JP4640794B2 - Matrix converter protection device - Google Patents

Description

  The present invention relates to an industrial power conversion device, and more particularly to a protection device for a matrix converter that performs power conversion directly from a three-phase AC power source to a three-phase load.

  FIG. 2 is a block diagram showing this type of direct conversion type power converter using a matrix converter as the main converter. Here, the most common three phases are shown as examples of polyphases, and the input side (power supply side) is called R, S, T phase, and the output side (load side) is called U, V, W phase. To do.

In FIG. 2, 1 is a three-phase AC power source, 3 is an AC filter comprising a filter reactor 31 and a filter capacitor 32, 2 is a matrix converter comprising bidirectional switches 21 to 29, 4 is an inductive load such as an electric motor, 7 Shows a conventional matrix converter protection device which is a clamp or protection circuit which is attached so that an excessive voltage is not applied to the bidirectional switches 21 to 29. The matrix converter 2 fulfills the purpose of power conversion by giving an on / off (conduction prevention) signal to the gates of the bidirectional switches 21 to 29 from the controller.
Here, the bidirectional switches 21 to 29 are configured, for example, by connecting two semiconductor switching elements such as IGBTs having a reverse blocking function in antiparallel.

  As is well known, regarding the conversion operation of the matrix converter 2, at any time, any one of three switches connected to each output phase (for example, the switches 21, 22, 23 connected to the U phase). One must be on. Otherwise, the return path of the inductive energy accumulated in the inductive load 4 disappears, so that a large surge voltage is generated at both ends of the switch and the element is destroyed.

  On the other hand, the switching (commutation) operation between switches in switching control is not unique, and changes complicatedly depending on the polarity of the load current, etc. Therefore, if an uncertain element such as noise is mixed in the current sensor signal, it is unexpected. May cause a commutation failure and a large surge voltage. In addition, when some failure occurs in the system, it is common to turn off the bidirectional switches 21 to 29 constituting the matrix converter all at once, but in this case as well, the element is turned on for the same reason as the commutation failure. There is a risk of destroying it.

  In order to prevent the occurrence of the surge voltage, conventionally, as shown in FIG. 2, a rectification snubber circuit is constituted by the input / output full-wave rectifiers 71 and 72 and the electrolytic capacitor 73, and the induced energy at the time of commutation failure or forced stop. Is absorbed by the electrolytic capacitor 73 (see, for example, Patent Document 1). Since the voltage across the bidirectional switch is clamped below the voltage of the electrolytic capacitor 73, the purpose of overvoltage protection is fulfilled.

  This type of protection circuit can effectively prevent surge voltage, but, as shown in the conventional matrix converter protection device 7 of FIG. 2, the configuration has a high speed at least as high as that of the main circuit element. Since twelve diodes and one large-capacitance electrolytic capacitor are required, sacrifices must be made in terms of cost and size of the entire converter. Furthermore, since the electrolytic capacitor 73 has a short lifetime, there is also a disadvantage that regular maintenance must be performed.

JP 2000-139076 (FIGS. 5, 7, etc.)

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described points, and the object of the present invention is to provide a protection circuit that can easily suppress the surge voltage with a low number of parts, low cost, and low cost. Is to provide.

In other words, in order to achieve the purpose, in the protection device of the matrix converter that performs power conversion directly from the multiphase AC power source to the multiphase AC load,
According to the first aspect of the present invention, a varistor is connected between the neutral point of the filter capacitor that is star-connected on the input side of the matrix converter and each phase on the matrix converter output side.
The invention described in claim 2 is configured such that a bidirectional Zener diode is connected between the neutral point of the filter capacitor that is star-connected on the input side of the matrix converter and each phase on the output side of the matrix converter. is there.
According to the third aspect of the present invention, a zener diode connected in series in the opposite direction is connected between the neutral point of the filter capacitor that is star-connected on the input side of the matrix converter and each phase on the output side of the matrix converter. It is configured as follows.

  According to the claims of the present invention, since the voltage surge protection device of the matrix converter is effectively configured with a small number of parts, it can contribute to a reduction in size and weight of the system and a reduction in cost. In addition, since a short-life component such as an electrolytic capacitor is not used, the life of the system can be extended.

  FIG. 1 is a configuration diagram showing an embodiment of the present invention, and is a diagram showing a configuration of a matrix converter protection device. In the figure, 1 is a three-phase AC power source, 3 is an AC filter comprising a filter reactor 31 and a filter capacitor 32, 2 is a matrix converter comprising bidirectional switches 21 to 29, and 4 is an inductive load such as an electric motor. . Reference numeral 5 denotes a circuit configuration of the matrix converter protection device according to the first aspect of the present invention, which includes only three varistors 51. One end of the varistor is connected to the neutral point of the filter capacitor 32 that is star-connected, and the other end is connected to each phase (U phase, V phase, W phase) on the output side of the matrix converter 2. The present invention achieves the protection purpose by clamping the surge voltage generated by a commutation error or the like with the varistor 51 by providing the matrix converter protection device according to claim 1 of the present invention.

Hereinafter, the principle of the protection device 5 for the matrix converter according to claim 1 of the present invention shown in FIG. 1 as an embodiment of the present invention will be described in detail.
As is well known, when the voltage applied to the varistor is lower than the varistor voltage (Vz), almost no current flows and the varistor is almost turned off. On the other hand, when a voltage higher than the varistor voltage Vz is applied, the impedance is suddenly reduced, current bypass is allowed, and further voltage rise is prevented. By utilizing this characteristic, it has been conventionally used as a bidirectional voltage clamp or a surge absorber.
On the other hand, the matrix converter is a step-down type semiconductor converter, and when operating normally, the voltage of each output phase is between the maximum phase voltage and the minimum phase voltage of the power supply side three-phase input voltage. When the effective value of the input phase voltage is expressed as Ep (peak value √2Ep) and the output voltage value is expressed as Vo, it is clear that the expression (1) holds.

逆に、出力電圧がこの範囲を超えた場合、むしろ正常動作としては認めず、何らかの対策を取らなければならない。
図１において、出力電圧が正常範囲内にある場合、バリスタ５１が動作せず、等価的にオフ状態になるので、星型結線されているフィルタ用コンデンサ３２の中性点の電位がほぼゼロである。従って、各相に接続されているバリスタ５１の両端にかかる電圧がその相の出力電圧と等しくなる。バリスタ５１は出力電圧が異常な場合のみ作動するから、バリスタ電圧Vzは（２）式を満たすように選定される。

On the contrary, if the output voltage exceeds this range, it is rather not recognized as a normal operation, and some measures must be taken.
In FIG. 1, when the output voltage is in the normal range, the varistor 51 does not operate and is equivalently turned off, so that the potential at the neutral point of the filter capacitor 32 connected in a star shape is almost zero. is there. Therefore, the voltage applied to both ends of the varistor 51 connected to each phase becomes equal to the output voltage of that phase. Since the varistor 51 operates only when the output voltage is abnormal, the varistor voltage Vz is selected so as to satisfy the expression (2).

次に、本発明請求項１のマトリックスコンバータ保護装置５がクランプ状態にある場合、双方向スイッチ２１〜２９両端に印加されている電圧を概算してみる。一般性を失わず、R相電源とU相出力の間の双方向スイッチ２１を例として、その両端電圧を計算してみる。いま図１において、U相の双方向スイッチ（２１，２２，２３）が全てオープンしたとしよう。誘導性負荷４のU相誘導エネルギーの正常流れルートが無くなったので、勢いでU相に接続されているバリスタ５１を導通させ、U相電圧がVzでクランプされる。よって、双方向スイッチ２１両端の電圧はVur=Vz-Vrとなり、その最大値が（３）式を満たしているのは明らかである。

Next, when the matrix converter protection device 5 according to the first aspect of the present invention is in a clamped state, the voltage applied to both ends of the bidirectional switches 21 to 29 will be roughly estimated. Without loss of generality, let's calculate the voltage at both ends of the bidirectional switch 21 between the R-phase power supply and the U-phase output as an example. Suppose that all the U-phase bidirectional switches (21, 22, 23) are opened in FIG. Since the normal flow route of the U-phase induced energy of the inductive load 4 is lost, the varistor 51 connected to the U-phase is turned on and the U-phase voltage is clamped at Vz. Therefore, the voltage across the bidirectional switch 21 is Vur = Vz−Vr, and it is clear that the maximum value satisfies the expression (3).

バリスタ電圧Vzを（２）式の右辺と等しく選択した場合、双方向スイッチ２１〜２９両端電圧が２√２Ep以下に抑えられることが分かる。
以上は本発明請求項１に請求した内容であり、少ない部品数で双方向スイッチ２１〜２９両端電圧を効果的に抑えられることが明らかである。なお、本発明の請求項２では、本発明請求項１のマトリックスコンバータ保護装置５の構成部品であるバリスタ５１を同等な機能をもつ双方向ツェナーダイオードで置換えたもので、同等な効果を果たせることが明らかである。また、本発明の請求項３も本発明請求項１のバリスタ５１を同等機能の逆直列接続のツェナーダイオードで置換えたのみなので、同じような機能を果たせる。

It can be seen that when the varistor voltage Vz is selected to be equal to the right side of the equation (2), the voltage across the bidirectional switches 21 to 29 can be suppressed to 2√2Ep or less.
The above is what is claimed in claim 1 of the present invention, and it is clear that the voltages across the bidirectional switches 21 to 29 can be effectively suppressed with a small number of parts. In claim 2 of the present invention, the varistor 51, which is a component of the matrix converter protection device 5 of claim 1 of the present invention, is replaced with a bidirectional Zener diode having an equivalent function, and the same effect can be achieved. Is clear. Further, since the varistor 51 according to the first aspect of the present invention is simply replaced with a Zener diode having an equivalent series connected in reverse series, the same function can be achieved.

  Although the present invention has been described by taking a three-phase matrix converter as an example, the present invention can also be applied to a power converter that directly converts multiphase AC voltages other than three-phase.

  As described in detail above, if the matrix converter protection device 5 according to the first aspect of the present invention is used, a small-sized and low-cost matrix converter can be configured, and therefore, it can be used for an industrial matrix converter.

It is a block diagram which shows one Embodiment of this invention. It is a block diagram which shows the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Three-phase alternating current power supply 2 Matrix converter 3 AC filter 4 Inductive load 5 Matrix converter protection apparatus of this invention 1 Conventional matrix converter protection apparatus 21-29 Bidirectional switch 31 Reactor for filter 32 Capacitor for filter 51 Varistor 71 72 Full wave rectifier circuit 73 Electrolytic capacitor
R, S, T R, S, T phase of matrix converter input
U, V, W Matrix converter output U, V, W phase
Vo output voltage value
Ep Input phase voltage effective value
Vz Varistor voltage value
Voltage across the bidirectional switch between Vur U and R phases

Claims (3)

In a matrix converter protection device that converts power directly from a polyphase AC power source to a polyphase AC load,
A protection device for a matrix converter, comprising a varistor connected between a neutral point of a filter capacitor that is star-connected on the input side of the matrix converter and each phase on the output side of the matrix converter. The protection device for a matrix converter according to claim 1,
A protection device for a matrix converter, wherein the varistor according to claim 1 is replaced with a bidirectional Zener diode. The protection device for a matrix converter according to claim 1,
A protective device for a matrix converter, wherein the varistor according to claim 1 is replaced with a Zener diode connected in series in opposite directions.

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