JP2005020932A

JP2005020932A - Power conversion circuit

Info

Publication number: JP2005020932A
Application number: JP2003184465A
Authority: JP
Inventors: Toshiji Matsukuma; 利治松熊; Tsugio Watabe; 二男渡部
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2003-06-27
Filing date: 2003-06-27
Publication date: 2005-01-20
Anticipated expiration: 2023-06-27
Also published as: JP4129817B2

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the radiation noise generated with the resonance of a circuit without increasing an inductance of a snubber circuit including a snubber diode and a snubber capacitor. <P>SOLUTION: In the power conversion circuit, a common mode choke 15 is inserted between an IGBT 2 and the snubber circuit including the snubber capacitor 4 and the snubber diode 5. A capacitor 8 and a resistor 9 are connected to both ends of the snubber diode 5. Currents in the mutually opposite directions are made to flow in a first coil 15a and a second coil 15b of the common mode choke 15 immediately after turning off the IGBT 2. The inductance component in each coil is canceled. Also, a surge voltage is absorbed with the snubber capacitor 4, the energy absorbed with the snubber capacitor 4 is absorbed with the capacitor 8 via the snubber diode 5. When the energy accumulated in the capacitor 8 is discharged via the resistor 9, an IGBT 3 and a discharging resistor 12 in the power conversion circuit, the second coil 15b of the common mode choke 15 is inserted in the middle of the route, and then, the high frequency current is suppressed by the inductance L2 of the coil 15b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、電力変換回路に係り、特に、複数のスイッチング素子を用いて直流電力を交流電力にあるいは交流電力を直流電力に変換するに好適な電力変換回路に関する。
【０００２】
【従来の技術】
近年、ＰＷＭインバータ・コンバータ装置などの電力変換回路は、省エネルギー、装置の小型化、高性能化を目的として、ＭＯＳＦＥＴやＩＧＢＴなどの半導体素子を用い、スイッチング動作を高速化する方向にある。しかし、このスイッチング動作の高速化に伴い、電力変換回路から発生する輻射ノイズが増加することが知られている。
【０００３】
具体的には、例えば、ＩＧＢＴを用いたインバータ回路においては、ＩＧＢＴがオンからオフに移行するときに発生するサージ電圧を吸収するために、直流電源を基準にして正側と負側に分かれて配置されているとともに互いに直列接続された各相のＩＧＢＴのコレクタとエミッタ間には、互いに直列に接続されたスナバコンデンサとスナバダイオードが接続されており、スナバダイオードには、互いに直列に接続されたスナバダイオード用コンデンサと抵抗が並列に接続されている。このスナバコンデンサとスナバダイオードはＩＧＢＴがオンからオフに移行するときに発生するサージ電圧を吸収することができるようになっており、スナバダイオード用コンデンサと抵抗は、スナバダイオードがオフする際に、スナバダイオードにリカバリ電流が流れるときのリカバリエネルギーを吸収するようになっている。さらに、スナバダイオード用コンデンサに蓄えられたエネルギーを、スナバダイオードとスナバコンデンサとの接続点と直流電源（平滑コンデンサ）のプラス端子又はマイナス端子に接続された放電抵抗を介して電源に放電する構成が採用されている。
【０００４】
スナバダイオード用コンデンサに蓄えられたエネルギーが放電抵抗によって放電されるときに、スナバダイオード用コンデンサと配線インダクタンスとによって共振し、その共振周波数は概ね数ＭＨｚから数１０ＭＨｚであり、スナバダイオード用コンデンサに蓄積されたエネルギーが放電される際に流れる高周波電流が輻射ノイズの要因となっている。
【０００５】
そこで、スナバ回路内の共振により発生する高周波電流を抑制するために、正側ＩＧＢＴのコレクタとスナバコンデンサとの間にインダクタを挿入するとともに負側ＩＧＢＴのエミッタとスナバコンデンサとの間にインダクタを挿入し、回路の共振による高周波電流を抑制するようにしたもの提案されている（特許文献１参照）。
【０００６】
【特許文献１】
【０００７】
特開平１１−８９６８号公報（第２頁から第３頁、図１）
【発明が解決しようとする課題】
上記従来技術においては、正側ＩＧＢＴのコレクタとスナバコンデンサとの間にインダクタを挿入するとともに、負側ＩＧＢＴのエミッタとスナバコンデンサとの間にインダクタを挿入しているため、各インダクタのインダクタンス成分によって、回路の共振による高周波電流を抑制することはできる。しかし、各ＩＧＢＴのスイッチング動作時に発生するサージ電圧が、インダクタの挿入に伴って増加し、サージ電圧によってはＩＧＢＴに悪影響を与える恐れがある。
【０００８】
本発明の課題は、スナバダイオードとスナバコンデンサを含むスナバ回路のインダクタンスを大きくすることなく、回路の共振に伴って発生する輻射ノイズを抑制することにある。
【０００９】
【課題を解決するための手段】
前記課題を解決するために、本発明は、正側スイッチング素子と負側スイッチング素子と並列にスナバコンデンサとスナバダイオードを含むスナバ回路を接続し、スナバダイオードにはスナバダイオードのリカバリ時に発生するサージ電圧を吸収する補助サージ電圧吸収素子を並列に接続し、スナバコンデンサと補助サージ電圧吸収素子との接続点に各スナバコンデンサに蓄積され電荷を、電源を放電回路の一要素として放電する放電抵抗を接続し、各正側のスイッチング素子の第１の電極（コレクタ）を正側の第１のコイルを介して正側のスナバコンデンサに接続し、各正側のスイッチング素子の第２の電極（エミッタ）を正側の第２のコイルを介して正側のスナバダイオードに接続し、各負側のスイッチング素子の第２の電極（エミッタ）を負側の第１のコイルを介して負側のスナバコンデンサに接続し、各負側のスイッチング素子の第１の電極（コレクタ）を負側の第２のコイルを介して負側のスナバダイオードに接続し、各第１のコイルと各第２のコイルに互いに逆方向の電流が流れるときに、各第１のコイルと各第２のコイルにおいてインダクタンスを相殺するようにしたものである。この場合、第１のコイルと第２のコイルを一対としてコモンモードチョークで構成することができる。
【００１０】
また、前記各正側のスイッチング素子の第１の電極と正側の各スナバコンデンサとを結ぶ正側の第１の配線（導体板）と、前記各正側のスイッチング素子の第２の電極と正側の各スナバダイオードとを結ぶ正側の第２の配線（導体板）とを積層化し、前記各負側のスイッチング素子の第２の電極と負側の各スナバコンデンサとを結ぶ負側の第１の配線（導体板）と、前記各負側のスイッチング素子の第１の電極と負側の各スナバダイオードとを結ぶ負側の第２の配線（導体板）とを積層化してなる構成を採用することで、各スイッチング素子と各スナバ回路とを結ぶ回路の配線インダクタンスを小さくすることができる。
【００１１】
【発明の実施の形態】
以下、本発明の一実施形態を図面に基づいて説明する。図１は本発明の一実施形態を示す三相用電力変換回路の一相分の回路構成図である。図１において、インバータ装置を構成する電力変換回路はスイッチング信号に応答してスイッチング動作するスイッチング素子（半導体素子）としてのＩＧＢＴ２．３を備えており、各ＩＧＢＴ２．３は互いに直列に接続されている。正側のＩＧＢＴ２は、第１の電極としてのコレクタが、直流電源としての平滑コンデンサ１のプラス（プラス端子）側に接続され、第２の電極としてのエミッタがＩＧＢＴ３のコレクタに接続されているとともに電動機１４に接続されている。ＩＧＢＴ２のコレクタとエミッタにはフリーホイールダイオード２ａが逆並列接続されているとともに、コモンモードチョーク１５が接続されている。
【００１２】
コモンモードチョーク１５は、第１のコイル１５ａと第２のコイル１５ｂを備え、各コイル１５ａ、１５ｂは、その巻初めを同一とするとともに巻方向を同一として構成されており、第１のコイル１５ａの一端側がＩＧＢＴ２のエミッタに接続され、他端側がスナバコンデンサ４に接続されている。第２のコイル１５ｂはその一端側がＩＧＢＴ２のエミッタに接続され、その他端側がスナバダイオード５のカソード側に接続されている。スナバコンデンサ４とスナバダイオード５は、スナバ回路を構成する回路素子として互いに直列に接続されている。スナバダイオード５の両端には、スナバダイオード５のリカバリ時に発生するサージ電圧を吸収する補助サージ電圧吸収素子として、コンデンサ８と抵抗９が互いに直列に接続された状態で接続されている。さらにスナバダイオード５とスナバコンデンサ４との接続点には放電抵抗１２が接続されており、放電抵抗１２の一端側は、直流電源を放電回路の要素とするために、平滑コンデンサ１のマイナス（マイナス端子）側に接続されている。
【００１３】
一方、負側のスイッチング素子としてのＩＧＢＴ３は、第１の電極としてのコレクタと第２の電極としてのエミッタにフリーホイールダイオード３ａが逆並列接続されているとともに、コモンモードチョーク１６が接続されている。コモンモードチョーク１６はコモンモードチョーク１５と同一の仕様で構成されており、第１のコイル１６ａの一端側がＩＧＢＴ３のエミッタに接続され、他端側がスナバコンデンサ６に接続されている。第２のコイル１６ｂはＩＧＢＴ３のコレクタに接続され、他端側がスナバダイオード７のアノード側に接続されている。スナバコンデンサ６とスナバダイオード７はスナバ回路を構成する回路素子として互いに直列に接続されており、スナバダイオード７の両端には、スナバダイオード７のリカバリ時に発生するサージ電圧を吸収する補助サージ電圧吸収素子として、コンデンサ１０と抵抗１１とが互いに直列に接続された状態で並列に接続されている。またスナバコンデンサ６とスナバダイオード７との接続点には放電抵抗１３が接続されており、放電抵抗１３の他端側は、直流電源を放電回路の一要素として放電するために、平滑コンデンサ１のプラス（プラス端子）に接続されている。
【００１４】
上記構成において、例えば、ＩＧＢＴ２のベースにスイッチング信号が入力されてオンすると、平滑コンデンサ１からの電流はＩＧＢＴ２のコレクタ、エミッタを介して電動機１４に流れる。このあとＩＧＢＴ２がオフになると、ＩＧＢＴ２の電流変化率ｄｉ／ｄｔと回路の配線インダクタンスＬとにより、ＩＧＢＴ２のコレクタ側には、次の（１）式に示すように、平滑コンデンサ１の電圧を超えたサージ電圧ｄＶが発生する。
【００１５】
【数１】

このとき発生するサージ電圧によるエネルギーは、ＩＧＢＴ２のコレクタ、第１のコイル１５ａ、スナバコンデンサ４、スナバダイオード５、第２のコイル１５ｂ、電動機１４を介して流れ、スナバコンデンサ４によって吸収される。スナバコンデンサ４に吸収されたサージエネルギーがなくなると、スナバコンデンサ４に蓄えられたエネルギーは第１のコイル１５ａ、平滑コンデンサ１、放電抵抗１２を介して放電される。
【００１６】
さらに、スナバコンデンサ４に蓄積されたエネルギーが放電される際には、スナバダイオード５にはＩＧＢＴ２がオフした直後に流れる電流とは逆方向のリカバリ電流が流れ、スナバダイオード５がオフしたときに発生するリカバリ電圧がスナバダイオード用コンデンサ８と抵抗９によって吸収される。
【００１７】
次に、コンデンサ８に蓄えられたエネルギーは、抵抗９、第２のコイル１５ｂ、ＩＧＢＴ３、放電抵抗１２を介して放電される。このとき第１のコイル１５ａに流れる電流がないと仮定すると、コモンモードチョーク１５の第２のコイル１５ｂの両端にかかる電圧Ｖ２は、次の（２）式で表される。
【００１８】
【数２】

（２）式において、電流Ｉ１＝０なので、電圧Ｖ２に影響するインダクタンス成分は、コモンモードチョーク１５の第２のコイル１５ｂが有するインダクタンスＬ２のみとなる。この結果、スナバダイオード用コンデンサ８、ＩＧＢＴ３、放電抵抗１２の経路に、第２のコイル１５ｂによるインダクタンスＬ２を挿入したことになるため、このインダクタンスＬ２により高周波電流を抑制することができる。
【００１９】
次に、コモンモードチョーク１５を挿入することによるスナバコンデンサ４、スナバダイオード５の直列回路に流れる電流に対する影響を考察する。図１における電圧Ｖ２は（２）式であり、Ｖ１は次の（３）式で表される。
【００２０】
【数３】

ここで、第１のコイル１５ａのインダクタンスＬ１と第２のコイル１５ｂのインダクタンスＬ２が同一とすると、Ｌ１＝Ｌ２＝Ｍ（Ｍはコモンモードチョーク１５の相互インダクタンスを示す。）となる。また、電流Ｉ１と電流Ｉ２は大きさが等しく、向きが逆方向になるので、Ｉ１＝−Ｉ２となる。この関係を（２）式および（３）式に代入すると、（２）式、（３）式におけるインダクタンス成分は０になる。
【００２１】
よって、スナバコンデンサ４からスナバダイオード５に流れる電流に関して、コモンモードチョーク１５を追加することによってインダクタンス成分が増加することはないので、インダクタンス成分の増加に伴うサージ電圧の増加よってＩＧＢＴ２、３が破壊するのを防止することができる。
【００２２】
このように、本実施形態によれば、ＩＧＢＴ２からスナバ回路への経路にコモンモードチョーク１５を挿入することにより、スナバコンデンサ４とスナバダイオード５からなるスナバ回路（直列回路）のインダクタンスを大きくすることなく、ＩＧＢＴ２とコンデンサ８との間にインダクタンスＬ２を挿入することが可能になるため、回路内の共振で発生する高周波電流を抑制することができる。
【００２３】
なお、前記実施形態においては、ＩＧＢＴ２について述べたが、ＩＧＢＴ３についても同様に、ＩＧＢＴ３とスナバ回路との間にコモンモードチョーク１６を挿入することにより、スナバダイオード７とスナバコンデンサ６によるスナバ回路（直列回路）のインダクタンスを大きくすることなく、ＩＧＢＴ３とコンデンサ１０との間にインダクタンスＬ２を挿入することが可能になるため、回路内の共振で発生する高周波電流を抑制することができる。
【００２４】
次に、本発明の他の実施形態を図２にしたがって説明する。本実施形態はＩＧＢＴ２、３と各スナバ回路間の配線を積層化したものである。例えば、ＩＧＢＴ２と、スナバコンデンサ４とスナバダイオード５を含むスナバ回路とを接続するに際して、例えば、銅を用いてほぼ矩形形状に形成された導体板１８ａ、１８ｂを配線として積層化し、導体板１８ａの一端側をＩＧＢＴ２のコレクタに接続し、導体板１８ａの他端側をスナバコンデンサ４に接続し、導体板１８ｂの一端側をＩＧＢＴ２のエミッタに接続し、導体板１８ｂの他端側をスナバダイオード５のカソード側に接続し、スナバ回路を構成する回路素子などをスナバモジュール１７内に収納する。なお、ＩＧＢＴ３の場合も同様に、導体板１８ａ、１８ｂを用いて、ＩＧＢＴ３とスナバ回路とを導体板１８ａ、１８ｂを介して接続することができる。
【００２５】
ＩＧＢＴ２とスナバ回路とを導体板１８ａ、１８ｂを用いて接続すると、導体板１８ａ、１８ｂが互いに近接して積層化されているので、ＩＧＢＴ２とスナバ回路間の回路インダクタンスＬが相殺され、ＩＧＢＴ２、スナバコンデンサ４、スナバダイオード５の経路に係わるインダクタンスＬが低減される。このインダクタンスＬの低減により、（１）式に示したサージ電圧の低減が可能になり、スナバダイオード用コンデンサ８に印加されるエネルギーも低減されるため、エネルギー放電の際に発生する高周波電流を低減することも可能になる。
【００２６】
また、ＩＧＢＴ２．３とスナバ回路とを導体板１８ａ、１８ｂを用いて接続するに際しては、導体板１８ａ、１８ｂの途中にコモンモードチョーク１５、１６を挿入することで、サージ電圧および高周波電流をさらに低減することが可能になる。
【００２７】
【発明の効果】
以上説明したように、本発明によれば、スナバコンデンサとスナバダイオードを含むスナバ回路のインダクタンスを大きくすることなく、補助サージ電圧吸収素子を含む回路内で発生する高周波ノイズを抑制することができ、ノイズ環境が大幅に改善され、ノイズによる内部および外部機器の誤動作を減少させることが可能になり、電力変換回路を用いた装置の信頼性を向上させることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態を示す回路構成図である。
【図２】本発明の他の実施形態を示す斜視図である。
【符号の説明】
１平滑コンデンサ
２、３ＩＧＢＴ
４、６スナバコンデンサ
５、７スナバダイオード
８、１０スナバダイオード用コンデンサ
９、１１スナバダイオード用抵抗
１２、１３スナバコンデンサ放電抵抗
１４電動機
１５、１６コモンモードチョーク
１５ａ、１６ａ第１のコイル
１５ｂ、１６ｂ第２のコイル
１７スナバモジュール
１８ａ、１８ｂ導体板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power conversion circuit, and more particularly to a power conversion circuit suitable for converting DC power into AC power or AC power into DC power using a plurality of switching elements.
[0002]
[Prior art]
2. Description of the Related Art In recent years, power conversion circuits such as PWM inverter / converter devices have been in the direction of speeding up switching operations using semiconductor elements such as MOSFETs and IGBTs for the purpose of energy saving, device miniaturization, and high performance. However, it is known that the radiation noise generated from the power conversion circuit increases as the switching operation speeds up.
[0003]
Specifically, for example, in an inverter circuit using an IGBT, in order to absorb a surge voltage generated when the IGBT shifts from on to off, the inverter circuit is divided into a positive side and a negative side with reference to the DC power supply. A snubber capacitor and a snubber diode connected in series with each other are connected between the collector and emitter of each phase IGBT that is arranged and connected in series with each other, and the snubber diode is connected in series with each other. A snubber diode capacitor and a resistor are connected in parallel. The snubber capacitor and the snubber diode can absorb a surge voltage generated when the IGBT shifts from on to off. The snubber diode capacitor and the resistor are connected to the snubber diode when the snubber diode is turned off. The recovery energy is absorbed when the recovery current flows through the diode. Furthermore, the energy stored in the capacitor for the snubber diode is discharged to the power source through the discharge resistor connected to the connection point between the snubber diode and the snubber capacitor and the positive terminal or the negative terminal of the DC power source (smoothing capacitor). It has been adopted.
[0004]
When the energy stored in the snubber diode capacitor is discharged by the discharge resistor, it resonates with the snubber diode capacitor and the wiring inductance, and the resonance frequency is approximately several MHz to several tens of MHz, and is stored in the snubber diode capacitor. The high-frequency current that flows when the generated energy is discharged is a cause of radiation noise.
[0005]
Therefore, in order to suppress high-frequency current generated by resonance in the snubber circuit, an inductor is inserted between the collector of the positive IGBT and the snubber capacitor and an inductor is inserted between the emitter of the negative IGBT and the snubber capacitor. However, there has been proposed one that suppresses high-frequency current due to circuit resonance (see Patent Document 1).
[0006]
[Patent Document 1]
[0007]
Japanese Patent Laid-Open No. 11-8968 (pages 2 to 3, FIG. 1)
[Problems to be solved by the invention]
In the above prior art, an inductor is inserted between the collector of the positive IGBT and the snubber capacitor, and an inductor is inserted between the emitter of the negative IGBT and the snubber capacitor. High frequency current due to circuit resonance can be suppressed. However, the surge voltage generated during the switching operation of each IGBT increases as the inductor is inserted, and there is a possibility that the IGBT may be adversely affected depending on the surge voltage.
[0008]
An object of the present invention is to suppress radiation noise generated due to circuit resonance without increasing the inductance of a snubber circuit including a snubber diode and a snubber capacitor.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention connects a snubber circuit including a snubber capacitor and a snubber diode in parallel with a positive side switching element and a negative side switching element, and the snubber diode has a surge voltage generated at the time of recovery of the snubber diode. Auxiliary surge voltage absorption elements that absorb the noise are connected in parallel, and the charge accumulated in each snubber capacitor is connected to the connection point between the snubber capacitor and the auxiliary surge voltage absorption element, and a discharge resistor that discharges the power supply as an element of the discharge circuit is connected Then, the first electrode (collector) of each positive-side switching element is connected to the positive-side snubber capacitor via the positive-side first coil, and the second electrode (emitter) of each positive-side switching element. Is connected to the positive snubber diode via the positive second coil, and the second electrode (emitter) of each negative switching element is connected. Are connected to the negative snubber capacitor via the negative first coil, and the first electrode (collector) of each negative switching element is connected to the negative snubber diode via the negative second coil. Are connected to each other, and when currents flowing in opposite directions flow through the first coils and the second coils, the inductances of the first coils and the second coils are canceled out. In this case, the first coil and the second coil can be configured as a pair with a common mode choke.
[0010]
A positive first wiring (conductor plate) connecting the first electrode of each positive switching element and each positive snubber capacitor; and a second electrode of each positive switching element; The second wiring (conductor plate) on the positive side that connects each positive snubber diode is laminated, and the negative electrode that connects the second electrode of each negative switching element and each negative snubber capacitor. A configuration in which a first wiring (conductor plate) and a negative second wiring (conductor plate) connecting the first electrode of each negative switching element and each negative snubber diode are stacked. By adopting, the wiring inductance of the circuit connecting each switching element and each snubber circuit can be reduced.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit configuration diagram for one phase of a three-phase power conversion circuit showing an embodiment of the present invention. In FIG. 1, the power conversion circuit constituting the inverter device includes IGBT 2.3 as a switching element (semiconductor element) that performs a switching operation in response to a switching signal, and each IGBT 2.3 is connected in series with each other. . The positive-side IGBT 2 has a collector as the first electrode connected to the plus (plus terminal) side of the smoothing capacitor 1 as a DC power supply, and an emitter as the second electrode connected to the collector of the IGBT 3. It is connected to the electric motor 14. A free wheel diode 2a is connected in reverse parallel to the collector and emitter of the IGBT 2, and a common mode choke 15 is connected.
[0012]
The common mode choke 15 includes a first coil 15a and a second coil 15b, and the coils 15a and 15b are configured to have the same winding start and the same winding direction. Is connected to the emitter of the IGBT 2, and the other end is connected to the snubber capacitor 4. The second coil 15 b has one end connected to the emitter of the IGBT 2 and the other end connected to the cathode side of the snubber diode 5. The snubber capacitor 4 and the snubber diode 5 are connected in series as circuit elements constituting the snubber circuit. A capacitor 8 and a resistor 9 are connected to both ends of the snubber diode 5 as an auxiliary surge voltage absorbing element that absorbs a surge voltage generated during recovery of the snubber diode 5 in series. Further, a discharge resistor 12 is connected to a connection point between the snubber diode 5 and the snubber capacitor 4, and one end side of the discharge resistor 12 has a minus (minus) of the smoothing capacitor 1 in order to use a DC power source as an element of the discharge circuit. Terminal) side.
[0013]
On the other hand, in the IGBT 3 as a negative side switching element, a free wheel diode 3a is connected in reverse parallel to a collector as a first electrode and an emitter as a second electrode, and a common mode choke 16 is connected. . The common mode choke 16 has the same specifications as the common mode choke 15, and one end of the first coil 16 a is connected to the emitter of the IGBT 3, and the other end is connected to the snubber capacitor 6. The second coil 16 b is connected to the collector of the IGBT 3, and the other end side is connected to the anode side of the snubber diode 7. The snubber capacitor 6 and the snubber diode 7 are connected in series as circuit elements constituting a snubber circuit, and an auxiliary surge voltage absorbing element that absorbs a surge voltage generated at the time of recovery of the snubber diode 7 at both ends of the snubber diode 7. The capacitor 10 and the resistor 11 are connected in parallel with each other in series. A discharge resistor 13 is connected to a connection point between the snubber capacitor 6 and the snubber diode 7, and the other end side of the discharge resistor 13 is connected to the smoothing capacitor 1 in order to discharge a DC power source as an element of the discharge circuit. Connected to positive (positive terminal).
[0014]
In the above configuration, for example, when a switching signal is input to the base of the IGBT 2 and turned on, the current from the smoothing capacitor 1 flows to the motor 14 via the collector and emitter of the IGBT 2. After that, when the IGBT 2 is turned off, the voltage of the smoothing capacitor 1 is exceeded on the collector side of the IGBT 2 by the current change rate di / dt of the IGBT 2 and the wiring inductance L of the circuit as shown in the following equation (1). A surge voltage dV is generated.
[0015]
[Expression 1]

The energy generated by the surge voltage generated at this time flows through the collector of the IGBT 2, the first coil 15 a, the snubber capacitor 4, the snubber diode 5, the second coil 15 b, and the electric motor 14, and is absorbed by the snubber capacitor 4. When the surge energy absorbed by the snubber capacitor 4 disappears, the energy stored in the snubber capacitor 4 is discharged through the first coil 15a, the smoothing capacitor 1, and the discharge resistor 12.
[0016]
Further, when the energy stored in the snubber capacitor 4 is discharged, a recovery current in the direction opposite to the current that flows immediately after the IGBT 2 is turned off flows in the snubber diode 5 and occurs when the snubber diode 5 is turned off. The recovery voltage to be absorbed is absorbed by the snubber diode capacitor 8 and the resistor 9.
[0017]
Next, the energy stored in the capacitor 8 is discharged through the resistor 9, the second coil 15 b, the IGBT 3, and the discharge resistor 12. Assuming that there is no current flowing through the first coil 15a at this time, the voltage V2 applied to both ends of the second coil 15b of the common mode choke 15 is expressed by the following equation (2).
[0018]
[Expression 2]

In the equation (2), since the current I1 = 0, the inductance component affecting the voltage V2 is only the inductance L2 included in the second coil 15b of the common mode choke 15. As a result, since the inductance L2 due to the second coil 15b is inserted in the path of the snubber diode capacitor 8, the IGBT 3, and the discharge resistor 12, the high frequency current can be suppressed by the inductance L2.
[0019]
Next, the influence of the insertion of the common mode choke 15 on the current flowing through the series circuit of the snubber capacitor 4 and the snubber diode 5 will be considered. The voltage V2 in FIG. 1 is represented by equation (2), and V1 is represented by the following equation (3).
[0020]
[Equation 3]

Here, if the inductance L1 of the first coil 15a and the inductance L2 of the second coil 15b are the same, L1 = L2 = M (M represents the mutual inductance of the common mode choke 15). Further, since the currents I1 and I2 are equal in magnitude and opposite in direction, I1 = −I2. By substituting this relationship into equations (2) and (3), the inductance component in equations (2) and (3) becomes zero.
[0021]
Therefore, with respect to the current flowing from the snubber capacitor 4 to the snubber diode 5, the inductance component does not increase by adding the common mode choke 15, so that the IGBTs 2 and 3 are destroyed by the increase of the surge voltage accompanying the increase of the inductance component. Can be prevented.
[0022]
Thus, according to the present embodiment, the inductance of the snubber circuit (series circuit) composed of the snubber capacitor 4 and the snubber diode 5 is increased by inserting the common mode choke 15 in the path from the IGBT 2 to the snubber circuit. In addition, since it is possible to insert the inductance L2 between the IGBT 2 and the capacitor 8, it is possible to suppress high-frequency current generated by resonance in the circuit.
[0023]
In the above-described embodiment, the IGBT 2 has been described. Similarly, for the IGBT 3, a snubber circuit (in series) including the snubber diode 7 and the snubber capacitor 6 is inserted by inserting the common mode choke 16 between the IGBT 3 and the snubber circuit. Since it is possible to insert the inductance L2 between the IGBT 3 and the capacitor 10 without increasing the inductance of the circuit), it is possible to suppress high-frequency current generated by resonance in the circuit.
[0024]
Next, another embodiment of the present invention will be described with reference to FIG. In the present embodiment, the wiring between the IGBTs 2 and 3 and each snubber circuit is laminated. For example, when connecting the IGBT 2 and the snubber circuit including the snubber capacitor 4 and the snubber diode 5, for example, the conductor plates 18a and 18b formed in a substantially rectangular shape using copper are laminated as wirings, and the conductor plate 18a One end side is connected to the collector of the IGBT 2, the other end side of the conductor plate 18 a is connected to the snubber capacitor 4, one end side of the conductor plate 18 b is connected to the emitter of the IGBT 2, and the other end side of the conductor plate 18 b is connected to the snubber diode 5. The circuit elements constituting the snubber circuit are accommodated in the snubber module 17. Similarly, in the case of the IGBT 3, the IGBT 3 and the snubber circuit can be connected via the conductor plates 18a and 18b using the conductor plates 18a and 18b.
[0025]
When the IGBT 2 and the snubber circuit are connected using the conductor plates 18a and 18b, the conductor plates 18a and 18b are stacked close to each other, so that the circuit inductance L between the IGBT 2 and the snubber circuit is canceled out, and the IGBT 2 and the snubber circuit are offset. The inductance L related to the path of the capacitor 4 and the snubber diode 5 is reduced. By reducing the inductance L, the surge voltage shown in the equation (1) can be reduced, and the energy applied to the snubber diode capacitor 8 is also reduced, thereby reducing the high-frequency current generated during energy discharge. It is also possible to do.
[0026]
Further, when connecting the IGBT 2.3 and the snubber circuit using the conductor plates 18a and 18b, the surge voltage and the high-frequency current can be further increased by inserting the common mode chokes 15 and 16 in the middle of the conductor plates 18a and 18b. It becomes possible to reduce.
[0027]
【The invention's effect】
As described above, according to the present invention, it is possible to suppress high-frequency noise generated in the circuit including the auxiliary surge voltage absorbing element without increasing the inductance of the snubber circuit including the snubber capacitor and the snubber diode, The noise environment is greatly improved, the malfunction of internal and external devices due to noise can be reduced, and the reliability of the device using the power conversion circuit can be improved.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.
FIG. 2 is a perspective view showing another embodiment of the present invention.
[Explanation of symbols]
1 Smoothing capacitor 2, 3 IGBT
4, 6 Snubber capacitor 5, 7 Snubber diode 8, 10 Snubber diode capacitor 9, 11

Snubber diode resistor

12, 13 Snubber capacitor discharge resistor 14

Motor

15, 16 Common mode choke 15a, 16a First coil 15b, 16b Two coils 17 Snubber modules 18a and 18b Conductor plate

Claims

A plurality of switching elements which are arranged separately on the positive side and the negative side with respect to the power supply and are connected in series with each other and perform switching operation in response to a switching signal, and are generated in accordance with the switching operation of the plurality of switching elements. A plurality of snubber circuits including a snubber capacitor and a snubber diode connected in series as circuit elements that absorb the surge voltage generated for each switching element, and a plurality of auxiliary circuits that absorb the surge voltage generated during recovery of each snubber diode A surge voltage absorbing element; and a plurality of discharge resistors for discharging the electric charge accumulated in each of the snubber capacitors using the power supply as an element of a discharge circuit, and the first electrode of each of the positive side switching elements is connected to the positive side Each positive switch is connected to a positive snubber capacitor via a first coil. The second electrode of the switching element is connected to the positive snubber diode via the positive second coil, and the second electrode of each negative switching element is connected via the negative first coil. Connected to a negative snubber capacitor, and connected to a negative snubber diode via a negative second coil, the first electrode of each negative switching element is connected to each negative coil. A power conversion circuit formed by canceling out inductance in each of the first coils and each of the second coils when currents in opposite directions flow through the second coils.

A plurality of switching elements which are arranged separately on the positive side and the negative side with respect to the power supply and are connected in series with each other and perform switching operation in response to a switching signal, and are generated in accordance with the switching operation of the plurality of switching elements. A plurality of snubber circuits including a snubber capacitor and a snubber diode connected in series as circuit elements that absorb the surge voltage generated for each switching element, and a plurality of auxiliary circuits that absorb the surge voltage generated during recovery of each snubber diode A surge voltage absorbing element; and a plurality of discharge resistors for discharging the electric charge accumulated in each of the snubber capacitors using the power supply as an element of a discharge circuit, and the first electrode of each of the positive side switching elements is connected to the positive side Each positive switch is connected to a positive snubber capacitor via a first coil. The second electrode of the switching element is connected to the positive snubber diode via the positive second coil, and the second electrode of each negative switching element is connected via the negative first coil. Connected to a negative snubber capacitor, and connected to a negative snubber diode via a negative second coil, the first electrode of each negative switching element is connected to each negative coil. A power conversion circuit comprising a common mode choke as a pair of second coils.

3. The power conversion circuit according to claim 1, wherein the positive-side first wiring connecting the first electrode of each positive-side switching element and each positive-side snubber capacitor, and each positive-side switching. A second wiring on the positive side connecting the second electrode of the element and each snubber diode on the positive side is laminated, and the second electrode of each switching element on the negative side and each snubber capacitor on the negative side are connected. An electric power comprising: a negative first wiring and a negative second wiring connecting the first electrode of each negative switching element and each negative snubber diode. Conversion circuit.

A plurality of switching elements which are arranged separately on the positive side and the negative side with respect to the power supply and are connected in series with each other and perform switching operation in response to a switching signal, and are generated in accordance with the switching operation of the plurality of switching elements. A plurality of snubber circuits including a snubber capacitor and a snubber diode connected in series as circuit elements that absorb the surge voltage generated for each switching element, and a plurality of auxiliary circuits that absorb the surge voltage generated during recovery of each snubber diode A surge voltage absorbing element; and a plurality of discharge resistors for discharging the electric charge accumulated in each of the snubber capacitors using the power supply as an element of a discharge circuit, the first electrode of each positive side switching element and the positive side A positive first wiring connecting each snubber capacitor, and each positive switching element; Negative electrode connecting the second electrode of each switching element on the negative side and each snubber capacitor on the negative side, by laminating the second electrode on the positive side and the second wiring on the positive side connecting each snubber diode on the positive side. A power conversion circuit formed by laminating a first wiring on the side and a second wiring on the negative side connecting the first electrode of each switching element on the negative side and each snubber diode on the negative side.