JP2010279193A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter having small power loss. <P>SOLUTION: A microcomputer 20 exerts on/off control for N-channel MOS transistors 42 and 43 and IGBT 7 and 10 in a low-current region, in which the saturation voltage of the N-channel MOS transistors 42 and 43 is lower than that of the IGBT 6 and 9 and exerts on/off control for IGBT6, 7, 9, and 10, in a high-current region in which the saturation voltage of the IGBT6 and 9 is lower than that of the N-channel MOS transistors 42 and 43. Thus, the DC loss of a transistor is reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power conversion device, and more particularly to a power conversion device that converts DC power into AC power and supplies it to a load.

  A solar power generation system is a system that converts DC power generated by a solar cell into AC power by a power conditioner and supplies the AC power to household electrical equipment. Since the power generation efficiency of the solar cell is not high, it is necessary to efficiently convert the electric power generated by the solar cell into AC power with a power conditioner. An IPM (Intelligent Power Module) is used for the power conditioner, and power loss in the IPM is reduced (for example, see Patent Document 1).

JP 2008-79475 A

However, the power loss of the conventional IPM is still large.
Therefore, a main object of the present invention is to provide a power conversion device with low power loss.

  A power conversion device according to the present invention is a power conversion device that converts DC power into AC power and supplies the load to a load between a first power supply terminal that receives a first DC voltage and one terminal of the load. A first insulated gate bipolar transistor and a MOS transistor connected in parallel, a second power supply terminal receiving a second DC voltage different from the first DC voltage, and a second terminal connected to the other terminal of the load An insulated gate bipolar transistor, first and second diodes connected in reverse parallel to the first and second insulated gate bipolar transistors, a current detector for detecting a load current, and a control circuit, respectively It is provided. When the load current is lower than a predetermined threshold current, the control circuit performs on / off control of the MOS transistor at the first frequency and controls the second insulated gate bipolar transistor from the first frequency. When the on / off control is performed at a high second frequency and the current flowing through the load is higher than the threshold current, the first insulated gate bipolar transistor is controlled on / off at the first frequency and the second The insulated gate bipolar transistor is turned on / off at the second frequency. Therefore, since the transistor having the lower saturation voltage of the first insulated gate bipolar transistor and the MOS transistor is used according to the load current, the power loss can be reduced.

  Another power converter according to the present invention is a power converter that converts DC power into AC power and supplies the power to a load, the first power supply terminal receiving the first DC voltage and one terminal of the load. A plurality of first insulated gate bipolar transistors that are connected in parallel with each other and controlled to be turned on / off at a first frequency, and a second power source that receives a second DC voltage different from the first DC voltage A second insulated gate bipolar transistor connected between the terminal and the other terminal of the load and controlled to be turned on / off at a second frequency higher than the first frequency, and a plurality of first insulated gate bipolar transistors A first diode connected in antiparallel to the transistor and a second diode connected in antiparallel to the second insulated gate bipolar transistor are provided. Therefore, since the plurality of first insulated gate bipolar transistors are connected in parallel in the low-speed arm, the power loss can be reduced.

  Still another power conversion device according to the present invention is a power conversion device that converts DC power into AC power and supplies the load to a load, wherein one of the first power supply terminal that receives the first DC voltage and the load. A first insulated gate bipolar transistor connected between the first terminal and on / off-controlled at a first frequency; a second power supply terminal receiving a second DC voltage different from the first DC voltage; and a load And a second insulated gate bipolar transistor that is connected to the other terminal of the first and second transistors and is controlled to be turned on / off at a second frequency higher than the first frequency. A plurality of first diodes connected in parallel and a second diode connected in antiparallel to the second insulated gate bipolar transistor. Therefore, since the plurality of first diodes are connected in parallel in the low-speed arm, the power loss can be reduced.

  Still another power conversion device according to the present invention is a power conversion device that converts DC power into AC power and supplies the load to a load, wherein one of the first power supply terminal that receives the first DC voltage and the load. A first insulated gate bipolar transistor connected between the first terminal and on / off-controlled at a first frequency; a second power supply terminal receiving a second DC voltage different from the first DC voltage; and a load A second insulated gate bipolar transistor connected to the other terminal of the first and second transistors, and controlled to be turned on / off at a second frequency higher than the first frequency, and the first and second insulated gate bipolar transistors, respectively. And first and second diodes connected in antiparallel. The saturation voltage of the first insulated gate bipolar transistor is set lower than the saturation voltage of the second insulated gate bipolar transistor. Therefore, the DC loss of the first insulated gate bipolar transistor can be reduced in the low speed side arm, and the switching loss of the second insulated gate bipolar transistor can be reduced in the high speed side arm, thereby reducing the power loss. Can be planned.

  As described above, according to the present invention, the power loss of the power conversion device can be reduced.

It is a circuit block diagram which shows the structure of IPM of the power converter device used as the foundation of this invention. It is a circuit block diagram which shows the other part of the power converter device shown in FIG. It is a circuit block diagram which shows the structure of IPM of the power converter device by Embodiment 1 of this invention. It is a circuit block diagram which shows the structure of the power converter device provided with IPM shown in FIG. It is a figure which shows operation | movement of the resistive element and filter circuit which were shown in FIG. FIG. 5 is a diagram showing current-saturation voltage characteristics of the IGBT and the N-channel MOS transistor shown in FIG. 4. FIG. 6 is a circuit block diagram illustrating a modification of the first embodiment. It is a circuit block diagram which shows the structure of IPM of the power converter device by Embodiment 2 of this invention. It is a circuit block diagram which shows the structure of the power converter device provided with IPM shown in FIG. FIG. 10 is a diagram showing current-voltage characteristics of the IGBT and the diode shown in FIG. 9. It is a circuit block diagram which shows the structure of IPM of the power converter device by Embodiment 3 of this invention. It is a circuit block diagram which shows the structure of the power converter device provided with IPM shown in FIG. It is a figure which shows the saturation voltage and turn-off loss of IGBT shown in FIG. It is a figure which shows the direct current | flow loss and turn-off loss of IGBT shown in FIG.

  Before describing the embodiment, a power conversion device as the basis of the present invention will be described. As shown in FIG. 1, this power conversion device includes an IPM 1. The IPM 1 includes a plurality of terminals T1 to T26, a high breakdown voltage HVIC 2 to 4, a low breakdown voltage LVIC 5, an IGBT (Insulated Gate Bipolar Transistor) 6 to 11, and a free wheeling diode (Free Wheeling Diode). ) 12-17.

  The bias terminals T1, T5 and T9 receive the bias voltages VB1 to VB3, respectively, and are connected to the bias terminals (VB) of the HVICs 2 to 4, respectively. Source terminals T2, T6, and T10 receive source voltages VS1 to VS3, respectively, and are connected to source terminals (VS) of HVICs 2 to 4, respectively. The source terminals (VS) of the HVICs 2 to 4 are connected to AC output terminals T23 to T25, respectively.

  Power supply terminals T3, T7, and T11 all receive DC power supply voltage VCC (for example, 15V) and are connected to power supply terminals (VCC) of HVICs 2 to 4, respectively. Signal input terminals T4, T8, and T12 receive control signals φUP, φVP, and φWP, respectively, and are connected to signal input terminals (IN) of HVICs 2 to 4, respectively. The common terminal T13 receives the reference voltage VNC and is connected to the common terminals (COM) of the HVICs 2 to 4.

  The power supply terminal T14 receives the DC power supply voltage VCC and is connected to the power supply terminal (VCC) of the LVIC5. Signal input terminals T15 to T17 receive control signals φUN, φVN, and φWN, respectively, and are connected to signal input terminals (UN, VN, WN) of LVIC5, respectively. Predetermined signals FO and CFO are output from the LVIC 5 to the signal output terminals T18 and T20, respectively. The common terminal T19 receives the reference voltage VNC and is connected to the ground terminal (GND) and the reference voltage terminal (VNO) of the LVIC5. For example, a signal CIN indicating the level of the load current is input to the signal input terminal T21.

  A positive DC voltage VP generated by the solar cell is applied to the positive voltage terminal T22. A negative DC voltage VN generated by the solar cell is applied to the negative voltage terminal T26. Three-phase AC voltages VU, VV, and VW are output to the AC output terminals T23 to T25, for example, a three-phase motor is connected.

  The collectors of the IGBTs 6 to 8 are connected to the positive voltage terminal T22, their gates are connected to the output terminals (HO) of the HVICs 2 to 4, respectively, and their emitters are connected to the AC output terminals T23 to T25, respectively. The collectors of the IGBTs 9 to 11 are connected to the AC output terminals T23 to T25, their gates are connected to the signal output terminals (UO, VO, WO) of the LVIC 5, and their emitters are connected to the negative voltage terminal T26. The Diodes 12 to 17 are connected in antiparallel to IGBTs 6 to 11, respectively.

  In addition, as shown in FIG. 2, the power converter includes a microcomputer 20, diodes 21, 26, 31, resistance elements 22, 27, 32, 36, capacitors 23 to 25, 28 to 30, 33 to 35, 37. , 39 and a DC power supply 38.

  The microcomputer 20 generates control signals [phi] UP, [phi] VP, [phi] WP, [phi] UN, [phi] VN, [phi] WN and supplies them to the signal input terminals T4, T8, T12, T15 to T17. The DC power supply 38 supplies the power supply voltage VCC to the power supply terminals T3, T7, T11, and T14. The power supply terminals T3, T7, T11, and T14 are grounded through capacitors 25, 30, 35, and 37, respectively.

  The diode 21 and the resistance element 22 are connected in series to the power supply voltage VCC line (the positive electrode of the DC power supply 38) and the bias terminal T1. The capacitors 23 and 24 are connected in parallel between the terminals T1 and T2. The diode 26 and the resistance element 27 are connected in series between the line of the power supply voltage VCC and the bias terminal T5. Capacitors 28 and 29 are connected in parallel between terminals T5 and T6. The diode 31 and the resistance element 32 are connected in series between the line of the power supply voltage VCC and the bias terminal T9. Capacitors 33 and 34 are connected in parallel between terminals T9 and T10.

  The common terminals T <b> 13 and T <b> 19 are connected to the negative electrode of the DC power supply 38 and to the common terminal of the microcomputer 20. The signal output terminal T18 is connected to the line of the power supply voltage Vdd (for example, 5V) through the resistance element 36 and is also connected to the microcomputer 20.

  By connecting in this way, the microcomputer 20 performs on / off control of the IGBTs 6 to 11 and generates the three-phase AC voltages VU, VV, VW based on the DC voltages VP, VN, like a three-phase AC motor. It is possible to drive a load. However, such a power conversion device has a large power loss.

[Embodiment 1]
FIG. 3 is a circuit block diagram showing a configuration of IPM 41 of the power conversion device according to Embodiment 1 of the present invention, and is compared with FIG. In FIG. 3, the IPM 41 is different from the IPM 1 in FIG. 1 in that the IGBTs 8 and 11 are replaced by N-channel MOS transistors 42 and 43, respectively, and the AC output terminal T25 is removed.

  The drain of the transistor 42 is connected to the positive voltage terminal T22, the gate is connected to the output terminal (HO) of the HVIC4, and the source is connected to the AC output terminal T23. The drain of the transistor 43 is connected to the AC output terminal T23, its gate is connected to the output terminal (WO) of the LVIC 5, and its source is connected to the negative voltage terminal T26. That is, the transistors 42 and 43 are connected in parallel to the IGBTs 6 and 9, respectively. Between the AC output terminals T23 and T24, a single-phase AC voltage VAC is output and a household electrical device is connected. As shown in FIG. 2, the power supply voltage VCC is supplied to the terminals T1 to T19.

  FIG. 4 is a circuit block diagram showing the overall configuration of the power converter. In FIG. 4, this power conversion device includes a capacitor 44, a resistance element 45, a filter circuit 46, and the microcomputer 20 in addition to the IPM 41.

  One terminal of the capacitor 44 is connected to the positive voltage terminal T22, and the other terminal is grounded. The capacitor 44 is charged with a DC voltage generated by the solar battery. One terminal of the resistor element 45 is connected to the negative voltage terminal T26, and the other terminal is grounded. Therefore, a bus current I having a level corresponding to the load current flows through the resistance element 45, and a voltage VD having a level corresponding to the bus current I is generated at the negative voltage terminal T26. As shown in FIG. 5, the bus current I includes a pulsed spike current, and the voltage VD includes a pulsed spike voltage. The filter circuit 46 is a low-pass filter that removes the spike voltage from the voltage VD. The output voltage VDF of the filter circuit 46 is given to the microcomputer 20.

  FIG. 6 is a diagram comparing the current-saturation voltage characteristics of each IGBT and the current-saturation voltage characteristics of each N-channel MOS transistor. As shown in FIG. 6, when the current I flowing through the transistor is smaller than the threshold current ITH, the saturation voltage of the N-channel MOS transistor is lower than the saturation voltage of the IGBT, and the current I flowing through the transistor is the threshold current. When it is larger than ITH, the saturation voltage of the IGBT is lower than the saturation voltage of the N-channel MOS transistor. Therefore, an N-channel MOS transistor is used in a low current region where the current I flowing through the transistor is lower than the threshold current ITH, and an IGBT is used in a high current region where the current I flowing through the transistor is higher than the threshold current ITH. Thus, direct current loss generated in the transistor can be reduced.

  Therefore, when the voltage VDF that has passed through the filter circuit 46 is lower than the predetermined threshold voltage VTH, the microcomputer 20 controls the N-channel MOS transistors 42 and 43 and the IGBTs 7 and 10 to turn on / off, When VDF is higher than the threshold voltage VTH, the IGBTs 6, 7, 9, and 10 are on / off controlled.

  That is, when the voltage VDF is lower than the threshold voltage VTH, the IGBTs 6 and 9 are fixed to the off state, and during the period of supplying a positive current to the load, the transistor 42 is turned on and the IGBT 10 operates at the carrier frequency (for example, In the period during which the negative current is supplied to the load, the transistor 43 is turned on and the IGBT 7 is on / off controlled at the carrier frequency. The transistors 42 and 43 are on / off controlled at a commercial frequency (50 Hz or 60 Hz). Further, the gate voltages of the IGBTs 7 and 10 are subjected to pulse width modulation so that a sinusoidal current flows through the load.

  When the voltage VDF is higher than the threshold voltage VTH, the transistors 42 and 43 are fixed in an off state, and the IGBT 6 is turned on and the IGBT 10 is turned on / off at the carrier frequency during a period in which a positive current is supplied to the load. In the period during which a negative current is supplied to the load, the IGBT 9 is turned on and the IGBT 7 is on / off controlled at the carrier frequency. The IGBTs 6 and 9 are on / off controlled at a commercial frequency.

  In the first embodiment, N-channel MOS transistors 42 and 43 are used when the load current is lower than threshold current ITH, and IGBTs 6 and 9 are used when the load current is higher than threshold current ITH. Therefore, the DC loss generated in the transistor can be reduced, and the power loss in the IPM 41 can be reduced.

  In the first embodiment, the N-channel MOS transistors 42 and 43 are connected in parallel only to the low-speed side IGBTs 6 and 9, and the IGBTs 6 and 9 and the N-channel MOS transistors 42 and 43 are selectively used according to the load current. N-channel MOS transistors may be connected in parallel to each of the high-speed side IGBTs 7 and 10, and the IGBTs 7 and 10 and the N-channel MOS transistors may be selectively used in accordance with the load current. However, since low-speed transistors are turned on / off at low speed (50 Hz or 60 Hz), 99% or more of the total loss is DC loss, but high-speed transistors are turned on / off at high speed (15 kHz or higher). Since the control is performed, 30% of the total loss becomes DC loss and 70% becomes switching loss. Therefore, the effect of using N-channel MOS transistors in parallel with each of high-speed IGBTs 7 and 10 is small compared to the effect of using N-channel MOS transistors 42 and 43 in parallel with low-speed IGBTs 6 and 9.

  FIG. 7 is a circuit block diagram showing a modified example of the first embodiment, which is compared with FIG. In FIG. 7, this power conversion device is different from the power conversion device in FIG. 4 in that the resistance element 45 and the filter circuit 46 are replaced with a current sensor 47 and a current detection circuit 48. The current sensor 47 outputs a signal having a level corresponding to the load current. The current detection circuit 48 gives a signal indicating the level of the load current to the microcomputer 20 based on the output signal of the current sensor 47. When the load current is lower than a predetermined threshold current, microcomputer 20 controls on / off of N-channel MOS transistors 42 and 43 and IGBTs 7 and 10, and the load current is higher than the threshold current. In this case, the IGBTs 6, 7, 9, and 10 are on / off controlled. Even in this modified example, the same effect as in the first embodiment can be obtained.

[Embodiment 2]
FIG. 8 is a circuit block diagram showing a configuration of IPM 51 of the power conversion device according to Embodiment 2 of the present invention, and is a diagram compared with FIG. In FIG. 8, this IPM 51 is different from the IPM 1 in FIG. 1 in that the emitter of the IGBT 8, the anode of the diode 14, the collector of the IGBT 11, and the cathode of the diode 17 are all connected to the AC output terminal T23, and the AC output terminal T25 is removed. It is a point that has been. Between the AC output terminals T23 and T24, a single-phase AC voltage VAC is output and a household electrical device is connected. As shown in FIG. 2, the power supply voltage VCC and the like are supplied to the terminals T1 to T19.

  FIG. 9 is a circuit block diagram showing the overall configuration of the power converter. In FIG. 9, the power converter includes a capacitor 44 and a microcomputer 20 in addition to the IPM 51. The capacitor 44 is connected between the positive voltage terminal T22 and the negative voltage terminal T26, and is charged with a DC voltage generated by the solar cell.

  The microcomputer 20 turns on the IGBTs 6 and 8 while the positive current is supplied to the load and controls the IGBT 10 to be turned on / off at the carrier frequency, and turns on the IGBTs 9 and 11 during the period when the negative current is supplied to the load. The IGBT 7 is on / off controlled at the carrier frequency. The IGBTs 6, 8, 9, and 11 are on / off controlled at a commercial frequency. Further, the gate voltages of the IGBTs 7 and 10 are subjected to pulse width modulation so that a sinusoidal current flows through the load.

  FIG. 10A is a diagram comparing the collector current-saturation voltage characteristics (dotted line) of one IGBT 6 and the collector current-saturation voltage characteristics (solid line) of two IGBTs 6 and 8 connected in parallel. FIG. 10B shows the forward current-forward voltage characteristics (dotted line) of one diode 12 and the forward current-forward voltage characteristics (solid line) of a parallel connection body of two diodes 12 and 14. It is a figure to compare. As can be seen from FIGS. 10A and 10B, the saturation voltages of the two IGBTs 6 and 8 are lower than the single IGBT 6, and the two diodes 12 and 14 have a forward voltage higher than the single diode 12. Becomes lower.

  Therefore, in the second embodiment, it is possible to reduce the DC loss that occurs in the low-speed side IGBT, and to reduce the power loss in the IPM.

  In the second embodiment, a plurality of IGBT parallel connections are used on the low speed side, and one IGBT is used on the high speed side. However, a plurality of IGBT parallel connections may also be used on the high speed side. . However, since low-speed IGBTs are controlled on / off at low speed (50 Hz or 60 Hz), 99% or more of the total loss is DC loss, but high-speed IGBTs are on / off at high speed (15 kHz or higher). Since the control is performed, 30% of the total loss becomes DC loss and 70% becomes switching loss. Therefore, the effect of using a parallel connection body of a plurality of IGBTs on the high speed side is smaller than the effect of using a parallel connection body of a plurality of IGBTs on the low speed side.

[Embodiment 3]
FIG. 11 is a circuit block diagram showing a configuration of IPM 55 of the power conversion device according to the third embodiment of the present invention, which is compared with FIG. In FIG. 11, the IPM 55 is different from the IPM 1 in FIG. 1 in that the HVIC 4, IGBTs 8 and 11, diodes 14 and 17, and terminals T9 to T12 and T25 are removed. Further, low speed IGBTs with low turn-off speed but low saturation voltage are used for each of the low speed IGBTs 6 and 9, and high speed specifications with high turn-off speed but high saturation voltage are used for each of the high speed IGBTs 7 and 10. IGBTs are used. Between the AC output terminals T23 and T24, a single-phase AC voltage VAC is output and a household electrical device is connected. As shown in FIG. 2, the power supply voltage VCC and the like are supplied to the terminals T1 to T8 and T13 to T19.

  FIG. 12 is a circuit block diagram showing the overall configuration of this power converter. In FIG. 12, the power conversion device includes a capacitor 44 and a microcomputer 20 in addition to the IPM 55. The capacitor 44 is connected between the positive voltage terminal T22 and the negative voltage terminal T26, and is charged with a DC voltage generated by the solar cell.

  The microcomputer 20 turns on the IGBT 6 and controls the IGBT 10 on / off at the carrier frequency during a period for supplying a positive current to the load, and turns on the IGBT 9 and sets the IGBT 7 at a carrier frequency during the period for supplying a negative current to the load. ON / OFF control with. The IGBTs 6 and 9 are on / off controlled at a commercial frequency. Further, the gate voltages of the IGBTs 7 and 10 are subjected to pulse width modulation so that a sinusoidal current flows through the load.

  Here, the power loss of the IGBT will be described. The power loss of the IGBT is the sum of the DC loss and the switch loss. DC loss is the product of the saturation voltage and collector current of the IGBT. Switch loss is the sum of turn-on loss and turn-off loss.

  FIG. 13 is a diagram showing the saturation voltage and turn-off loss of each of the IGBTs 6 and 7. As shown in FIG. 13, the saturation voltage V1 of the low-speed specification IGBT 6 is smaller than the saturation voltage V2 of the high-speed specification IGBT 7, but the turn-off loss W1 generated in the IGBT 6 is larger than the turn-off loss W2 generated in the IGBT 7. Thus, the saturation voltage of the IGBT and the turn-off loss are in a trade-off relationship.

  14A is a diagram showing the collector-emitter voltage Vce, collector current Ic, DC loss, and turn-off loss of the low-speed specification IGBT 6, and FIG. 14B is the collector-emitter of the high-speed specification IGBT 7. It is a figure which shows inter-voltage Vce, collector current Ic, DC loss, and turn-off loss.

  As can be seen from FIGS. 14A and 14B, since the saturation voltage of the low-speed specification IGBT 6 is smaller than the saturation voltage of the high-speed specification IGBT 7, the DC loss of the IGBT 6 is smaller than the DC loss of the IGBT 7. On the other hand, since the turn-off speed of the low-speed specification IGBT 6 is slower than the turn-off speed of the high-speed specification IGBT 7, the turn-off loss of the IGBT 6 is larger than the turn-off loss of the IGBT 7.

  Since the IGBTs 6 and 9 on the low speed side are turned on / off at a low frequency (50 Hz or 60 Hz), 99% or more of the losses of the IGBTs 6 and 9 become DC losses. Therefore, as the low-speed IGBTs 6 and 9, the loss in the IGBTs 6 and 9 is smaller when the low-speed IGBT is used than when the high-speed IGBT is used.

  On the other hand, since the IGBTs 7 and 10 on the high speed side are turned on / off at a high frequency (15 kHz or more), about 70% or more of the loss of the IGBTs 7 and 10 is the switch loss. Therefore, as the high-speed IGBTs 7 and 10, the loss in the IGBTs 7 and 10 is smaller when the high-speed specification IGBT is used than when the low-speed specification IGBT is used.

  Therefore, in this Embodiment 3, the power loss which generate | occur | produces in IGBT6,7,9,10 can be made small, and the reduction of the power loss in IPM55 can be aimed at.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  T1-T26 terminal, 1,41,51,55 IPM, 2-4 HVIC, 5 LVIC, 6-11 IGBT, 12-17, 21,26, 31 diode, 20 microcomputer, 22, 27, 32, 36, 45 resistor elements, 23-25, 28-30, 33-35, 37, 39, 44 capacitors, 42, 43 N-channel MOS transistors, 46 filter circuits, 47 current sensors, 48 current detection circuits.

Claims (5)

A power conversion device that converts DC power into AC power and supplies it to a load,
A first insulated gate bipolar transistor and a MOS transistor connected in parallel between a first power supply terminal receiving a first DC voltage and one terminal of the load;
A second insulated gate bipolar transistor connected between a second power supply terminal receiving a second DC voltage different from the first DC voltage and the other terminal of the load;
First and second diodes connected in antiparallel to the first and second insulated gate bipolar transistors, respectively;
A current detector for detecting the load current;
When the load current is lower than a predetermined threshold current, the MOS transistor is controlled to be turned on / off at a first frequency, and the second insulated gate bipolar transistor is controlled to be lower than the first frequency. On / off control is performed at a high second frequency, and when the current flowing through the load is higher than the threshold current, the first insulated gate bipolar transistor is controlled on / off at the first frequency. And a control circuit that controls on / off of the second insulated gate bipolar transistor at the second frequency. A power conversion device that converts DC power into AC power and supplies it to a load,
A plurality of first insulated gate bipolar transistors that are connected in parallel between a first power supply terminal that receives a first DC voltage and one terminal of the load, both of which are on / off controlled at a first frequency;
On / off control at a second frequency higher than the first frequency is connected between a second power supply terminal receiving a second DC voltage different from the first DC voltage and the other terminal of the load. A second insulated gate bipolar transistor,
A first diode connected in anti-parallel to the plurality of first insulated gate bipolar transistors;
And a second diode connected in antiparallel to the second insulated gate bipolar transistor.   The power conversion device according to claim 2, wherein a plurality of the first diodes are provided. A power conversion device that converts DC power into AC power and supplies it to a load,
A first insulated gate bipolar transistor connected between a first power supply terminal receiving a first DC voltage and one terminal of the load and controlled to be turned on / off at a first frequency;
On / off control at a second frequency higher than the first frequency is connected between a second power supply terminal receiving a second DC voltage different from the first DC voltage and the other terminal of the load. A second insulated gate bipolar transistor,
A plurality of first diodes each connected in anti-parallel to the first insulated gate bipolar transistor;
And a second diode connected in antiparallel to the second insulated gate bipolar transistor. A power conversion device that converts DC power into AC power and supplies it to a load,
A first insulated gate bipolar transistor connected between a first power supply terminal receiving a first DC voltage and one terminal of the load and controlled to be turned on / off at a first frequency;
On / off control at a second frequency higher than the first frequency is connected between a second power supply terminal receiving a second DC voltage different from the first DC voltage and the other terminal of the load. A second insulated gate bipolar transistor,
First and second diodes connected in antiparallel to the first and second insulated gate bipolar transistors, respectively,
The power conversion device, wherein a saturation voltage of the first insulated gate bipolar transistor is set lower than a saturation voltage of the second insulated gate bipolar transistor.

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