JP4289002B2

JP4289002B2 - Induction heating device

Info

Publication number: JP4289002B2
Application number: JP2003120023A
Authority: JP
Inventors: 浩次新山; 裕二藤井; 泉生弘田; 貴宏宮内; 篤志藤田; 学高橋
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2002-04-24
Filing date: 2003-04-24
Publication date: 2009-07-01
Anticipated expiration: 2023-04-24
Also published as: JP2004006331A

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、整流回路と、前記整流回路の出力端に接続されたチョークコイル、前記チョークコイルにより昇圧された電圧が供給される平滑コンデンサ、前記平滑コンデンサの両端に接続された第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、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、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、及び前記第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を有し前記第１のスイッチング素子と第２のスイッチング素子が排他的に導通することにより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と前記共振回路が前記加熱コイルに供給する電流の共振周波数より前記スイッチング素子の駆動周波数が低くなるように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、前記出力制御手段は、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、前記駆動時間比を略一定にして徐々に駆動周波数を低下させ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、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と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周波数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、整流回路と、前記整流回路の出力端に接続されたチョークコイル、前記チョークコイルにより昇圧された電圧が供給される平滑コンデンサ、前記平滑コンデンサの両端に接続された第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、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、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、及び前記第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を有し前記第１のスイッチング素子と第２のスイッチング素子が排他的に導通することにより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と前記共振回路が前記加熱コイルに供給する電流の共振周波数より前記スイッチング素子の駆動周波数が低くなるように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、前記出力制御手段は、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、前記駆動時間比を略一定にして徐々に駆動周波数を低下させ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、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と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周波数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周波数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から駆動周波数変更モードへの移行と駆動周波数変更モードから駆動時間比変更モードへの移行とを交互に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が所定の駆動時間比に到達す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、駆動周波数が共振周波数付近になると入力電力が急峻に増加し前記共振周波数でピークとなり、前記共振周波数より高周波数側及び低周波数側の谷間付近で低出力領域となる前記駆動周波数と前記入力電力の特性において、出力制御手段は、前記高周波数側の前記谷間付近の低出力値で起動し、前記低周波数側の所定の出力値までインバータの出力を到達させる期間内において、起動後第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前記駆動時間比が所定の駆動時間比に到達すると前記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共振周波数付近の高出力領域を避け、前記低周波数側の谷間付近の低出力領域に移行させると同時に前記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してから前記駆動時間比を一定にして前記駆動周波数を徐々に低下させて前記インバータの出力を前記所定の出力まで上昇させることにより、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、駆動周波数が共振周波数付近になると入力電力が急峻に増加し前記共振周波数でピークとなり、前記共振周波数より高周波数側及び低周波数側の谷間付近で低出力領域となる前記駆動周波数と前記入力電力の特性において、出力制御手段は、前記高周波数側の前記谷間付近の低出力値で起動し、前記低周波数側の所定の出力値までインバータの出力を到達させる期間内において、起動後第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、前記第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しかつ前記低周波数側の谷間付近の低出力値になる前記駆動周波数と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前記駆動周波数を低下させ前記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、駆動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、駆動周波数変更モードで駆動周波数を所定の時間間隔で所定の傾きで低下させるとともに、前記移動検知手段が前記負荷の浮きまたはずれを検知後、駆動周波数を変化させる前記時間間隔を、前記駆動周波数変更モードにおける前記駆動周波数を変化させる前記時間間隔より長くしかつ前記駆動周波数の低下の傾きを前記駆動周波数変更モードにおける前記駆動周波数の低下の傾きより小さくした第２の駆動周波数変更モードになることにより、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知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駆動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駆動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、出力制御手段は、駆動周波数変更モードにおいて駆動周波数が所定の（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、駆動周波数が所定の値より低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加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）より低くなると、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]
BACKGROUND OF THE INVENTION
The present invention relates to an induction heating apparatus such as an induction heating cooker used in general homes, offices, restaurants, factories, and the like, a water heater using induction heating, and a heating apparatus.
[0002]
[Prior art]
An induction heating cooker will be described with reference to FIG. 13 as an example of a conventional induction heating device. The power source 31 is a 200V commercial power source, rectified by a rectifier circuit 32 that is a bridge diode, and converted into DC power by a smoothing capacitor 33. An inverter 34 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 resonant capacitor 39. The first switching element 35 and the second switching element 36 are driven to generate a high-frequency magnetic field 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, and the 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, thereby providing power. To control. Here, the output control means 43 performs power control according to either the driving frequency or the driving time ratio of the first switching element 35 and the second switching element 43.
[0004]
FIG. 14A is a graph showing drive frequency-input power characteristics, and the output control means 43 uses the characteristics shown in FIG. 14A to keep the drive time ratio of the switching elements constant and drive frequency. 14 (B) is a graph showing the drive time ratio-input power characteristics, and the output control means 43 uses the characteristics shown in FIG. 14 (B). The 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 that reaches the set power when the output control means 43 controls the drive time ratio to perform power control. When starting up the inverter, the first switching element and the second switching element are driven at a driving time ratio that provides the minimum output, and the first driving time ratio changing mode is provided in which the driving time is increased by a certain time. Yes.
[0006]
Moreover, the technique which concerns on the induction heating cooking apparatus which heats aluminum load, suppressing the loss of a switching element is proposed (for example, refer patent document 1).
[0007]
[Patent Document 1]
JP 2001-160484 A
[0008]
[Problems to be solved by the invention]
In the induction heating device having the conventional configuration, 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 increases due to low resistance, and the input to the drive frequency Power change is large, power control by controlling the drive frequency and power control by controlling the drive time ratio for fine power control are also required, and it takes a long time to reach the set power after starting the inverter There was a problem of becoming. Further, the technique described in Patent Document 1 has a problem in output controllability and is unusable.
[0009]
The object of the present invention is to reduce the time to reach the set power to the same or less than the start time of the inverter that heats the conventional iron-based load, and to improve the controllability, such as aluminum and other low resistance and low magnetic permeability materials. Provided is a method for controlling an induction heating apparatus for induction heating a load of
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the induction heating device of the present invention comprises: A rectifier circuit, a choke coil connected to the output terminal of the rectifier circuit, a smoothing capacitor to which a voltage boosted by the choke coil is supplied, and connected to both ends of the smoothing capacitor Series connection of first switching element and second switching element body, A first reverse conducting element connected in parallel to the first switching element; Child, A second reverse conducting element connected in parallel to the second switching element; Child, 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. The road Yes Before First switching element and second switching element Is exclusively Continuity To do By When a high conductivity and low permeability load such as aluminum is induction-heated, the drive frequency of the switching element becomes lower than the resonance frequency of the current supplied to the heating coil by the resonance circuit. Resonating inverter, the first switching element and the second switching element Lead Output control means for controlling the output, and output detection means for detecting the input current of the inverter or a voltage or current substantially equivalent thereto. ,in front The output control means includes the first Switching element and said A driving time ratio change mode in which the driving time ratio of the second switching element is gradually changed to increase the output of the inverter; Memoir The drive frequency is gradually increased with the dynamic time ratio substantially constant. Reduce Driving frequency change mode for increasing the output of the inverter, When induction heating a load with high conductivity and low permeability such as aluminum The output of the inverter, the drive time ratio change mode and the drive frequency By combining the change modes to reach a predetermined output value from the low output value at startup, high conductivity and low magnetic permeability loads such as aluminum and copper suppress induction of increase in switching element loss and induction heating In addition, it is possible to provide an induction heating device that shortens the time of the soft start operation from the start of the inverter until the set power is reached, and that is less likely to cause the switching element to fail and has good controllability.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The invention described in claim 1 A rectifier circuit, a choke coil connected to the output terminal of the rectifier circuit, a smoothing capacitor to which a voltage boosted by the choke coil is supplied, and connected to both ends of the smoothing capacitor Series connection of first switching element and second switching element body, A first reverse conducting element connected in parallel to the first switching element; Child, A second reverse conducting element connected in parallel to the second switching element; Child, 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. The road Yes Before First switching element and second switching element Is exclusively Continuity To do By When a high conductivity and low permeability load such as aluminum is induction-heated, the drive frequency of the switching element becomes lower than the resonance frequency of the current supplied to the heating coil by the resonance circuit. Resonating inverter, the first switching element and the second switching element Lead Output control means for controlling the output, and output detection means for detecting the input current of the inverter or a voltage or current substantially equivalent thereto. ,in front The output control means includes the first Switching element and said A driving time ratio change mode in which the driving time ratio of the second switching element is gradually changed to increase the output of the inverter; Memoir The drive frequency is gradually increased with the dynamic time ratio substantially constant. Reduce Driving frequency change mode for increasing the output of the inverter, When induction heating a load with high conductivity and low permeability such as aluminum The output of the inverter, the drive time ratio change mode and the drive frequency By combining the change modes and reaching a predetermined output value from the low output value at the time of startup, the switching element drive frequency can be made lower than the resonance frequency of the resonance current of the current supplied to the heating coil. It is possible to inductively heat a load having conductivity and low permeability, and to reduce switching loss of the switching element.
[0012]
Also, the inverter output is driven with the drive time ratio change mode. frequency Since the change mode is combined to reach the predetermined output value from the low output value at the time of start-up, the load can be detected accurately and stably, and the output of the inverter can be rapidly increased to the set output. Accordingly, it is possible to prevent the switching element from being destroyed due to an abnormal voltage generated in the inverter at the time of start-up, and at the same time improve the usability. In the drive time ratio change mode, output control at a constant frequency can be performed.
[0013]
In the invention according to claim 2, in particular, the output control means is in either one of the drive time ratio change mode and the drive frequency change mode within a period in which the low output value at the time of start-up reaches a predetermined output value. By providing a period for increasing the output of the inverter only, the output control characteristics are simplified during this period, so that the control is facilitated and the control output is easily stabilized.
[0014]
In the invention according to claim 3, in particular, the output control means includes a drive time ratio change mode. From Drive frequency change mode And transition from drive frequency change mode to drive time ratio change mode Alternating West However, by allowing the output of the inverter to reach a predetermined output value from the low output value at the time of startup, fine output control can be performed corresponding to the output change at the resonance frequency of the resonance circuit of the inverter. Further, it is possible to quickly reach a predetermined output value.
[0015]
According to a fourth aspect of the present invention, in particular, the output control means includes the first switching element and the second switching element at startup. The drive of The inverter output is increased by changing the dynamic time ratio, and the drive time ratio is made substantially constant from the middle, and the drive frequency of the first switching element and the second switching element is changed to increase the output of the inverter. By startup To drive By changing the dynamic time ratio, it is possible to detect an abnormal load with a low output and a low output change speed. In addition, by changing the drive frequency while keeping the drive time ratio substantially constant, it is easy to obtain a large output change, so that the time for increasing the output can be shortened. Further, when changing the drive time ratio, the drive frequency can be made constant.
[0016]
Further, in the invention according to claim 5, the output control means is particularly in the drive time ratio change mode within the period for reaching the predetermined output value from the low output value at the time of startup. Of the first switching element and the second switching element. Drive time ratio is a predetermined drive time ratio To reach Then, 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, and can be easily realized by a microcomputer or the like.
[0017]
The invention of claim 6 is particularly When the drive frequency is close to the resonance frequency, the input power sharply increases and peaks at the resonance frequency, and the drive frequency and the input power become a low output region near the valley between the high frequency side and the low frequency side from the resonance frequency. In characteristics, The output control means is Near the valley on the high frequency side Low output value Start at the low frequency side Up to a predetermined output value Inverter output Within the time period to reach After starting Of the first switching element and the second switching element. Change the drive time ratio When the drive time ratio reaches a predetermined drive time ratio Above Change the drive frequency discretely with a change width greater than the previous change width. Above Avoid high power areas near the resonance frequency, On the low frequency side Move to low power area near the valley Done At the same time Above The drive time ratio is discretely changed with a change width larger than the previous change width. Then, the drive time ratio is made constant and the drive frequency is gradually lowered to increase the output of the inverter to the predetermined output. Therefore, it is possible to transit to a region where control is discretely and stably to a low frequency of other output without going through a state (drive frequency) in which the output near the resonance frequency of the inverter increases, so that the switching element Therefore, it is possible to prevent the application of excessive voltage or current duty to the output control.
[0018]
The invention according to claim 7 is particularly When the drive frequency is close to the resonance frequency, the input power sharply increases and peaks at the resonance frequency, and the drive frequency and the input power become a low output region near the valley between the high frequency side and the low frequency side from the resonance frequency. In characteristics, The output control means is With a low output value near the valley on the high frequency side Start-up Shi , After startup, within the period of reaching the output of the inverter to the predetermined output value on the low frequency side The heating output is increased by changing the driving time ratio of the first switching element and the second switching element so that the driving period of the first switching element is shorter than the resonance period of the resonance current, and the predetermined driving time ratio is obtained. When you reach Above The drive period of the first switching element is longer than the period of the resonance current Shi And On the low frequency side Low output value near the valley It becomes the drive frequency So that the drive period is gradually increased Above Reduce the drive frequency Above By increasing the output of the inverter from the low output value to a predetermined output value, the output in the vicinity of the resonance frequency of the inverter does not go through a state of increasing, and discretely and stably at a low frequency of the other output. Since it is possible to make a transition to a region where control is performed, output control can be performed by preventing an excessive voltage or current duty from being applied to the switching element.
[0019]
In the invention according to claim 8, the output control means is Drive The output is gradually increased by the frequency change mode, and after detecting that the output value of the inverter has reached a predetermined output value smaller than the set output value by the output of the output detection means, the mode shifts to the drive time ratio change mode. By gradually increasing the output, the output is increased in a short time by the frequency change mode, and the drive time ratio change mode is entered before the set output, and the output is slightly changed. Therefore, an excessive load is not applied to each component such as the switching element, and a highly reliable induction heating apparatus can be obtained.
[0020]
Further, in the ninth aspect of the invention, in particular, the output control means has the first output fixing mode in which the output is performed at the drive frequency and the drive time ratio at which the output becomes substantially minimum for a predetermined time after the inverter is started. The current is stable and reliable control is possible.
[0021]
In the invention according to claim 10, in particular, the output control means reduces the drive frequency or the drive time ratio discretely with a change width larger than the immediately preceding change width, and then for a predetermined time, drive frequency and drive time. By having the second output fixing mode for fixing the output of the ratio, the output in the vicinity of the resonance frequency of the inverter does not go through a state (driving frequency), and discretely and stably at a low frequency of other outputs Since it is possible to make a transition to a region where control is performed, output control can be performed by preventing an excessive voltage or current duty from being applied to the switching element.
[0022]
Further, the invention according to claim 11 has a movement detecting means for detecting the floating or deviation of the load when the high conductivity and low permeability load is inductively heated, and the output control means is In the drive frequency change mode, the drive frequency is decreased at a predetermined slope at predetermined time intervals, and The mobile inspection Knowledge Means detect floating or deviation of the load rear, Change drive frequency Above Before time interval Memoir In dynamic frequency change mode Above Change drive frequency Above Longer than time interval And the slope of the drive frequency drop is smaller than the slope of the drive frequency drop in the drive frequency change mode. did Enters the second drive frequency change mode As a result, the time during which the output is fixed is lengthened, and a moving detection that detects the floating or deviation of the load when a high conductivity and low permeability load is induction-heated. Knowledge The detection accuracy of the means can be improved, and in the case of loads of other materials (for example, magnetic accessory loads), the load detection speed is increased to suppress the temperature rise of the load when left in the detection state. A high induction heating device can be provided.
[0023]
Further, in the invention described in claim 12, in particular, 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 If the set output is not reached even if the drive time ratio is changed within a predetermined range due to the change of the drive frequency, the set output is reached by changing the drive frequency. Even if the output power fluctuates greatly, a stable set power can be obtained quickly by changing the drive frequency, and the fluctuation range of the output can be suppressed by changing the drive time ratio in the vicinity of the set output. A transient excessive voltage or current is not applied to each component such as a switching element, and a highly reliable induction heating device can be achieved.
[0024]
The invention according to claim 13 is particularly effective when the output control means is in the first output fixing mode or the time ratio change mode within a period in which the low output value at the time of startup reaches a predetermined output value. By having the accessory detection means that determines that the detection means does not perform normal heating operation when the detection means exceeds a predetermined value, the low output state is maintained for a predetermined time (the maintenance includes a state with a small change width). Therefore, it is possible to provide an induction heating device that can detect small objects with high accuracy and that does not apply excessive transient voltage or current to each component such as a switching element, and that has few failures.
[0025]
In the invention according to claim 13, particularly, the output control means is in the first output fixed mode or in the period in which the low output value at the time of startup reaches the predetermined output value. Drive When in the time ratio change mode, if the output detection means exceeds a predetermined value, it is judged that an abnormal state has occurred and the normal heating operation is not performed. Therefore, an induction heating apparatus with few failures can be provided.
[0026]
Further, the invention according to claim 14 is particularly within a period in which the output control means allows the low output value at the time of startup to reach a predetermined output value. Drive In the frequency change mode, heating is performed because the diameter is small by having the small object detecting means that determines that the normal heating operation is not performed when the output of the output detecting means does not reach the predetermined value until the predetermined frequency is reached. It is possible to stop by detecting a load that cannot be performed.
[0027]
Further, the invention according to claim 15 is particularly the output control means. Is the drive frequency in the drive frequency change mode. When controlling at a driving frequency within a predetermined frequency range (the output of the inverter should be greater than or equal to a predetermined value) Drive frequency Is more than the predetermined value Low Since there is an accessory detection means that determines that it is an accessory when it is detected, it can be always detected during use, so it is easy to use and no other detection means is required, so it is simple and inexpensive. Reliable guidance Addition A thermal device can be provided.
[0028]
In the invention of claim 16, in particular, 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, and with a simple and inexpensive configuration. The output detection 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 apparatus of this embodiment. The power source 1 is a 200V commercial power source that is a low-frequency AC power source, and is connected to the 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 the output terminals of the rectifier circuit 2. A series connection body 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 to face an aluminum pan 13 that is an object to be heated (load).
[0030]
4 is 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 the 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 body of the heating coil 12 and the resonance capacitor 10 is connected in parallel to the second switching element 7.
[0031]
The first diode 8 (first reverse conducting element) is connected in antiparallel to the first switching element 6 (the cathode of the first diode 8 and the collector of the first switching element 6 are connected), and the second Similarly, the diode 9 (second reverse conducting element) is connected in antiparallel to the second switching element 7.
[0032]
Reference numeral 14 denotes current detection means for detecting an input current flowing from the power source 1, and the output control means 15 sends signals 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 apparatus configured as described above will be described below. The power source 1 is full-wave rectified by a rectifier circuit 2 and supplied to a first smoothing capacitor 3 connected to the output terminal of the rectifier circuit 2. The first smoothing capacitor 3 serves as a supply source for supplying a high-frequency current to the inverter.
[0034]
The first switching element 6 on the high potential side and the second switching element 7 on the low potential side are alternately and exclusively driven. While the second switching element 7 is being driven, it resonates in a closed circuit formed by the (second switching element 7 or the second diode 9), the heating coil 12, and the resonant capacitor 10, and the first switching 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 and the voltage of the second smoothing capacitor 11 is boosted. The vibration can be maintained by enlarging the pressure, and a low resistance, low permeability load such as aluminum can be induction-heated at a high output.
[0035]
In this embodiment, the driving time of the first switching element 6 and the driving time of the second switching element 7 are the predetermined outputs (2 kW in this embodiment), and the resonance currents flowing in the heating coil 12 and the resonance capacitor 10 respectively. Since the impedances of the heating coil 12 and the resonance capacitor 10 are set so as to be approximately 2/3 of the resonance period, if the drive frequency is about 20 kHz, the frequency of the resonance current is about 60 kHz.
[0036]
FIG. 2A is a diagram illustrating the drive frequency and input power characteristics of the first switching element 6 and the second switching element 7. The drive time ratio of both switching elements is fixed at about 1: 1. When the resonance frequency of the heating coil 12 and the resonance capacitor 10 is fc, resonance is caused by the second harmonic and the third harmonic when the drive frequencies are fc / 2 and fc / 3, respectively, and the input as shown in FIG. Power characteristics. In the present embodiment, the drive frequency of the first switching element 6 and the second switching element 7 is lowered to about one third of the resonance frequency of the current flowing through the heating coil 12 by setting the drive frequency in the vicinity of fc / 3. This enables induction heating with low switching loss and high efficiency.
[0037]
In addition, in the case of aluminum, copper, etc., since the Q of resonance between the heating coil and the resonance capacitor in a state where the load is magnetically coupled is large, the input power steeply near each peak with respect to the frequency as shown in FIG. Changes (increases).
[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 made substantially constant (20 kHz). is there. As shown in this figure, in this embodiment, a heating output of about 2 kW is obtained when the on-time of the second switching element 7 is about 1/2 of the driving cycle (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, stable control can be performed by setting the lower limit Tonmin and the upper limit Tonmax of the drive time or the drive time ratio limiter as shown in FIG.
[0039]
FIG. 3 is a diagram showing 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 shows the change of the drive frequency with time, and the broken line shows the change of the drive time ratio. . As shown in FIG. 3, the output control means 15 keeps the driving frequency of the first switching element 6 and the second switching element 7 constant (about 36 kHz) after starting, and the driving time during which the second switching element 7 is turned on. Is gradually increased (the driving time ratio of the second switching element 7 with respect to the first switching element 6 is gradually increased). When in the first drive time ratio change mode, the output control means 15 increases the drive time in units of 0.1 microseconds 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 the predetermined ratio (3/4). For example, when the drive frequency is about 33 kHz, the frequency is changed to about 24 kHz.
[0040]
As a result, a low output region between fc / 3 and fc / 2 from a low output region (indicated by a point P) near the valley on the high frequency side (right side in the drawing) of fc / 2 shown in FIG. Transition to the first drive frequency change mode, and then the drive time ratio is kept constant until the set output is reached, and the drive frequency is gradually decreased to increase the output. Let Therefore, it is possible to avoid the high output region near fc / 2 and shift to the low output region near fc / 3.
[0041]
As described above, according to the present embodiment, the drive frequency and drive time ratio of the first switching element 6 and the second switching element 7 of the inverter 4 that heats a load having a low resistance and a low magnetic permeability such as aluminum. By performing soft start control alternately in both modes, it is possible to reliably obtain a set output in the vicinity of fc / 3 without entering the high output area in the vicinity of fc / 2. Also, the soft start can be completed in the same time as when the power is controlled by either the driving frequency or the driving time ratio with respect to 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]
Further, although the induction heating cooker has been described in the above embodiment, the present invention can be applied to other types of induction heating apparatuses such as an iron or a water heater for heating a high conductivity and low magnetic permeability material such as aluminum.
[0044]
In the above embodiment, the half-bridge type inverter using two switching elements as shown in FIG. 1 has been described. However, the present invention is not limited to this. The present invention includes at least a series connection body 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 second switching element in parallel. A second reverse conducting element connected to the first switching element or a heating circuit connected in parallel to the second switching element and a resonance circuit including a resonance capacitor; Any inverter that resonates by conduction between the switching element and the second switching element, and output control means for controlling the conduction exclusively between the first switching element and the second switching element may be used. It can also be applied to other inverters.
[0045]
(Example 2)
FIG. 4 is a diagram illustrating a soft start operation in the second embodiment. When shifting from the first drive time ratio change mode to the first drive frequency change mode, the drive time ratio is also changed discretely at a predetermined ratio or a predetermined value at the same time. It is something to change. For example, if the drive time ratio is ¼, it is changed to ３.
[0046]
As described above, according to the present embodiment, even when the set power is large, the set power can be reached quickly, and the position of the resonance frequency is searched in the region where the output of the inverter is small. However, by changing the drive frequency and the drive time ratio discretely, the switching loss is reduced and the reliability is increased.
[0047]
Note that in the frequency characteristics of the output, searching for the portion in the peak or 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 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 reach the set output quickly by the first drive frequency change mode, and the set power is increased. Since it does not change, an excessive load is not applied to the power components constituting the inverter such as a switching element, and a highly reliable induction heating apparatus can be provided.
[0050]
(Example 4)
FIG. 6 is a diagram illustrating a soft start operation in the fourth embodiment.
[0051]
A first output fixing mode is added to fix the output for a predetermined time (0.1 seconds) after starting the inverter with the drive frequency and drive time ratio of the first and second switching elements that are the minimum output of the inverter 4 It is a thing.
[0052]
As described above, according to the present embodiment, after the start-up, until the input current is stabilized at the minimum value or maintained at the output for a predetermined time, the output control such as soft start is delayed, thereby stabilizing the load. A control operation such as a detection operation can be realized.
[0053]
(Example 5)
FIG. 7 is a diagram illustrating a soft start operation according to the fifth embodiment.
[0054]
Similar to the fourth embodiment, when the driving frequency and the driving time ratio are changed discretely, a second output fixing mode for fixing the output for about 0.1 second is added after the change. By delaying the control until the output of the input detection unit becomes stable, 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 in FIG. 1 described in the first embodiment, only the difference will be described.
[0057]
Reference numeral 16 denotes voltage detection means for detecting the voltage of the first resonant capacitor 10, reference numeral 17 denotes movement detection means for detecting a lift or deviation of the load based on the output of the voltage detection means 16, and the movement detection means 17 is a soft start. It observes the state of the output change at the time and detects the lift and deviation of the load. In this embodiment, when the output is increased during the soft start period, it is detected that the voltage change within a certain period of time is smaller than that at the time, and that the load is lifted or shifted. Detected. Note that the voltage detection means 16 can similarly detect that the load has been 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 driving frequency is changed to the second driving frequency changing mode after the movement detecting means is operated, rather than the first driving frequency changing mode in which the second driving frequency changing mode is added and the movement detecting means 17 is not operated. 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 drive frequency and a drive time ratio during 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 decreased by the minimum control unit (period is 0.1 microsecond). 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 decreased until time t4.
[0061]
Further, at t4, the drive time ratio becomes the minimum of the control range, and the drive frequency is increased by the minimum control unit (period is 0.1 microsecond). As described above, fine power control can be performed by controlling the drive frequency and the drive time ratio.
[0062]
(Example 8)
FIG. 11 shows a circuit diagram of the induction heating apparatus according to the eighth embodiment of the present invention, which is basically the same as that of the first embodiment, and only the differences will be described.
[0063]
In FIG. 11, reference numeral 18 denotes an accessory detection unit that detects an accessory at the start-up by the output of the current detection unit 14 and causes the output control unit 15 to stop the inverter.
[0064]
FIG. 12 is a diagram showing the relationship between the drive time of the second switching element 7 and the input current. When the time drive ratio is increased, there is no load due to the change in the input current, and there is no load, knife, fork, etc. Can detect small loads.
[0065]
In the present invention, in the drive time ratio change mode in which the drive frequency is kept constant and the drive time ratio is gradually increased at the drive frequency and drive time ratio at which the output is minimized when the inverter is started, the characteristics shown in FIG. By using this, an accurate accessory detection means is provided.
[0066]
Example 9
The ninth embodiment has the same configuration as that of the eighth embodiment, and the output control unit 15 in FIG. 9 has a predetermined frequency (30) in the first frequency change mode. k If the frequency is lower than (Hz), it is determined as an accessory.
[0067]
While the inverter 4 is activated, a load that is small in diameter and cannot be heated is detected and the inverter 4 is stopped. Therefore, an induction heating device that is safe and has few failures can be provided.
[0068]
(Example 10)
The tenth embodiment has the same configuration as that of the eighth embodiment, and after the inverter 4 is activated and detects a predetermined power or more, it is determined as an accessory when the output of the current detection means 14 becomes lower than a predetermined value. Is.
[0069]
When the inverter is operating with the set power, when the load is taken, the inverter 4 is stopped as soon as the output of the current detection means 14 is reduced. Therefore, an induction heating apparatus that is safe and has few failures can be provided.
[0070]
Instead of the current detection means 15, an output detection means corresponding thereto may be configured by detecting 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 permeability such as aluminum and copper can be induction-heated while suppressing an increase in loss of the switching element, and the driving frequency of the switching element can be reduced. By combining the variable control with the variable control of the drive time ratio of the switching element, it is possible to easily perform fine power control using a microcomputer, and to shorten the time from startup to output stabilization. It is possible to realize an induction heating device that is less likely to fail the switching element 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 drive frequency and input power characteristics of the induction heating cooker of the first embodiment.
(B) The figure which shows the drive time ratio and input electric power characteristic of the induction heating cooking appliance of 1st Example.
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 drive time ratio and input power characteristics 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 drive frequency and input power characteristics of a conventional induction heating apparatus.
(B) The figure which shows the drive time ratio and input power characteristic of the conventional induction heating apparatus
FIG. 15 is a diagram showing a soft start operation of a conventional induction heating apparatus.
[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 rectifier circuit; a choke coil connected to an output terminal of the rectifier circuit; a smoothing capacitor to which a voltage boosted by the choke coil is supplied; a first switching element connected to both ends of the smoothing capacitor; A series connection body of switching elements, a first reverse conducting element connected in parallel to the first switching element, a second reverse conducting element connected in parallel to the second switching element, and the first A switching circuit or a resonance circuit including a heating capacitor and a resonance capacitor connected in parallel to the second switching element, and the first switching element and the second switching element are electrically connected to each other, such as aluminum When induction heating is applied to a load with high conductivity and low permeability, the resonance circuit uses the resonance frequency of the current supplied to the heating coil. An inverter that resonates so that the driving frequency of the switching element is low, an output control means that controls conduction of the first switching element and the second switching element, an input current of the inverter or a voltage substantially equivalent thereto, or Output detection means for detecting current, wherein the output control means gradually changes the drive time ratio of the first switching element and the second switching element to increase the output of the inverter. It has a change mode and a drive frequency change mode that raises the output of the inverter by gradually lowering the drive frequency while keeping the drive time ratio substantially constant, and induces a load with high conductivity and low permeability such as aluminum. When heated, the output of the inverter is combined with the drive time ratio change mode and the drive frequency change mode. Te, induction heater to reach from the low output value at startup to a predetermined output value.

The output control means provides a period for increasing the output of the inverter only in one of the drive time ratio change mode and the drive frequency change mode within the period for reaching from the low output value at the start to the predetermined output value. The induction heating apparatus according to claim 1.

The output control means alternates the transition from the drive time ratio change mode to the drive frequency change mode and the shift from the drive frequency change mode to the drive time ratio change mode while changing the output of the inverter from the low output value at the start to a predetermined value. The induction heating device according to claim 1 or 2, wherein the output value is reached.

The output control means increases the output of the inverter by changing the drive time ratio of the first switching element and the second switching element at the time of start-up, and makes the drive time ratio substantially constant from the middle to make the first switching element The induction heating device according to claim 3, wherein the output of the inverter is increased by changing the driving frequency of the second switching element.

The output control means has a drive time ratio between the first switching element and the second switching element at a predetermined drive in the drive time ratio change mode within a period of time from the low output value at the start to the predetermined output value. The induction heating apparatus according to claim 3 or 4, wherein when the time ratio is reached, the driving frequency changing mode is entered.

When the drive frequency is close to the resonance frequency, the input power sharply increases and peaks at the resonance frequency, and the drive frequency and the input power become a low output region near the valley between the high frequency side and the low frequency side from the resonance frequency. In the characteristics, the output control means starts with a low output value near the valley on the high frequency side and performs first switching after the start in a period in which the output of the inverter reaches the predetermined output value on the low frequency side. element and the second near the resonance frequency the driving time ratio by changing the driving time ratio is discretely changed by the change width is larger than the variation width immediately before the driving frequency and reaches a predetermined driving time ratio of the switching element of avoiding the high output region, the discretely simultaneously the driving time ratio when the migrated to the low output region near the valley of the low frequency side by the change width is larger than the variation width of the immediately preceding Further to the induction heating apparatus according to the output of the inverter is gradually decreasing the driving frequency is constant the driving time ratio to any one of the predetermined claims 3-5 which Ru is increased to output from the .

When the drive frequency is close to the resonance frequency, the input power sharply increases and peaks at the resonance frequency, and the drive frequency and the input power become a low output region near the valley between the high frequency side and the low frequency side from the resonance frequency. In the characteristics, the output control means starts with a low output value near the valley on the high frequency side and performs first switching after the start in a period in which the output of the inverter reaches the predetermined output value on the low frequency side. increasing the heating output drive period of the device by changing the driving time ratio of the first switching element and second switching element so as to be shorter than the resonant period of the resonant current reaches the predetermined driving time ratio, wherein so that said drive frequency at which the driving period of the first switching element to a low output value in the vicinity of the valley longer than the period and the low-frequency side of the resonant current Any one of to change discretely long of claims 1 to 6 comprising increasing the output of the inverter is lowered gradually lengthened to the driving frequency of the driving period to a predetermined output value from the low output value The induction heating apparatus according to item 1.

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

The induction heating apparatus according to any one of claims 1 to 8, wherein the induction heating apparatus has a first output fixing mode for outputting at a drive frequency and a drive time ratio at which the output is substantially minimum for a predetermined time after the inverter is started.

The output control means is a second output fixing mode for fixing the output of the driving frequency and the driving time ratio for a predetermined time after discretely lowering the driving frequency or the driving time ratio with a change width larger than the immediately preceding change width. The induction heating device according to any one of claims 1 to 9, wherein

It has a movement detecting means for detecting floating or deviation of the load when induction load is applied to a load with high conductivity and low permeability, and the output control means sets the drive frequency at a predetermined time interval in the drive frequency change mode. And the time interval for changing the drive frequency after the movement detecting means detects the floating or deviation of the load is longer than the time interval for changing the drive frequency in the drive frequency change mode. The induction heating apparatus according to any one of claims 1 to 10, wherein the induction heating device is in a second drive frequency change mode in which a slope of the drive frequency drop is smaller than a slope of the drive frequency drop in the drive frequency change mode. .

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

When the output control means is in the first output fixed mode or the drive time ratio change mode within the period for reaching the predetermined output value from the low output value at the time of start-up, if the output detection means exceeds the predetermined value, the abnormal state The induction heating apparatus according to any one of claims 1 to 12, wherein normal heating operation is not performed because it is determined that a problem has occurred.

In the drive frequency change mode within a period in which the output control means reaches from the low output value at the start to the predetermined output value, the output of the output detection means has a predetermined value until the predetermined frequency is reached. The induction heating device according to any one of claims 1 to 13, further comprising an accessory detection unit that determines that an accessory that does not perform a normal heating operation when it does not reach the point.

Output control means, the driving frequency change mode, the drive frequency induction heating device of claim 1 1 having a small detection means determines that the small detects that less than a predetermined value.

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.