JP2004171934A

JP2004171934A - Induction heating device

Info

Publication number: JP2004171934A
Application number: JP2002336457A
Authority: JP
Inventors: Atsushi Fujita; 篤志藤田; Motonari Hirota; 泉生弘田; Yuji Fujii; 裕二藤井; Takahiro Miyauchi; 貴宏宮内; Koji Niiyama; 浩次新山
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2002-11-20
Filing date: 2002-11-20
Publication date: 2004-06-17

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device which reduces the time until re-start by quickly reducing the voltage of a smoothing means when stopping the heating. <P>SOLUTION: The induction heating device stops the heating after reducing the output of a boosting means 35 in order to reduce the voltage of a smoothing means 22, soon after the stopping of an inverter 22, before heating shutdown. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、一般家庭やオフィス、レストラン、工場等で使用される誘導加熱調理器、誘導加熱を利用した湯沸かし器、加温装置等の誘導加熱装置に関するものである。
【０００２】
【従来の技術】
誘導加熱装置の例として、誘導加熱調理器について説明する。誘導加熱調理器では、誘導加熱コイルから高周波磁界が発生し、加熱コイル近傍に置かれた金属製の鍋等の被加熱体に電磁誘導によって渦電流が発生し、被加熱体が加熱される。このような原理のため、誘導加熱には鉄をはじめとする高抵抗率金属製の被加熱体が適している。
【０００３】
しかしながら近年、誘導加熱調理器には、アルミ、銅等の低抵抗率金属製の鍋も誘導加熱できることが求められている。このような鍋を加熱するために、一般にはインバータの出力周波数を高めることで、被加熱体の表皮抵抗を増加させ、さらに加熱コイルのターン数を増加させると共に、インバータ電源を昇圧することで磁界を強める必要があった。
【０００４】
また、インバータ電源にリプルが生じている場合には、加熱コイルと低抵抗率金属製の鍋間の反発力に起因して、リプル周波数に応じた不快音が発生するため、インバータ電源を平滑する必要があった。
【０００５】
上記課題を解決するための方法として、例えば特許文献１に開示された従来の誘導加熱調理器の例を説明する。図６は、従来の誘導加熱調理器の回路構成を示す図である。図において、電源１は商用電源であり、整流回路２によって整流され、第１の平滑コンデンサ３に伝達される。チョークコイル４は第２のスイッチング素子７の導通時にエネルギを蓄え、第２のスイッチング素子７が遮断された時に第１のダイオード６を通して第２の平滑コンデンサ１２に蓄えたエネルギを放出する。
【０００６】
すなわち、チョークコイル４、第２のスイッチング素子７、第１のダイオード６は、昇圧手段を構成している。また、第２のスイッチング素子７は、加熱コイル９と共振コンデンサ１０の共振周波数で共振する共振電流を発生させ、被加熱体である鍋１１に高周波磁界を供給し、誘導加熱する。第１のスイッチング素子５は、第２のスイッチング素子７が遮断期間中に、第２の平滑コンデンサ１２に蓄えられたエネルギを加熱コイル９及び共振コンデンサ１０に放出し、共振を継続させる。このように、第２の平滑コンデンサ１２に一度エネルギを蓄えることにより、加熱コイル９及び共振コンデンサ１０にかかる電圧及び流れる電流を平滑化することが可能となり、商用周波数で生じるリプルを軽減し、加熱コイル９と鍋１１間の反発力による不快音を抑制することが出来る。
【０００７】
【特許文献１】
特開２００２−７５６２０号公報
【０００８】
【発明が解決しようとする課題】
しかしながら、前記従来の構成では、加熱時において加熱コイル９と鍋１１間の反発力による不快音を抑制し、昇圧電源を平滑する第２の平滑コンデンサ１２の容量が大きいために、加熱停止後の第２の平滑コンデンサ１２電圧の低下が緩やかである。そのため、加熱停止後、即座に加熱開始すると、第２のスイッチング素子７導通開始時における第２のスイッチング素子７電圧が高いために、過大な短絡電流が流れ、第２のスイッチング素子７の負荷が大きくなる。これを回避するために、加熱停止後に一定期間再起動を受け付けない制御を行えば、使用者による加熱停止後の再起動や、異常検知時の一時停止後の再起動に時間がかかるという課題が生じる。
【０００９】
また、アルミなどの低抵抗率金属製の鍋１１以外の材質のものを加熱するため、加熱コイル９あるいは共振コンデンサ１０容量を切り換えるべくリレーなどのインピーダンス変更手段を備えた場合においても、加熱停止後に一定期間停止期間を設けなければ、インピーダンス変更手段両端に電圧がかかった状態でインピーダンスの変更が行われることになるため、インピーダンス変更手段動作開始時の突入電流で、インピーダンス変更手段の耐久性が問題となる。
【００１０】
【課題を解決するための手段】
前記従来の課題を解決するために、本発明は、高周波磁界を発生し被加熱体を加熱する加熱コイルと、前記加熱コイルに高周波電流を供給するインバータと、前記インバータ電源を昇圧する昇圧手段と、昇圧された前記インバータ電源を平滑する平滑手段と、前記インバータ及び前記昇圧手段の出力の大きさを制御する制御手段とを備え、前記制御手段は、加熱停止前に、前記平滑手段の電圧を所定の電圧以下にするべく、前記昇圧手段の出力を低下させた後、加熱停止する誘導加熱装置とするものである。
【００１１】
これによって、加熱停止時において、平滑手段の電圧が速やかに低下するため、再起動に時間のかからない誘導加熱装置を提供することが出来る。
【００１２】
【発明の実施の形態】
請求項１に記載の発明は、高周波磁界を発生し被加熱体を加熱する加熱コイルと、スイッチング素子と、前記加熱コイルに高周波電流を供給するインバータと、前記インバータ電源を昇圧する昇圧手段と、昇圧された前記インバータ電源を平滑する平滑手段と、前記インバータ及び前記昇圧手段の出力の大きさを制御する制御手段とを備え、前記制御手段は、加熱停止前に、前記インバータ停止直後の前記平滑手段の電圧を所定の電圧以下にすべく、前記昇圧手段の出力を低下させた後、加熱停止する誘導加熱装置とするものである。
【００１３】
この請求項１に記載の発明により、加熱停止前の昇圧手段の出力の低下に伴い、平滑手段へのエネルギの供給が抑制され、また平滑手段からのエネルギ放出が継続するために、平滑手段の電圧が速やかに低下する。平滑手段の電圧が所定の電圧以下となってから再起動を行えば、再起動時におけるスイッチング素子に流れる短絡電流を抑制することが可能となる。
【００１４】
請求項２に記載の発明は、昇圧手段は、インバータの出力に応じて昇圧動作を行うとともに、制御手段は、加熱停止前に、前記インバータ停止直後の平滑手段の電圧を所定の電圧以下にすべく、前記インバータの出力を低下させた後、加熱停止する誘導加熱装置とするものである。
【００１５】
この請求項２に記載に発明により、昇圧手段はインバータの出力に応じて昇圧動作を行うため、制御手段がインバータの出力を低下させる制御を行うことで、昇圧手段の出力も低下し、平滑手段へのエネルギの供給が抑制され、また平滑手段からのエネルギ放出が継続するために、平滑手段の電圧が速やかに低下する。平滑手段の電圧が所定の電圧以下となってから再起動を行えば、再起動時におけるスイッチング素子に流れる短絡電流を抑制することが可能となる。
【００１６】
請求項３に記載の発明は、高周波磁界を発生し被加熱体を加熱する加熱コイルと、前記加熱コイルと共振する共振コンデンサと、前記加熱コイルまたは前記共振コンデンサのインピーダンスを変更するインピーダンス変更手段と、スイッチング素子と、前記加熱コイルに高周波電流を供給するインバータと、前記インバータ電源を昇圧する昇圧手段と、昇圧された前記インバータ電源を平滑する平滑手段と、前記インバータ及び前記昇圧手段の出力の大きさを制御する制御手段とを備え、前記制御手段は、前記インピーダンス変更手段動作直前の前記インピーダンス変更手段にかかる電圧を所定の電圧以下にすべく、前記昇圧手段の出力を低下させた後、前記インピーダンス変更手段を動作させる誘導加熱装置とするものである。
【００１７】
被加熱体材質によっては、所定の共振を得るべく、加熱コイルまたは共振コンデンサのインピーダンスを切り換える必要が生じた場合、請求項３に記載の発明により、インピーダンス変更手段の両端に加わる電圧が速やかに所定の電圧以下になるよう、昇圧手段の出力を低下させるため、インピーダンス変更手段両端の電位差によってインピーダンス変更手段投入時に突入電流が流れるといった現象を抑制することが可能となる。
【００１８】
請求項４に記載の発明は、昇圧手段は、インバータの出力に応じて昇圧動作を行うとともに、制御手段は、インピーダンス変更手段動作直前の前記インピーダンス変更手段にかかる電圧を所定の電圧以下にすべく、前記インバータの出力を低下させた後、インピーダンス変更手段を動作させる誘導加熱装置とするものである。
【００１９】
この請求項４に記載に発明により、昇圧手段はインバータの出力に応じて昇圧動作を行うため、制御手段がインバータの出力を低下させる制御を行うことで、昇圧手段の出力が低下し、インピーダンス変更手段の両端に加わる電圧も速やかに低下する。従ってインピーダンス変更手段両端の電位差によってインピーダンス変更手段投入時に突入電流が流れるといった現象を抑制することが可能となる。
【００２０】
請求項５に記載の発明は、高周波磁界を発生し被加熱体を加熱する加熱コイルと、前記加熱コイルに高周波電流を供給するインバータと、導通期間が前記インバータの出力制御に関連するスイッチング素子と、共振動作を継続させ前記インバータの出力制御に寄与しないスイッチング素子と、前記インバータの出力に応じて前記インバータ電源の昇圧動作を行う昇圧手段と、昇圧された前記インバータ電源を平滑する平滑手段と、前記インバータ及び前記昇圧手段の出力の大きさを制御する制御手段とを備え、前記制御手段は、加熱停止前に、前記インバータ停止直後の前記平滑手段の電圧を所定の電圧以下にすべく、前記インバータの出力制御に寄与しないスイッチング素子を所定期間駆動させた後、加熱停止する誘導加熱装置とするものである。
【００２１】
この請求項５に記載の発明により、インバータの出力制御に寄与しないスイッチング素子を所定期間駆動させるため、平滑手段へのエネルギ供給は行われないことに加え、インバータ出力は増加しないが共振が継続されるために、平滑手段のエネルギは被加熱体加熱に使用され、速やかに電圧が低下して、再起動までの時間を短縮することが可能である。
【００２２】
請求項６に記載の発明は、高周波磁界を発生し被加熱体を加熱する加熱コイルと、前記加熱コイルと共振する共振コンデンサと、前記加熱コイルまたは前記共振コンデンサのインピーダンスを変更するインピーダンス変更手段と、前記加熱コイルに高周波電流を供給するインバータと、導通期間が前記インバータの出力制御に関連するスイッチング素子と、共振動作を継続させ前記インバータの出力制御に寄与しないスイッチング素子と、前記インバータの出力に応じて前記インバータ電源の昇圧動作を行う昇圧手段と、昇圧された前記インバータ電源を平滑する平滑手段と、前記インバータ及び前記昇圧手段の出力の大きさを制御する制御手段とを備え、前記制御手段は、前記インピーダンス変更手段動作直前の前記インピーダンス変更手段にかかる電圧を所定の電圧以下にすべく、前記インバータの出力制御に寄与しないスイッチング素子を所定期間駆動させた後、インピーダンス変更手段を動作させる誘導加熱装置とするものである。
【００２３】
この請求項６に記載の発明により、インバータの出力制御に寄与しないスイッチング素子を所定期間駆動させるため、昇圧手段の出力が増加しないことに加えて、インバータ出力は増加しないが共振が継続されるために、平滑手段のエネルギは被加熱体加熱に使用されて速やかに電圧が低下して、インピーダンス変更手段の両端に加わる電圧も速やかに低下する。従ってインピーダンス変更手段両端の電位差によってインピーダンス変更手段投入時に突入電流が流れるといった現象を抑制することが可能となる。
【００２４】
【実施例】
以下本発明の実施例について、図面を参照しながら説明する。
【００２５】
（実施例１）
図１は、本実施例の誘導加熱装置の回路構成を示す図である。
【００２６】
電源１４は低周波交流電源である２００Ｖ商用電源であり、ブリッジダイオードである整流回路１５の入力端に接続される。整流回路１５の出力端間に第１の平滑コンデンサ１６が接続される。整流回路１５の出力端間には、さらにチョークコイル１７と第１のスイッチング素子１８の直列接続対が接続される。加熱コイル１９は被加熱体である鍋２０と対向して配置されている。
【００２７】
２１はインバータであり、第２の平滑コンデンサ２２の低電位側端子（エミッタ）は整流回路１５の負極端子に接続され、第２の平滑コンデンサ２２の高電位側端子は第２のスイッチング素子（ＩＧＢＴ）２３の高電位側端子（コレクタ）に接続され、第２のスイッチング素子（ＩＧＢＴ）２３の低電位側端子はチョークコイル１７と第１のスイッチング素子（ＩＧＢＴ）１８の高電位側端子（コレクタ）との接続点に接続される。加熱コイル１９と共振コンデンサ２４の直列接続体が第１のスイッチング素子１８に並列に接続される。
【００２８】
第１の逆導通素子２５（第１のダイオード）は第１のスイッチング素子１８に逆並列に接続（第１のダイオード２５のカソードと第１のスイッチング素子１８のコレクタとを接続）され、第２の逆導通素子２６（第２のダイオード）は第２のスイッチング素子２３に逆並列に接続される。補正用共振コンデンサ２８とリレー２９の直列接続体は共振コンデンサ２４に並列に接続されている。制御手段３０は、第１のスイッチング素子１８を駆動する第１の駆動手段３２と、第２のスイッチング素子２３を駆動する第２の駆動手段３３と、リレー２９の駆動コイル（図示せず）に信号を出力する。
【００２９】
また、制御手段３０は、電源１４からの入力電流を検知するカレントトランス３１の検知信号を入力するとともに、被加熱体２０の材質を判別する材質判別手段を内包する。
【００３０】
また、３４は、使用者が動作開始、停止、出力調整等を行うための動作設定手段である。
【００３１】
以上のように構成された誘導加熱装置において、以下動作を説明する。電源１４は整流回路１５により全波整流され、整流回路１５の出力端に接続された第１の平滑コンデンサ１６に供給される。この第１の平滑コンデンサ１６はインバータ２１に高周波電流を供給する供給源として働く。
【００３２】
図２、図３は上記回路における各部波形を示す図であり、図２は鍋２０の材質が低抵抗率金属であるアルミなどのものの場合である。
【００３３】
図２（ａ）は第１のスイッチング素子１８と第１の逆導通素子２５に流れる電流を、同図（ｂ）は第２のスイッチング素子２３と第２の逆導通素子２６に流れる電流を、同図（ｃ）は第１のスイッチング素子１８駆動制御端子電圧を、同図（ｄ）は第２のスイッチング素子２３駆動制御端子電圧を、同図（ｅ）は加熱コイル１９に流れる電流をそれぞれ示している。
【００３４】
第１の駆動手段３２は、制御手段３０からの信号に基づき、時点ｔ０から時点ｔ１まで図２（ｃ）に示すように第１のスイッチング素子１８駆動制御端子に駆動期間がＴ１（約２４μ秒）である駆動信号を出力する。この駆動期間Ｔ１の間では第１のスイッチング素子１８及び第１の逆導通素子２５と、加熱コイル１９と、共振コンデンサ２４で形成される閉回路で共振し、鍋２０がアルミ製などの鍋であるときの共振周期（１／ｆ）が駆動期間Ｔ１の約２／３倍（約１６μ秒）となるように加熱コイル１９の巻き数（４４Ｔ）と共振コンデンサ２４の容量（０．０３μＦ）と、駆動期間Ｔ１が設定されている。チョークコイル１７はこの第１のスイッチング素子１８の駆動期間Ｔ１において、第１の平滑コンデンサ１６の静電エネルギを磁気エネルギとして蓄える。
【００３５】
次に、第１のスイッチング素子１８に流れる共振電流の第２番目のピークと共振電流が次に零となる間のタイミングである時点ｔ１、すなわち第１のスイッチング素子１８の順方向に電流が流れている時点で第１のスイッチング素子１８の駆動が停止される。
【００３６】
第１のスイッチング素子１８の遮断後、第１のスイッチング素子１８のコレクタと接続されたチョークコイル１７の端子電圧が立ち上がり、この電位が第２の平滑コンデンサ２２の電位を越えると、第２の逆導通素子２６を通して第２の平滑コンデンサ２２に充電して、チョークコイル１７に蓄えた磁気エネルギを放出する。
【００３７】
第２の平滑コンデンサ２２の電圧は、整流回路１５の出力電圧のピーク値よりも高くなるよう昇圧される。すなわち、チョークコイル１７、第１のスイッチング素子１８及び第２の逆導通素子２５によって昇圧手段３５が構成され、第２の平滑コンデンサ２２は昇圧手段３５の出力を平滑する平滑手段となる。昇圧されるレベルは第１のスイッチング素子１８の駆動期間に依存し、駆動期間が長くなると第２の平滑コンデンサ２２に発生する電圧が高くなる傾向にある。
【００３８】
このように、第２の平滑コンデンサ２２−第２のスイッチング素子２３あるいは第２の逆導通素子２６−加熱コイル１９−共振コンデンサ２４で形成される閉回路で共振する際に直流電源として働く第２の平滑コンデンサ２２の電圧レベルが昇圧されることにより、図２（ａ）で示す第１のスイッチング素子１８に流れる共振電流の尖頭値、及び共振経路を変えて継続して共振する同図（ｂ）の第２のスイッチング素子２３に流れる共振電流の尖頭値が零とならないように、あるいは小さくならないようにして、高導電率で非磁性であるアルミなどの鍋を高出力で誘導加熱し、かつ出力を連続的に増減して制御するように出来る。
【００３９】
また、図２（ｃ）、（ｄ）で示すように、第２の駆動手段３３は、制御手段３０からの信号に基づき、時点ｔ１から両スイッチング素子が同時遮断期間後の時点ｔ２において、第２のスイッチング素子２３駆動制御端子に駆動信号を出力する。この結果、同図（ｂ）に示すように加熱コイル１９−共振コンデンサ２４−第２のスイッチング素子２３または第２の逆導通素子２６−第２の平滑コンデンサ２２とからなる閉回路に経路を変えて共振電流が流れることになる。この駆動信号の駆動期間Ｔ２は、この場合にはＴ１とほぼ同じ期間に設定されているので、第１のスイッチング素子１８が導通していた場合と同様に、駆動期間Ｔ１の約２／３倍の周期の共振電流が流れる。
【００４０】
従って、加熱コイル１９に流れる電流は、図２（ｅ）に示すような波形となり、第１及び第２のスイッチング素子１８、２３の駆動周期（Ｔ１とＴ２と同時遮断期間の和）は共振電流の周期の約３倍となり、第１及び第２のスイッチング素子１８、２３の駆動周波数が約２０ｋＨｚであれば、加熱コイル１９に流れる共振電流の周波数は約６０ｋＨｚとなる。
【００４１】
図３は鍋２０の材質がアルミなどに比較して高抵抗率である鉄系のものの場合である。
【００４２】
図３（ａ）は第１のスイッチング素子１８と第１の逆導通素子２５に流れる電流を、同図（ｂ）は第２のスイッチング素子２３と第２の逆導通素子２６に流れる電流を、同図（ｃ）は第１のスイッチング素子１８駆動制御端子電圧を、同図（ｄ）は第２のスイッチング素子２３駆動制御端子電圧を、同図（ｅ）は加熱コイル１９に流れる電流をそれぞれ示している。
【００４３】
この場合においても、基本的な動作は図２に示すような、鍋２０の材質が低抵抗率であるアルミなどの場合と変わらない。しかしながら、鉄系の鍋を誘導加熱するには、共振電流周波数が従来の約２０ｋＨｚ程度で十分であるため、共振電流が約２０ｋＨｚになるよう、リレー２９を投入して、共振コンデンサ２４（０．０３μＦ）と補正用共振コンデンサ２８（０．２１μＦ）が電気的に並列接続されるよう切り換える。さらに、第１のスイッチング素子１８と第２のスイッチング素子２３を一定の周波数（約２３ｋＨｚ）で所定の出力となるよう、駆動時間比で設定する。共振電流は約２０ｋＨｚ程度になるよう共振コンデンサ２４及び補正用共振コンデンサ２８が接続されているため、第１のスイッチング素子１８に流れる共振電流は第２番目のピークとなる前に駆動が停止される。
【００４４】
次に、起動時から安定動作までの一連の動作について説明する。制御手段３０はリレー２９を遮断状態にし、約３６ｋＨｚの駆動周波数で第１のスイッチング素子１８と第２のスイッチング素子２３を交互に駆動する。起動直後の短絡電流による第１及び第２のスイッチング素子１８、２３破壊を防止するために、起動時には、第１のスイッチング素子１８駆動時間を最小となるよう駆動し（本実施例では、約２μ秒）、徐々に所定の駆動時間比（本実施例では第１のスイッチング素子１８駆動時間比が約０．２５）になるよう制御する。
【００４５】
所定の駆動時間比に達した後は、駆動時間比を固定したまま、約３０ｋＨｚとなるまで駆動周波数を挿引する。その間に制御手段３０は被加熱体２０の材質を判別する。
【００４６】
この時、被加熱体２０が鉄などの高抵抗金属製であると判別した場合、制御手段３０は加熱を一時停止し、共振コンデンサ２４と補正用共振コンデンサ２８が並列接続されるよう、リレー２９を投入し、再度加熱を開始する。制御手段３０は、第１のスイッチング素子１８駆動時間を最小で、駆動周波数が約２０ｋＨｚとなるようにして駆動開始し、駆動周波数固定のまま、徐々に駆動時間比を増加させて所定の出力が得られるよう制御する。駆動周波数を固定とするのは、上記のように加熱コイル１９に流れる共振電流が約２０ｋＨｚになるよう設定しており、かつ隣接の加熱コイル（図示せず）との共振電流周波数の差により電磁音が発生しないようにするためである。
【００４７】
一方、被加熱体２０がアルミなどの低抵抗金属製であると判別した場合、制御手段３０は第１のスイッチング素子１８駆動時間比が約０．５となるよう設定し、徐々に駆動周波数を下げ、所定の出力が得られるよう制御する。制御手段３０は、カレントトランス３１から得られる検知出力から判断し、出力が所定値よりも小さければ制御手段３０が制御可能な最小単位の数倍で、所定値より大きければ最小単位で駆動周波数を変化させる。
【００４８】
また、ほぼ所定出力が得られたと判断すれば、出力の微調整が可能なように、駆動時間比を約０．４９から約０．５１まで可変とし制御を行う。本実施例では、被加熱体２０が通常のアルミ鍋である場合、第１のスイッチング素子１８駆動周波数が約２０ｋＨｚで加熱コイル１９に流れる共振電流周波数が約６０ｋＨｚとなり、最大出力（本実施例では２０００Ｗ）が得られるよう設定されている。
【００４９】
以上のような一連の加熱動作を行う中で、例えば、鍋２０が鉄などの高抵抗率金属製であった場合、制御手段３０は上記のように駆動周波数一定で、駆動時間比を可変としてインバータ２１出力を制御する。第１のスイッチング素子１８、チョークコイル１７、第２の逆導通素子２６は、昇圧手段３５を構成しており、第１のスイッチング素子１８導通期間が長ければ第２の平滑コンデンサ２２電圧が高くなる。第２の平滑コンデンサ２２は電源１４に同期したリプルを軽減するため、非常に大きな容量とされているため、第１及び第２のスイッチング素子１８、２３の駆動を停止しただけでは第２の平滑コンデンサ２２電圧は、第２の平滑コンデンサ２２に並列接続される検知抵抗、放電抵抗（図示せず）を通じた放電のみが行われる。
【００５０】
検知抵抗、放電抵抗は、待機時の消費電力を抑制するために高い抵抗値のものが使用されるため、第２の平滑コンデンサ２２電圧の低下が非常に緩やかとなる。図４は、本実施例における各部波形を示している。
【００５１】
同図（ａ）は第１のスイッチング素子１８電圧を示しており、そのピークを結んだ包絡線は第２の平滑コンデンサ２２電圧と同じとなる。同図（ｂ）は電源１４電圧のゼロ点でＨｉからＬｏｗ、ＬｏｗからＨｉに反転するゼロボルトパルス（回路など図示せず、以下ＺＶＰと称す）で、同図（ｃ）は電源１４電圧を示している。
【００５２】
図４に示すように、時点ｔ１で使用者が動作設定手段３４より加熱停止設定を行い、動作設定手段３４から制御手段３０へ信号が出力された場合、制御手段３０はＺＶＰに同期した一連の制御の終了後、次のＺＶＰ反転が得られるタイミングとなる時点ｔ２から所定時間後にＺＶＰ反転が得られる時点ｔ３にわたって第１のスイッチング素子１８の駆動時間比を徐々に低下させることにより、昇圧手段３５としての出力を低下させるとともに、第２の平滑コンデンサ２２に蓄えられたエネルギを鍋２０に消費させているため、第２の平滑コンデンサ２２電圧が速やかに低下する。
【００５３】
第２の平滑コンデンサ２２電圧が所定の電圧以下となる所定時間後、すなわち時点ｔ３後に、制御手段３０はインバータ２１を停止させ、再起動可能な状態として動作設定手段３４からの出力信号を待ち受ける。使用者が動作設定手段３４より再度加熱開始設定を行った場合、加熱停止設定後からの時間が短くても、第２の平滑コンデンサ２２電圧が所定値以下であるため、起動時の第１及び第２のスイッチング素子１８、２３の短絡電流は抑制されており、制御手段３０も起動可能な状態として待ち受けているため、動作設定手段３４から制御手段３０に加熱開始信号が出力された時点ｔ４後、制御手段３０はＺＶＰ反転が得られるタイミングとなる時点ｔ５から加熱を開始する。
【００５４】
また、同様に、インバータ２１異常を検知し（検知回路など図示せず）、制御手段３０がインバータ２１を一時停止させる場合においても、一時停止の前に、制御手段３０は第１のスイッチング素子１８の駆動時間比を徐々に低下させ、第２の平滑コンデンサ２２電圧を速やかに低下させるため、再起動するまでの所定時間を短く設定することが可能である。
【００５５】
さらに、例えば起動時の材質判別により、鍋２０が鉄などの高抵抗率金属製であると判別された場合、制御手段３０は第１のスイッチング素子１８の駆動時間比を徐々に低下させて、第２の平滑コンデンサ２２電圧を速やかに低下させる。リレー２９両端に加わる電圧が所定の電圧以下になると思われる所定時間後に、制御手段３０はリレー２９を投入し、上記のような鉄などの高抵抗率金属製鍋２０加熱動作に移行する。
【００５６】
（実施例２）
図５は、本発明の第２の実施例を示すもので、前記第１の実施例との相違は、加熱停止時の第２のスイッチング素子２３駆動方法にあり、その他の点は第１の実施例と同様であるので、同一部分には同一符号を付して相違ある部分についてのみ説明する。
【００５７】
図５は、使用者が動作設定手段３４より加熱停止設定を行った時のインバータ２１各部波形を示すものであり、図５（ａ）は第１のスイッチング素子１８と第１の逆導通素子２５に流れる電流を、同図（ｂ）は第２のスイッチング素子２３と第２の逆導通素子２６に流れる電流を、同図（ｃ）は第１のスイッチング素子１８駆動制御端子電圧を、同図（ｄ）は第２のスイッチング素子２３駆動制御端子電圧を、同図（ｅ）は第２の平滑コンデンサ２２電圧を、同図（ｆ）は加熱コイル１９に流れる電流をそれぞれ示している。
【００５８】
使用者が動作設定手段３４より加熱停止設定を行い、動作設定手段３４から制御手段３０へ信号が出力された場合、制御手段３０は、次のＺＶＰ反転が得られるタイミングとなる時点ｔ１から時点ｔ２までの所定時間第２のスイッチング素子２３を駆動する。このとき、第１のスイッチング素子１８は遮断されたままであるため、電源１４からは電力が供給されず、第２の平滑コンデンサ２２−第２のスイッチング素子２３あるいは第２の逆導通素子２６−加熱コイル１９−共振コンデンサ２４で形成される閉回路で共振を継続することになる。
【００５９】
第２の平滑コンデンサ２２に蓄えられたエネルギは、共振が継続される中で、鍋２０や閉回路を形成する部品に消費されるため、第２の平滑コンデンサ２２電圧は急速に低下する。
【００６０】
第２の平滑コンデンサ２２電圧が所定の電圧以下となる所定時間後、すなわち時点ｔ２後に、制御手段３０は再起動可能な状態として動作設定手段３４からの出力信号を待ち受ける。使用者が動作設定手段３４より再度加熱開始設定を行った場合、加熱停止設定後からの時間が短くても、第２の平滑コンデンサ２２電圧が所定値以下であるため、起動時の第１及び第２のスイッチング素子１８、２３の短絡電流は抑制されており、制御手段３０も起動可能な状態として待ち受けているため、動作設定手段３４から制御手段３０に加熱開始信号が出力された後、制御手段３０はＺＶＰ反転が得られるタイミングとなる時点（図示せず）から加熱を開始する。
【００６１】
また、同様に、インバータ２１異常を検知し（検知回路など図示せず）、制御手段３０がインバータ２１を一時停止させる場合においても、一時停止の前に、制御手段３０は第２のスイッチング素子２３を所定時間駆動させ、第２の平滑コンデンサ２２電圧を速やかに低下させるため、再起動するまでの所定時間を短く設定することが可能である。
【００６２】
さらに、例えば起動時の材質判別により、鍋２０が鉄などの高抵抗率金属製であると判別された場合、制御手段３０は第２のスイッチング素子２３を所定時間駆動させ、第２の平滑コンデンサ２２電圧を速やかに低下させる。リレー２９両端に加わる電圧が所定の電圧以下になると思われる所定時間後に、制御手段３０はリレー２９を投入し、上記のような鉄などの高抵抗率金属製鍋２０加熱動作に移行する。
【００６３】
【発明の効果】
以上のように、本発明は、加熱停止時の平滑手段の電圧を速やかに低下させ、再起動までの時間を短縮する誘導加熱装置を提供することが出来る。
【図面の簡単な説明】
【図１】本発明の実施例１における誘導加熱調理器の回路構成を示す図
【図２】同、各部波形を示す図
【図３】同、各部波形を示す図
【図４】同、各部波形を示す図
【図５】本発明の実施例２における誘導加熱調理器の各部波形を示す図
【図６】従来の誘導加熱調理器の回路構成を示す図
【符号の説明】
１８第１のスイッチング素子
１９加熱コイル
２０鍋（被加熱体）
２１インバータ
２２第２の平滑コンデンサ（平滑手段）
２３第２のスイッチング素子
２９リレー（インピーダンス変更手段）
３０制御手段
３５昇圧手段[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an induction heating cooker used in general households, offices, restaurants, factories, and the like, a water heater using induction heating, and an induction heating device such as a heating device.
[0002]
[Prior art]
As an example of the induction heating device, an induction heating cooker will be described. In the induction heating cooker, a high-frequency magnetic field is generated from the induction heating coil, and an eddy current is generated by electromagnetic induction in a heated object such as a metal pot placed near the heating coil, thereby heating the heated object. Due to such a principle, an object to be heated made of a high resistivity metal such as iron is suitable for induction heating.
[0003]
However, in recent years, induction heating cookers have been required to be capable of induction heating even low-resistance metal pots such as aluminum and copper. In order to heat such a pan, generally increasing the output frequency of the inverter increases the skin resistance of the object to be heated, further increasing the number of turns of the heating coil, and increasing the inverter power supply to increase the magnetic field. Had to be strengthened.
[0004]
Also, when ripples occur in the inverter power supply, an unpleasant sound corresponding to the ripple frequency is generated due to the repulsive force between the heating coil and the low-resistance metal pot, so that the inverter power supply is smoothed. Needed.
[0005]
As a method for solving the above-mentioned problem, an example of a conventional induction heating cooker disclosed in Patent Document 1, for example, will be described. FIG. 6 is a diagram showing a circuit configuration of a conventional induction heating cooker. In the figure, a power supply 1 is a commercial power supply, which is rectified by a rectifier circuit 2 and transmitted to a first smoothing capacitor 3. The choke coil 4 stores energy when the second switching element 7 is turned on, and discharges energy stored in the second smoothing capacitor 12 through the first diode 6 when the second switching element 7 is cut off.
[0006]
That is, the choke coil 4, the second switching element 7, and the first diode 6 constitute a booster. Further, the second switching element 7 generates a resonance current that resonates at the resonance frequency of the heating coil 9 and the resonance capacitor 10, supplies a high-frequency magnetic field to the pan 11, which is the object to be heated, and performs induction heating. The first switching element 5 discharges the energy stored in the second smoothing capacitor 12 to the heating coil 9 and the resonance capacitor 10 while the second switching element 7 is in a cutoff period, and continues resonance. As described above, by temporarily storing energy in the second smoothing capacitor 12, it becomes possible to smooth the voltage applied to the heating coil 9 and the resonance capacitor 10 and the flowing current, to reduce the ripple generated at the commercial frequency, and to reduce the heating. Unpleasant noise due to the repulsive force between the coil 9 and the pan 11 can be suppressed.
[0007]
[Patent Document 1]
JP-A-2002-75620
[0008]
[Problems to be solved by the invention]
However, in the conventional configuration, the uncomfortable sound due to the repulsive force between the heating coil 9 and the pan 11 is suppressed during heating, and the capacity of the second smoothing capacitor 12 for smoothing the boost power supply is large. The voltage of the second smoothing capacitor 12 drops slowly. Therefore, if the heating is started immediately after the stop of the heating, an excessive short-circuit current flows due to a high voltage of the second switching element 7 when the conduction of the second switching element 7 is started, and the load of the second switching element 7 is reduced. growing. In order to avoid this, if control is performed that does not accept restart for a certain period after stopping heating, there is a problem that it takes time for the user to restart after stopping heating or restart after stopping temporarily when abnormality is detected. Occurs.
[0009]
In addition, in order to heat a material other than the low-resistivity metal pot 11 such as aluminum, the heating coil 9 or the resonance capacitor 10 is also provided with an impedance changing means such as a relay for switching the capacity. If a fixed period is not provided, the impedance is changed while a voltage is applied to both ends of the impedance changing means. Therefore, the inrush current at the start of the operation of the impedance changing means causes a problem in the durability of the impedance changing means. It becomes.
[0010]
[Means for Solving the Problems]
In order to solve the conventional problems, the present invention provides a heating coil that generates a high-frequency magnetic field and heats an object to be heated, an inverter that supplies a high-frequency current to the heating coil, and a booster that boosts the inverter power supply. A smoothing means for smoothing the boosted inverter power supply, and a control means for controlling the magnitude of the output of the inverter and the boosting means, wherein the control means adjusts the voltage of the smoothing means before stopping heating. An induction heating device that stops heating after reducing the output of the boosting means so as to keep the voltage below a predetermined value.
[0011]
Thus, when the heating is stopped, the voltage of the smoothing unit is quickly reduced, so that it is possible to provide an induction heating device that does not require a long time to restart.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 is a heating coil that generates a high-frequency magnetic field and heats an object to be heated, a switching element, an inverter that supplies a high-frequency current to the heating coil, and a step-up unit that steps up the inverter power supply. A smoothing means for smoothing the boosted inverter power supply; and a control means for controlling a magnitude of an output of the inverter and the boosting means, wherein the control means performs the smoothing immediately after the inverter is stopped before heating is stopped. An induction heating device that stops heating after decreasing the output of the boosting means so that the voltage of the means is equal to or lower than a predetermined voltage.
[0013]
According to the first aspect of the present invention, the supply of energy to the smoothing means is suppressed and the energy release from the smoothing means is continued with a decrease in the output of the boosting means before the heating is stopped. The voltage drops quickly. If the restart is performed after the voltage of the smoothing unit becomes equal to or lower than the predetermined voltage, it becomes possible to suppress the short-circuit current flowing through the switching element at the time of the restart.
[0014]
According to a second aspect of the present invention, the boosting means performs a boosting operation in accordance with the output of the inverter, and the control means reduces the voltage of the smoothing means immediately after stopping the inverter to a predetermined voltage or less before stopping the heating. Therefore, the induction heating device is configured to stop the heating after reducing the output of the inverter.
[0015]
According to the second aspect of the present invention, the boosting means performs a boosting operation in accordance with the output of the inverter. Therefore, the control means performs control to reduce the output of the inverter, so that the output of the boosting means also decreases, and the smoothing means Since the supply of energy to the smoothing means is suppressed and the energy release from the smoothing means is continued, the voltage of the smoothing means rapidly decreases. If the restart is performed after the voltage of the smoothing unit becomes equal to or lower than the predetermined voltage, it becomes possible to suppress the short-circuit current flowing through the switching element at the time of the restart.
[0016]
According to a third aspect of the present invention, there is provided a heating coil that generates a high-frequency magnetic field and heats an object to be heated, a resonance capacitor that resonates with the heating coil, and an impedance changing unit that changes impedance of the heating coil or the resonance capacitor. A switching element, an inverter that supplies a high-frequency current to the heating coil, a booster that boosts the inverter power, a smoother that smoothes the boosted inverter power, and a magnitude of an output of the inverter and the booster. Control means for controlling the impedance, the control means reduces the output of the boosting means to reduce the voltage applied to the impedance changing means immediately before the operation of the impedance changing means to a predetermined voltage or less, The induction heating device operates the impedance changing means.
[0017]
In the case where it is necessary to switch the impedance of the heating coil or the resonance capacitor in order to obtain a predetermined resonance depending on the material to be heated, the voltage applied to both ends of the impedance changing means is quickly increased by the invention according to the third aspect. Since the output of the boosting means is reduced so as to be equal to or lower than the voltage of the impedance changing means, it is possible to suppress a phenomenon that a rush current flows when the impedance changing means is turned on due to a potential difference between both ends of the impedance changing means.
[0018]
According to a fourth aspect of the present invention, the boosting means performs a boosting operation in accordance with an output of the inverter, and the control means reduces the voltage applied to the impedance changing means immediately before the operation of the impedance changing means to a predetermined voltage or less. And an induction heating device for operating the impedance changing means after reducing the output of the inverter.
[0019]
According to the fourth aspect of the present invention, since the boosting means performs a boosting operation in accordance with the output of the inverter, the control means performs control to reduce the output of the inverter, so that the output of the boosting means decreases and the impedance is changed. The voltage across the means also drops quickly. Therefore, it is possible to suppress a phenomenon that a rush current flows when the impedance changing unit is turned on due to a potential difference between both ends of the impedance changing unit.
[0020]
The invention according to claim 5 includes a heating coil that generates a high-frequency magnetic field and heats the object to be heated, an inverter that supplies a high-frequency current to the heating coil, and a switching element whose conduction period is related to output control of the inverter. A switching element that continues the resonance operation and does not contribute to the output control of the inverter, a boosting unit that performs a boosting operation of the inverter power supply according to the output of the inverter, and a smoothing unit that smoothes the boosted inverter power supply, Control means for controlling the magnitude of the output of the inverter and the boosting means, the control means, before heating stop, to reduce the voltage of the smoothing means immediately after the inverter stop to a predetermined voltage or less, An induction heating device that stops heating after driving a switching element that does not contribute to the output control of the inverter for a predetermined period. A.
[0021]
According to the fifth aspect of the present invention, since the switching element that does not contribute to the output control of the inverter is driven for a predetermined period, energy is not supplied to the smoothing means, and the inverter output does not increase but resonance continues. Therefore, the energy of the smoothing means is used for heating the object to be heated, and the voltage is quickly reduced, so that the time until the restart can be shortened.
[0022]
The invention according to claim 6 is a heating coil that generates a high-frequency magnetic field to heat the object to be heated, a resonance capacitor that resonates with the heating coil, and an impedance changing unit that changes the impedance of the heating coil or the resonance capacitor. An inverter that supplies a high-frequency current to the heating coil, a switching element whose conduction period is related to output control of the inverter, a switching element that continues resonance operation and does not contribute to output control of the inverter, and an output of the inverter. A boosting means for performing a boosting operation of the inverter power supply, a smoothing means for smoothing the boosted inverter power supply, and a control means for controlling magnitudes of outputs of the inverter and the boosting means. Is the impedance changing means immediately before the operation of the impedance changing means. Order to the voltage applied to the predetermined voltage or less, after the switching element which does not contribute to the output control of the inverter by a predetermined period of time driving, it is an induction heating device for operating the impedance changing means.
[0023]
According to the sixth aspect of the present invention, the switching element that does not contribute to the output control of the inverter is driven for a predetermined period. In addition to the output of the booster not increasing, the inverter output does not increase but resonance continues. In addition, the energy of the smoothing means is used for heating the object to be heated, and the voltage is quickly reduced, and the voltage applied to both ends of the impedance changing means is also quickly reduced. Therefore, it is possible to suppress a phenomenon that a rush current flows when the impedance changing unit is turned on due to a potential difference between both ends of the impedance changing unit.
[0024]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0025]
(Example 1)
FIG. 1 is a diagram illustrating a circuit configuration of the induction heating device according to the present embodiment.
[0026]
The power supply 14 is a 200 V commercial power supply that is a low-frequency AC power supply, and is connected to an input terminal of a rectifier circuit 15 that is a bridge diode. The first smoothing capacitor 16 is connected between the output terminals of the rectifier circuit 15. A series connection pair of a choke coil 17 and a first switching element 18 is further connected between the output terminals of the rectifier circuit 15. The heating coil 19 is arranged so as to face a pot 20 which is the object to be heated.
[0027]
Reference numeral 21 denotes an inverter. The low potential side terminal (emitter) of the second smoothing capacitor 22 is connected to the negative terminal of the rectifier circuit 15, and the high potential side terminal of the second smoothing capacitor 22 is connected to a second switching element (IGBT). ) 23 is connected to the high-potential side terminal (collector), and the low-potential side terminal of the second switching element (IGBT) 23 is connected to the high-potential side terminal (collector) of the choke coil 17 and the first switching element (IGBT) 18. Is connected to the connection point. A series connection of the heating coil 19 and the resonance capacitor 24 is connected to the first switching element 18 in parallel.
[0028]
The first reverse conducting element 25 (first diode) is connected in antiparallel to the first switching element 18 (the cathode of the first diode 25 and the collector of the first switching element 18 are connected), and the second The reverse conducting element 26 (second diode) is connected to the second switching element 23 in anti-parallel. The series connection of the correction resonance capacitor 28 and the relay 29 is connected to the resonance capacitor 24 in parallel. The control unit 30 includes a first driving unit 32 for driving the first switching element 18, a second driving unit 33 for driving the second switching element 23, and a driving coil (not shown) of the relay 29. Output a signal.
[0029]
In addition, the control means 30 receives a detection signal of the current transformer 31 for detecting an input current from the power supply 14 and includes a material discriminating means for discriminating the material of the object 20 to be heated.
[0030]
Reference numeral 34 denotes operation setting means for the user to start, stop, adjust output, and the like.
[0031]
The operation of the induction heating device configured as described above will be described below. The power supply 14 is full-wave rectified by a rectifier circuit 15 and is supplied to a first smoothing capacitor 16 connected to an output terminal of the rectifier circuit 15. The first smoothing capacitor 16 functions as a supply source for supplying a high-frequency current to the inverter 21.
[0032]
2 and 3 show waveforms at various points in the circuit. FIG. 2 shows a case where the material of the pot 20 is aluminum, which is a low resistivity metal.
[0033]
2A shows a current flowing through the first switching element 18 and the first reverse conducting element 25, and FIG. 2B shows a current flowing through the second switching element 23 and the second reverse conducting element 26. FIG. 4C shows the drive control terminal voltage of the first switching element 18, FIG. 4D shows the drive control terminal voltage of the second switching element 23, and FIG. 4E shows the current flowing through the heating coil 19. Is shown.
[0034]
Based on the signal from the control means 30, the first drive means 32 applies a drive period of T1 (about 24 μsec) to the first switching element 18 drive control terminal from time t0 to time t1, as shown in FIG. ) Is output. During this driving period T1, the first switching element 18 and the first reverse conducting element 25, the heating coil 19, and the resonance capacitor 24 resonate in a closed circuit, and the pan 20 is a pan made of aluminum or the like. The number of turns (44T) of the heating coil 19 and the capacitance (0.03 μF) of the resonance capacitor 24 are set so that the resonance period (1 / f) at a certain time is about ／ times (about 16 μs) of the drive period T1. , A drive period T1 is set. The choke coil 17 stores the electrostatic energy of the first smoothing capacitor 16 as magnetic energy during the drive period T1 of the first switching element 18.
[0035]
Next, a current flows in the forward direction of the first switching element 18 at a time t1, which is a timing between the second peak of the resonance current flowing through the first switching element 18 and the next time the resonance current becomes zero. At this point, the driving of the first switching element 18 is stopped.
[0036]
After the first switching element 18 is cut off, the terminal voltage of the choke coil 17 connected to the collector of the first switching element 18 rises, and when this potential exceeds the potential of the second smoothing capacitor 22, the second reverse The second smoothing capacitor 22 is charged through the conductive element 26, and the magnetic energy stored in the choke coil 17 is released.
[0037]
The voltage of the second smoothing capacitor 22 is boosted so as to be higher than the peak value of the output voltage of the rectifier circuit 15. That is, the choke coil 17, the first switching element 18, and the second reverse conducting element 25 constitute a booster 35, and the second smoothing capacitor 22 functions as a smoother for smoothing the output of the booster 35. The boosted level depends on the drive period of the first switching element 18, and the longer the drive period, the higher the voltage generated in the second smoothing capacitor 22 tends to be.
[0038]
As described above, the second functioning as a DC power supply when resonating in a closed circuit formed by the second smoothing capacitor 22 -the second switching element 23 or the second reverse conducting element 26 -the heating coil 19 -the resonance capacitor 24. 2A, the voltage level of the smoothing capacitor 22 is boosted to change the peak value of the resonance current flowing through the first switching element 18 and the resonance path shown in FIG. b) Induction heating of a high-conductivity, non-magnetic aluminum pan or the like with a high output so that the peak value of the resonance current flowing through the second switching element 23 in b) does not become zero or does not become small. , And the output can be continuously increased or decreased for control.
[0039]
Further, as shown in FIGS. 2C and 2D, the second driving unit 33 performs a second driving operation based on a signal from the control unit 30 at a time point t2 after the simultaneous shutoff period from the time point t1. A drive signal is output to the drive control terminal of the second switching element 23. As a result, the path is changed to a closed circuit including the heating coil 19, the resonance capacitor 24, the second switching element 23 or the second reverse conducting element 26, and the second smoothing capacitor 22, as shown in FIG. As a result, a resonance current flows. In this case, the drive period T2 of the drive signal is set to be substantially the same as T1. Therefore, similar to the case where the first switching element 18 is conducting, the drive period T2 is about ／ times the drive period T1. A resonance current having a period of?
[0040]
Accordingly, the current flowing through the heating coil 19 has a waveform as shown in FIG. 2E, and the driving cycle of the first and second switching elements 18 and 23 (the sum of T1 and T2 and the simultaneous cutoff period) is the resonance current. And the driving frequency of the first and second switching elements 18 and 23 is about 20 kHz, the frequency of the resonance current flowing through the heating coil 19 is about 60 kHz.
[0041]
FIG. 3 shows a case in which the pot 20 is made of an iron-based material having a higher resistivity than aluminum or the like.
[0042]
FIG. 3A shows a current flowing through the first switching element 18 and the first reverse conducting element 25, and FIG. 3B shows a current flowing through the second switching element 23 and the second reverse conducting element 26. FIG. 4C shows the drive control terminal voltage of the first switching element 18, FIG. 4D shows the drive control terminal voltage of the second switching element 23, and FIG. 4E shows the current flowing through the heating coil 19. Is shown.
[0043]
Also in this case, the basic operation is the same as the case where the material of the pan 20 is aluminum or the like having a low resistivity as shown in FIG. However, the resonance current frequency of about 20 kHz in the related art is sufficient for induction heating of the iron-based pan, so the relay 29 is turned on so that the resonance current becomes about 20 kHz, and the resonance capacitor 24 (0. 03 μF) and the correction resonance capacitor 28 (0.21 μF) are electrically connected in parallel. Further, the driving time ratio is set so that the first switching element 18 and the second switching element 23 have a predetermined output at a constant frequency (about 23 kHz). Since the resonance capacitor 24 and the correction resonance capacitor 28 are connected so that the resonance current becomes about 20 kHz, the drive is stopped before the resonance current flowing through the first switching element 18 reaches the second peak. .
[0044]
Next, a series of operations from startup to stable operation will be described. The control means 30 turns off the relay 29 and alternately drives the first switching element 18 and the second switching element 23 at a driving frequency of about 36 kHz. In order to prevent the destruction of the first and second switching elements 18 and 23 due to the short-circuit current immediately after the startup, at the time of startup, the first switching element 18 is driven so as to minimize the drive time (in this embodiment, about 2 μm). Second), and control is performed so as to gradually reach a predetermined drive time ratio (in this embodiment, the drive time ratio of the first switching element 18 is about 0.25).
[0045]
After reaching the predetermined drive time ratio, the drive frequency is subtracted until the frequency becomes about 30 kHz while the drive time ratio is fixed. In the meantime, the control means 30 determines the material of the object to be heated 20.
[0046]
At this time, if it is determined that the object to be heated 20 is made of a high-resistance metal such as iron, the control means 30 temporarily suspends the heating and sets the relay 29 so that the resonance capacitor 24 and the correction resonance capacitor 28 are connected in parallel. And heating is started again. The control means 30 starts driving with the driving time of the first switching element 18 being the minimum and the driving frequency being about 20 kHz, and gradually increasing the driving time ratio while keeping the driving frequency fixed to output a predetermined output. Control to obtain. The drive frequency is fixed because the resonance current flowing through the heating coil 19 is set to be about 20 kHz as described above, and the electromagnetic wave is generated by the difference between the resonance current frequencies of the adjacent heating coils (not shown). This is to prevent sound from being generated.
[0047]
On the other hand, if it is determined that the object to be heated 20 is made of a low-resistance metal such as aluminum, the control unit 30 sets the driving time ratio of the first switching element 18 to about 0.5, and gradually sets the driving frequency. Control to obtain a predetermined output. The control means 30 judges from the detection output obtained from the current transformer 31 that if the output is smaller than a predetermined value, it is several times the minimum unit that can be controlled by the control means 30; Change.
[0048]
If it is determined that a substantially predetermined output is obtained, the drive time ratio is varied from about 0.49 to about 0.51 and controlled so that the output can be finely adjusted. In this embodiment, when the object to be heated 20 is a normal aluminum pan, the driving frequency of the first switching element 18 is about 20 kHz, the resonance current frequency flowing through the heating coil 19 is about 60 kHz, and the maximum output (in this embodiment, 2000 W).
[0049]
During the series of heating operations as described above, for example, when the pot 20 is made of a high-resistivity metal such as iron, the control unit 30 sets the drive frequency to be constant and the drive time ratio to be variable as described above. The output of the inverter 21 is controlled. The first switching element 18, the choke coil 17, and the second reverse conducting element 26 constitute a step-up means 35, and the longer the conduction period of the first switching element 18, the higher the voltage of the second smoothing capacitor 22. . Since the second smoothing capacitor 22 has a very large capacity in order to reduce ripples synchronized with the power supply 14, the second smoothing capacitor 22 simply stops driving the first and second switching elements 18 and 23 to perform the second smoothing. Only the discharge of the voltage of the capacitor 22 is performed through a detection resistor and a discharge resistor (not shown) connected in parallel to the second smoothing capacitor 22.
[0050]
Since the detection resistor and the discharge resistor have high resistance values in order to suppress the power consumption during standby, the voltage of the second smoothing capacitor 22 decreases very slowly. FIG. 4 shows waveforms at various points in this embodiment.
[0051]
FIG. 5A shows the voltage of the first switching element 18, and the envelope connecting the peaks is the same as the voltage of the second smoothing capacitor 22. FIG. 3B shows a zero volt pulse (not shown, such as a circuit, hereinafter referred to as ZVP) inverting from Hi to Low and from Low to Hi at the zero point of the power supply 14 voltage, and FIG. ing.
[0052]
As shown in FIG. 4, when the user performs the heating stop setting from the operation setting unit 34 at time t1 and a signal is output from the operation setting unit 34 to the control unit 30, the control unit 30 performs a series of operations synchronized with ZVP. After the end of the control, the drive time ratio of the first switching element 18 is gradually decreased from the time point t2 at which the next ZVP inversion is obtained to a time point t3 at which the ZVP inversion is obtained after a predetermined time, thereby increasing the boosting means 35. And the energy stored in the second smoothing capacitor 22 is consumed by the pot 20, so that the voltage of the second smoothing capacitor 22 decreases quickly.
[0053]
After a predetermined time when the voltage of the second smoothing capacitor 22 becomes equal to or lower than the predetermined voltage, that is, after a time point t3, the control means 30 stops the inverter 21 and waits for an output signal from the operation setting means 34 as a restartable state. When the user performs the heating start setting again from the operation setting means 34, even if the time after the heating stop setting is short, the voltage of the second smoothing capacitor 22 is equal to or lower than the predetermined value. Since the short-circuit current of the second switching elements 18 and 23 is suppressed, and the control unit 30 is also in a standby state in which it can be activated, after the time point t4 when the heating start signal is output from the operation setting unit 34 to the control unit 30. , The control means 30 starts heating from the time point t5 when ZVP reversal is obtained.
[0054]
Similarly, when the inverter 21 is abnormally detected (a detection circuit or the like is not shown) and the control unit 30 temporarily stops the inverter 21, the control unit 30 also controls the first switching element 18 before the temporary stop. In order to gradually decrease the drive time ratio of the second and the voltage of the second smoothing capacitor 22 quickly, it is possible to shorten the predetermined time until the restart.
[0055]
Further, for example, when the pot 20 is determined to be made of a high resistivity metal such as iron by the material determination at the time of startup, the control unit 30 gradually reduces the drive time ratio of the first switching element 18, The voltage of the second smoothing capacitor 22 is immediately reduced. After a predetermined time when the voltage applied to both ends of the relay 29 is considered to be equal to or lower than the predetermined voltage, the control means 30 turns on the relay 29 and shifts to the heating operation of the high resistivity metal pan 20 such as iron as described above.
[0056]
(Example 2)
FIG. 5 shows a second embodiment of the present invention. The difference from the first embodiment is the method of driving the second switching element 23 when heating is stopped, and the other points are the same as those of the first embodiment. Since the configuration is the same as that of the embodiment, the same portions are denoted by the same reference numerals, and only different portions will be described.
[0057]
5A and 5B show waveforms of respective parts of the inverter 21 when the user sets the heating stop by the operation setting means 34. FIG. 5A shows the first switching element 18 and the first reverse conducting element 25. FIG. 3B shows the current flowing through the second switching element 23 and the second reverse conducting element 26, and FIG. 3C shows the driving control terminal voltage of the first switching element 18. (D) shows the drive control terminal voltage of the second switching element 23, (e) shows the voltage of the second smoothing capacitor 22, and (f) shows the current flowing through the heating coil 19.
[0058]
When the user performs the heating stop setting from the operation setting unit 34 and a signal is output from the operation setting unit 34 to the control unit 30, the control unit 30 changes the time t 1 to the time t 2 from the time when the next ZVP inversion is obtained. The second switching element 23 is driven for a predetermined period of time. At this time, since the first switching element 18 remains cut off, power is not supplied from the power supply 14 and the second smoothing capacitor 22-the second switching element 23 or the second reverse conducting element 26-heating Resonance continues in a closed circuit formed by the coil 19 and the resonance capacitor 24.
[0059]
The energy stored in the second smoothing capacitor 22 is consumed by the pot 20 and components forming a closed circuit while the resonance is continued, so that the voltage of the second smoothing capacitor 22 rapidly decreases.
[0060]
After a predetermined time when the voltage of the second smoothing capacitor 22 becomes equal to or lower than the predetermined voltage, that is, after time t2, the control unit 30 waits for an output signal from the operation setting unit 34 as a restartable state. When the user performs the heating start setting again from the operation setting means 34, even if the time after the heating stop setting is short, the voltage of the second smoothing capacitor 22 is equal to or less than the predetermined value. Since the short-circuit current of the second switching elements 18 and 23 is suppressed, and the control unit 30 is also in a standby state, the control unit 30 waits for a start-up state. The means 30 starts heating at the time (not shown) when ZVP inversion is obtained.
[0061]
Similarly, when the inverter 21 is abnormally detected (a detection circuit or the like is not shown) and the control unit 30 temporarily stops the inverter 21, before the temporary stop, the control unit 30 switches to the second switching element 23. Is driven for a predetermined time, and the voltage of the second smoothing capacitor 22 is quickly reduced, so that the predetermined time until restarting can be set short.
[0062]
Further, for example, when it is determined that the pot 20 is made of a high-resistivity metal such as iron by the material determination at the time of starting, the control unit 30 drives the second switching element 23 for a predetermined time, and the second smoothing capacitor 22 The voltage is quickly reduced. After a predetermined time when the voltage applied to both ends of the relay 29 is considered to be equal to or lower than the predetermined voltage, the control means 30 turns on the relay 29 and shifts to the heating operation of the high resistivity metal pan 20 such as iron as described above.
[0063]
【The invention's effect】
As described above, the present invention can provide an induction heating device that quickly reduces the voltage of the smoothing unit when heating is stopped and shortens the time until restart.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circuit configuration of an induction heating cooker according to a first embodiment of the present invention.
FIG. 2 is a diagram showing waveforms of respective parts of the same.
FIG. 3 is a diagram showing waveforms of the respective parts.
FIG. 4 is a diagram showing waveforms of the respective parts.
FIG. 5 is a diagram showing waveforms at various points in the induction heating cooker according to the second embodiment of the present invention.
FIG. 6 is a diagram showing a circuit configuration of a conventional induction heating cooker.
[Explanation of symbols]
18 First switching element
19 heating coil
20 pots (heated body)
21 Inverter
22 Second smoothing capacitor (smoothing means)
23 Second switching element
29 relay (impedance changing means)
30 control means
35 booster

Claims

A heating coil that generates a high-frequency magnetic field to heat the object to be heated; a switching element; an inverter that supplies a high-frequency current to the heating coil; a boosting unit that boosts the inverter power supply; and smoothes the boosted inverter power supply. A smoothing means, and a control means for controlling the magnitude of the output of the inverter and the boosting means, wherein the control means reduces the voltage of the smoothing means immediately after the inverter is stopped to a predetermined voltage or less before stopping the heating. An induction heating device that stops the heating after reducing the output of the boosting means to reduce the output.

The boosting means performs a boosting operation in accordance with the output of the inverter, and the control means lowers the output of the inverter before the heating is stopped so that the voltage of the smoothing means immediately after the stop of the inverter becomes a predetermined voltage or less. The induction heating device according to claim 1, wherein the heating is stopped after the heating.

A heating coil that generates a high-frequency magnetic field and heats the object to be heated; a resonance capacitor that resonates with the heating coil; impedance changing means that changes the impedance of the heating coil or the resonance capacitor; a switching element; An inverter for supplying a high-frequency current; boosting means for boosting the inverter power supply; smoothing means for smoothing the boosted inverter power supply; and control means for controlling the magnitude of the output of the inverter and the boosting means. An induction heating device for operating the impedance changing unit after reducing the output of the boosting unit so as to reduce the voltage applied to the impedance changing unit immediately before the operation of the impedance changing unit to a predetermined voltage or less.

The boosting means performs a boosting operation in accordance with the output of the inverter, and the control means reduces the output of the inverter so as to reduce the voltage applied to the impedance changing means immediately before the operation of the impedance changing means to a predetermined voltage or less. 4. The induction heating apparatus according to claim 3, wherein the impedance changing unit is operated after that.

A heating coil that generates a high-frequency magnetic field and heats the object to be heated; an inverter that supplies a high-frequency current to the heating coil; a switching element whose conduction period is related to output control of the inverter; A switching element that does not contribute to output control; a boosting unit that performs a boosting operation of the inverter power supply in accordance with an output of the inverter; a smoothing unit that smoothes the boosted inverter power supply; Control means for controlling the magnitude, wherein the control means, prior to the stop of the heating, to reduce the voltage of the smoothing means immediately after the stop of the inverter to a predetermined voltage or less, a switching element which does not contribute to the output control of the inverter. Is driven for a predetermined period of time and then stops heating.

A heating coil that generates a high-frequency magnetic field and heats the object to be heated; a resonance capacitor that resonates with the heating coil; impedance changing means that changes the impedance of the heating coil or the resonance capacitor; and supplies a high-frequency current to the heating coil. An inverter, a switching element whose conduction period is related to the output control of the inverter, a switching element that continues the resonance operation and does not contribute to the output control of the inverter, and a boosting operation of the inverter power supply according to the output of the inverter. Boosting means for performing, a smoothing means for smoothing the boosted inverter power supply, and a control means for controlling the magnitude of the output of the inverter and the boosting means, wherein the control means immediately before the operation of the impedance changing means A voltage applied to the impedance changing means is changed to a predetermined voltage. In order to below, after the switching element which does not contribute to the output control of the inverter by a predetermined period of time driving, the induction heating device for operating the impedance changing means.