuring the amount and determining the state of charge of the secondary battery based on the amount of discharged electricity, the discharge capacity of the secondary battery, and the first reference charge state;
(D) Measurement of the state of charge in the second reference charge state at a point in time when the battery state includes a set in the discharge characteristic table corresponding to the second reference charge state (hereinafter referred to as a second definite point). Replacing values;
(E) The discharge current of the secondary battery is integrated from the second deterministic point and the amount of discharge electricity is measured. Based on the amount of discharge electricity, the discharge capacity, and the second reference charge state of the secondary battery, Determining the state of charge;
(F) At a point in time when the battery state of the secondary battery includes a set in the discharge characteristic table corresponding to the third reference charge state (hereinafter referred to as a third definite point), the third reference charge state Replacing the measured state of charge; and
(G) A value obtained by dividing the amount of discharge electricity between the first to second fixed points by the difference between the battery voltage determined by the battery temperature and the discharge current in the first and second reference charging states, The battery in the discharge characteristics table so as to coincide with the value obtained by dividing the amount of discharge electricity between the fixed points from 1 to 3 by the difference between the battery voltages of the first and third reference charge states Correcting the set of voltage, battery current, and battery temperature;
A charging state measuring method comprising: (A) A step of setting a discharge characteristic table indicating a set of a battery voltage, a battery current, and a battery temperature in a reference charge state for the secondary battery;
(B) Monitoring battery status including a set of battery voltage, battery current, and battery temperature for the secondary battery;
(C) Detecting a sudden drop in battery voltage at the start of discharging of the secondary battery, and determining an internal resistance of the secondary battery based on a change in the battery state at that time;
(D) The secondary battery charge state is integrated from the time when the charge state of the secondary battery is equal to the reference charge state, and the discharge current of the secondary battery is measured by integrating the discharge current of the secondary battery. Determining a charge state of the secondary battery based on a capacity and the reference charge state;
(E) When the battery state includes one set in the discharge characteristic table corresponding to the reference charge state Substituting the measured value of the state of charge with the reference state of charge; and
(F) Correcting a set of battery voltage, battery current, and battery temperature in the discharge characteristics table based on a change in the internal resistance for each discharge;
A charging state measuring method comprising: (A) Integrating the discharge current for each discharge of the secondary battery to measure the amount of discharge electricity, and determining the discharge capacity based on the amount of discharge electricity and the measured value of the state of charge; and
(B) The measured value of the internal resistance used in the step of correcting the set of the battery voltage, the battery current, and the battery temperature in the discharge characteristics table based on the change of the discharge capacity for each discharge and the measured value of the charge state. Correcting step;
The charge state measuring method according to claim 9, further comprising: A change for each discharge of the secondary battery is obtained for the measured value of the internal resistance, and a set of the battery voltage, the battery current, and the battery temperature in the discharge characteristic table is determined based on the change and the measured value of the charge state. Correcting the measured value of the internal resistance used in the correcting step;
The charge state measuring method according to claim 9, further comprising:

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