JP4893251B2 - Matrix converter and device equipped with the same - Google Patents

Description

  The present invention relates to a power conversion circuit for variable-speed driving of an AC motor from an AC power source, and more particularly, direct power for converting AC power to AC power for an AC motor without converting the power of the AC power to DC power. The present invention relates to a converter, a so-called matrix converter.

  Conventionally, a circuit as shown in FIG. 8 has been generally employed to drive an AC motor at a variable speed using AC power supplied from an AC power supply. That is, a high power factor rectifier circuit including a power factor improving reactor 401 and a three-phase bridge circuit 402 is configured for the three-phase AC power source 1 and converted into DC power using the smoothing capacitor 403. Thereafter, another three-phase bridge circuit 404 is provided to convert to a pseudo AC power source having a voltage and frequency different from those of the three-phase AC power source 1 and drive the three-phase AC motor 2.

  In the case of this method, although the conversion principle is relatively simple, the power factor improving reactor 401 and the smoothing capacitor 403 are large in shape. Further, when an electrolytic capacitor is used as the smoothing capacitor 403, there is a problem that the life is shortened due to the influence of the ripple voltage (see, for example, Patent Document 1).

  On the other hand, as shown in FIG. 9, the wiring between the three-phase AC power source 1 and the three-phase AC motor 2 is arranged in a matrix form on the topology surface, and switch elements 501 to 509 are provided at each intersection, A so-called matrix converter is also proposed in which a pseudo-AC power source having a voltage and frequency different from those of the three-phase AC power source 1 is supplied to the three-phase AC motor 2 by independently turning on / off 509 ( For example, refer nonpatent literature 1).

  This matrix converter can realize not only the control of the three-phase AC motor 2 on the output side but also the current control of the three-phase AC power source 1 on the input side, and the power factor improving reactor 401 shown in FIG. Since the smoothing capacitor 403 provided between the three-phase bridge circuits 402 and 404 is not required, the circuit can be reduced in size.

Next, in an actual matrix converter, a semiconductor element is used as a switch element. However, since the semiconductor element has only a function of flowing or blocking a current in one direction, FIG. As shown in FIG. 2, bidirectional switch elements are arranged by combining two pairs of forward and reverse semiconductor switches such as SW _UR and SW _RU .

  FIG. 10 shows an example in which an IGBT is used as a semiconductor element. The diode inserted in series with the IGBT is for preventing the IGBT from being destroyed when a reverse voltage is applied between the collector and the emitter of the IGBT. As a method for realizing the bidirectional switch element, there is a method in which the IGBTs shown in FIG. 10 are arranged in parallel, and the IGBTs in the opposite directions are arranged in series with a common emitter.

  Further, in order to actually drive the circuit shown in FIG. 10, a power source for driving all the semiconductor switches is required as shown in FIG. Specifically, the potential on the input side is the reference, that is, the three negative electrodes are connected to the three phases of the three-phase AC power source 1, and the potential on the output side is the reference, that is, the negative electrode is A total of six types of power sources including three power sources connected to the three phases of the three-phase AC motor 2 are required.

In FIG. 11, the power supply outputs of the transformer 701 are insulated and separated, and operate as separate DC power supplies including rectifier diodes (711 to 716) and smoothing capacitors (722, 732, etc.) (see, for example, Patent Document 2).
JP 2006-42579 A JP 2004-282940 A IEEJ Technical Report No. 998 (February 2005), pages 3-4

  However, the conventional configuration has a problem that the six DC power sources for driving the bidirectional switch elements are insulated from each other, resulting in an increase in circuit scale.

Further, as shown in FIG. 12, generally, command information for on / off control of semiconductor switches (in the figure, SW _RU , SW _UR ) is realized using a microcomputer 200. In this case, since the circuit for controlling the on / off of the semiconductor switch is configured using an isolated power source, it is necessary to transmit a command from the microcomputer 200 to the switch element via an insulating means such as the photocoupler 821. There is.

  For this reason as well, there is a problem that the circuit scale becomes large. The present invention solves the above-described conventional problems, and provides a matrix converter that realizes a power supply for each semiconductor switch constituting the matrix converter and a power supply for a control microcomputer by a single DC power supply. It is intended to do.

  In order to achieve the above object, a matrix converter according to the present invention is a matrix converter that converts AC power from a single-phase or three-phase AC power supply and provides desired AC power to a three-phase AC load. A DC power supply that provides a DC voltage based on the lowest potential of the switch, and a switch group that controls bidirectional energization between the AC power supply and the three-phase AC load, from the three-phase AC load to the AC power supply. A switch group having a first switch for controlling energization, a second switch for controlling energization from the AC power source to the three-phase AC load, and the first voltage using a DC voltage from the DC power source. A first drive circuit for driving a switch; a second drive circuit for driving the second switch using a DC voltage from the DC power supply; and a current from the DC power supply to the AC power supply. A first driving power source that is charged by a current and provides a power source for the first driving circuit; and a power source for the second driving circuit that is charged by a current from the DC power source to the three-phase AC load. And a second drive power supply for providing

  When the phase of the three-phase AC power supply reaches the minimum potential, the matrix converter of the present invention supplies a current to the capacitor that drives the second switch corresponding to the first switch corresponding to the phase of the three-phase AC power supply. By supplying, it is possible to convert AC power from a three-phase AC power source using one system of driving power source and provide desired AC power to a three-phase AC load.

A first aspect of the present invention is a matrix converter that converts AC power from a single-phase or three-phase AC power supply and provides desired AC power to a three-phase AC load, and provides a DC voltage based on the minimum potential of the AC power supply. And a first switch that controls energization from the three-phase AC load to the AC power source, and a switch group that controls bidirectional energization between the AC power source and the three-phase AC load. A switch group having a second switch for controlling energization from the AC power supply to the three-phase AC load, and a first drive circuit for driving the first switch using a DC voltage from the DC power supply A second drive circuit that drives the second switch using a DC voltage from the DC power supply, and is charged by a current from the DC power supply to the AC power supply, for the first drive circuit Power supply A first driving power source to be provided; and a second driving power source that is charged by a current from the DC power source to the three-phase AC load and provides a power source for the second driving circuit. .

  As a result, a current can be supplied to the capacitor driving each switch when the phase of the corresponding three-phase AC power supply is at the lowest potential, and as a result, the three-phase drive power supply can be used. A matrix converter that converts AC power from an AC power source and provides desired AC power to a three-phase AC load can be realized.

  According to a second invention, in the first invention, the rectifier diode is connected to the positive electrode of the DC power supply and blocks a current from the AC power supply, and is connected to the positive electrode of the DC power supply. And a rectifier diode for blocking current. Thereby, it can prevent that the electric current of a reverse direction flows into DC power supply.

  According to a third invention, in the first invention, a control circuit is provided which receives a voltage from the DC power supply and controls the first and second drive circuits. As a result, the drive power supply for the control circuit can be made common with the drive power supply for the first and second drive circuits, so that the control circuit can be reduced in size and simplified.

  According to a fourth invention, in the third invention, the control circuit turns on the first switch corresponding to the phase of the AC power source that is the lowest voltage before the operation of the three-phase AC load, 2 is charged. Thereby, the charge required for the operation of the three-phase AC load can be stored in the first and second drive power supplies.

  According to a fifth invention, in the third invention, a voltage obtained by dividing a voltage between the AC power supply and a negative electrode of the DC power supply is provided to the control circuit. As a result, the control circuit can grasp the phase of the current lowest potential, and can grasp the relative potential of the other phases with respect to the lowest potential phase.

  In a sixth aspect based on the first aspect, the direct current power source includes a rectifier circuit that full-wave rectifies the alternating voltage from the alternating current power source, and a direct current that receives the output voltage of the rectifier circuit and generates a predetermined direct current voltage. And a power supply circuit. As a result, the minimum potential of the AC power supply appears at the negative electrode of the rectifier circuit, and the DC power supply can operate based on the potential.

  In a seventh aspect based on the first aspect, the direct-current power source includes a transformer in which a neutral point of the alternating-current power source having three phases and any one of the three phases is connected to a primary side. A rectifier circuit for full-wave rectification of an AC voltage from the AC power supply, and a DC power supply circuit connected to the secondary side of the transformer and operating with reference to the negative electrode of the rectifier circuit.

  Thereby, since the voltage of the DC power supply becomes a phase voltage lower than the line voltage, the withstand voltage of the circuit components can be lowered, and the DC power supply circuit can be reduced in size and simplified.

  In an eighth aspect based on the first aspect, the DC power source is connected to a rectifier circuit for half-wave rectifying an AC voltage from the AC power source, and a neutral point of the AC power source having three phases. And a DC power supply circuit that operates on the basis of the output potential.

  Thereby, since the voltage of the DC power supply becomes a phase voltage lower than the line voltage, the withstand voltage of the circuit components can be lowered, and the DC power supply circuit can be reduced in size and simplified.

  According to a ninth aspect, in the seventh or eighth aspect, the DC power supply includes a current control circuit that controls the current flowing through the rectifier circuit so as not to become a predetermined value or less. As a result, the load power of the DC power supply can be reduced, and the DC power supply circuit can be further miniaturized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a configuration diagram showing a matrix converter according to Embodiment 1 of the present invention. As shown in FIG. 1, bidirectional semiconductor switches are arranged in a matrix to connect each phase of a three-phase AC power source 1 and a three-phase AC motor 2 that is a three-phase AC load.

Of the semiconductor switches constituting this semiconductor switch group, the one that flows current from the three-phase AC motor 2 to the three-phase AC power source 1 is SW _YX as the first semiconductor switch, and the three-phase AC power source 1 is three-phase. SW _XY (X is R, S or T, Y is U, V or W) is attached as a second semiconductor switch to the current flowing to the AC motor 2.

Hereinafter, when a specific semiconductor switch is not intended, the first semiconductor switch will be described as SW _YX and the second semiconductor switch will be described as SW _XY .

First, for example, the R phase of the three-phase AC power source 1 and the U phase of the three-phase AC motor 2 are connected via the semiconductor switches SW _UR and SW _RU. When current flows through the U phase of the AC motor 2, current flows through SW _RU . Conversely, when current flows from the U phase of the three-phase AC motor 2 to the R phase of the three-phase AC power source 1, it passes through SW _UR . Current flows.

For example, IGBTs SW _XY and SW _YX use IGBTs (for example, IGBTs 10 and 12 respectively for SW _RU and SW _UR ), and reverse voltage prevention diodes are inserted in series with each of them (for example, , SW _RU and SW _UR , diodes 11 and 13), respectively.

The SW _UR is connected to a drive circuit 131 that drives the SW _UR and a capacitor 132 that is a first drive power supply that supplies a voltage to the drive circuit 131. The SW _RU is connected to a drive circuit 121 that drives the SW _RU and a capacitor 122 that is a second drive power supply that supplies a voltage to the drive circuit 121.

  A current is supplied from the DC power supply circuit 101 to the drive circuits 121 and 131 via the rectifier diodes 114 and 111.

On the other hand, the AC power that is the output of the three-phase AC power source 1 is full-wave rectified by the three-phase full-wave rectifier circuit 100, and the DC power source circuit 101 operates with the negative side as a reference. The output voltage of the DC power supply circuit 101 is set to be an appropriate voltage for driving the gates of the IGBTs (for example, IGBTs 10 and 12 for SW _RU and SW _UR , respectively).

The positive output terminal of the DC power supply circuit 101 is connected to the positive electrodes of three drive power supplies for the semiconductor switch SW _YX via rectifier diodes 111, 112, and 113, respectively. Further, they are connected to positive electrodes of three drive power sources for the semiconductor switch SW _XY via rectifier diodes 114, 115 and 116, respectively.

In addition, the resistor 1003 that is a light load is provided on the output side of the three-phase full-wave rectifier circuit 100 so that any phase of the three-phase full-wave rectifier circuit 100 is always conducted. It is also possible to substitute the input power to the DC power supply circuit 101 which is a DC power supply.

  In the present embodiment, the three-phase full-wave rectifier circuit 100, the DC power supply circuit 101, and the resistor 1003 constitute a DC power supply that generates a DC voltage from the output AC voltage of the three-phase AC power supply 1.

  The operation of the matrix converter configured as described above will be described. First, the negative-side output of the three-phase full-wave rectifier circuit 100 is the same potential as the lowest potential phase of the three-phase AC power supply 1. For example, when the R-phase potential is the lowest, the DC output of the three-phase full-wave rectifier circuit 100 is the same as the R-phase potential, and the positive output of the DC power supply circuit 101 is higher than the R-phase potential. The potential becomes higher by the output voltage of the circuit 101.

For this reason, the capacitor 132 can be charged when a current flows from the DC power supply circuit 101 to the R phase of the three-phase AC power supply 1 via the rectifier diode 111 and the capacitor 132. The charge stored in the capacitor 132, it is possible to drive the semiconductor switch SW _UR. Similarly, the driving power for the semiconductor switch SW _YX can be supplied to the other phases.

Next, with reference to FIG. 2, illustrating the power supply to the semiconductor switch SW _XY. FIG. 2 shows an output waveform of the three-phase AC power source. The phase of the lowest potential in each section of these waveforms is shown in the table in the figure. For example, in the first interval, the S phase is the lowest potential.

At this time, when the semiconductor switch SW _US is turned on, the potential of the U phase becomes equal to the potential of the S phase. As a result, the semiconductor SW _SU , SW _RU , and SW _TU are driven via the diode 114. Charge can be stored in each capacitor. Similarly, when each of the semiconductor switches SW _VS and SW _WS is turned on, a capacitor for driving the remaining semiconductor switches SW _XY can be charged. This operation by performing prior to the operation of the three-phase AC motor 2, can be ready for all the semiconductor switches SW _XY.

Further, during the operation of the three-phase AC motor 2, a semiconductor switch SW _XY that is between the phase of the phase and the lowest potential of the three-phase AC motor 2 of the lowest potential of the three-phase AC power source 1, and on during that period, The two lowest potentials are made equal. Thus, current flows from the DC power supply circuit 101 to its lowest potential as a reference, are each charged in the capacitor corresponding to the semiconductor switch SW _XY. For the other phases of the three-phase AC motor 2, the capacitor corresponding to the corresponding semiconductor switch SW _XY is similarly charged at the timing when the phase becomes the lowest potential.

  With the above-described configuration and control method, the driving power source of the matrix converter can be realized by a single DC power source.

3, for illustrating an operation control signal of the ON / OFF each semiconductor switch SW _XY is transferred, is a more detailed circuit diagram. Sequence control, that is, control of on / off operation of each semiconductor switch is performed using the microcomputer 200, and the control signal is sent to the drive circuit 121.

  The drive circuit 121 is a so-called high-side switch drive circuit, which once pulses the drive control on / off signal, sends information to the high voltage side with a high voltage MOS switch, and malfunctions with a filter or the like. After prevention, the flip-flop restores the original on / off signal.

As shown in FIG. 3, as the power source for the microcomputer 200, a DC power source for each semiconductor switch of the matrix converter is used.
It operates with reference to the lowest potential in the matrix converter.

For this reason, when the microcomputer 200 is considered as a reference, all other potentials are voltages higher than that, and the semiconductor switch SW _RU can be driven using a well-known high-side switch drive circuit. By this method, it is not necessary to use a part having spatial insulation such as a photocoupler, and the circuit can be reduced in size.

(Embodiment 2)
FIG. 4 is obtained by adding a circuit for allowing the microcomputer 200 to detect the voltage of the three-phase AC power supply 1 to the circuit of FIG. As shown in FIG. 4, the voltage from the three-phase AC power source 1 is divided using resistors 901 and 902, and the divided voltage is input to the microcomputer 200.

  Thereby, the microcomputer 200 can know which phase has the lowest potential, and can know the relative potential of the other phases with respect to the lowest potential phase. This makes it possible to:

  1) The microcomputer 200 can calculate each phase voltage, and can be used as information for realizing high power factor sequence control.

  2) The microcomputer 200 can grasp the frequency of the three-phase AC power supply 1 by measuring the period in which each phase is sequentially the lowest voltage.

  3) When each phase does not reach the minimum voltage in turn, the microcomputer 200 can determine that an abnormal situation such as a disconnection has occurred, and can send the information to a higher-level management system.

  4) The microcomputer 200 knows the order in which each phase has the lowest voltage, so that the phase order of the three-phase AC power supply 1 can be known, and information such as the connection being reversed is sent to the upper management system. Can be sent to.

(Embodiment 3)
FIG. 5 shows a case where the power supply for controlling the matrix converter is supplied from between a neutral point N, which is a relatively low voltage, and any of R, S, and T phases. As for the stabilized power supply for control, the voltage applied as an input is 57.7% (the phase voltage / the line voltage is less than the line voltage of the three-phase AC power supply 1 as the supply source). As a result, it is not necessary to use high voltage components in the stabilized power supply.

  As shown in FIG. 5, the voltage between the neutral point N and the T phase is supplied to the stabilized power source 1001 via the insulating transformer 1002 to be a DC power source for driving the matrix converter. The negative output of the stabilized power supply 1001 is connected to the negative side of the three-phase full-wave rectifier circuit 100.

  In order for the negative potential of the three-phase full-wave rectifier circuit 100 to be the same potential as the lowest potential phase of the three-phase AC power supply 1, it is necessary for current to flow through the three-phase full-wave rectifier circuit 100. For that purpose, a slight load such as a resistor 1003 may be connected.

(Embodiment 4)
FIG. 6 shows an embodiment provided with a circuit for further reducing power consumption at the light load (resistor 1003) in FIG.

  As shown in FIG. 6, a current control circuit 1101, a transistor 1102, and a current detection resistor 1103 are connected between the three-phase full-wave rectifier circuit 100 and the DC power supply circuit 101. When the transistor 1102 is turned on, a current flows through the load resistor 1113, and as a result, the current flowing through the current detection resistor 1103 is prevented from falling below a predetermined value.

  That is, when the current of the current detection resistor 1103 becomes equal to or less than a predetermined value, the current output from the full-wave rectifier circuit 100 can be increased by turning on the transistor 1102 and passing the current through the load resistor 1113.

  In this case, the threshold value is set to a value close to zero so that a current of only a load such as a control circuit normally flows. For this reason, the electric power passing through the full-wave rectifier circuit 100 has a small value.

  The current from the full-wave rectifier circuit 100 becomes zero due to some load fluctuation, the full-wave rectifier circuit 100 is turned off, and the potential of the negative electrode potential of the DC power supply is different from the lowest potential phase of the three-phase AC power supply. Only when there is a possibility that the load of the DC power supply will increase, the potential of the negative electrode of the DC power supply and the potential of the lowest potential phase of the three-phase AC power supply can always be kept the same.

  As described above, according to the present embodiment, since the DC power supply circuit 101 is used as the power supply for current control, a new power supply circuit is unnecessary. In the present embodiment, the resistor 1103 is used as the current detection means, but it is obvious that other current detection sensors can be applied. As a result, the load on the three-phase full-wave rectifier circuit 100 is always kept at a minimum, and the power supply circuit for control can be downsized.

(Embodiment 5)
FIG. 7 is a circuit diagram showing an embodiment for further downsizing the control circuit using the neutral point of the three-phase AC power supply. As shown in FIG. 7, diodes 1200 </ b> R, 1200 </ b> S, and 1200 </ b> T are connected to the respective phases of the three-phase AC power supply 1.

  Since the lowest potential phase of the three-phase AC voltage output from the three-phase AC power supply 1 is lower than the neutral potential, current flows only through the lowest voltage phase in these diodes. A half-wave rectifier circuit is configured.

  That is, when the R phase is the lowest voltage, a current flows from the neutral point N via the load resistor 1213, the transistor 1202, the current detection resistor 1203, and the diode 1200R. Similarly, when the other phase reaches the minimum potential, a current flows through the corresponding diode. Since the phase voltage of the three-phase circuit is 57.7% of the line voltage, components with lower withstand voltage can be used in the DC power supply circuit 1211, and the circuit can be further miniaturized and simplified.

  As described above, according to the matrix converter of the present invention, the semiconductor switch and the control circuit for sequence control can be driven by one DC power supply while sharing the reference potential, and the entire circuit can be downsized. It becomes possible to do. As a result, the present invention can be applied not only to industrial equipment but also to home air conditioners using a three-phase AC power source.

  Although a three-phase AC power supply is used in this embodiment, the present invention can be applied to a single-phase AC power supply by reducing the corresponding semiconductor switches, and the same effect can be obtained. it can.

Further, although a three-phase AC motor is used in the present embodiment, the present invention can be applied to a single-phase AC motor by reducing the corresponding semiconductor switches, and the same effect can be obtained. it can.

  Furthermore, in the embodiment of the present invention, a semiconductor switch in which an IGBT and a diode are connected in series is used. However, in recent years, a switch capable of applying a reverse voltage between the emitter and collector of the IGBT has been developed. If such a semiconductor element is used, the diode for preventing reverse voltage inserted in series can be eliminated. With such a configuration, it is possible to suppress the occurrence of circuit loss consumed by the diode for preventing reverse voltage.

  The present invention is useful when a single-phase or three-phase AC load is controlled using a single-phase or three-phase AC power source, and is used, for example, in a device having an electric motor as a load such as an air conditioner, a refrigerator, or a washing machine. can do.

1 is a circuit configuration diagram of a matrix converter according to Embodiment 1 of the present invention. Waveform diagram of three-phase AC voltage for explaining the operation of the present invention More detailed circuit configuration diagram of the matrix converter according to the first embodiment of the present invention. The circuit block diagram of the matrix converter in Embodiment 2 of this invention The circuit block diagram of the matrix converter in Embodiment 3 of this invention The circuit block diagram of the matrix converter in Embodiment 4 of this invention The circuit block diagram of the matrix converter in Embodiment 5 of this invention Circuit diagram in the conventional example Diagram showing basic concept of matrix converter The figure which shows that the matrix converter is constituted using the bidirectional semiconductor switch Circuit diagram of conventional matrix converter More detailed circuit diagram of conventional matrix converter

Explanation of symbols

1,1000 Three-phase AC power supply 2 Three-phase AC motor (three-phase AC load)
100 three-phase full-wave rectifier circuit 101 DC power supply circuit 111, 112, 113, 114, 115, 116 rectifier diode 121, 131 drive circuit 122 capacitor (second drive power supply)
132 capacitor (first drive power supply)
200 Microcomputer 1003 Resistance 1101, 1201 Current control circuit 1103, 1203 Current detection resistance

Claims (10)

In a matrix converter that converts AC power from a single-phase or three-phase AC power source and provides desired AC power to a three-phase AC load, a DC power source that provides a DC voltage based on the lowest potential of the AC power source, and A switch group for controlling bidirectional energization between an AC power source and the three-phase AC load, the first switch for controlling energization from the three-phase AC load to the AC power source; A switch group having a second switch for controlling energization to a three-phase AC load; a first drive circuit for driving the first switch using a DC voltage from the DC power supply; A second drive circuit that drives the second switch using a direct current voltage; and a first drive circuit that is charged by a current from the direct current power supply to the alternating current power supply and that provides a power supply for the first drive circuit. A driving power source, the charged by current to the three-phase AC load from the DC power source, a second matrix converter with a driving power source for providing power for the second driving circuit. A rectifier diode connected to a positive electrode of the DC power supply and blocking a current from the AC power supply, and a rectifier diode connected to a positive electrode of the DC power supply and blocking a current from the three-phase AC load. The matrix converter according to 1. The matrix converter according to claim 1, further comprising a control circuit that receives a voltage from the DC power supply and controls the first and second drive circuits. The control circuit turns on the first switch corresponding to the phase of the AC power source that is the lowest voltage and charges the second driving power source prior to the operation of the three-phase AC load. The matrix converter described. 4. The matrix converter according to claim 3, wherein a voltage obtained by dividing a voltage between the AC power supply and a negative electrode of the DC power supply is provided to the control circuit. 2. The DC power supply according to claim 1, comprising: a rectifier circuit that full-wave rectifies an AC voltage from the AC power supply; and a DC power supply circuit that receives an output voltage of the rectifier circuit and generates a predetermined DC voltage. Matrix converter. The DC power supply includes a transformer in which a neutral point of the AC power supply having three phases and any one of the three phases is connected to a primary side, and full-wave rectification of an AC voltage from the AC power supply. The matrix converter according to claim 1, further comprising: a rectifying circuit that operates; and a DC power supply circuit that is connected to a secondary side of the transformer and operates with reference to a negative electrode of the rectifying circuit. The DC power supply includes a rectifier circuit that half-wave rectifies an AC voltage from the AC power supply, a DC power supply circuit that is connected to a neutral point of the AC power supply having three phases and operates based on an output potential of the rectifier circuit; A matrix converter according to claim 1 comprising: The matrix converter according to any one of claims 6 to 8, wherein the DC power source includes a current control circuit that controls the current flowing through the rectifier circuit so as not to become a predetermined value or less. The apparatus provided with the three-phase alternating current load and the matrix converter of any one of Claims 1-9.

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