JP2004006331A

JP2004006331A - Induction heating apparatus

Info

Publication number: JP2004006331A
Application number: JP2003120023A
Authority: JP
Inventors: Koji Niiyama; 新山　浩次; Yuji Fujii; 藤井　裕二; Motonari Hirota; 弘田　泉生; Takahiro Miyauchi; 宮内　貴宏; Atsushi Fujita; 藤田　篤志; Manabu Takahashi; 高橋　学
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2002-04-24
Filing date: 2003-04-24
Publication date: 2004-01-08
Anticipated expiration: 2023-04-24
Also published as: JP4289002B2

Abstract

<P>PROBLEM TO BE SOLVED: To improve a controllability by shortening a software start time in an inverter heating a load with a low resistance and a low permeability such as aluminum. <P>SOLUTION: This induction heating apparatus comprises an output control means 15 performing an output control by varying the the drive frequencies and the drive time ratios of a first switching element 6 and a second switching element 7. The output control means 15 comprises a time ratio changing mode for gradually raising the drive time ratios with the drive frequencies set at constants and a frequency changing mode for gradually lowering the drive frequencies with the drive time ratios set at constants. When the switching elements reach given drive time ratios or the drive times in a time ratio changing mode, they transfer to the frequency changing mode and lower the drive frequencies. <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、工場など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、加温装置などの誘導加熱装置に関する。
【０００２】
【従来の技術】
従来の誘導加熱装置の例として誘導加熱調理器について、図１３に基づいて説明する。電源３１は２００Ｖ商用電源で、ブリッジダイオードである整流回路３２で整流され、平滑コンデンサ３３にて直流電力に変換させる。３４はインバータで、第１のスイッチング素子３５および第２のスイッチング素子３６と第１の逆導通素子３７および第２の逆導通素子３８と、共振コンデンサ３９により構成される。第１のスイッチング素子３５および第２のスイッチング素子３６を駆動して高周波磁界を加熱コイル４０に発生させ、負荷４１を誘導加熱する。
【０００３】
４２は、インバータの入力電流を検知する電流検知手段で、出力制御手段４３は、電流検知手段４２の出力に応じて、第１のスイッチング素子３５および第２のスイッチング素子４３を駆動して、電力を制御する。ここで、出力制御手段４３は第１のスイッチング素子３５と第２のスイッチング素子４３の駆動周波数または駆動時間比のいずれかにより電力制御を行っていた。
【０００４】
図１４（Ａ）は、駆動周波数−入力電力特性を示すグラフであり、出力制御手段４３は、図１４（Ａ）に示す特性を利用して、スイッチング素子の駆動時間比を一定して駆動周波数を可変することにより電力制御を行い、また、図１４（Ｂ）は、駆動時間比−入力電力特性を示すグラフで、出力制御手段４３は、図１４（Ｂ）に示す特性を利用して、駆動周波数を一定にしてスイッチング素子の駆動時間比を可変することにより電力制御を行っていた。
【０００５】
図１３は、出力制御手段４３が駆動時間比を制御して電力制御を行う場合において、設定された電力に到達するソフトスタート動作を示している。インバータを起動する場合、最小の出力となる駆動時間比で第１のスイッチング素子および第２のスイッチング素子を駆動し、一定時間づつ駆動時間を長くする第１の駆動時間比変更モードを有している。
【０００６】
また、アルミニウム製の負荷をスイッチング素子の損失を抑制しながら加熱する誘導加熱調理装置に係る技術が提案されている（例えば、特許文献１参照）。
【０００７】
【特許文献１】
特開２００１−１６０４８４号公報
【０００８】
【発明が解決しようとする課題】
前記従来の構成の誘導加熱装置は、アルミニウムや銅など低抵抗金属からなる負荷を誘導加熱した場合、低抵抗のため負荷と磁気結合した状態での加熱コイルのＱが大きくなり、駆動周波数に対する入力電力の変化が大きく、駆動周波数の制御による電力制御と、細かな電力制御が行うための駆動時間比の制御による電力制御も必要であり、インバータ起動後、設定電力に到達するまでの時間が長くなるという課題があった。また、特許文献１に記載の技術は出力制御性に問題があり使い勝手が悪いものであった。
【０００９】
本発明の目的は、設定電力に到達するまでの時間を従来の鉄系負荷を加熱するインバータの起動時間と同等以下に短縮し、制御性を向上したアルミ等の低抵抗、低透磁率の材質の負荷を誘導加熱する誘導加熱装置の制御方法を提供する。
【００１０】
【課題を解決するための手段】
上記目的を達成するために、本発明の誘導加熱装置は、第１のスイッチング素子と第２のスイッチング素子の直列接続体と、前記第１のスイッチング素子に並列に接続された第１の逆導通素子と、前記第２のスイッチング素子に並列に接続された第２の逆導通素子と、前記第１のスイッチング素子または前記第２のスイッチング素子に並列に接続された加熱コイルと共振コンデンサを含む共振回路とを有し直流電圧を入力して前記第１のスイッチング素子と第２のスイッチング素子の導通により共振するインバータと、前記第１のスイッチング素子と前記第２のスイッチング素子を排他的に導通制御する出力制御手段と、前記インバータの入力電流又はそれに略等価な電圧若しくは電流を検知する出力検知手段とを備え、前記第１のスイッチング素子または前記第１の逆導通素子に流れる共振電流が、前記加熱コイルの発生する磁界が高導電率かつ低透磁率の負荷を誘導加熱すると前記第１のスイッチング素子の駆動期間より短い周期で共振する加熱モードを有するとともに、前記出力制御手段は、前記第１及び第２のスイッチング素子の駆動時間比を徐々に変更して前記インバータの出力を上昇させる駆動時間比変更モードと、前記第１及び第２のスイッチング素子の駆動時間比を略一定にして徐々に駆動周波数を変更して前記インバータの出力を上昇させる駆動周波数変更モードとを備え、前記インバータの出力を、前記駆動時間比変更モードと前記駆動時間比変更モードを組み合わせて、起動時の低出力値から所定の出力値まで到達させることにより、アルミや銅などの高導電率かつ低透磁率の負荷をスイッチング素子の損失の増大を抑制して誘導加熱することができるとともに、インバータ起動から設定電力に到達するまでソフトスタート動作の時間を短縮し、スイッチング素子が故障しにくく制御性のよい誘導加熱装置が提供することができる。
【００１１】
【発明の実施の形態】
請求項１記載の発明は、第１のスイッチング素子と第２のスイッチング素子の直列接続体と、前記第１のスイッチング素子に並列に接続された第１の逆導通素子と、前記第２のスイッチング素子に並列に接続された第２の逆導通素子と、前記第１のスイッチング素子または前記第２のスイッチング素子に並列に接続された加熱コイルと共振コンデンサを含む共振回路とを有し直流電圧を入力して前記第１のスイッチング素子と第２のスイッチング素子の導通により共振するインバータと、前記第１のスイッチング素子と前記第２のスイッチング素子を排他的に導通制御する出力制御手段と、前記インバータの入力電流又はそれに略等価な電圧若しくは電流を検知する出力検知手段とを備え、前記第１のスイッチング素子または前記第１の逆導通素子に流れる共振電流が、前記加熱コイルの発生する磁界が高導電率かつ低透磁率の負荷を誘導加熱すると前記第１のスイッチング素子の駆動期間より短い周期で共振する加熱モードを有するとともに、前記出力制御手段は、前記第１及び第２のスイッチング素子の駆動時間比を徐々に変更して前記インバータの出力を上昇させる駆動時間比変更モードと、前記第１及び第２のスイッチング素子の駆動時間比を略一定にして徐々に駆動周波数を変更して前記インバータの出力を上昇させる駆動周波数変更モードとを備え、前記インバータの出力を、前記駆動時間比変更モードと前記駆動時間比変更モードを組み合わせて、起動時の低出力値から所定の出力値まで到達させることにより、加熱コイルに供給する電流の共振電流の共振周波数より、スイッチング素子の駆動周波数を低くでき、アルミニウムなどの高導電率かつ低透磁率の負荷を誘導加熱することができるとともに、スイッチング素子のスイッチング損失を低減することができる。
【００１２】
また、インバータの出力を、駆動時間比変更モードと駆動時間比変更モードを組み合わせて、起動時の低出力値から所定の出力値まで到達させるので、負荷の検知を精度良く安定して行うとともに、迅速に設定出力までインバータの出力を増加させることができる。したがって、起動時にインバータに異常な電圧が発生してスイッチング素子が破壊するのを防止すると同時に使い勝手を良くすることができる。なお、駆動時間比変更モードにおいては、一定周波数による出力制御をおこなうこともできる。
【００１３】
請求項２記載の発明は、特に、出力制御手段は、起動時の低出力値から所定の出力値まで到達させる期間内において、駆動時間比変更モードまたは駆動周波数変更モードのいずれか一方のモードでのみインバータの出力を増加させる期間を設けたことにより、当該期間においては、出力制御特性が単純化されるので制御が行いやすくなり制御出力を安定化し易くなる。
【００１４】
また、請求項３記載の発明は、特に、出力制御手段は、駆動時間比変更モードと駆動周波数変更モードに交互に移行しながらインバータの出力を起動時の低出力値から所定の出力値に到達させてなることにより、インバータの共振回路の共振周波数における出力の変化に対応してきめこまかな出力の制御を行うことができる、また所定の出力値に迅速に到達させることができる。
【００１５】
また、請求項４記載の発明は、特に、出力制御手段は、起動時、第１のスイッチング素子と第２のスイッチング素子の駆動駆動時間比を変えてインバータの出力を増加させ、途中から前記駆動時間比を略一定にして前記第１のスイッチング素子と前記第２のスイッチング素子の駆動周波数を変えインバータの出力を増加させてなることにより、起動時に駆動駆動時間比を変えることにより、出力の変化速度を緩やかにして、出力の小さい状態にて異常な負荷を検出することができる。また、駆動時間比を略一定にして駆動周波数を変えることにより、大きな出力変化が得やすいので出力を増加させる時間を短縮することができる。また、駆動時間比を変える場合には、駆動周波数を一定とすることもできる。
【００１６】
また、請求項５記載の発明は、特に、出力制御手段は、起動時の低出力値から所定の出力値まで到達させる期間内において、駆動時間比変更モードのときに駆動時間比が所定の駆動時間比を越えると駆動周波数変更モードに移行することにより、駆動時間比変更モードから駆動周波数変更モードに移行する制御が簡単にできるので、マイクロコンピュータ等で容易に実現することができる。
【００１７】
また、請求項６記載の発明は、特に、出力制御手段は、起動時の低出力値から所定の出力値まで到達させる期間内において、駆動周波数を直前の変化幅より大きい変化幅で離散的に変更して前記インバータの出力を上昇させると同時に駆動時間比を直前の変化幅より大きい変化幅で離散的に変更することにより、インバータの共振周波数付近の出力が増大する状態（駆動周波数）を経由せず、他の出力の低い周波数に離散的に安定的に制御を行う領域に遷移することができるのでスイッチング素子に過大な電圧や電流の責務が印加するのを防止して、出力制御を行うことができる。
【００１８】
また、請求項７記載の発明は、特に、出力制御手段は、起動時、第１のスイッチング素子の駆動期間が共振電流の共振周期より短くなるようにして第１のスイッチング素子と第２のスイッチング素子の駆動時間比を変えて加熱出力を増加させ、所定の駆動時間比に到達すると、第１のスイッチング素子の駆動期間を共振電流の周期より長くかつ低出力値になるように離散的に長く変更してから前記駆動期間を徐々に長くして駆動周波数を低下させインバータの出力を前記低出力値から所定の出力値まで増加させてなることにより、インバータの共振周波数付近の出力が増大する状態を経由せず、他の出力の低い周波数に離散的に安定的に制御を行う領域に遷移することができるのでスイッチング素子に過大な電圧や電流の責務が印加するのを防止して、出力制御を行うことができる。
【００１９】
また、請求項８記載の発明は、特に、出力制御手段は、周波数変更モードにより出力を徐々に増加させるとともに、出力検知手段の出力によってインバータの出力値が設定された出力値より小さい所定の出力値に到達したことを検知した後、駆動時間比変更モードに移行して出力を徐々に増加させることにより、周波数変更モードにより短時間で出力を増加させ、設定出力の手前で駆動時間比変更モードに移行して出力の微変更をおこなうので設定出力を大きく超える電力にならず、スイッチング素子等の各部品に過大な負荷がかかることがなく、信頼性の高い誘導加熱装置ができる。
【００２０】
また、請求項９記載の発明は、特に、出力制御手段は、インバータ起動後所定の時間略最小の出力となる駆動周波数および駆動時間比で出力する第１の出力固定モードを有することにより、入力電流が安定し、信頼性の高い制御ができる。
【００２１】
また、請求項１０記載の発明は、特に、出力制御手段は、駆動周波数または駆動時間比を直前の変化幅より大きい変化幅で離散的に低下させた後、所定の時間、駆動周波数と駆動時間比の出力を固定する第２の出力固定モードを有することにより、インバータの共振周波数付近の出力が増大する状態（駆動周波数）を経由せず、他の出力の低い周波数に離散的に安定的に制御を行う領域に遷移することができるのでスイッチング素子に過大な電圧や電流の責務が印加するのを防止して、出力制御を行うことができる。
【００２２】
また、請求項１１記載の発明は、特に、高導電率かつ低透磁率の負荷を誘導加熱した場合の前記負荷の浮きまたはずれを検知する移動検知手段を有し、出力制御手段は、前記移動検出手段が前記負荷の浮きまたはずれを検知している場合の駆動周波数変更モードにおける駆動周波数を変化させる時間間隔を、前記移動検出手段が前記負荷の浮きまたはずれを検知していない場合の駆動周波数変更モードにおける駆動周波数を変化させる時間間隔より長くしたことにより、出力が固定される時間が長くなり、高導電率かつ低透磁率の負荷を誘導加熱した場合の前記負荷の浮きまたはずれを検知する移動検出手段の検知精度を向上させることができ、他の材質の負荷（例えば磁性の小物負荷）においては負荷検知の速度を速め検知状態で放置された場合の負荷の温度上昇を抑制するなど安全性の高い誘導加熱装置を提供できる。
【００２３】
また、請求項１２記載の発明は、特に、出力制御手段は、出力検知手段の検知出力を入力して、インバータの出力を前記検知出力に基づき設定出力に到達させた後において、前記インバータの出力が変化して所定の範囲で駆動時間比を変更しても前記設定出力に到達しない場合に、駆動周波数を変更することにより前記設定出力に到達させてなるので、ソフトスタート動作終了後の安定状態において出力電力が大きく変動しても、駆動周波数を変更することによりすばやく安定した設定電力を得ることができ、また、設定出力付近では駆動時間比を変更することにより出力の変動幅を抑制してスイッチング素子等の各部品に過渡的な過大な電圧や電流がかかることがなく、信頼性の高い誘導加熱装置ができる。
【００２４】
また、請求項１３記載の発明は、特に、出力制御手段が第１の出力固定モードまたは起動時の低出力値から所定の出力値まで到達させる期間内における時間比変更モードにある場合に、出力検知手段が所定の値を超えると通常の加熱動作を行わない小物と判定する小物検知手段を有することにより、低出力状態が所定時間維持される（維持には変化幅が少ない状態を含む）ので、精度良く小物検知ができ、スイッチング素子等の各部品に過渡的な過大な電圧や電流がかかることがなく、故障の少ない誘導加熱装置を提供できる。
【００２５】
また、請求項１３記載の発明は、特に、出力制御手段が第１の出力固定モードまたは起動時の低出力値から所定の出力値まで到達させる期間内における時間比変更モードにある場合に、出力検知手段が所定の値を超えると異常状態が起きていると判断して通常の加熱動作を行わないことにより、スイッチング素子等の各部品に過渡的な過大な電圧や電流がかかることがなく、故障の少ない誘導加熱装置を提供できる。
【００２６】
また、請求項１４記載の発明は、特に、出力制御手段が起動時の低出力値から所定の出力値まで到達させる期間内における周波数変更モードにおいて、所定の周波数に到達するまでに出力検知手段の出力が所定の値に到達しないとき通常の加熱動作を行わない小物と判定する小物検知手段を有することにより、直径が小さいため加熱できない負荷を検知して停止することができる。
【００２７】
また、請求項１５記載の発明は、特に、出力制御手段が所定の（インバータの出力が所定の値以上得られるべき）周波数範囲内の駆動周波数で制御しているときに、出力検知手段の出力が所定の値より小さいことを検知すると小物と判定する小物検知手段を有することにより、使用中、常に小物検知ができるので、使い勝ってがよく、また、他の検知手段が必要ないので、簡単な方法で安価に信頼性の高い誘導過熱装置を提供できる。
【００２８】
また、請求項１６記載の発明は、特に、出力検知手段はインバータの入力電流を検知する入力電流検知手段とすることにより、インバータの実効電力を精度良く検知するとともに、簡単で安価な構成で、請求項１〜１５の発明に必要な出力検知手段を実現することができる。
【００２９】
【実施例】
（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。電源１は低周波交流電源である２００Ｖ商用電源であり、全波整流を行うブリッジダイオードである整流回路２の入力端に接続される。整流回路２の出力端間に第１の平滑コンデンサ３が接続される。整流回路２の出力端間には、さらに、チョークコイル５と第２のスイッチング素子７の直列接続体が接続される。加熱コイル１２は被加熱物（負荷）であるアルミニウム製の鍋１３と対向して配置されている。
【００３０】
４はインバータ（加熱コイル１２を除く）であり、第２の平滑コンデンサ１１の低電位側端子（エミッタ）は整流回路２の負極端子に接続され、第２の平滑コンデンサ１１の高電位側端子は第１のスイッチング素子（ＩＧＢＴ）６の高電位側端子（コレクタ）に接続され、第１のスイッチング素子（ＩＧＢＴ）６の低電位側端子（エミッタ）はチョークコイル５と第２のスイッチング素子（ＩＧＢＴ）７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１２と共振コンデンサ１０の直列接続体が第２のスイッチング素子７に並列に接続される。
【００３１】
第１のダイオード８（第１の逆導通素子）は第１のスイッチング素子６に逆並列に接続（第１のダイオード８のカソードと第１のスイッチング素子６のコレクタとを接続）され、第２のダイオード９（第２の逆導通素子）は第２のスイッチング素子７に同様に逆並列に接続される。
【００３２】
１４は、電源１から流れる入力電流を検知する電流検知手段で、出力制御手段１５は、電流検知手段１４の出力に応じて、第１のスイッチング素子６と第２のスイッチング素子７のゲートに信号を出力する。
【００３３】
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１は整流回路２により全波整流され、整流回路２の出力端に接続された第１の平滑コンデンサ３に供給される。この第１の平滑コンデンサ３はインバータに高周波電流を供給する供給源として働く。
【００３４】
高電位側の第１のスイッチング素子６と低電位側の第２のスイッチング素子７は交互にかつ互いに排他的に駆動される。第２のスイッチング素子７が駆動されている間に、（第２のスイッチング素子７又は第２のダイオード９）と加熱コイル１２と共振コンデンサ１０で形成される閉回路で共振し、第１のスイッチング素子６を駆動している間に、第２の平滑コンデンサと第１のスイッチング素子６（又は第１のダイオード８）と加熱コイル１２と共振コンデンサ１０で形成される閉回路で共振する。第２のスイッチング素子７をオフすると、チョークコイル５に蓄積された磁気エネルギーが第２の平滑コンデンサ１１に移動することにより、第２の平滑コンデンサ１１の電圧が昇圧されるので、上記の共振電流を大きくして振動を維持することができ、アルミ等の低抵抗、低透磁率の負荷を高出力で誘導加熱できる。
【００３５】
本実施例では、第１のスイッチング素子６の駆動時間と、第２のスイッチング素子７の駆動時間が所定の出力で（本実施例では２ｋＷ）、それぞれ加熱コイル１２と共振コンデンサ１０に流れる共振電流の共振周期の略２／３になるように加熱コイル１２及び共振コンデンサ１０のインピーダンスが設定されているため、駆動周波数が約２０ｋＨｚであれば、共振電流の周波数は約６０ｋＨｚになる。
【００３６】
図２（Ａ）は、第１のスイッチング素子６及び第２のスイッチング素子７の駆動周波数と入力電力の特性を示す図である。両スイッチング素子の駆動時間比は約１：１で固定されている。加熱コイル１２と共振コンデンサ１０の共振周波数をｆｃとすると駆動周波数がｆｃ／２、ｆｃ／３の時にそれぞれ第２高調波、第３高調波による共振が起こり、図２（Ａ）のような入力電力特性となる。本実施例では駆動周波数をｆｃ／３近傍とすることで加熱コイル１２に流れる電流の共振周波数の３分の１程度に第１のスイッチング素子６及び第２のスイッチング素子７の駆動周波数を低くすることが出来、スイッチング損失が小さく効率の良い誘導加熱を実現している。
【００３７】
また、アルミニウムや銅などの場合、負荷を磁気結合した状態での加熱コイルと共振コンデンサの共振のＱが大きいため、図２（Ａ）のように周波数に対して各ピーク付近で急峻に入力電力が変化する（増大する）特性となる。
【００３８】
図２（Ｂ）は第１のスイッチング素子６と第２のスイッチング素子７の駆動周波数を略一定（２０ｋＨｚ）にしたときの第２のスイッチング素子７のオン時間と入力電力の関係を示す図である。この図が示すように、本実施例においては、第２のスイッチング素子７のオン時間が駆動周期の１／２付近（駆動時間比約１／２）で約２ｋＷの加熱出力がえられ、その付近のピークから第２のスイッチング素子の駆動期間を短くしていけば出力を線形的に低下することができる。従って、図２（Ｂ）に示すように駆動時間あるいは駆動時間比のリミッタの下限Ｔｏｎｍｉｎと上限Ｔｏｎｍａｘを設定すれば、安定した制御を行うことができる。
【００３９】
図３はインバータ起動からインバータ１０の出力が設定電力に到達するまでのソフトスタート動作を示す図であり、実線は駆動周波数の時間経過に対する変化を示し、破線は駆動時間比の変化を示している。図３に示すとおり、出力制御手段１５は、起動後、第１のスイッチング素子６と第２のスイッチング素子７の駆動周波数を一定（約３６ｋＨｚ）にし、第２のスイッチング素子７がオンする駆動時間を徐々に長くする（第１のスイッチング素子６に対する第２のスイッチング素子７の駆動時間比を徐々に大きくする）第１の駆動時間比変更モードとなる。出力制御手段１５は、第１の駆動時間比変更モードになると、電源１に同期した時間単位間隔（約１０ミリ秒）で、０．１マイクロ秒単位で駆動時間を長くしている。その後、駆動時間比が所定の比率（１／４）に到達すると、駆動周波数を所定の比率（３／４）で離散的に変化させる。例えば、約３３ｋＨｚの駆動周波数の場合は、約２４ｋＨｚに変化させる。
【００４０】
この結果、図２（Ａ）で示すｆｃ／２の高周波数側（図で右側）谷間付近の低出力領域（点Ｐで示す）から、ｆｃ／３とｆｃ／２の間の低出力領域（点Ｍで示す）に離散的に移行するので、その後、第１の駆動周波数変更モードに移行して、設定出力に到達するまで駆動時間比を一定にし、駆動周波数を徐々に低下させ出力を増加させる。従って、ｆｃ／２付近の高出力領域を避けて、ｆｃ／３付近の低出力領域に移行することができる。
【００４１】
以上のように、本実施例によれば、アルミ等の低抵抗、低透磁率の負荷を加熱するインバータ４の第１のスイッチング素子６と第２のスイッチング素子７の駆動周波数と駆動時間比の両方のモードにより交互にソフトスタート制御することにより、確実に、ｆｃ／２付近の高出力の領域に入ることなく、ｆｃ／３の付近で設定出力を得ることができる。また、共振周波数の出力を駆動周波数または駆動時間比のどちらか一方で電力を制御する場合と同様の時間で、ソフトスタートを終了することができ、制御性のよい誘導加熱装置が実現できるものである。
【００４２】
また、本実施例における出力制御手段１５は、マイクロコンピュータを利用して容易に実現できる。
【００４３】
また、上記実施例では誘導加熱調理器について説明したがアルミニウムなどの高導電率かつ低透磁率材料を加熱するアイロンや湯沸かし器など他の種の誘導加熱装置にも応用できるものである。
【００４４】
なお、上記実施例においては、図１のように２個のスイッチング素子によるハーフブリッジ型のインバータで説明したが、これに限定されるものではない。本願発明は、少なくとも、第１のスイッチング素子と第２のスイッチング素子の直列接続体と、第１のスイッチング素子に並列に接続された第１の逆導通素子と、第２のスイッチング素子に並列に接続された第２の逆導通素子と、第１のスイッチング素子または第２のスイッチング素子に並列に接続された加熱コイルと共振コンデンサを含む共振回路とを有し直流電圧を入力して第１のスイッチング素子と第２のスイッチング素子の導通により共振するインバータと、第１のスイッチング素子と第２のスイッチング素子を排他的に導通制御する出力制御手段とを有するものであれば良く、いわゆるフルブリッジ型のインバータにも適用することができる。
【００４５】
（実施例２）
図４は、実施例２におけるソフトスタート動作を示す図である。第１の駆動時間比変更モードから第１の駆動周波数変更モードに移行する場合に駆動周波数のみを離散的に変化させていたのを駆動時間比も同時に所定の比率または所定の値で離散的に変化させるものである。例えば、駆動時間比が１／４であれば、１／３に変化させる。
【００４６】
以上のように、本実施例によれば、設定電力が大きい場合においても、すばやく設定電力に到達することができ、インバータの出力が小さい領域にて、共振周波数の位置がどこにあるかをサーチしながら駆動周波数と駆動時間比を離散的に変化させることにより、スイッチング損失も少なくなり信頼性が高くなる。
【００４７】
なお、出力の周波数特性において、ピーク、あるいは谷間のどの部分にいるかどうかをサーチするのは周波数を変え出力の増減を観察することにより行うことができる。
【００４８】
（実施例３）
図５は、実施例３におけるソフトスタート動作を示す図である。実施例１、２において、出力設定手段１５は、第１の駆動周波数変更モードに移行後、設定出力より少し小さい入力電流を検知した場合に第１の駆動周波数変更モードから第２の駆動時間比変更モードに移行することによって、インバータの入力電流が設定出力を大きく超えることがないようにするものである。
【００４９】
以上のように、本実施例によれば、設定電力が大きい場合においても、第１の駆動周波数変更モードにより迅速に、インバータ４の出力を設定出力に到達させることができるとともに、設定電力を大きくこえることがないので、スイッチング素子等のインバータを構成するパワー部品に過大な負荷がかからず信頼性の高い誘導加熱装置が提供できる。
【００５０】
（実施例４）
図６は、実施例４におけるソフトスタート動作を示す図である。
【００５１】
インバータ４の最小の出力となる第１と第２のスイッチング素子の駆動周波数と駆動時間比でインバータを起動後、所定の時間（０．１秒）出力を固定する第１の出力固定モードを付加したものである。
【００５２】
以上のように、本実施例によれば、起動後、入力電流が最小の値で安定するまで、またはその出力で所定時間維持して、ソフトスタートなどの出力制御を遅らせることにより、安定した負荷検知動作等の制御動作を実現できるものである。
【００５３】
（実施例５）
図７は、実施例５におけるソフトスタート動作を示す図である。
【００５４】
実施例４と同様に、駆動周波数と駆動時間比を離散的に変化させた場合に、変化後、約０．１秒間出力を固定する第２の出力固定モードを付加している。入力検知手段の出力が安定するまで制御を遅らせることで、第１の駆動周波数変更モードでの動作において、安定した出力制御ができる。
【００５５】
（実施例６）
図８は、実施例６の回路構成を示す図である。
【００５６】
実施例１で説明した図１とほぼ同じ構成であるので、違いのみ説明する。
【００５７】
１６は、第１の共振コンデンサ１０の電圧を検知する電圧検知手段で、１７は電圧検知手段１６の出力により負荷の浮きやずれを検知する移動検知手段であり、移動検知手段１７は、ソフトスタート時の出力変化の状態を観察して負荷の浮きやずれを検知するものである。本実施例では、ソフトスタート期間中に出力を増加させている際に、一定時間内の電圧変化がある時点でそれまでよりも小さくなることを検知して負荷の浮きまたはずれが起きたことを検知している。なお、電圧検知手段１６は入力電流を検知することでも同様に負荷の浮きまたはずれが起きたことを検知できる。
【００５８】
図９は、実施例６のソフトスタート動作を示す図である。
【００５９】
第２の駆動周波数変更モードを付加し、移動検知手段１７が動作しない第１の駆動周波数変更モードにおけるよりも、移動検知手段が動作した後の第２の駆動周波数変更モードになったほうが駆動周波数を変化させる時間間隔を長くすることにより、移動検知手段の検知精度を向上させることができる。
【００６０】
（実施例７）
図１０は、設定電力に到達した後の電力制御時における駆動周波数と駆動時間比を示す図である。ｔ０からｔ１まで駆動時間比を上昇することにより、電力を少しずつ上昇させる。ｔ１では、駆動時間比が制御範囲の最大となり、駆動周波数を最小制御単位（周期で０．１マイクロ秒）で低下させる。さらに、ｔ２からｔ３まで駆動時間比を上昇し、電力を少しずつ上昇させ、ｔ３で設定電力を超えるとｔ４時点まで駆動時間比を低下させる。
【００６１】
また、ｔ４では、駆動時間比が制御範囲の最小となり、駆動周波数を最小制御単位（周期で０．１マイクロ秒）で上昇させる。以上のように、駆動周波数と駆動時間比を制御することにより、細かな電力制御を行うことができる。
【００６２】
（実施例８）
図１１は本発明の実施例８における誘導加熱装置の回路図を示すもので、基本的に実施例１と同じであるので、相違点のみ説明する。
【００６３】
図１１において、１８は小物検知手段で電流検知手段１４の出力により起動時に小物検知を行い、出力制御手段１５にインバータを停止させる。
【００６４】
図１２は、第２のスイッチング素子７の駆動時間と入力電流の関係を示す図であり、時間駆動比を上昇させると、入力電流の変化の違いにより、負荷がない場合やナイフ、フォーク等の小物負荷を検知できる。
【００６５】
本発明では、インバータの起動時、出力が最小になる駆動周波数と駆動時間比において、駆動周波数を一定にして、駆動時間比を徐々に上昇させる駆動時間比変更モードにおいて、図１２に示す特性を利用することにより、精度のよい小物検知手段を提供する。
【００６６】
（実施例９）
実施例９は、実施例８と同じ構成とし、出力制御手段１５は、図９において、第１の周波数変更モードにある場合に、所定の周波数（３０ＫＨｚ）より小さくなると、小物と判断するようにしたものである。
【００６７】
インバータ４を起動中に、直径が小さく、加熱できない負荷を検知し、インバータ４を停止させるので、安全で故障の少ない誘導加熱装置を提供できる。
【００６８】
（実施例１０）
実施例１０は、実施例８と同じ構成とし、インバータ４が起動して所定の電力以上を検知した後に、電流検知手段１４の出力が所定値より低くなった場合に小物と判断するようにしたものである。
【００６９】
インバータが設定電力で動作している場合に、負荷を取った場合、すぐに電流検知手段１４の出力が低下するとインバータ４を停止させるので、安全で故障の少ない誘導加熱装置を提供できる。
【００７０】
なお、電流検知手段１５に代え、それに相当する出力検知手段をインバータの電流あるいは電圧を検知して構成しても良い。
【００７１】
【発明の効果】
以上のように、本発明によれば、アルミや銅などの高導電率かつ低透磁率の負荷をスイッチング素子の損失の増大を抑制して誘導加熱することができるとともに、スイッチング素子の駆動周波数の可変制御とスイッチング素子の駆動時間比の可変制御を組み合わせて出力制御を行うことで、マイクロコンピュータを使って容易にきめ細かな電力制御を行うことができ、起動から出力安定までの時間を早くするとともにスイッチング素子が故障しにくく制御性がよい誘導加熱装置を実現することができる。
【図面の簡単な説明】
【図１】第１の実施例の誘導加熱調理器の回路図
【図２】（Ａ）第１の実施例の誘導加熱調理器の駆動周波数と入力電力特性を示す図
（Ｂ）第１の実施例の誘導加熱調理器の駆動時間比と入力電力特性を示す図
【図３】第１の実施例の誘導加熱調理器の動作波形を示す図
【図４】第１の実施例の誘導加熱調理器のソフトスタート動作を示す図
【図５】第２の実施例の誘導加熱調理器のソフトスタート動作を示す図
【図６】第３の実施例の誘導加熱調理器のソフトスタート動作を示す図
【図７】第４の実施例の誘導加熱調理器のソフトスタート動作を示す図
【図８】第５の実施例の誘導加熱調理器のソフトスタート動作を示す図
【図９】第６の実施例の誘導加熱調理器の回路図
【図１０】第６の実施例の誘導加熱調理器のソフトスタート動作を示す図
【図１１】第８の実施例の誘導加熱調理器の回路図
【図１２】第８の実施例の誘導加熱調理器の駆動時間比と入力電力特性を示す図
【図１３】従来の誘導加熱装置の回路図
【図１４】（Ａ）従来の誘導加熱装置の駆動周波数と入力電力特性を示す図
（Ｂ）従来の誘導加熱装置の駆動時間比と入力電力特性を示す図
【図１５】従来の誘導加熱装置のソフトスタート動作を示す図
【符号の説明】
４　インバータ
６　第１のスイッチング素子
７　第２のスイッチング素子
１２　加熱コイル
１３　負荷
１４　電流検知手段
１５　出力制御手段[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an induction heating device such as an induction heating cooker, a water heater using induction heating, and a heating device used in general households, offices, restaurants, factories, and the like.
[0002]
[Prior art]
An induction heating cooker will be described as an example of a conventional induction heating device with reference to FIG. The power supply 31 is a 200 V commercial power supply, which is rectified by a rectifier circuit 32 which is a bridge diode, and converted into DC power by a smoothing capacitor 33. Reference numeral 34 denotes an inverter, which includes a first switching element 35 and a second switching element 36, a first reverse conducting element 37 and a second reverse conducting element 38, and a resonance capacitor 39. By driving the first switching element 35 and the second switching element 36, a high-frequency magnetic field is generated in the heating coil 40, and the load 41 is induction-heated.
[0003]
Reference numeral 42 denotes current detection means for detecting the input current of the inverter. Output control means 43 drives the first switching element 35 and the second switching element 43 in accordance with the output of the current detection means 42, Control. Here, the output control means 43 performs power control by using either the drive frequency or the drive time ratio of the first switching element 35 and the second switching element 43.
[0004]
FIG. 14A is a graph showing a driving frequency-input power characteristic, and the output control means 43 uses the characteristic shown in FIG. 14 (B) is a graph showing a drive time ratio-input power characteristic, and the output control means 43 uses the characteristic shown in FIG. Power control is performed by changing the drive time ratio of the switching element while keeping the drive frequency constant.
[0005]
FIG. 13 shows a soft start operation to reach the set power when the output control means 43 performs power control by controlling the drive time ratio. When the inverter is started, the first switching element and the second switching element are driven at a driving time ratio at which the output becomes the minimum, and a first driving time ratio changing mode is provided for increasing the driving time by a fixed time. I have.
[0006]
In addition, a technology related to an induction heating cooking device that heats a load made of aluminum while suppressing loss of a switching element has been proposed (for example, see Patent Document 1).
[0007]
[Patent Document 1]
JP 2001-160484 A
[0008]
[Problems to be solved by the invention]
In the conventional induction heating device, when a load made of a low-resistance metal such as aluminum or copper is induction-heated, the Q of the heating coil in a state of being magnetically coupled to the load becomes large due to low resistance, and the input to the drive frequency is increased. The change in power is large, and power control by controlling the drive frequency and power control by controlling the drive time ratio for fine power control are also necessary.After starting the inverter, the time it takes to reach the set power is long. There was a problem of becoming. In addition, the technology described in Patent Document 1 has a problem in output controllability and is inconvenient.
[0009]
An object of the present invention is to reduce the time required to reach the set power to be equal to or less than the startup time of a conventional inverter for heating an iron-based load, and to improve the controllability of a low-resistance, low-permeability material such as aluminum. The present invention provides a method for controlling an induction heating device for induction heating a load.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, an induction heating device according to the present invention includes a series connection body of a first switching element and a second switching element, and a first reverse conduction connected in parallel to the first switching element. An element, a second reverse conducting element connected in parallel to the second switching element, and a resonance including a heating coil and a resonance capacitor connected in parallel to the first switching element or the second switching element. And an inverter that receives a DC voltage and resonates by conduction of the first switching element and the second switching element, and exclusively controls conduction of the first switching element and the second switching element. Output control means for detecting the input current of the inverter or a voltage or current substantially equivalent to the input current of the inverter, wherein the first switch When the magnetic field generated by the heating coil inductively heats a load having a high conductivity and a low magnetic permeability, the resonance current flowing through the switching element or the first reverse conducting element has a cycle shorter than the drive period of the first switching element. A driving time ratio changing mode for gradually changing a driving time ratio of the first and second switching elements to increase an output of the inverter; And a drive frequency change mode in which the drive frequency is gradually changed and the output of the inverter is increased by making the drive time ratio of the second switching element substantially constant, wherein the output of the inverter is controlled by the drive time ratio change mode. And the drive time ratio change mode are combined so as to reach a predetermined output value from a low output value at the time of starting, so that a high conductivity such as aluminum or copper can be obtained. And low-permeability load can be induction-heated by suppressing the increase of the loss of the switching element, and shorten the time of the soft-start operation from the start of the inverter to the set power, making the switching element hard to break down. An induction heating device with good controllability can be provided.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 includes a series connection of a first switching element and a second switching element, a first reverse conducting element connected in parallel to the first switching element, and the second switching element. A second reverse conducting element connected in parallel to the element, a resonance circuit including a heating coil and a resonance capacitor connected in parallel to the first switching element or the second switching element, and a DC voltage. An inverter that receives and resonates by conduction between the first switching element and the second switching element, output control means that exclusively controls conduction of the first switching element and the second switching element, and the inverter Output detecting means for detecting an input current or a voltage or current substantially equivalent thereto, wherein the first switching element or the first reverse A resonance current flowing through the element has a heating mode in which when a magnetic field generated by the heating coil inductively heats a load having high conductivity and low magnetic permeability, resonance occurs in a cycle shorter than a driving period of the first switching element. The output control means includes: a drive time ratio change mode for gradually changing a drive time ratio of the first and second switching elements to increase an output of the inverter; and a drive time of the first and second switching elements. A drive frequency changing mode for gradually increasing the output of the inverter by gradually changing the drive frequency while keeping the ratio substantially constant, and combining the output of the inverter with the drive time ratio change mode and the drive time ratio change mode. Thus, by reaching a predetermined output value from a low output value at the time of starting, the resonance frequency of the current supplied to the heating coil can be reduced. , Can be lowered driving frequency of the switching element, a high electrical conductivity, such as aluminum and it is possible to inductively heat the load of low permeability, it is possible to reduce the switching loss of the switching element.
[0012]
Moreover, since the output of the inverter reaches a predetermined output value from a low output value at the time of starting by combining the drive time ratio change mode and the drive time ratio change mode, load detection can be performed accurately and stably. The output of the inverter can be quickly increased to the set output. Therefore, it is possible to prevent the switching element from being broken due to the occurrence of an abnormal voltage in the inverter at the time of startup, and to improve the usability. In the drive time ratio change mode, output control with a constant frequency can be performed.
[0013]
According to a second aspect of the present invention, in particular, the output control means operates in one of the drive time ratio change mode and the drive frequency change mode during a period from the low output value at start-up to a predetermined output value. By providing a period for increasing the output of the inverter only, the output control characteristic is simplified in this period, so that control is facilitated and the control output is easily stabilized.
[0014]
According to a third aspect of the present invention, in particular, the output control means changes the output of the inverter from the low output value at startup to a predetermined output value while alternately shifting to the drive time ratio change mode and the drive frequency change mode. By doing so, fine output control can be performed in response to a change in output at the resonance frequency of the inverter resonance circuit, and a predetermined output value can be quickly reached.
[0015]
According to a fourth aspect of the present invention, in particular, the output control means increases the output of the inverter by changing the drive driving time ratio of the first switching element and the second switching element at the time of start-up, and increases the output of the inverter in the middle. By changing the driving frequency of the inverter by changing the driving frequency of the first switching element and the second switching element while keeping the time ratio substantially constant, by changing the driving time ratio at the time of starting, the output change An abnormal load can be detected in a state where the output is small by reducing the speed. Further, by changing the drive frequency while keeping the drive time ratio substantially constant, a large output change is easily obtained, so that the time for increasing the output can be shortened. When changing the drive time ratio, the drive frequency can be fixed.
[0016]
According to a fifth aspect of the present invention, in particular, the output control means sets the drive time ratio to the predetermined drive time in the drive time ratio change mode during a period from the low output value at the time of starting to the predetermined output value. When the time ratio is exceeded, by shifting to the drive frequency change mode, the control for shifting from the drive time ratio change mode to the drive frequency change mode can be easily performed, so that it can be easily realized by a microcomputer or the like.
[0017]
According to a sixth aspect of the present invention, in particular, the output control means discretely increases the drive frequency in a variation range larger than the immediately preceding variation range during a period from the low output value at start-up to the predetermined output value. Change the drive time ratio at the same time as increasing the output of the inverter, and discretely changing the drive time ratio with a change width larger than the immediately preceding change width, so that the output near the resonance frequency of the inverter increases (drive frequency). Without switching, it is possible to make a transition to a region in which control is performed discretely and stably at a low frequency of another output, so that an excessive voltage or current duty is prevented from being applied to the switching element, and output control is performed. be able to.
[0018]
According to a seventh aspect of the present invention, in particular, the output control means sets the first switching element and the second switching element such that the driving period of the first switching element is shorter than the resonance period of the resonance current at the time of startup. When the heating output is increased by changing the drive time ratio of the element, and reaches a predetermined drive time ratio, the drive period of the first switching element is discretely extended to be longer than the cycle of the resonance current and to have a low output value. A state in which the output near the resonance frequency of the inverter increases by gradually increasing the drive period and changing the drive frequency from the low output value to the predetermined output value after changing the drive period. It is possible to make a transition to a region in which control is performed discretely and stably at a low frequency of other output without passing through, so that excessive voltage or current duty is applied to the switching element. Sealed, it is possible to perform the output control.
[0019]
In addition, in the invention according to claim 8, the output control means gradually increases the output in the frequency change mode, and the output value of the inverter is smaller than the set output value by the output of the output detection means. After detecting that the value has been reached, the mode is changed to the drive time ratio change mode and the output is gradually increased, so that the output is increased in a short time by the frequency change mode and the drive time ratio change mode is set before the set output. Then, the output is finely changed, so that the power does not greatly exceed the set output, and no excessive load is applied to each component such as the switching element, and a highly reliable induction heating device can be obtained.
[0020]
According to a ninth aspect of the present invention, in particular, the output control means has a first output fixed mode in which the output is performed at a drive frequency and a drive time ratio that are substantially the minimum output for a predetermined period of time after the inverter is started. The current is stable and highly reliable control can be performed.
[0021]
According to a tenth aspect of the present invention, in particular, after the output control means discretely lowers the drive frequency or the drive time ratio with a change width larger than the immediately preceding change width, the output control means sets the drive frequency and the drive time for a predetermined time. By having the second output fixed mode in which the output of the ratio is fixed, it does not go through a state where the output near the resonance frequency of the inverter is increased (drive frequency), and is discretely and stably set to another low output frequency. Since it is possible to make a transition to a region where control is performed, it is possible to prevent output of an excessive duty or current from being applied to the switching element and to perform output control.
[0022]
The invention according to claim 11 further includes a movement detecting means for detecting a lift or a deviation of the load when the load having a high electric conductivity and a low magnetic permeability is induction-heated, and the output control means includes: The time interval at which the drive frequency is changed in the drive frequency change mode when the detecting means detects the lifting or displacement of the load is the driving frequency when the movement detecting means does not detect the lifting or displacement of the load. By setting the drive frequency in the change mode longer than the time interval for changing the drive frequency, the time during which the output is fixed is increased, and the floating or displacement of the load when the load having high conductivity and low magnetic permeability is induction-heated is detected. The detection accuracy of the movement detecting means can be improved, and when a load of another material (for example, a magnetic small object load) is used, the speed of the load detection is increased, and the load is left in the detection state. The temperature rise of the load in the case can provide an induction heating apparatus having high safety, such as inhibiting.
[0023]
According to a twelfth aspect of the present invention, in particular, the output control means inputs the detection output of the output detection means and causes the output of the inverter to reach a set output based on the detection output. Is changed and the set output is not reached even when the drive time ratio is changed within a predetermined range, the drive frequency is changed to reach the set output. Even if the output power fluctuates greatly, it is possible to quickly obtain a stable set power by changing the drive frequency, and to suppress the fluctuation range of the output by changing the drive time ratio near the set output. Transient excessive voltage or current is not applied to each component such as the switching element, and a highly reliable induction heating device can be obtained.
[0024]
In addition, the invention according to claim 13 is particularly advantageous when the output control means is in the first output fixed mode or the time ratio change mode in a period in which the output control means reaches a predetermined output value from a low output value at startup. Since the low output state is maintained for a predetermined period of time by maintaining the small object detection unit that determines that the normal heating operation is not performed when the detection unit exceeds a predetermined value (maintenance includes a state with a small change width). In addition, it is possible to provide an induction heating device that can accurately detect small objects, does not apply excessively large voltage or current to each component such as a switching element, and has few failures.
[0025]
In addition, the invention according to claim 13 is particularly advantageous when the output control means is in the first output fixed mode or the time ratio change mode in a period in which the output control means reaches a predetermined output value from a low output value at startup. When the detection means exceeds a predetermined value, it is determined that an abnormal state has occurred and the normal heating operation is not performed, so that excessive excessive voltage or current is not applied to each component such as the switching element, An induction heating device with less failure can be provided.
[0026]
Further, in the frequency change mode in a period in which the output control means reaches a predetermined output value from a low output value at the time of starting, the output control means may detect the output detection means until the predetermined frequency is reached. When the output does not reach the predetermined value, by having the accessory detection means for determining that the accessory does not perform the normal heating operation, a load that cannot be heated due to a small diameter can be detected and stopped.
[0027]
The invention according to claim 15 is particularly advantageous when the output control means controls the output of the output detection means when the output frequency is controlled at a drive frequency within a predetermined frequency range (an output of the inverter should be equal to or more than a predetermined value). Is smaller than a predetermined value, it is easy to use because it can always detect small items during use by using small object detection means, and it is easy to use. And a reliable induction heating device can be provided at a low cost by a simple method.
[0028]
In addition, the invention according to claim 16 has a simple and inexpensive configuration, in which the output detection means is an input current detection means for detecting the input current of the inverter, thereby accurately detecting the effective power of the inverter. The output detecting means required for the inventions of claims 1 to 15 can be realized.
[0029]
【Example】
(Example 1)
FIG. 1 is a diagram showing a circuit configuration of the induction heating device of the present embodiment. The power supply 1 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 2 that is a bridge diode that performs full-wave rectification. A first smoothing capacitor 3 is connected between output terminals of the rectifier circuit 2. A series connection of the choke coil 5 and the second switching element 7 is further connected between the output terminals of the rectifier circuit 2. The heating coil 12 is disposed so as to face an aluminum pot 13 which is an object to be heated (load).
[0030]
Reference numeral 4 denotes an inverter (excluding the heating coil 12). The low potential side terminal (emitter) of the second smoothing capacitor 11 is connected to the negative terminal of the rectifier circuit 2, and the high potential side terminal of the second smoothing capacitor 11 is The first switching element (IGBT) 6 is connected to a high potential side terminal (collector), and the first switching element (IGBT) 6 has a low potential side terminal (emitter) connected to the choke coil 5 and the second switching element (IGBT). ) 7 is connected to the connection point with the high potential side terminal (collector). A series connection of the heating coil 12 and the resonance capacitor 10 is connected to the second switching element 7 in parallel.
[0031]
The first diode 8 (first reverse conducting element) is connected in antiparallel to the first switching element 6 (connecting the cathode of the first diode 8 and the collector of the first switching element 6), and Is connected to the second switching element 7 in an anti-parallel manner.
[0032]
Reference numeral 14 denotes current detection means for detecting an input current flowing from the power supply 1. Output control means 15 outputs a signal to the gates of the first switching element 6 and the second switching element 7 in accordance with the output of the current detection means 14. Is output.
[0033]
The operation of the induction heating device configured as described above will be described below. The power supply 1 is full-wave rectified by a rectifier circuit 2 and supplied to a first smoothing capacitor 3 connected to an output terminal of the rectifier circuit 2. The first smoothing capacitor 3 functions as a supply source for supplying a high-frequency current to the inverter.
[0034]
The first switching elements 6 on the high potential side and the second switching elements 7 on the low potential side are driven alternately and mutually exclusively. While the second switching element 7 is being driven, resonance occurs in a closed circuit formed by the (second switching element 7 or the second diode 9), the heating coil 12, and the resonance capacitor 10, and the first switching is performed. While the element 6 is being driven, resonance occurs in a closed circuit formed by the second smoothing capacitor, the first switching element 6 (or the first diode 8), the heating coil 12, and the resonance capacitor 10. When the second switching element 7 is turned off, the magnetic energy stored in the choke coil 5 moves to the second smoothing capacitor 11, so that the voltage of the second smoothing capacitor 11 is boosted. , Vibration can be maintained, and a load of low resistance and low magnetic permeability such as aluminum can be induction-heated with high output.
[0035]
In the present embodiment, the driving time of the first switching element 6 and the driving time of the second switching element 7 are given outputs (2 kW in the present embodiment), and the resonance current flowing through the heating coil 12 and the resonance capacitor 10 respectively. Since the impedance of the heating coil 12 and the resonance capacitor 10 is set so as to be approximately 2/3 of the resonance period of the above, if the driving frequency is approximately 20 kHz, the frequency of the resonance current is approximately 60 kHz.
[0036]
FIG. 2A is a diagram illustrating characteristics of the driving frequency and the input power of the first switching element 6 and the second switching element 7. The drive time ratio between the two switching elements is fixed at about 1: 1. Assuming that the resonance frequency of the heating coil 12 and the resonance capacitor 10 is fc, when the driving frequencies are fc / 2 and fc / 3, resonance by the second harmonic and the third harmonic occurs, respectively, and the input as shown in FIG. Power characteristics. In this embodiment, the driving frequency of the first switching element 6 and the second switching element 7 is reduced to about one third of the resonance frequency of the current flowing through the heating coil 12 by setting the driving frequency to around fc / 3. This realizes efficient induction heating with small switching loss.
[0037]
In the case of aluminum or copper, the Q of the resonance between the heating coil and the resonance capacitor in a state where the load is magnetically coupled is large, and therefore, as shown in FIG. Is changed (increased).
[0038]
FIG. 2B is a diagram showing the relationship between the on-time of the second switching element 7 and the input power when the driving frequency of the first switching element 6 and the second switching element 7 is substantially constant (20 kHz). is there. As shown in this figure, in the present embodiment, a heating output of about 2 kW is obtained when the ON time of the second switching element 7 is around 1/2 of the driving cycle (the driving time ratio is about 1/2). If the drive period of the second switching element is shortened from the nearby peak, the output can be reduced linearly. Therefore, if the lower limit Tonmin and the upper limit Tonmax of the drive time or the drive time ratio limiter are set as shown in FIG. 2B, stable control can be performed.
[0039]
FIG. 3 is a diagram illustrating a soft-start operation from the start of the inverter to the time when the output of the inverter 10 reaches the set power. The solid line indicates a change in the drive frequency over time, and the broken line indicates a change in the drive time ratio. . As shown in FIG. 3, after starting, the output control means 15 sets the drive frequency of the first switching element 6 and the second switching element 7 constant (about 36 kHz), and sets the drive time during which the second switching element 7 is turned on. Is gradually increased (the drive time ratio of the second switching element 7 to the first switching element 6 is gradually increased) to enter a first drive time ratio change mode. In the first drive time ratio change mode, the output control means 15 extends the drive time in 0.1 microsecond units at time unit intervals (about 10 milliseconds) synchronized with the power supply 1. Thereafter, when the drive time ratio reaches a predetermined ratio (1/4), the drive frequency is discretely changed at a predetermined ratio (3/4). For example, when the driving frequency is about 33 kHz, the frequency is changed to about 24 kHz.
[0040]
As a result, from the low output region (indicated by the point P) near the valley on the high frequency side (right side in FIG. 2) of fc / 2 shown in FIG. 2A, the low output region between fc / 3 and fc / 2 ( (Indicated by a point M), and thereafter, the mode shifts to the first drive frequency change mode, in which the drive time ratio is kept constant until the set output is reached, the drive frequency is gradually lowered, and the output is increased. Let it. Therefore, it is possible to avoid the high output area near fc / 2 and shift to the low output area near fc / 3.
[0041]
As described above, according to the present embodiment, the drive frequency and the drive time ratio of the first switching element 6 and the second switching element 7 of the inverter 4 for heating a load having low resistance and low magnetic permeability such as aluminum are used. By alternately performing soft-start control in both modes, a set output can be reliably obtained near fc / 3 without entering a high output region near fc / 2. In addition, the soft start can be completed in the same time as when power is controlled by either the drive frequency or the drive time ratio of the output of the resonance frequency, and an induction heating device with good controllability can be realized. is there.
[0042]
Further, the output control means 15 in this embodiment can be easily realized using a microcomputer.
[0043]
In the above embodiment, the induction heating cooker has been described. However, the present invention can be applied to other types of induction heating devices such as an iron and a water heater for heating a material having high conductivity and low magnetic permeability such as aluminum.
[0044]
In the above embodiment, a half-bridge type inverter having two switching elements has been described as shown in FIG. 1, but the invention is not limited to this. The present invention provides at least a series connection of a first switching element and a second switching element, a first reverse conducting element connected in parallel to the first switching element, and a parallel connection to the second switching element. A second reverse conducting element connected thereto, and a first switching element or a resonance circuit including a resonance capacitor connected in parallel to the second switching element and including a resonance capacitor; What is necessary is just to have an inverter which resonates by conduction between the switching element and the second switching element, and output control means for exclusively controlling conduction of the first switching element and the second switching element. Can be applied to the inverters.
[0045]
(Example 2)
FIG. 4 is a diagram illustrating a soft start operation according to the second embodiment. When shifting from the first drive time ratio change mode to the first drive frequency change mode, only the drive frequency is discretely changed, but the drive time ratio is also discretely changed at the same time at a predetermined ratio or a predetermined value. To change it. For example, if the drive time ratio is 1/4, it is changed to 1/3.
[0046]
As described above, according to the present embodiment, even when the set power is large, the set power can be quickly reached, and in the region where the output of the inverter is small, the position of the resonance frequency is searched. However, by discretely changing the drive frequency and the drive time ratio, switching loss is reduced and reliability is improved.
[0047]
In the frequency characteristic of the output, the search for the peak or the valley can be performed by changing the frequency and observing the increase or decrease of the output.
[0048]
(Example 3)
FIG. 5 is a diagram illustrating a soft start operation according to the third embodiment. In the first and second embodiments, the output setting unit 15 switches from the first drive frequency change mode to the second drive time ratio when detecting an input current that is slightly smaller than the set output after shifting to the first drive frequency change mode. By shifting to the change mode, the input current of the inverter does not greatly exceed the set output.
[0049]
As described above, according to the present embodiment, even when the set power is large, the output of the inverter 4 can quickly reach the set output in the first drive frequency change mode, and the set power is increased. Since it does not exceed this, an excessive load is not applied to the power components constituting the inverter such as the switching element, and a highly reliable induction heating device can be provided.
[0050]
(Example 4)
FIG. 6 is a diagram illustrating a soft start operation according to the fourth embodiment.
[0051]
A first output fixing mode for fixing the output for a predetermined time (0.1 second) after starting the inverter with the driving frequency and the driving time ratio of the first and second switching elements, which is the minimum output of the inverter 4, is added. It was done.
[0052]
As described above, according to the present embodiment, after starting, until the input current is stabilized at the minimum value, or by maintaining the output for a predetermined time, and delaying output control such as soft start, a stable load is obtained. The control operation such as the detection operation can be realized.
[0053]
(Example 5)
FIG. 7 is a diagram illustrating a soft start operation in the fifth embodiment.
[0054]
Similar to the fourth embodiment, when the drive frequency and the drive time ratio are discretely changed, a second output fixing mode for fixing the output for about 0.1 second after the change is added. By delaying the control until the output of the input detection means is stabilized, stable output control can be performed in the operation in the first drive frequency change mode.
[0055]
(Example 6)
FIG. 8 is a diagram illustrating a circuit configuration of the sixth embodiment.
[0056]
Since the configuration is almost the same as that of FIG. 1 described in the first embodiment, only the differences will be described.
[0057]
Reference numeral 16 denotes voltage detection means for detecting the voltage of the first resonance capacitor 10, reference numeral 17 denotes movement detection means for detecting the lifting or displacement of the load based on the output of the voltage detection means 16, and movement detection means 17 includes a soft start. The state of the output change at that time is observed to detect the lifting or deviation of the load. In the present embodiment, when the output is increased during the soft start period, it is detected that the voltage change within a certain period of time becomes smaller than before at a certain point in time, and the occurrence of the floating or deviation of the load has been detected. Detected. The voltage detecting means 16 can also detect that the load is lifted or shifted by detecting the input current.
[0058]
FIG. 9 is a diagram illustrating a soft start operation according to the sixth embodiment.
[0059]
The second drive frequency change mode after the movement detection means is operated is higher than the drive frequency in the first drive frequency change mode in which the movement detection means 17 is not operated by adding the second drive frequency change mode. The detection accuracy of the movement detection means can be improved by lengthening the time interval for changing.
[0060]
(Example 7)
FIG. 10 is a diagram illustrating a driving frequency and a driving time ratio at the time of power control after reaching the set power. By increasing the drive time ratio from t0 to t1, the power is gradually increased. At t1, the drive time ratio becomes the maximum of the control range, and the drive frequency is reduced in the minimum control unit (0.1 microsecond in cycle). Further, the drive time ratio is increased from t2 to t3, the power is gradually increased, and when the set power is exceeded at t3, the drive time ratio is reduced until time t4.
[0061]
At t4, the drive time ratio becomes the minimum of the control range, and the drive frequency is increased in the minimum control unit (0.1 microsecond in cycle). As described above, fine power control can be performed by controlling the driving frequency and the driving time ratio.
[0062]
(Example 8)
FIG. 11 is a circuit diagram of an induction heating apparatus according to an eighth embodiment of the present invention, which is basically the same as that of the first embodiment. Therefore, only different points will be described.
[0063]
In FIG. 11, reference numeral 18 denotes a small object detecting means for detecting small objects at the time of startup by the output of the current detecting means 14, and causing the output control means 15 to stop the inverter.
[0064]
FIG. 12 is a diagram illustrating the relationship between the drive time of the second switching element 7 and the input current. When the time drive ratio is increased, the difference in the input current causes a change in the input current to cause no load, a knife, a fork, or the like. Small object load can be detected.
[0065]
In the present invention, when the inverter is started, the drive frequency is kept constant at the drive frequency and the drive time ratio at which the output is minimized, and in the drive time ratio change mode in which the drive time ratio is gradually increased, the characteristic shown in FIG. By using this, an accurate small object detecting means is provided.
[0066]
(Example 9)
The ninth embodiment has the same configuration as the eighth embodiment. In FIG. 9, the output control unit 15 determines that the frequency is smaller than a predetermined frequency (30 KHz) in the first frequency change mode. It was done.
[0067]
During startup of the inverter 4, a load having a small diameter that cannot be heated is detected and the inverter 4 is stopped, so that it is possible to provide an induction heating device that is safe and has few troubles.
[0068]
(Example 10)
The tenth embodiment has the same configuration as that of the eighth embodiment. When the output of the current detecting means 14 becomes lower than a predetermined value after the inverter 4 starts and detects a predetermined power or more, it is determined to be a small object. Things.
[0069]
If the load is taken while the inverter is operating at the set power and the output of the current detection means 14 immediately drops, the inverter 4 is stopped, so that a safe and less troublesome induction heating device can be provided.
[0070]
Instead of the current detecting means 15, an output detecting means corresponding thereto may be configured to detect the current or voltage of the inverter.
[0071]
【The invention's effect】
As described above, according to the present invention, a load having high conductivity and low magnetic permeability such as aluminum or copper can be induction-heated while suppressing an increase in the loss of the switching element, and the driving frequency of the switching element can be reduced. By combining variable control and variable control of the switching element drive time ratio to perform output control, it is possible to easily perform fine power control using a microcomputer, and to shorten the time from startup to output stabilization and It is possible to realize an induction heating device in which the switching element does not easily break down and has good controllability.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an induction heating cooker according to a first embodiment.
FIG. 2A is a diagram showing a driving frequency and an input power characteristic of the induction heating cooker according to the first embodiment.
(B) A diagram showing the drive time ratio and the input power characteristics of the induction heating cooker according to the first embodiment.
FIG. 3 is a diagram showing operation waveforms of the induction heating cooker according to the first embodiment.
FIG. 4 is a diagram showing a soft start operation of the induction heating cooker according to the first embodiment.
FIG. 5 is a diagram showing a soft start operation of the induction heating cooker according to the second embodiment.
FIG. 6 is a diagram showing a soft start operation of the induction heating cooker according to the third embodiment.
FIG. 7 is a diagram showing a soft start operation of the induction heating cooker according to the fourth embodiment.
FIG. 8 is a diagram showing a soft start operation of the induction heating cooker according to the fifth embodiment.
FIG. 9 is a circuit diagram of an induction heating cooker according to a sixth embodiment.
FIG. 10 is a diagram showing a soft start operation of the induction heating cooker according to the sixth embodiment.
FIG. 11 is a circuit diagram of an induction heating cooker according to an eighth embodiment.
FIG. 12 is a diagram showing a driving time ratio and an input power characteristic of the induction heating cooker according to the eighth embodiment.
FIG. 13 is a circuit diagram of a conventional induction heating device.
FIG. 14A is a diagram showing a driving frequency and an input power characteristic of a conventional induction heating device.
(B) A diagram showing a drive time ratio and an input power characteristic of a conventional induction heating device.
FIG. 15 is a diagram showing a soft start operation of a conventional induction heating device.
[Explanation of symbols]
4 Inverter
6. First switching element
7. Second switching element
12 heating coil
13 Load
14 Current detection means
15 Output control means

Claims

A series connection of a first switching element and a second switching element, a first reverse conducting element connected in parallel to the first switching element, and a first reverse conducting element connected in parallel to the second switching element. A second switching element, and a resonance circuit including a heating coil and a resonance capacitor connected in parallel to the first switching element or the second switching element. An inverter that resonates by conduction between the element and the second switching element; an output control means that exclusively controls conduction between the first switching element and the second switching element; and an input current of the inverter or substantially equivalent thereto. Output detection means for detecting a voltage or a current, and a resonance current flowing through the first switching element or the first reverse conducting element. A heating mode in which when a magnetic field generated by the heating coil inductively heats a load having a high conductivity and a low magnetic permeability, the heating mode resonates in a cycle shorter than a driving period of the first switching element, and the output control means includes: A drive time ratio change mode in which the drive time ratio of the first and second switching elements is gradually changed to increase the output of the inverter, and a drive time ratio of the first and second switching elements is made substantially constant. A drive frequency change mode in which the drive frequency is gradually changed to increase the output of the inverter, and the output of the inverter is reduced by combining the drive time ratio change mode and the drive time ratio change mode to reduce the start-up time. An induction heating device that reaches an output value to a predetermined output value.

The output control means is provided with a period in which the output of the inverter is increased only in one of the drive time ratio change mode and the drive frequency change mode within a period from the low output value at start-up to a predetermined output value. The induction heating device according to claim 1.

3. The induction according to claim 1, wherein the output control means causes the output of the inverter to reach a predetermined output value from a low output value at the time of starting while alternately shifting to the drive time ratio change mode and the drive frequency change mode. Heating equipment.

The output control means increases the output of the inverter by changing the drive driving time ratio of the first switching element and the second switching element at the time of startup, and makes the driving time ratio substantially constant in the middle of the first switching element. The induction heating apparatus according to claim 3, wherein the drive frequency of the element and the second switching element is changed to increase the output of the inverter.

The output control means shifts to the drive frequency change mode when the drive time ratio exceeds the predetermined drive time ratio in the drive time ratio change mode during the period from the low output value at start-up to the predetermined output value. The induction heating device according to claim 3.

The output control means increases the output of the inverter by discretely changing the drive frequency within a range of a change from a low output value at start-up to a predetermined output value with a change width larger than the immediately preceding change width. The induction heating device according to any one of claims 1 to 5, wherein the drive time ratio is discretely changed with a change width larger than the immediately preceding change width.

The output control means increases the heating output by changing the driving time ratio between the first switching element and the second switching element so that the driving period of the first switching element is shorter than the resonance cycle of the resonance current at the time of startup. When a predetermined drive time ratio is reached, the drive period of the first switching element is discretely changed to be longer than the cycle of the resonance current and to have a low output value, and then the drive period is gradually increased. The induction heating device according to any one of claims 1 to 6, wherein the drive frequency is reduced to increase the output of the inverter from the low output value to a predetermined output value.

The output control means gradually increases the output in the frequency change mode, and after detecting from the output of the output detection means that the output value of the inverter has reached a predetermined output value smaller than the set output value, the driving time. The induction heating device according to any one of claims 1 to 7, wherein the output is gradually increased by shifting to a ratio change mode.

The induction heating device according to any one of claims 1 to 8, further comprising a first fixed output mode in which a drive frequency and a drive time ratio are output at a substantially minimum output for a predetermined time after the inverter is started.

The output control means discretely lowers the drive frequency or the drive time ratio by a change width larger than the immediately preceding change width, and then fixes the output of the drive frequency and the drive time ratio for a predetermined time. The induction heating device according to any one of claims 1 to 9, comprising:

When the load having high conductivity and low magnetic permeability is induction-heated, the load detection unit has a movement detection unit for detecting the lift or deviation of the load, and the output control unit detects that the movement detection unit detects the lift or deviation of the load. The time interval at which the drive frequency is changed in the drive frequency change mode is longer than the time interval at which the drive frequency is changed in the drive frequency change mode when the movement detecting means does not detect the lifting or displacement of the load. The induction heating device according to claim 1.

The output control means inputs the detection output of the output detection means, and after the output of the inverter reaches the set output based on the detection output, the output of the inverter changes and the drive time ratio is changed within a predetermined range. The induction heating device according to any one of claims 1 to 11, wherein when the set output does not reach the set output, the drive frequency is changed to reach the set output.

If the output control means is in the first output fixed mode or in the time ratio change mode within a period in which the output control means reaches a predetermined output value from a low output value at the time of starting, an abnormal state occurs when the output detection means exceeds a predetermined value. The induction heating device according to any one of claims 1 to 12, wherein it is determined that the heating has occurred and the normal heating operation is not performed.

In the frequency change mode in a period in which the output control means reaches a predetermined output value from a low output value at the time of starting, the output of the output detection means reaches a predetermined value before the output frequency reaches the predetermined frequency. The induction heating device according to any one of claims 1 to 13, further comprising a small object detection unit that determines that the small object does not perform the normal heating operation when the small object does not arrive.

15. The apparatus according to claim 1, further comprising: a small object detection unit that determines that the output is small when the output of the output detection unit is smaller than a predetermined value when the output control unit controls the driving frequency within a predetermined frequency range. The induction heating device according to claim 1.

The induction heating device according to any one of claims 1 to 15, wherein the output detection means detects an input current of the inverter.