JP2004274906A - Direct ac-ac power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To share snubber capacitors which absorb inductive energy when all the switches of a matrix converter or the like are off between a power converter and a capacitor for input filter, and thereby obviate the necessity for film capacitor and reduce the size and cost of the power converter. <P>SOLUTION: The snubber capacitors which absorb energy produced by an inductive load 40 when all the bidirectional switches 31 to 39 in a main converter, such as a matrix converter 30, are off are formed of capacitor groups 97 and 98. These capacitors are shared between the converter and a capacitor for input filter. A discharging means 100 is connected with both the ends of a series circuit of the capacitor groups 97 and 98. When the direct-current voltage exceeds a predetermined value, the capacitors are discharged and the discharged energy is consumed by a resistor 104. Thereby, the capacitors are prevented from being applied with overvoltage. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２２】
次に、コンデンサ群９７，９８を構成する各コンデンサ９１〜９６に印加される電圧について説明する。例えば、Ｒ相に接続されたコンデンサ９１，９２の電圧をＶ_９１，Ｖ_９２とし、全波整流回路７０の出力電圧（全波整流回路６０，７０間の直流リンク電圧）をＶ_ｄｃとすれば、数式２の関係がある。
【００２３】
【数２】

【００２４】
また、Ｒ相の電源電圧をｖ_Ｒとすれば、各コンデンサ９１，９２の電圧Ｖ_９１，Ｖ_９２は数式３で表される。
【００２５】
【数３】

【００２６】
各コンデンサ９１，９２には相電圧実効値Ｖ_{ｐｈａｓｅ}の最大電圧が充電されることを考えると、直流リンク電圧Ｖ_ｄｃとの間に数式４の関係が成立する。
【００２７】
【数４】

【００２８】
数式４を数式３に代入して、コンデンサ電圧を求めると、数式５が得られる。
【００２９】
【数５】

【００３０】
−√２Ｖ_{ｐｈａｓｅ}≦ｖ_Ｒ≦√２Ｖ_{ｐｈａｓｅ}であるから、各コンデンサ９１，９２の電圧は直流であることがわかる。
他のＳ相、Ｔ相についても同様に考えられるため、コンデンサ群９７，９８に使用するコンデンサ９１〜９６には安価な電解コンデンサを使用することが使用できる。ここで、前述のようにコンデンサ９１〜９６は入力フィルタ用コンデンサとしても機能するので、従来の如くスナバコンデンサ以外に高価なフィルムコンデンサを用いることが不要になる。
【００３１】
次に、図２は図１における放電手段１００の具体例を示している。
放電手段１００は、コンデンサ群９７，９８の直列回路の両端に接続されてこの直列回路の両端電圧（全波整流回路７０の直流出力電圧）を検出する電圧検出手段１０１と、抵抗１０４及び半導体スイッチング素子１０５の直列回路と、電圧検出手段１０１による電圧検出値を閾値（上限値及び下限値）と比較する比較手段１０２と、この比較手段１０２からのオンオフ指令により前記スイッチング素子１０５を駆動するドライブ回路１０３とから構成されている。
【００３２】
図３は、放電手段１００の動作を示すものである。
前記比較手段１０２にはヒステリシス付きのものが用いられており、比較手段１０２は、電圧検出手段１０１により検出される直流電圧が上限値に達すると、下限値に減少するまでの一定期間、ドライブ回路１０３を介してスイッチング素子１０５にオン指令を送出する。なお、図３において、時刻ｔ_０は、異常発生により制御手段５０からマトリクスコンバータ３０の全ての双方向スイッチ３１〜３９に対するゲートオフ指令が出力されるタイミングを示す。
【００３３】
図２におけるスイッチング素子１０５のオンにより、コンデンサ群９７，９８に蓄えられた電荷は抵抗１０４を介して放電され、直流電圧は減少していく。そして、直流電圧が下限値に達したら、ドライブ回路１０３を介したオフ指令によってスイッチング素子１０５をオフする。以後は同じ動作の繰り返しにより、コンデンサ群９７，９８の直列回路の両端電圧が所定範囲を超えないように制御が行われ、コンデンサ群９７，９８に対する過電圧の印加が防止される。
【００３４】
抵抗１０４の寄生インダクタンスが大きい場合や抵抗１０４とスイッチング素子１０５との間の配線による配線インダクタンスを無視できない場合には、スイッチング素子１０５を保護するために抵抗１０４に並列にダイオードを接続すれば良い。
【００３５】
本実施形態では、コンデンサの放電手段１００として抵抗１０４によるエネルギー消費手段を示したが、放電手段１００としては、コンデンサのエネルギーをスイッチング素子の動作により電源に回生しても良く、負荷４０に供給しても良い。
なお、本発明は、三相以外の多相交流電圧を直接変換する電力変換器にも適用可能である。
【００３６】
【発明の効果】
以上のように本発明によれば、マトリクスコンバータ等において、異常発生によりスイッチを全てオフした際に発生する負荷の誘導性エネルギーを吸収するスナバコンデンサを入力フィルタ用コンデンサと共用したため、この共用コンデンサとして安価な電解コンデンサのみを使用することができる。
従って、従来のように入力フィルタ用のフィルムコンデンサを不要として電力変換器全体の低価格化を図ることができる。
また、本発明に必要とされるコンデンサ全体の容量は従来のスナバコンデンサに相当する容量のみで足りるため、電力変換器の小型化も期待することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態を示す構成図である。
【図２】図１における放電手段の具体例を示す構成図である。
【図３】図２の放電手段の動作説明図である。
【図４】従来技術を示す構成図である。
【符号の説明】
１０：三相交流電源
２１：フィルタ用リアクトル
３０：マトリクスコンバータ
３１〜３９：双方向スイッチ
４０：負荷
５０：制御手段
７０：全波整流回路
９１〜９６：コンデンサ
９７，９８：コンデンサ群
１００：放電手段
１０１：電圧検出手段
１０２：比較手段
１０３：ドライブ回路
１０４：抵抗
１０５：半導体スイッチング素子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an AC-AC direct conversion type power converter that directly converts a multi-phase AC voltage into a multi-phase AC voltage using a semiconductor switching element and outputs the converted power, and in particular, a large energy such as a capacitor or a reactor. A matrix converter without a buffer is characterized by a snubber circuit for processing energy stored in an inductive load when all switches of a main converter are turned off during operation.
[0002]
[Prior art]
FIG. 4 is a block diagram showing this type of direct conversion type power converter using a matrix converter as a main converter. Here, the most common three-phase is illustrated as an example of polyphase, 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. And
[0003]
4, reference numeral 10 denotes a three-phase AC power supply, 20 denotes an input filter including a reactor 21 and a capacitor 22, 30 denotes a matrix converter including bidirectional switches 31 to 39, and 40 denotes an inductive load such as an electric motor. Are controlled by the control unit 50.
Here, the bidirectional switches 31 to 39 are configured by connecting two semiconductor switching elements such as IGBTs in series in the reverse direction, and connecting a free-wheeling diode to each switching element in antiparallel.
As is well known, the matrix converter 30 selects a bidirectional switch connected to each phase by paying attention to the maximum voltage and the minimum voltage of the power supply voltage, and changes the input AC voltage to a desired magnitude and frequency by PWM control. Is directly converted into an AC voltage having
[0004]
Since the matrix converter 30 does not have a large-sized energy buffer such as a capacitor or a reactor, when an abnormality such as an overcurrent or an overvoltage occurs, all the bidirectional switches 31 to 39 must be turned off to stop the operation. However, when an inductive load such as an electric motor is connected as the load 40, when the control means 50 that has received an abnormality occurrence signal such as an overcurrent causes the bidirectional switches 31 to 39 to be turned off all at once, the load 40 is connected to the load 40. Since there is no return path for the stored inductive energy, a large surge voltage is generated at the switch end, and the element is destroyed.
[0005]
Conventionally, as shown in FIG. 4, a full-wave rectifier circuit 70 is connected to the output side of the matrix converter 30 as a so-called rectified snubber circuit to prevent the generation of the surge voltage. Are connected. Thus, for example, even if the bidirectional switches 31 to 39 are turned off all at once when an abnormality occurs, the energy stored in the load 40 is absorbed by the snubber capacitor 81 via the full-wave rectifier circuit 70, and eventually the snubber resistor 82 Since the power is consumed, application of a surge voltage to the switch terminal can be prevented.
[0006]
The full-wave rectifier circuit 60 on the input side of the matrix converter 30 and connected in parallel with the full-wave rectifier circuit 70 protects the bidirectional switches 31 to 39 from a surge voltage generated by wiring inductance on the input side. In this case, the energy stored in the wiring inductance is absorbed by the snubber capacitor 81 via the full-wave rectifier circuit 60.
[0007]
Here, a power converter including an input filter, a matrix converter, its control means, a protection circuit (rectifier snubber circuit) when the bidirectional switch is completely turned off, and the like shown in FIG. Have been.
[0008]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-139076 (FIG. 5, FIG. 7, etc.)
[0009]
[Problems to be solved by the invention]
The snubber capacitor 81 shown in FIG. 4 is used to absorb the energy generated due to the inductive load when the bidirectional switch is completely turned off and to suppress a rise in the DC voltage between the full-wave rectifier circuits 60 and 70. , Large capacity is required.
On the other hand, in a direct conversion type power converter such as a matrix converter, a bidirectional switch is connected in series to each phase, so that the input current has an intermittent waveform. Therefore, in order to prevent higher-frequency harmonics near the switching frequency from flowing out to the system (three-phase AC power supply 10) side, as shown in FIG. 4, the input side of the matrix converter 30 includes a reactor 21 and a capacitor 22. An input filter 20 is provided.
[0010]
Normally, a film capacitor is used as the capacitor 22 of the input filter 20. However, the film capacitor tends to be large because of lower energy density than the electrolytic capacitor, and the price is higher than the electrolytic capacitor. .
Therefore, the drawbacks of these film capacitors have caused an increase in the size and cost of the entire power converter.
[0011]
Accordingly, the present invention provides an AC-AC direct conversion that enables miniaturization and cost reduction by sharing a snubber capacitor that absorbs energy generated due to an inductive load with an input filter capacitor as described above. It is an object of the present invention to provide a type power converter.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 provides a multi-phase converter that converts a polyphase AC voltage input to the main converter into a DC voltage by switching a semiconductor switching element in the main converter. In an AC-AC direct conversion type power converter that converts to AC voltage,
A snubber capacitor for absorbing energy generated due to an inductive load when the semiconductor switching element is turned off is shared with a capacitor for an input filter of the main converter.
[0013]
According to a second aspect of the present invention, in the AC-AC direct conversion type power converter according to the first aspect,
The main converter is a matrix converter, and the snubber capacitor absorbs energy generated due to an inductive load when all bidirectional switches as semiconductor switching elements constituting the matrix converter are turned off. .
[0014]
According to a third aspect of the present invention, in the AC-AC direct conversion type power converter according to the first or second aspect,
A full-wave rectifier circuit is connected to the output side of the main converter, and the snubber capacitor includes at least two groups of capacitors each connected in a star shape between each phase on the input side of the main converter. One end on the output side is connected to the neutral point of one capacitor group, and the other end on the output side of the full-wave rectifier circuit is connected to the neutral point of another capacitor group.
[0015]
According to a fourth aspect of the present invention, in the AC-AC direct conversion type power converter according to the first, second or third aspect,
When the DC voltage of the snubber capacitor exceeds a predetermined value, the snubber capacitor is discharged by the operation of the semiconductor switching element.
Here, the discharging means of the snubber capacitor is constituted by a circuit that consumes energy by a resistor connected in series to the semiconductor switching element, or a circuit that regenerates energy to the power supply side or supplies energy to the load side.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of the present invention. The same components as those in FIG. 4 are denoted by the same reference numerals, and the following description focuses on the differences from FIG.
[0017]
In FIG. 1, one end of a reactor 21 for an input filter is connected to each phase of the three-phase AC power supply 10, and the other ends thereof are connected to interconnection points between a capacitor group 97 and a capacitor group 98, respectively. I have.
Here, the capacitor group 97 is composed of star-connected capacitors 91, 93 and 95, and the capacitor group 98 is also composed of star-connected capacitors 92, 94 and 96. Connection points, interconnection points 93 and 94, and interconnection points 95 and 96 are connected to the other ends of the R-phase, S-phase, and T-phase reactors 21, respectively. That is, the capacitors 91 to 96 constitute a three-phase bridge circuit as a whole. Discharge means 100 is connected to both ends of the series circuit of the capacitor groups 97 and 98, and both ends of the full-wave rectifier circuit 70 Connected to DC output side. Note that the AC input side of the full-wave rectifier circuit 70 is connected to each phase (U phase, V phase, W phase) on the output side of the matrix converter 30 as in FIG.
[0018]
Next, the operation of this embodiment will be described.
When an abnormality occurrence signal is input due to an overcurrent or an overcurrent, the control unit 50 turns off all the bidirectional switches 31 to 39 of the matrix converter 30. At this time, since the inductive energy accumulated in the load 40 such as a motor flows into the full-wave rectifier circuit 70, its output voltage (DC voltage) increases, and the respective capacitor series circuits of the capacitor groups 97 and 98 are charged. Thus, the energy can be absorbed. Therefore, the capacitors 91 to 96 function as snubber capacitors.
[0019]
On the other hand, in the configuration of FIG. 1, since the capacitor groups 97 and 98 are star-connected to the three-phase AC power supply 10, it is apparent that they function not only as snubber capacitors but also as input filter capacitors.
If the capacity of the capacitor groups 97 and 98 alone is not enough to absorb the inductive energy of the load 40, a capacitor having a capacity to make up the shortage is separately connected to the output side of the full-wave rectifier circuit 70. Is also good. In this case, the capacity of the added capacitor can be smaller than that of the conventional snubber capacitor 81 in FIG. 4 because of the capacity of the capacitor groups 97 and 98.
[0020]
The capacity of a conventional snubber capacitor 81 of FIG. 4 as _{C 0,} if the capacitance of the capacitors 91-96 constituting the capacitor group 97 and 98 (both are equal) and _{C F,} the capacitor capacitance should supplement _{C C} Is represented by Equation 1.
[0021]
(Equation 1)

[0022]
Next, the voltage applied to each of the capacitors 91 to 96 constituting the capacitor groups 97 and 98 will be described. For example, if the voltages of the capacitors 91 and 92 connected to the R phase are V ₉₁ and V ₉₂ and the output voltage of the full-wave rectifier circuit 70 (the DC link voltage between the full-wave rectifier circuits 60 and 70) is V _dc. , Equation 2
[0023]
(Equation 2)

[0024]
Further, if the power supply voltage of R-phase and _{v R,} the voltage _{V 91, V 92} of the capacitors 91 and 92 is represented by Equation 3.
[0025]
[Equation 3]

[0026]
Considering that the capacitors 91 and 92 are charged with the maximum voltage of the phase voltage effective value V _phase , the relationship of Expression 4 holds between the capacitors 91 and 92 and the DC link voltage V _dc .
[0027]
(Equation 4)

[0028]
By substituting equation (4) into equation (3) and calculating the capacitor voltage, equation (5) is obtained.
[0029]
(Equation 5)

[0030]
Since −√2V _phase ≦ v _R ≦ √2V _phase , it is understood that the voltage of each of the capacitors 91 and 92 is DC.
Since other S-phase and T-phase can be considered in the same manner, inexpensive electrolytic capacitors can be used for the capacitors 91 to 96 used for the capacitor groups 97 and 98. Here, since the capacitors 91 to 96 also function as input filter capacitors as described above, it becomes unnecessary to use expensive film capacitors other than the snubber capacitors as in the related art.
[0031]
Next, FIG. 2 shows a specific example of the discharging means 100 in FIG.
The discharging means 100 is connected to both ends of a series circuit of the capacitor groups 97 and 98, and detects voltage across the series circuit (the DC output voltage of the full-wave rectifier circuit 70), a resistor 104 and semiconductor switching. A serial circuit of the elements 105, a comparing means 102 for comparing a voltage detection value by the voltage detecting means 101 with thresholds (upper and lower limits), and a drive circuit for driving the switching element 105 in response to an on / off command from the comparing means 102 103.
[0032]
FIG. 3 shows the operation of the discharging means 100.
When the DC voltage detected by the voltage detecting means 101 reaches the upper limit value, the comparing means 102 uses a drive circuit for a certain period of time until it decreases to the lower limit value. An ON command is sent to the switching element 105 via 103. In FIG. 3, time t ₀ indicates a timing at which a gate-off command is output from control means 50 to all bidirectional switches 31 to 39 of matrix converter 30 due to occurrence of an abnormality.
[0033]
When the switching element 105 in FIG. 2 is turned on, the charges stored in the capacitor groups 97 and 98 are discharged through the resistor 104, and the DC voltage decreases. Then, when the DC voltage reaches the lower limit, the switching element 105 is turned off by an off command via the drive circuit 103. Thereafter, by repeating the same operation, control is performed so that the voltage across the series circuit of the capacitor groups 97 and 98 does not exceed a predetermined range, and application of an overvoltage to the capacitor groups 97 and 98 is prevented.
[0034]
When the parasitic inductance of the resistor 104 is large or when the wiring inductance of the wiring between the resistor 104 and the switching element 105 cannot be ignored, a diode may be connected in parallel with the resistor 104 to protect the switching element 105.
[0035]
In the present embodiment, the energy consuming means by the resistor 104 is shown as the discharging means 100 of the capacitor. However, the discharging means 100 may regenerate the energy of the capacitor to the power supply by the operation of the switching element. May be.
Note that the present invention is also applicable to a power converter that directly converts a multi-phase AC voltage other than three-phase.
[0036]
【The invention's effect】
As described above, according to the present invention, in the matrix converter or the like, the snubber capacitor that absorbs the inductive energy of the load generated when all the switches are turned off due to the occurrence of an abnormality is shared with the input filter capacitor. Only inexpensive electrolytic capacitors can be used.
Therefore, the cost of the entire power converter can be reduced by eliminating the need for a film capacitor for an input filter as in the related art.
Further, since the capacity of the entire capacitor required for the present invention is sufficient only with the capacity corresponding to the conventional snubber capacitor, a reduction in the size of the power converter can be expected.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of the present invention.
FIG. 2 is a configuration diagram showing a specific example of a discharging unit in FIG. 1;
FIG. 3 is an explanatory diagram of the operation of the discharging means of FIG. 2;
FIG. 4 is a configuration diagram showing a conventional technique.
[Explanation of symbols]
10: Three-phase AC power supply 21: Filter reactor 30: Matrix converter 31-39: Bidirectional switch 40: Load 50: Control means 70: Full-wave rectifier circuits 91-96: Capacitors 97, 98: Capacitor group 100: Discharge means 101: voltage detecting means 102: comparing means 103: drive circuit 104: resistor 105: semiconductor switching element

Claims (4)

In an AC-AC direct conversion type power converter that converts a polyphase AC voltage input to the main converter into a polyphase AC voltage without converting the DC voltage into a DC voltage by switching a semiconductor switching element in the main converter,
AC-AC direct conversion type power conversion, wherein a snubber capacitor that absorbs energy generated due to an inductive load when the semiconductor switching element is turned off is shared with a capacitor for an input filter of the main converter. vessel. The AC-AC direct conversion type power converter according to claim 1,
The main converter is a matrix converter, and the energy generated due to the inductive load when all the bidirectional switches as the semiconductor switching elements constituting the matrix converter are turned off is absorbed by the snubber capacitor. Characteristic AC-AC direct conversion type power converter. The AC-AC direct conversion power converter according to claim 1 or 2,
A full-wave rectifier circuit is connected to the output side of the main converter,
The snubber capacitor includes at least two capacitor groups each connected in a star shape between each input side phase of the main converter,
One end on the output side of the full-wave rectifier circuit is connected to the neutral point of one capacitor group, and the other end on the output side of the full-wave rectifier circuit is connected to the neutral point of another capacitor group. AC-AC direct conversion type power converter. The AC-AC direct conversion type power converter according to claim 1, 2, or 3,
An AC-AC direct conversion type power converter, wherein when the DC voltage of the snubber capacitor exceeds a predetermined value, the snubber capacitor is discharged by operation of a semiconductor switching element.

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