JP3656113B2

JP3656113B2 - Solar power plant

Info

Publication number: JP3656113B2
Application number: JP2000214310A
Authority: JP
Inventors: 吉雄江口
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2000-07-14
Filing date: 2000-07-14
Publication date: 2005-06-08
Anticipated expiration: 2020-07-14
Also published as: JP2002034175A

Description

【０００１】
【発明の属する技術分野】
本発明は、電力系統あるいは他の発電設備と連系運転を行う太陽光発電装置に関する。
【０００２】
【従来の技術】
太陽光発電システムとしては、太陽電池の直流電力を交流に変換し、既存の電力系統に連系して運転するシステムが実用化されている。この種システムの中には、災害時や系統事故時にも運転が可能なように、太陽電池に並列に蓄電池を設置したシステムがある。このようなシステムの構成例としては、例えば図２に示す特開平９−４６９２５号公報に記載のシステムがある。
図２において、太陽電池１は、電力変換器４に接続されるとともに、切替回路（スイッチ２ａ，２ｃ，２ｅ、整流器２ｂ、抵抗２ｄからなる）２を介して蓄電池３に接続されている。電力変換器４は、直流電力を交流電力に変換し、連系装置５Ａを介して系統８と連系運転を行い、一般負荷６に電力を供給している。負荷としては一般負荷６の他に連系装置５Ｂを介して自立運転負荷７が接続されている。自立運転負荷７は、通常時には一般負荷６と同様に系統８と電力変換器４の両方から電力供給を受けるが、系統事故などにより、系統８から電力供給が不可能な場合には蓄電池３を使用して電力供給が行われる。
上記の太陽光発電システムの運転方法は、系統８が正常な場合には切替回路２のスイッチ２ｃ、２ｅが開放されており、電力変換器４は太陽電池１からのみ電力供給をうけ、最大電力追従制御を行い、太陽電池１からの発電電力が最大となるように運転し、系統８へ電力供給を行っている。系統８が何らかの異常で停電した場合には、電力変換器４の運転を一旦停止し、切替回路２のスイッチ２ｅ、２ｃの順番に投入し、連系装置５Ａを開放、連系装置５Ｂを投入し、再度運転し、自立運転負荷７に太陽電池１と蓄電池３から電力を供給する。
ところで、このような蓄電池３を設置した自立運転機能付きのシステムでは、蓄電池３が使用されるのは、系統停電などの事態の時だけであり、その他の殆どの時は利用されず、蓄電池３の利用率が非常に低い。そのため、蓄電池３を有効利用することを目的に、蓄電池３の貯蔵電力の一部を一般負荷６の電力供給にも使用する利用方法が考えられている。
この利用方法の一例として、負荷電力のピ−クカット運転があるが、これを図３を用いて説明する。
図２のシステムで系統８から受電している電力トレンドが図３（ａ）の受電電力ＰＬとする。図２では負荷に太陽電池１から電力供給を行っているため、受電電力は減少しているが、それでもＰＬのような電力を受電している状態とする。この時、電力制限値Ｐｄに受電電力ＰＬを抑制したいとすると、電力変換器４からさらに図３（ｂ）に示す電力を供給すれば良い。つまり、切替回路２で時刻ｔ１〜ｔ２にわたって蓄電池３を太陽電池１に並列に接続し、図３（ｂ）のピ−クカット電力出力指令Ｐｃを電力変換器４に与えることによりに、ピ−クカット運転が可能となる。このような運転を行うことにより、蓄電池３の貯蔵電力の一部を有効利用しながら、非常時の自立運転も可能なシステムを達成することができる。
なお、ピ−クカット運転のために、蓄電池３から放電された電力は、太陽電池１が発電できない夜間に電力変換器４を整流器運転し、系統電力によって充電される。
【０００３】
【発明が解決しようとする課題】
上記の従来システムにおいては、先に説明したように、太陽電池１だけ接続された時には、太陽電池１から最大電力を取り出すために、最大電力追従制御を行う。しかし、蓄電池３を接続した場合には、蓄電池３の内部インピ−ダンスが非常に小さく、直流電圧は蓄電池３で決まってしまうので、最大電力制御を行うことができない。
したがって、従来システムではピ−クカット運転を行う場合には、一旦電力変換器４を停止し、切替回路２で蓄電池３を接続し、制御方式も切り替えた後に再度電力変換器４を立ち上げ、系統８に接続後、ピ−クカット運転を開始するなどの非常に煩わしい手段を採っていた。また、運転切替時には、切替回路２のスイッチを投入、開放するため、これらスイッチの寿命の問題もあった。
【０００４】
本発明の課題は、蓄電池が並列に接続された太陽光発電設備において、蓄電池併用運転と太陽電池のみの運転を煩雑な切替操作なしに運転可能な太陽光発電装置を提供することにある。
【０００５】
【課題を解決するための手段】
上記課題を解決するために、太陽電池と充放電手段を介して並列に接続された蓄電池と、太陽電池の出力電力を交流電力に変換し、他の交流電源と連系する電力変換器と、太陽電池の出力が増加する方向へ動作指令値を変化させる最大電力追従制御手段と、最大電力追従制御手段による動作指令値が一定値以下となった場合に太陽電池の電圧を一定値とするように制御する直流定電圧制御手段と、外部からの電力指令により電力変換器の制御を最大電力追従制御から外部電力指令制御に切替える外部電力指令制御手段を備えた太陽光発電装置であって、直流定電圧制御手段により制御される一定電圧を前記蓄電池電圧より高く設定し、太陽電池の最大電力追従制御あるいは直流定電圧制御時には蓄電池の放電を阻止し、外部からの電力指令により外部電力指令制御手段を動作させて外部電力指令制御とした時には、蓄電池からの電力供給を行う。
ここで、蓄電池から電力供給を行わない場合には、太陽電池の最大電力追従制御または直流定電圧制御を行い、蓄電池から電力供給を行う場合には、外部からの電力指令にしたがって制御を行う。
また、蓄電池に電流検出器を設け、最大電力追従制御時あるいは直流定電圧制御時に蓄電池の放電電流を検出したとき、最大電力追従制御手段の動作指令値あるいは直流定電圧制御手段の電圧指令値を上昇させる補正手段を備える。
また、蓄電池に電圧検出器および直流−直流変換器を接続し、電圧検出器によって検出された蓄電池出力電圧を最大電力追従制御手段の動作指令値あるいは直流定電圧制御手段の電圧指令値より低くするように前記直流−直流変換器を制御する直流電圧調整手段を備える。
【０００６】
【発明の実施の形態】
以下、本発明の実施形態を図面を参照して説明する。
図１は、本発明の太陽光発電装置である第一の実施形態を示す。図２で説明した従来技術と同一番号の構成は図２と同一の機能を有する。
図１において、太陽電池１は、充電ブロック回路３０を介して蓄電池３と並列に接続され、電力変換器４に電力を供給する。充電ブロック回路３０内のスイッチ３０Ｓは通常開放され、後で説明する蓄電池３の充電時の時のみ接続される。
ここで、太陽電池１は、以下で説明する直流定電圧設定回路２２によって指示される電圧以上で制御されるが、直流定電圧設定回路２２の指令値は蓄電池３の電圧より高く設定されている。このため、太陽電池１の方が蓄電池電圧より高いので、充電ブロック回路３０内のダイオード３０ｄは逆方向にバイアスされ、蓄電池３からの電力放電はない。したがって、電力変換器４への電力の入力は太陽電池１の出力だけとなる。太陽電池１の出力は電力変換器４で交流に変換され、連系スイッチ５を介して電力系統８に接続され、一般負荷６に電力が供給される。
一方、太陽電池１で発電された電圧、電流は電流検出器９、電圧検出器１０を介して電力検出回路２０に送られ、太陽電池１の出力電力が演算される。電力検出回路２０の出力は、最大電力追従回路２１に送られ、ここで太陽電池１の最大電力が得られる直流電圧指令が出力される。
最大電力追従制御は、日射強度が強いときには太陽電池１の直流電圧を変えることにより、有効に電力を取り出すことができるが、日射強度が弱いときには直流定電圧で太陽電池１を制御しても効果は変わらなくなる。
【０００７】
図４は、上記の理由を説明するための太陽電池特性図であり、太陽電池の出力特性について、日射強度をＩ１＞Ｉ２＞Ｉ３の３ケースとした場合の太陽電池の電圧−電流特性Ｌ１〜Ｌ３およびで電圧−電力特性Ｐ１〜Ｐ３を示したものである。この特性図から分かるように、太陽電池の最大電力は、日射強度Ｉ１が十分にある場合には直流電圧を制御することにより、大きく変化するが、日射強度Ｉ３が小さくなると、最大電力を得る直流電圧が低下するとともにピークが平坦となり、直流電圧によって電力は大きく変化しない特性となる。ある日射強度以下の場合には、直流電圧一定制御しても効果は殆ど変わらなくなる。そのため、最大電力追従制御の結果、直流電圧が一定値以下になった場合には、その電圧で直流定電圧制御を行うことが多い。
このため、図１では最大電力追従運転から直流定電圧制御の移行電圧値Ｖｄを直流定電圧設定回路２２によって設定しておく。
【０００８】
高電圧選定回路２３は、最大電力追従回路２１の出力値と定電圧設定回路２２の出力とを比較し、どちらか高い方の電圧を優先的に選択する回路であり、日射強度が強い状態では最大電力追従回路２１の方が大きいので、こちらを選択するが、夕暮れ時や天候が悪く出力がでない場合などは、最大電力追従回路２１の出力が定電圧設定回路２２の出力以下になり、定電圧設定回路２２の出力を選択する。以上により、通常運転制御は、太陽電池１の最大電力追従制御となるため、高電圧選定回路２３は最大電力追従回路２１の信号を選択し、直流電圧制御回路２４に信号を送る。直流電圧制御回路２４の出力信号２４ａは、切替器２６に送られる。切替器２６は、外部電力指令回路２５の電力指令２５ａと、直流電圧制御回路２４の出力を切り替え選択し、通常運転時は直流電圧制御回路２４の出力信号２４ａが選択される。直流制御回路２４の出力信号２４ａは電流制御回路２７に入力され、また、電流検出器１１によって検出された電力変換器４の出力電流を電流制御回路２７に入力し、ゲート回路２８を介して電流制御回路２７の出力によって電力変換器４を制御し、太陽電池１の直流電圧を最大電力値となるように運転を行う。このように、外部からの電力指令２５ａがない状態では、従来と同様太陽電池１の最大電力追従制御が実施される。
【０００９】
さて、上記の運転中に、図３（ｂ）に示すように、時刻ｔ１〜ｔ２にかけて負荷のピークカット運転を行う場合には、外部電力指令回路２５から図３（ｂ）に示すピークカット電力出力指令Ｐｃを出力しておき、タイマー回路２９により切替器２６を外部電力指令回路２５の電力指令２５ａを選択するように切り替える。このように制御指令が外部からの電力指令２５ａに切り替わると、電力変換器４の制御は今まで述べてきた最大電力追従制御から、外部電力指令による電力指令に切り替わる。つまり、太陽電池１の直流電圧制御が開放され、電力変換器４の出力が外部電力指令回路２５の電力指令２５ａと一致するように動作する電力制御となる。
一方、外部電力指令回路２５の指令値は現状の出力にさらにＰｃ分の電力を出力する指令となるので、太陽電池１の最大電力値よりも大きい値となり、太陽電池はこの電力を負担できない。このため、太陽電池１の出力電圧は低下し、蓄電池電圧Ｖｂの値まで低下し、蓄電池３から不足電力を供給するように動作する。
つまり、図５に示すように、ＶｍａｘのＡ点で太陽電池１が運転していたときに、タイマー回路２９から切替指令が出力され、切替器２６が外部電力指令回路２５を選択すると、図３（ｂ）の電力指令Ｐｃが出力され、この電力指令Ｐｃは太陽電池１の最大電力値以上のため、直流電流が増大し、太陽電池１はＶｍａｘ電圧を維持できなく、電圧−電流特性にしたがって電圧が低下する。太陽電池電圧が蓄電池電圧ＶｂのＢ点まで低下すると、今まで通電が阻止されていた充電ブロック回路３０のダイオード３０ｄが導通し、蓄電池３からの電力供給が開始される。蓄電池３は、内部インピーダンスが低いため、外部電力指令回路２５の指令値の電力を十分供給可能なため、直流電圧は蓄電池電圧Ｖｂに維持され、電力供給と見合う電流のＣ点で運転を行うことになる。したがって、ピークカット運転時間内のｔ１〜ｔ２までの時間帯は、外部電力指令回路２５の指令値の電力が電力変換器４から出力される。
ピークカット運転が終了する時刻ｔ２に達すると、タイマー回路２９は切替器２６の選択を直流制御回路２４の出力側に切り替える。この時、切り替える前の直流電圧は蓄電池電圧Ｖｂとなっており、直流定電圧設定回路２２の設定値Ｖｄよりも低い値となっている。高電圧選択回路２３では直流定電圧設定回路２２の指令値Ｖｄか最大電力追従回路２１の出力のどちらか高い方値を選択するが、蓄電池電圧Ｖｂは何れの電圧よりも低くなるように構成されているので、この電圧で運転されると、充電ブロック回路３０のダイオード３０ｄは再び逆方向にバイアスされ、導通が阻止される。このため、蓄電池３からの電力供給はなくなり、太陽電池１からのみの電力供給に自動的に戻ることになる。したがって、以後太陽電池１の最大電力追従制御が再び可能となる。
【００１０】
以上で説明したように、本実施形態では、直流定電圧設定回路２２の設定電圧Ｖｄを蓄電池３の電圧Ｖｂより高い値になるように設定し、また、蓄電池３と直列に充電ブロック回路３０を設けることにより、煩雑な切替操作をなくして自動的に太陽電池１の最大電力追従制御およびピークカット運転が可能となる。
なお、充電ブロック回路３０のスイッチ３０Ｓは常時は開放されており、夜太陽電池が発電できなくなる時間帯に投入し、電力変換器４によって系統８の電力を使用して日中に放電した電力を充電する。充電を完了した時点でスイッチ３０Ｓは再び開放される。
【００１１】
図６は、本発明の第二の実施形態を示す。図１の第一の実施形態と異なる点は、蓄電池３に電流検出器４０を設置し、最大電力追従回路２１および直流定電圧設定回路２２にそれぞれ電圧補正回路４１、４２を接続することにある。
蓄電池３の電流検出器４０は蓄電池３の放電電流を監視し、太陽電池１の最大電力追従運転時、あるいは、直流定電圧運転時に電流検出器４０によって蓄電池３の放電電流が検出された場合には、電圧補正回路４１、４２により電圧指令値を上昇させ、電流検出器４０の電流が検出されなくなるまで電圧の設定値の補正を自動的に行う。
これにより、太陽電池１の最大電力追従運転あるいは直流定電圧運転を有効に行うことができ、太陽電池１の電力利用率を向上させることができる。
【００１２】
図７は、本発明の第三の実施形態を示す。図１の第一の実施形態と異なる点は、蓄電池３に電流検出器４０および直流−直流変換器５０を接続し、この直流−直流変換器５０と直流定電圧設定回路２２の間に直流電圧調整回路５２および電圧バイアス設定回路５３を設けることにある。
電圧バイアス設定回路５３は、直流定電圧設定回路２２の設定電圧に対してある一定値分だけ常に低い電圧を出力する。直流電圧調整回路５２は、電圧バイアス設定回路５３の信号を指令値とし、電圧検出器５１によって検出された蓄電池出力電圧が電圧バイアス設定回路５３の出力と同じくなるように直流−直流変換器５０を制御する。
直流−直流変換器５０は、蓄電池３の電圧を可変し、直流定電圧設定回路２２の設定電圧より低い電圧に蓄電池出力電圧を制御する。
これにより、蓄電池３の電圧が太陽電池運転電圧よりも高くとも、直流−直流変換器５０によって蓄電池３の出力電圧を直流定電圧設定回路２２の設定電圧より低くすることができ、図１と同じ効果が得られる。
【００１３】
【発明の効果】
以上説明したように、本発明によれば、太陽電池だけを使用した最大電力追従運転から蓄電池の貯蔵電力を使用した運転への切替あるいはその反対の切替操作も煩雑な操作を行うことなく、自動的に切り替えることが可能となる。
また、蓄電池の電圧を太陽電池の直流定電圧より小さい値とするように設定するので、太陽電池だけからの電力供給モードでも蓄電池からの電力供給モードにおいても、電力変換器停止操作、切替操作の煩わしさがを伴わず、運転が可能となり、また、太陽電池の電力利用率を上げることができる。
また、電力供給モードの運転切替時に用いる切替用のスイッチの省設備化により、メンテナンスが容易になり、低コスト化を図ることができる。
また、太陽電池の最大電力追従運転時あるいは直流定電圧運転時に蓄電池の放電電流が検出された場合には、蓄電池の出力電圧より直流回路の電圧指令値を上昇させるように自動的に補正するので、太陽電池の最大電力追従運転あるいは直流定電圧運転を有効に行うことができ、太陽電池の電力利用率を向上させることができる。
また、太陽電池の最大電力追従運転時あるいは直流定電圧運転時に蓄電池の放電電流が検出された場合には、蓄電池の出力電圧を直流定電圧制御の設定電圧より低くするので、太陽電池の最大電力追従運転あるいは直流定電圧運転を有効に行うことができ、太陽電池の電力利用率を向上させることができる。
【図面の簡単な説明】
【図１】本発明の太陽光発電装置である第一の実施形態を示す構成図
【図２】従来例による太陽光発電システム
【図３】ピークカット電力を説明する図
【図４】太陽電池の出力特性を説明する図
【図５】本発明の第一の実施形態の太陽電池の動作を説明する図
【図６】本発明の第二の実施形態を示す構成図
【図７】本発明の第三の実施形態を示す構成図
【符号の説明】
１…太陽電池、２…切替装置、３…蓄電池、４…電力変換器、５，５Ａ，５Ｂ…連系装置、６…一般負荷、７…自立運転負荷、８…系統、９…電流検出器、１０…電圧検出器、１１…電流検出器、２０…電力検出器、２１…最大電力追従回路、２２…直流定電圧設定回路、２３…高電圧選定回路、２４…直流電圧制御回路、２５…外部電力指令回路、２６…切替器、２７…定電流制御回路、２８…ゲート回路、２９…タイマー回路、３０…充電ブロック回路、４０…電流検出回路、４１…電圧補正回路、４２…電圧補正回路、５０…電圧−電圧変換器、５１…電圧検出器、５２…直流電圧調整回路、５３…電圧バイアス設定回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solar power generation apparatus that performs an interconnection operation with an electric power system or another power generation facility.
[0002]
[Prior art]
As a solar power generation system, a system that converts the direct current power of a solar cell into alternating current and operates in conjunction with an existing power system has been put into practical use. Among these systems, there is a system in which a storage battery is installed in parallel with a solar battery so that it can be operated even in the event of a disaster or a system failure. As an example of the configuration of such a system, for example, there is a system described in JP-A-9-46925 shown in FIG.
In FIG. 2, the solar cell 1 is connected to a power converter 4 and is connected to a storage battery 3 via a switching circuit (consisting of switches 2a, 2c, 2e, a rectifier 2b, and a resistor 2d) 2. The power converter 4 converts direct-current power into alternating-current power, performs interconnection operation with the system 8 via the interconnection device 5 </ b> A, and supplies electric power to the general load 6. As a load, in addition to the general load 6, a self-sustained operation load 7 is connected via the interconnection device 5B. The self-sustained operation load 7 is normally supplied with power from both the system 8 and the power converter 4 in the same manner as the general load 6, but when the power supply from the system 8 is impossible due to a system failure or the like, the storage battery 3 is connected. Used to supply power.
In the operation method of the solar power generation system described above, when the system 8 is normal, the switches 2c and 2e of the switching circuit 2 are opened, and the power converter 4 is supplied with power only from the solar cell 1, and the maximum power Follow-up control is performed so that power generated from the solar cell 1 is maximized, and power is supplied to the grid 8. In the event of a power failure due to any abnormality in the system 8, the operation of the power converter 4 is temporarily stopped, the switches 2e and 2c of the switching circuit 2 are turned on in this order, the interconnection device 5A is opened, and the interconnection device 5B is turned on. Then, it is operated again, and electric power is supplied from the solar cell 1 and the storage battery 3 to the self-supporting operation load 7.
By the way, in such a system with a self-sustaining operation function in which the storage battery 3 is installed, the storage battery 3 is used only in the event of a system power failure or the like, and is not used in most other cases. The utilization rate is very low. Therefore, a method of using a part of the stored power of the storage battery 3 also for power supply of the general load 6 has been considered for the purpose of effectively using the storage battery 3.
As an example of this utilization method, there is a peak cut operation of load power, which will be described with reference to FIG.
The power trend received from the system 8 in the system of FIG. 2 is the received power PL of FIG. In FIG. 2, since the power is supplied from the solar cell 1 to the load, the received power is reduced, but it is still in a state of receiving power such as PL. At this time, if it is desired to suppress the received power PL to the power limit value Pd, the power shown in FIG. That is, the switching circuit 2 connects the storage battery 3 in parallel to the solar battery 1 over time t1 to t2, and gives the peak power output command Pc of FIG. Driving is possible. By performing such an operation, it is possible to achieve a system that can perform an autonomous operation in an emergency while effectively using a part of the stored power of the storage battery 3.
For peak cut operation, the electric power discharged from the storage battery 3 is rectified by the power converter 4 at night when the solar battery 1 cannot generate power, and is charged by the system power.
[0003]
[Problems to be solved by the invention]
In the above conventional system, as described above, when only the solar cell 1 is connected, the maximum power follow-up control is performed in order to extract the maximum power from the solar cell 1. However, when the storage battery 3 is connected, the internal impedance of the storage battery 3 is very small, and the DC voltage is determined by the storage battery 3, so that maximum power control cannot be performed.
Therefore, in the conventional system, when performing peak cut operation, the power converter 4 is temporarily stopped, the storage battery 3 is connected by the switching circuit 2, the control system is switched, and then the power converter 4 is started up again. After connecting to 8, a very troublesome means such as starting a peak cut operation was taken. Further, since the switches of the switching circuit 2 are turned on and opened at the time of operation switching, there is a problem in the life of these switches.
[0004]
An object of the present invention is to provide a photovoltaic power generation apparatus capable of operating a combined storage battery operation and only a solar battery operation without complicated switching operation in a photovoltaic power generation facility in which storage batteries are connected in parallel.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, a storage battery connected in parallel via a solar battery and charging / discharging means, an output power of the solar battery is converted into AC power, and a power converter linked to other AC power supply, Maximum power follow-up control means for changing the operation command value in the direction in which the output of the solar cell increases, and when the operation command value by the maximum power follow-up control means falls below a certain value, the voltage of the solar cell is made constant. controlling the DC constant voltage control means, a photovoltaic device with an external power instruction control means for switching from the maximum power follow-up control to an external power command controls the control of the power converter by the power command from outside, DC a constant voltage which is controlled by the constant voltage control means is set higher than the battery voltage, to prevent the discharge of the storage battery is at the maximum power follow-up control or direct current constant voltage control of the solar cell, the power command from the outside When an external power command control operates the Rigaibu power instruction control means performs power supply from the storage battery.
Here, when power is not supplied from the storage battery, maximum power tracking control or DC constant voltage control of the solar battery is performed, and when power is supplied from the storage battery, control is performed according to an external power command.
In addition, when a storage battery is provided with a current detector and the discharge current of the storage battery is detected during maximum power tracking control or DC constant voltage control, the operation command value of the maximum power tracking control means or the voltage command value of the DC constant voltage control means is Correction means for raising is provided.
Further, a voltage detector and a DC-DC converter are connected to the storage battery, and the storage battery output voltage detected by the voltage detector is made lower than the operation command value of the maximum power tracking control means or the voltage command value of the DC constant voltage control means. Thus, a DC voltage adjusting means for controlling the DC-DC converter is provided.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a first embodiment which is a photovoltaic power generation apparatus of the present invention. The configuration with the same number as the prior art described in FIG. 2 has the same function as in FIG.
In FIG. 1, the solar cell 1 is connected in parallel with the storage battery 3 via the charging block circuit 30 and supplies power to the power converter 4. The switch 30S in the charging block circuit 30 is normally opened and is connected only when the storage battery 3 described later is charged.
Here, the solar cell 1 is controlled at a voltage higher than the voltage indicated by the DC constant voltage setting circuit 22 described below, but the command value of the DC constant voltage setting circuit 22 is set higher than the voltage of the storage battery 3. . For this reason, since the solar cell 1 is higher than the storage battery voltage, the diode 30d in the charging block circuit 30 is biased in the reverse direction, and there is no power discharge from the storage battery 3. Therefore, the power input to the power converter 4 is only the output of the solar cell 1. The output of the solar cell 1 is converted into alternating current by the power converter 4, connected to the power system 8 via the interconnection switch 5, and power is supplied to the general load 6.
On the other hand, the voltage and current generated by the solar cell 1 are sent to the power detection circuit 20 via the current detector 9 and the voltage detector 10, and the output power of the solar cell 1 is calculated. The output of the power detection circuit 20 is sent to the maximum power tracking circuit 21 where a DC voltage command for obtaining the maximum power of the solar cell 1 is output.
The maximum power tracking control can effectively extract electric power by changing the DC voltage of the solar cell 1 when the solar radiation intensity is strong. However, when the solar radiation intensity is weak, controlling the solar battery 1 with the DC constant voltage is also effective. Will not change.
[0007]
FIG. 4 is a solar cell characteristic diagram for explaining the above reason. Regarding the output characteristics of the solar cell, the voltage-current characteristics L1 to L1 of the solar cell when the solar radiation intensity is three cases of I1>I2> I3. L3 and voltage-power characteristics P1 to P3 are shown. As can be seen from this characteristic diagram, the maximum power of the solar cell varies greatly by controlling the DC voltage when the solar radiation intensity I1 is sufficient, but when the solar radiation intensity I3 is small, the direct current that obtains the maximum power is obtained. As the voltage decreases, the peak becomes flat, and the power does not change greatly due to the DC voltage. When the solar radiation intensity is below a certain level, the effect is hardly changed even if the DC voltage is controlled constant. For this reason, when the DC voltage becomes a certain value or less as a result of the maximum power follow-up control, DC constant voltage control is often performed with the voltage.
Therefore, in FIG. 1, the DC constant voltage control transition voltage value Vd from the maximum power following operation is set by the DC constant voltage setting circuit 22.
[0008]
The high voltage selection circuit 23 compares the output value of the maximum power tracking circuit 21 with the output of the constant voltage setting circuit 22 and preferentially selects the higher voltage, and in a state where the solar radiation intensity is strong The maximum power follower circuit 21 is larger, so this is selected. However, at dusk, when the weather is bad and there is no output, the output of the maximum power follower circuit 21 is less than the output of the constant voltage setting circuit 22 and is constant. The output of the voltage setting circuit 22 is selected. As described above, since the normal operation control is the maximum power follow-up control of the solar cell 1, the high voltage selection circuit 23 selects the signal of the maximum power follow-up circuit 21 and sends the signal to the DC voltage control circuit 24. The output signal 24 a of the DC voltage control circuit 24 is sent to the switch 26. The switch 26 switches between the power command 25a of the external power command circuit 25 and the output of the DC voltage control circuit 24, and the output signal 24a of the DC voltage control circuit 24 is selected during normal operation. The output signal 24 a of the DC control circuit 24 is input to the current control circuit 27, and the output current of the power converter 4 detected by the current detector 11 is input to the current control circuit 27, and the current is output via the gate circuit 28. The power converter 4 is controlled by the output of the control circuit 27, and the operation is performed so that the DC voltage of the solar cell 1 becomes the maximum power value. Thus, in the state where there is no power command 25a from the outside, the maximum power follow-up control of the solar cell 1 is performed as in the conventional case.
[0009]
Now, during the above operation, as shown in FIG. 3B, when the load peak cut operation is performed from time t1 to t2, the peak cut power shown in FIG. The output command Pc is output, and the switch 26 is switched by the timer circuit 29 so as to select the power command 25a of the external power command circuit 25. When the control command is thus switched to the power command 25a from the outside, the control of the power converter 4 is switched from the maximum power tracking control described so far to the power command based on the external power command. That is, the DC voltage control of the solar cell 1 is released, and power control is performed so that the output of the power converter 4 matches the power command 25a of the external power command circuit 25.
On the other hand, since the command value of the external power command circuit 25 is a command for outputting power corresponding to Pc to the current output, the value is larger than the maximum power value of the solar cell 1, and the solar cell cannot bear this power. For this reason, the output voltage of the solar cell 1 decreases, decreases to the value of the storage battery voltage Vb, and operates to supply insufficient power from the storage battery 3.
That is, as shown in FIG. 5, when the solar cell 1 is operating at the point A of Vmax, when the switching command is output from the timer circuit 29 and the switch 26 selects the external power command circuit 25, FIG. The power command Pc of (b) is output, and since this power command Pc is equal to or greater than the maximum power value of the solar cell 1, the direct current increases, the solar cell 1 cannot maintain the Vmax voltage, and according to the voltage-current characteristics. The voltage drops. When the solar battery voltage decreases to the point B of the storage battery voltage Vb, the diode 30d of the charging block circuit 30 that has been prevented from being energized until now is turned on, and power supply from the storage battery 3 is started. Since the storage battery 3 has a low internal impedance, it can sufficiently supply the power of the command value of the external power command circuit 25, so that the DC voltage is maintained at the storage battery voltage Vb and is operated at a point C of a current commensurate with the power supply. become. Therefore, the power of the command value of the external power command circuit 25 is output from the power converter 4 during the time period from t1 to t2 within the peak cut operation time.
When the time t2 when the peak cut operation ends is reached, the timer circuit 29 switches the selection of the switch 26 to the output side of the DC control circuit 24. At this time, the DC voltage before switching is the storage battery voltage Vb, which is lower than the set value Vd of the DC constant voltage setting circuit 22. The high voltage selection circuit 23 selects a higher value of the command value Vd of the DC constant voltage setting circuit 22 or the output of the maximum power tracking circuit 21, but the storage battery voltage Vb is configured to be lower than any voltage. Therefore, when operated at this voltage, the diode 30d of the charging block circuit 30 is again biased in the reverse direction and conduction is prevented. For this reason, there is no power supply from the storage battery 3, and it automatically returns to the power supply only from the solar battery 1. Therefore, the maximum power follow-up control of the solar cell 1 can be performed again thereafter.
[0010]
As described above, in the present embodiment, the setting voltage Vd of the DC constant voltage setting circuit 22 is set to be higher than the voltage Vb of the storage battery 3, and the charging block circuit 30 is connected in series with the storage battery 3. By providing, the maximum power follow-up control and peak cut operation of the solar cell 1 can be automatically performed without complicated switching operations.
Note that the switch 30S of the charging block circuit 30 is normally open, and is inserted in a time zone when the solar cell cannot generate electricity at night, and the electric power discharged by the power converter 4 during the daytime using the power of the system 8 is used. Charge. When the charging is completed, the switch 30S is opened again.
[0011]
FIG. 6 shows a second embodiment of the present invention. The difference from the first embodiment of FIG. 1 is that a current detector 40 is installed in the storage battery 3 and voltage correction circuits 41 and 42 are connected to the maximum power tracking circuit 21 and the DC constant voltage setting circuit 22, respectively. .
The current detector 40 of the storage battery 3 monitors the discharge current of the storage battery 3, and when the discharge current of the storage battery 3 is detected by the current detector 40 during the maximum power following operation of the solar battery 1 or during the DC constant voltage operation. Increases the voltage command value by the voltage correction circuits 41 and 42, and automatically corrects the voltage setting value until the current of the current detector 40 is no longer detected.
Thereby, the maximum power follow-up operation or DC constant voltage operation of the solar cell 1 can be effectively performed, and the power utilization rate of the solar cell 1 can be improved.
[0012]
FIG. 7 shows a third embodiment of the present invention. A difference from the first embodiment of FIG. 1 is that a current detector 40 and a DC-DC converter 50 are connected to the storage battery 3, and a DC voltage is connected between the DC-DC converter 50 and the DC constant voltage setting circuit 22. An adjustment circuit 52 and a voltage bias setting circuit 53 are provided.
The voltage bias setting circuit 53 always outputs a voltage lower than the set voltage of the DC constant voltage setting circuit 22 by a certain fixed value. The DC voltage adjustment circuit 52 uses the signal from the voltage bias setting circuit 53 as a command value, and sets the DC-DC converter 50 so that the storage battery output voltage detected by the voltage detector 51 is the same as the output from the voltage bias setting circuit 53. Control.
The DC-DC converter 50 varies the voltage of the storage battery 3 and controls the storage battery output voltage to a voltage lower than the setting voltage of the DC constant voltage setting circuit 22.
Thereby, even if the voltage of the storage battery 3 is higher than the solar battery operating voltage, the output voltage of the storage battery 3 can be made lower than the set voltage of the DC constant voltage setting circuit 22 by the DC-DC converter 50, which is the same as FIG. An effect is obtained.
[0013]
【The invention's effect】
As described above, according to the present invention, the switching from the maximum power follow-up operation using only the solar battery to the operation using the storage power of the storage battery or the reverse switching operation can be automatically performed without performing a complicated operation. Can be switched automatically.
Moreover, since the voltage of the storage battery is set to a value smaller than the DC constant voltage of the solar battery, the power converter stop operation and switching operation can be performed both in the power supply mode from the solar battery alone and in the power supply mode from the storage battery. The operation is possible without bothering, and the power utilization rate of the solar cell can be increased.
In addition, maintenance can be facilitated and costs can be reduced by reducing the number of switches used for switching the operation in the power supply mode.
In addition, if the discharge current of the storage battery is detected during the maximum power follow-up operation or DC constant voltage operation of the solar battery, it is automatically corrected so as to increase the voltage command value of the DC circuit from the output voltage of the storage battery. The maximum power follow-up operation or DC constant voltage operation of the solar cell can be effectively performed, and the power utilization factor of the solar cell can be improved.
Also, if the discharge current of the storage battery is detected during the maximum power follow-up operation or DC constant voltage operation of the solar battery, the output voltage of the storage battery is made lower than the set voltage of DC constant voltage control. Following operation or DC constant voltage operation can be performed effectively, and the power utilization factor of the solar cell can be improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a first embodiment of a solar power generation apparatus according to the present invention. FIG. 2 is a conventional solar power generation system. FIG. 3 is a diagram for explaining peak cut power. FIG. 5 is a diagram illustrating the operation of the solar cell according to the first embodiment of the present invention. FIG. 6 is a configuration diagram illustrating the second embodiment of the present invention. Schematic diagram showing the third embodiment of the present invention [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Solar cell, 2 ... Switching apparatus, 3 ... Storage battery, 4 ... Power converter, 5, 5A, 5B ... Interconnection apparatus, 6 ... General load, 7 ... Self-sustained operation load, 8 ... System, 9 ... Current detector DESCRIPTION OF SYMBOLS 10 ... Voltage detector, 11 ... Current detector, 20 ... Power detector, 21 ... Maximum power follow-up circuit, 22 ... DC constant voltage setting circuit, 23 ... High voltage selection circuit, 24 ... DC voltage control circuit, 25 ... External power command circuit, 26 ... switch, 27 ... constant current control circuit, 28 ... gate circuit, 29 ... timer circuit, 30 ... charge block circuit, 40 ... current detection circuit, 41 ... voltage correction circuit, 42 ... voltage correction circuit , 50 ... voltage-voltage converter, 51 ... voltage detector, 52 ... DC voltage adjustment circuit, 53 ... voltage bias setting circuit

Claims

A solar battery, a storage battery connected in parallel via the solar battery and charging / discharging means, a power converter that converts the output power of the solar battery into alternating current power, and is linked to another alternating current power source, and the sun Maximum power follow-up control means for changing the operation command value in a direction in which the battery output increases, and when the operation command value by the maximum power follow-up control means becomes a certain value or less, the voltage of the solar battery is made constant. And a DC constant voltage control means for controlling the power converter, and an external power command control means for switching the control of the power converter from the maximum power tracking control to the external power command control by an external power command. ,
The constant voltage controlled by the DC constant voltage control means is set higher than the storage battery voltage, and the discharge of the storage battery is prevented during the maximum power follow-up control or the DC constant voltage control of the solar battery , and the power command from the outside When the external power command control means is operated to set the external power command control, power is supplied from the storage battery .

In Claim 1, when not supplying power from the storage battery, maximum power tracking control or DC constant voltage control of the solar battery is performed, and when supplying power from the storage battery, the external power command The photovoltaic power generation apparatus characterized by performing control according to.

3. The operation command of the maximum power tracking control means according to claim 1 or 2, wherein a current detector is provided in the storage battery, and when the discharge current of the storage battery is detected during the maximum power tracking control or the DC constant voltage control. And a correction means for increasing the voltage command value of the DC constant voltage control means .

3. A voltage detector and a DC-DC converter are connected to the storage battery according to claim 1 or 2, and the storage battery output voltage detected by the voltage detector is used as an operation command value of the maximum power tracking control means or the DC. A photovoltaic power generator comprising a DC voltage adjusting means for controlling the DC-DC converter so as to be lower than a voltage command value of a constant voltage control means .