Power conversion device

Abstract

This power conversion device is provided with: a rotary electric machine (40) having windings (51U, 51V, 51W); a first inverter (20) having first upper and lower arm switches (SUHa-SWLa); and a second inverter (30) having second upper and lower arm switches (SUHb-SWLb). The power conversion device is provided with: a discharge resistor (70, 71) connected in parallel to only one of a first capacitor (15a) and a second capacitor (15b); and a switch unit (QHa, QHb, QLa, QLb, DH, DL, JH, JL) provided on at least one of a positive electrode-side bus (11) and a negative electrode-side bus (12). In a state in which power switches (MH, ML) are turned off, the discharge resistor and the switch unit are configured to allow a current to flow through a closed circuit including the discharge resistor and a specific capacitor from among the first capacitor and the second capacitor to which no discharge resistor is connected in parallel.

Description

Power Conversion Device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-011751 filed on January 30, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a power conversion device.

[0003] Conventionally, a power conversion device that controls a rotating electric machine using two inverters has been known. In this power conversion device, a first inverter is electrically connected to first ends of a multi-phase winding of the rotating electric machine, and a second inverter is electrically connected to second ends of the winding. A DC power supply and a first capacitor are electrically connected in parallel to the first inverter. A second capacitor is electrically connected in parallel to the second inverter. An example of such a technology is disclosed in Patent Document 1.

[0004] Japanese Patent Application Laid-Open No. 2021-125922

[0005] In the above-described power conversion device, when a power switch provided in a path electrically connecting the first inverter and the DC power supply is turned off, the current flow between the DC power supply and the rotating electric machine is terminated. For example, the power switch is turned off by a user instruction. In this case, the first capacitor and the second capacitor are discharged while the power switch is turned off.

[0006] However, even if an abnormality occurs in the power conversion device, the power switch may be turned off. In this regard, a technology is desired that appropriately realizes a configuration in the power conversion device that can discharge the first capacitor and the second capacitor when an abnormality occurs.

[0007] An object of the present disclosure is to provide a power conversion device that can appropriately realize a configuration that allows the first capacitor and the second capacitor to be discharged when an abnormality occurs.

[0008] A first configuration of the present disclosure is a power conversion device comprising: a rotating electric machine having windings for multiple phases; a first inverter having first upper arm switches and first lower arm switches connected in series for the same number of phases, wherein the series-connected assembly of the first upper arm switches and the first lower arm switches is connected in parallel to a DC power supply and a first capacitor; a second inverter having second upper arm switches and second lower arm switches connected in series for the same number of phases, wherein the series-connected assembly of the second upper arm switches and the second lower arm switches is connected in parallel to a second capacitor; a positive bus bar connecting a high potential side terminal of the first upper arm switch to a high potential side terminal of the second upper arm switch in each phase; a negative bus bar connecting a low potential side terminal of the first lower arm switch to a low potential side terminal of the second lower arm switch in each phase; and a power switch provided in a path connecting the first inverter and the DC power supply, wherein in each phase, the low potential side terminal of the first upper arm switch and the high potential side terminal of the first lower arm switch are connected to first ends of the windings, In each phase, the low potential side terminal of the second upper arm switch and the high potential side terminal of the second lower arm switch are connected to the second end of the winding, and the power supply comprises: a discharge resistor connected in parallel to only one of the first capacitor and the second capacitor; and a switch unit provided on a target bus which is at least one of the positive side bus and the negative side bus, wherein the discharge resistor and the switch unit are configured to be able to pass current through a closed circuit including the discharge resistor and a specific capacitor of the first capacitor and the second capacitor to which the discharge resistor is not connected in parallel when the power switch is turned off.

[0009] It is conceivable to provide resistors to enable the first and second capacitors to be discharged when an abnormality occurs in the power conversion device and the power switch is turned off. In this case, there is a concern that the number of components in the power conversion device will increase due to the provision of a resistor for discharging the first capacitor and a resistor for discharging the second capacitor. Therefore, there is a concern that the power conversion device may not be able to appropriately achieve a configuration that allows the first and second capacitors to be discharged when an abnormality occurs.

[0010] Therefore, in the first configuration, a discharge resistor is connected in parallel to only one of the first capacitor and the second capacitor. This allows the capacitor connected in parallel to the discharge resistor to discharge. The discharge resistor and switch unit are provided to allow current to flow through a closed circuit including the specific capacitor and the discharge resistor. This allows the specific capacitor to discharge. Therefore, by allowing the first capacitor and the second capacitor to be discharged by the discharge resistor, an increase in the number of components in the power conversion device can be suppressed. As a result, a configuration that allows the first capacitor and the second capacitor to be discharged in the event of an abnormality can be appropriately realized in the power conversion device.

[0011] The first configuration, in which "the discharge resistor and the switch unit are configured so that, when the power switch is turned off, a current can flow to a specific capacitor of the first capacitor and the second capacitor to which the discharge resistor is not connected in parallel, and a closed circuit including the discharge resistor," can be realized by the following second to fourth configurations.

[0012] The second configuration is the same as the first configuration, except that the discharge resistor is connected in parallel to only the first capacitor of the first and second capacitors, the switch unit has a changeover switch and a diode connected in parallel to the changeover switch, and the anode and cathode of the diode are oriented in a direction that allows the discharge current of the second capacitor to flow through the discharge resistor.

[0013] In the second configuration, the discharge current of the second capacitor flows through the diode, allowing a current to flow through a closed circuit including the second capacitor and the discharge resistor, thereby discharging the first capacitor and the second capacitor through the discharge resistor.

[0014] In a third configuration, in the first configuration, the switch section includes a normally-off type changeover switch and a normally-on type parallel switch connected in parallel to the changeover switch.

[0015] In the third configuration, the discharge current of the specific capacitor turns on the parallel switch, allowing a current to flow through a closed circuit including the specific capacitor and the discharge resistor, thereby discharging the first capacitor and the second capacitor through the discharge resistor.

[0016] In a fourth configuration, in the first configuration, the switch section has a normally-on switch.

[0017] In the fourth configuration, the discharge current of the specific capacitor turns on the normally-on switch, allowing a current to flow through a closed circuit including the specific capacitor and the discharge resistor, thereby discharging the first capacitor and the second capacitor through the discharge resistor.

[0018] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is an overall configuration diagram of a power conversion system according to a first embodiment, Fig. 2 is a functional block diagram of processing executed by a control device, Fig. 3 is a diagram showing a control mode of H drive control, Fig. 4 is a diagram showing a control mode of Y drive control, Fig. 5 is a flowchart showing a procedure of processing executed by a control device, Fig. 6 is a time chart showing an example of operation of the power conversion system, Fig. 7 is an overall configuration diagram of a power conversion system according to a second embodiment, Fig. 8 is a time chart showing an example of operation of the power conversion system, Fig. 9 is an overall configuration diagram of a power conversion system according to a third embodiment, Fig. 10 is a functional block diagram of processing executed by a control device, and Fig. 11 is a time chart showing an example of operation of the power conversion system.

[0019] Several embodiments will be described with reference to the drawings. In several embodiments, functionally and / or structurally corresponding and / or associated parts may be designated by the same reference numerals or reference numerals that differ in the hundredth or more digit. For corresponding and / or associated parts, reference may be made to the descriptions of other embodiments.

[0020] A first embodiment of a power conversion device according to the present disclosure will now be described with reference to the drawings. The power conversion device of this embodiment is mounted on an electrically powered vehicle such as an electric vehicle or a hybrid vehicle, and constitutes an on-board power conversion system.

[0021] As shown in FIG. 1 , the power conversion system 100 includes a battery 10 (corresponding to a "DC power supply"), a first inverter 20, a second inverter 30, and a rotating electrical machine 40. The battery 10 is, for example, a battery pack including a series connection of unit cells. The unit cell is a single battery cell or a series connection of multiple battery cells. The battery cell is, for example, a secondary battery such as a lithium-ion battery.

[0022] The first inverter 20 and the second inverter 30 are power conversion circuits that convert DC power supplied from the battery 10 into three-phase AC power and supply it to the rotating electric machine 40 .

[0023] The first inverter 20 includes a series connection of U-, V-, and W-phase first upper arm switches SUHa, SVHa, and SWHa and U-, V-, and W-phase first lower arm switches SULa, SVLa, and SWLa. The second inverter 30 includes a series connection of U-, V-, and W-phase second upper arm switches SUHb, SVHb, and SWHb and U-, V-, and W-phase second lower arm switches SULb, SVLb, and SWLb.

[0024] In this embodiment, voltage-controlled semiconductor switching elements, more specifically, IGBTs, are used as the switches SUHa to SWLa and SUHb to SWLb. In this embodiment, the high-potential terminal of each switch is the collector, and the low-potential terminal is the emitter. Freewheeling diodes DUHa, DVHa, DWHa, DULa, DVLa, DWLa, DUHb, DVHb, DWHb, DULb, DVLb, and DWLb are connected in anti-parallel to the switches SUHa, SVHa, SWHa, SULa, SVLa, SWLa, SUHb, SVHb, SWHb, SULb, SVLb, and SWLb, respectively.

[0025] The collectors of the first upper arm switches SUHa, SVHa, SWHa of each phase and the collectors of the second upper arm switches SUHb, SVHb, SWHb of each phase are electrically connected by a positive bus 11 such as a bus bar. The emitters of the first lower arm switches SULa, SVLa, SWLa of each phase and the emitters of the second lower arm switches SULb, SVLb, SWLb of each phase are electrically connected by a negative bus 12 such as a bus bar.

[0026] The positive terminal of the battery 10 is electrically connected to the positive bus 11 on the side opposite to the connection point with the second upper arm switches SUHb, SVHb, SWHb of each phase, relative to the connection point with the first upper arm switches SUHa, SVHa, SWHa of each phase. The negative terminal of the battery 10 is electrically connected to the negative bus 12 on the side opposite to the connection point with the second lower arm switches SULb, SVLb, SWLb of each phase, relative to the connection point with the first lower arm switches SULa, SVLa, SWLa of each phase.

[0027] The rotating electric machine 40 is an in-vehicle main motor. A rotor 41 of the rotating electric machine 40 is capable of transmitting power to drive wheels 43 of the vehicle. In this embodiment, the rotating electric machine 40 is a permanent magnet field type synchronous machine. The rotor 41 includes permanent magnets 42 (e.g., neodymium magnets) as field poles.

[0028] The rotating electric machine 40 includes a stator 50. The stator 50 includes armature windings, namely, a U-phase winding 51U, a V-phase winding 51V, and a W-phase winding 51W. The phase windings 51U, 51V, and 51W are arranged with an electrical angle offset of 120°. The phase windings 51U, 51V, and 51W are open-connected, and both ends of each phase winding 51U, 51V, and 51W are electrically connected to the first inverter 20 or the second inverter 30.

[0029] Specifically, in each phase, the first ends 51Ua, 51Va, 51Wa of the windings 51U, 51V, 51W are electrically connected to the emitters of the first upper switches SUHa, SVHa, SWHa and the collectors of the first lower switches SULa, SVLa, SWLa. In addition, the second ends 51Ub, 51Vb, 51Wb of the windings 51U, 51V, 51W are electrically connected to the emitters of the second upper switches SUHb, SVHb, SWHb and the collectors of the second lower switches SULb, SVLb, SWLb.

[0030] The power conversion system 100 includes a positive-side changeover switch QHa and a negative-side changeover switch QLa. The positive-side changeover switch QHa is provided on a positive-side bus 11 (corresponding to a "target bus") between the first inverter 20 and the second inverter 30. Specifically, the positive-side changeover switch QHa is provided on the positive-side bus 11 between a connection point between the first upper arm switches SUHa, SVHa, and SWHa of each phase and a connection point between the second upper arm switches SUHb, SVHb, and SWHb of each phase. When turned on, the positive-side changeover switch QHa electrically connects the first inverter 20 and the second inverter 30 of the positive-side bus 11, and when turned off, electrically disconnects the first inverter 20 and the second inverter 30 of the positive-side bus 11.

[0031] The negative-side changeover switch QLa is provided on the negative-side bus 12 (corresponding to the "target bus") between the first inverter 20 and the second inverter 30. Specifically, the negative-side changeover switch QLa is provided on the negative-side bus 12 between a connection point with the first lower arm switches SULa, SVLa, SWLa of each phase and a connection point with the second lower arm switches SULb, SVLb, SWLb of each phase. The negative-side changeover switch QLa electrically connects the first inverter 20 and the second inverter 30 when turned on, and electrically disconnects the first inverter 20 and the second inverter 30 when turned off.

[0032] In this embodiment, the positive-side changeover switch QHa and the negative-side changeover switch QLa are controlled by a control device 60 provided in the power conversion system 100. The positive-side changeover switch QHa and the negative-side changeover switch QLa are provided to switch the driving state of the power conversion system 100, as will be described later.

[0033] The power conversion system 100 includes a first capacitor 15a and a second capacitor 15b. Each of the capacitors 15a and 15b is a smoothing capacitor. For example, each of the capacitors 15a and 15b may be an electric double layer capacitor or an electrolytic capacitor.

[0034] A first end of the first capacitor 15a is electrically connected between a connection point of the positive bus 11 with the first upper arm switches SUHa, SVHa, SWHa of each phase and the positive terminal of the battery 10. A second end of the first capacitor 15a is electrically connected between a connection point of the negative bus 12 with the first lower arm switches SULa, SVLa, SWLa of each phase and the negative terminal of the battery 10. In other words, the first capacitor 15a is electrically connected in parallel to the series connection of the first upper arm switches SUHa, SVHa, SWHa of each phase and the first lower arm switches SULa, SVLa, SWLa of each phase.

[0035] A first end of the second capacitor 15b is electrically connected to the positive bus 11 on the side opposite to the connection point with the first upper arm switches SUHa, SVHa, SWHa of each phase, relative to the connection point with the second upper arm switches SUHb, SVHb, SWHb of each phase. A second end of the second capacitor 15b is electrically connected to the negative bus 12 on the side opposite to the connection point with the first lower arm switches SULa, SVLa, SWLa of each phase, relative to the connection point with the second lower arm switches SULb, SVLb, SWLb of each phase. In other words, the second capacitor 15b is electrically connected in parallel to the series connection of the second upper arm switches SUHb, SVHb, SWHb of each phase and the second lower arm switches SULb, SVLb, SWLb of each phase.

[0036] The power conversion system 100 includes a positive-side power switch MH and a negative-side power switch ML. The positive-side power switch MH is provided between a connection point of the positive-side bus 11 with a first end of the first capacitor 15a and the positive terminal of the battery 10. The negative-side power switch ML is provided between a connection point of the negative-side bus 12 with a second end of the first capacitor 15a and the negative terminal of the battery 10. Each of the power switches MH and ML is a normally-off switch, such as a relay or a semiconductor switching element. Each of the power switches MH and ML is controlled by a control device 60.

[0037] The power conversion system 100 includes a voltage sensor 61, a current sensor 62, a rotation angle sensor 63, a start switch 64, and an acceleration sensor 65. The voltage sensor 61 detects the voltage of the first capacitor 15a. The current sensor 62 detects the phase current flowing through each of the phase windings 51U, 51V, and 51W. In this embodiment, the current sensor 62 is provided on one of the ends of each of the phase windings 51U, 51V, and 51W that is closer to the first inverter 20. The current sensor 62 may also be provided on one of the ends of each of the phase windings 51U, 51V, and 51W that is closer to the second inverter 30. The rotation angle sensor 63 is, for example, a resolver, and detects the electrical angle of the rotor 41. The detected values ​​of the sensors 61 to 63 are input to the control device 60.

[0038] The start switch 64 is, for example, an ignition switch or a push-button start switch, and is operated by the vehicle user. The acceleration sensor 65 detects the acceleration a of the vehicle. A signal notifying that the start switch 64 has been turned on or off and the detected value of the acceleration sensor 65 are input to the control device 60.

[0039] The control device 60 is an electronic control unit (ECU) that performs various controls of the power conversion system 100, and includes a processor 60a and a storage unit 60b as hardware. In the power conversion system 100, each on-board device can be controlled by its corresponding ECU. However, for convenience, multiple ECUs are shown as a single control device 60 in FIG. 1 .

[0040] The memory unit 60b includes a memory and a storage as hardware. The memory is a storage device for storing data used in the processing of the control device 60. The memory provides the processor 60a with a working area for temporary use when the processor 60a performs processing, for example. The memory includes, for example, a ROM or a RAM. The storage is a storage device for storing various programs and data to be read and executed by the processor 60a, and is a non-transitory tangible storage medium. The storage includes, for example, an HDD or a flash memory. The storage stores program information and the like for the processing shown in FIGS. 2 and 5, which will be described later.

[0041] For example, program information stored in a non-transient physical recording medium is installed in the storage unit 60b. The recording medium is, for example, a USB memory, a CD-ROM, or a DVD. Also, for example, program information transmitted via a communication network, such as over the air (OTA), is installed in the storage unit 60b.

[0042] 2, the control device 60 includes an inverter control unit 80, a speed calculation unit 81, a selection unit 82, and a switch control unit 83. A signal indicating that the start switch 64 has been turned on or off is input to the switch control unit 83. When the signal indicating that the start switch 64 has been turned on is input to the switch control unit 83, the switch control unit 83 turns on the power switches MH and ML. When the signal indicating that the start switch 64 has been turned off is input to the switch control unit 83, the switch control unit 83 turns off the power switches MH and ML.

[0043] In order to control the control variable of the rotary electric machine 40 to a command value, the inverter control unit 80 controls the on / off of the switches SUHa to SWLa of the first inverter 20 and the switches SUHb to SWLb of the second inverter 30 while the power switches MH and ML are turned on. In this embodiment, the control variable is torque.

[0044] Specifically, the inverter control unit 80 receives as inputs a detected voltage Vr detected by a voltage sensor 61, phase currents Iur, Ivr, and Iwr detected by a current sensor 62, and an electrical angle θr detected by a rotation angle sensor 63. The inverter control unit 80 generates drive signals for the switches SUHa to SWLa and SUHb to SWLb based on the detected voltage Vr, the phase currents Iur, Ivr, and Iwr, and the electrical angle θr, in order to control the torque of the rotating electric machine 40 to a torque command value Trq* received from a control device that is higher in level than the control device 60. The drive signals include on and off commands for the switches.

[0045] The speed calculation unit 81 calculates the rotation speed Nr of the rotor 41 based on the electrical angle θr detected by the rotation angle sensor 63 .

[0046] The selector 82 determines whether the power conversion system 100 should perform Y-drive control or H-drive control. In the present embodiment, the selector 82 selects whether the power conversion system 100 should perform Y-drive control or H-drive control based on the operating point of the rotating electric machine 40, which is determined by the calculated rotation speed Nr and torque command value Trq*, and on the control map information. The control map information is information that defines the Y-drive control region and the H-drive control region in association with the rotation speed Nr and the torque command value Trq*. The control map information is stored in the memory 60b.

[0047] When the H drive control is selected by the selection unit 82, the switch control unit 83 turns on the changeover switches QHa and QLa as the H drive control, as shown in Fig. 3. When the H drive control is selected by the selection unit 82, the inverter control unit 80 PWM-drives the switches SUHa to SWLa of the first inverter 20 and also PWM-drives the switches SUHb to SWLb of the second inverter 30.

[0048] On the other hand, when Y-drive control is selected by the selector 82, the switch control unit 83 turns off the changeover switches QHa and QLa as Y-drive control, as shown in FIG. 4. When Y-drive control is selected by the selector 82, the inverter control unit 80 controls the switches SUHa to SWLa of the first inverter 20 to be PWM-driven. The inverter control unit 80 also fixes the second upper-arm switches SUHb, SVHb, and SWHb of each phase to be on, and fixes the second lower-arm switches SULb, SVLb, and SWLb of each phase to be off. This results in star-connection of the phase windings 51U, 51V, and 51W via the second inverter 30.

[0049] It is also possible to perform Y-drive control as follows. When the selector switches QHa and QLa are turned off, the inverter control unit 80 may fix the second upper arm switches SUHb, SVHb, and SWHb of each phase to off, and fix the second lower arm switches SULb, SVLb, and SWLb of each phase to on. Furthermore, when the Y-drive control is selected, the switch control unit 83 may turn off only the positive-side selector switch QHa of the selector switches QHa and QLa. In this case, the inverter control unit 80 may fix the second upper arm switches SUHb, SVHb, and SWHb of each phase to on, and fix the second lower arm switches SULb, SVLb, and SWLb of each phase to off. When the Y-drive control is selected, the switch control unit 83 may turn off only the negative-side selector switch QLa of the selector switches QHa and QLa. In this case, the inverter control unit 80 may fix the second upper arm switches SUHb, SVHb, SWHb of each phase to OFF, and fix the second lower arm switches SULb, SVLb, SWLb of each phase to ON.

[0050] Based on the generated drive signal, the inverter control unit 80 controls the charge / discharge current of the gates of the switches SUHa to SWLa and SUHb to SWLb in the first and second inverters 20 and 30. As a result, the on / off of the switches SUHa to SWLa and SUHb to SWLb in the first and second inverters 20 and 30 is controlled in accordance with the drive signal.

[0051] 5 is a flowchart showing the control process of the rotary electric machine 40 executed by the control device 60. The process shown in FIG. 5 is repeatedly executed by the processor 60a of the control device 60, for example, at a predetermined control cycle.

[0052] In step S10 , the selection unit 82 acquires the torque command value Trq* and the rotation speed Nr calculated by the speed calculation unit 81 .

[0053] In step S11, the selection unit 82 selects either the Y drive control or the H drive control based on the torque command value Trq* and the rotation speed Nr.

[0054] If the Y drive state is selected in step S11, the process proceeds to step S13, where the inverter control unit 80 and the switch control unit 83 execute the Y drive control shown in Fig. 4. On the other hand, if the H drive state is selected in step S11, the process proceeds to step S14, where the inverter control unit 80 and the switch control unit 83 execute the H drive control shown in Fig. 3.

[0055] When an abnormality occurs in the power conversion system 100, the power switches MH and ML may be turned off, causing the capacitors 15a and 15b to discharge.

[0056] 2, the control device 60 includes an abnormality determination unit 84. The abnormality determination unit 84 determines whether an abnormality has occurred in the power conversion system 100. If it is determined that an abnormality has occurred in the power conversion system 100, the switch control unit 83 turns off the power switches MH and ML. In this case, for example, with the power switches MH and ML in an OFF state, the inverter control unit 80 discharges the capacitors 15a and 15b by controlling the switching of the switches SUHa to SWLa and SUHb to SWLb so that a d-axis current flows through the phase windings 51U, 51V, and 51W.

[0057] In this embodiment, the acceleration ar of the vehicle detected by the acceleration sensor 65 is input to the abnormality determination unit 84. The abnormality determination unit 84 determines whether a vehicle collision has occurred based on the input acceleration ar to determine whether an abnormality has occurred in the power conversion system 100.

[0058] However, as an abnormality in the power conversion system 100, a failure may occur in at least one of the control device 60, the first inverter 20, and the second inverter 30. If a failure occurs in at least one of the inverters 20, 30, it may be impossible to perform switching control for discharging the capacitors 15 a, 15 b. Furthermore, if the control device 60 loses the abnormality determination function of the abnormality determination unit 84 or loses the switching control function of the inverter control unit 80, it may be impossible to discharge the capacitors 15 a, 15 b.

[0059] In this regard, it is conceivable to provide resistors so that the capacitors 15a, 15b can be discharged when an abnormality occurs in the power conversion system 100 and the power switches MH, ML are turned off. In this case, if a resistor for discharging the first capacitor 15a and a resistor for discharging the second capacitor 15b are provided in a comparative example different from this embodiment, there is a concern that the number of components in the power conversion system 100 will increase. Therefore, a technology is desired that appropriately realizes a configuration in the power conversion system 100 that can discharge the first capacitor 15a and the second capacitor 15b when an abnormality occurs.

[0060] Therefore, in this embodiment, the power conversion system 100 has the following configuration to enable the first capacitor 15a and the second capacitor 15b to be discharged when an abnormality occurs.

[0061] The power conversion system 100 includes a discharge resistor 70 as a passive element and a series switch Ka. The discharge resistor 70 is a resistor having a resistance value determined based on the voltage (e.g., rated voltage) of the battery 10 and the capacitance of each of the capacitors 15 a and 15 b.

[0062] The discharge resistor 70 is electrically connected in parallel to only the first capacitor 15a of the first capacitor 15a and the second capacitor 15b. Specifically, a first end of the discharge resistor 70 is electrically connected between the connection point of the positive bus 11 with the first end of the first capacitor 15a and the positive power switch MH. A second end of the discharge resistor 70 is electrically connected between the connection point of the negative bus 12 with the second end of the first capacitor 15a and the negative power switch ML.

[0063] The series switch Ka is connected in series to the discharge resistor 70 on the high potential side of the discharge resistor 70. Specifically, a first end of the discharge resistor 70 is electrically connected to the series switch Ka. The series switch Ka is electrically connected between the positive-side power switch MH and a connection point of the positive-side bus 11 with the first end of the first capacitor 15a. The series switch Ka is a normally-on switch. For example, the series switch Ka is a semiconductor switching element such as a normally closed mechanical relay or a depletion-type N-channel MOSFET. The series switch Ka is controlled by the switch control unit 83.

[0064] The switch control unit 83 turns off the series switch Ka when it is determined that no abnormality has occurred in the power conversion system 100. This prevents current from flowing through the discharge resistor 70 while the rotating electric machine 40 is running. On the other hand, when it is determined that an abnormality has occurred in the power conversion system 100, the switch control unit 83 turns on the series switch Ka.

[0065] In this embodiment, when the series switch Ka is turned on and the power switches MH and ML are turned off, it is possible to pass current through a closed circuit including the second capacitor 15b and the discharge resistor 70.

[0066] Specifically, normally-off semiconductor switching elements, specifically IGBTs, are used as the switches QHa and QLa. In this case, freewheel diodes DH and DL are connected in parallel to the switches QHa and QLa. The anode of the diode DH connected in parallel to the positive switch QHa is electrically connected to the emitter of the positive switch QHa, and the cathode is electrically connected to the collector of the positive switch QHa. The anode of the diode DL connected in parallel to the negative switch QLa is electrically connected to the emitter of the negative switch QLa, and the cathode is electrically connected to the collector of the negative switch QLa. The anode and cathode of each diode DH and DL are thus oriented so that the discharge current of the second capacitor 15b can flow to the discharge resistor 70.

[0067] In this embodiment, the changeover switches QHa, QLa and the diodes DH, DL correspond to a "switch unit." The buses 11, 12, the first inverter 20, the second inverter 30, the rotating electric machine 40, the discharge resistor 70, the power switches MH, ML, the changeover switches QHa, QLa, and the diodes DH, DL constitute a "power conversion device."

[0068] 6, a description will be given of the operation when an abnormality occurs in power conversion system 100. Here, it is assumed that a vehicle collision occurs at time t1, and the drive signals for switches SUHa-SWLa and SUHb-SWLb controlled by inverter control unit 80 and the control signals for switches MH, ML, QHa, QLa, and Ka controlled by switch control unit 83 are interrupted.

[0069] 6, (a) shows the transition of the voltages VC1 and VC2 of the capacitors 15a and 15b, (b) shows the transition of the currents IDH and IDL flowing through the diodes DH and DL connected in parallel to the change-over switches QHa and QLa, (c) shows the on / off states of the change-over switches QHa and QLa, (d) shows the on / off states of the series switch Ka, and (e) shows the on / off states of the power switches MH and ML. The signs of the currents IDH and IDL flowing through the diodes DH and DL are positive in the direction from the first inverter 20 to the second inverter 30 in each bus 11 and 12, and negative in the direction from the second inverter 30 to the first inverter 20.

[0070] Before time t1, the selector 82 selects H drive control. In this case, the switch controller 83 turns on the power switches MH and ML and the selector switches QHa and QLa, and turns off the series switch Ka. The inverter controller 80 controls the switching of the switches SUHa to SWLa and SUHb to SWLb.

[0071] After time t1, the drive signal from the inverter control unit 80 is discontinued, turning off the switches SUHa-SWLa and SUHb-SWLb. The control signal from the switch control unit 83 is discontinued, turning off the normally-off power switches MH and ML and the selector switches QHa and QLa. The normally-on series switch Ka is also turned on. In this state, current flows through the closed circuit including the first capacitor 15a, the buses 11 and 12, and the discharge resistor 70. This gradually reduces the voltage VC1 of the first capacitor 15a. Furthermore, the discharge current from the second capacitor 15b conducts through the diodes DH and DL, causing current to flow through the closed circuit including the second capacitor 15b, the buses 11 and 12, the diodes DH and DL, and the discharge resistor 70. This gradually reduces the voltage VC2 of the second capacitor 15b. In this embodiment, the second capacitor 15b corresponds to the "specific capacitor."

[0072] In the present embodiment, the discharge resistor 70 enables the first capacitor 15 a and the second capacitor 15 b to discharge when an abnormality occurs in the power conversion system 100. Therefore, compared to the comparative example in which a resistor is provided corresponding to each of the capacitors 15 a and 15 b, an increase in the number of components in the power conversion system 100 can be suppressed. As a result, the power conversion system 100 can appropriately achieve a configuration that enables the first capacitor 15 a and the second capacitor 15 b to discharge when an abnormality occurs.

[0073] The power conversion system 100 includes a series switch Ka electrically connected in series to the discharge resistor 70. With this, when the power switches MH and ML are turned on, the series switch Ka is turned off, thereby suppressing current from flowing through the discharge resistor 70. Therefore, it is possible to suppress an increase in power loss occurring in the power conversion system 100 while the rotating electric machine 40 is being driven.

[0074] A normally-on switch is used as the series switch Ka. This allows the series switch Ka to be reliably turned on even when an abnormality occurs in the power conversion system 100 and the control signal from the control device 60 to the series switch Ka is interrupted. This makes it possible to realize a configuration that is suitable for discharging the capacitors 15a, 15b when an abnormality occurs.

[0075] Second Embodiment The second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, as shown in FIG. 7 , the power conversion system 100 includes a positive-side changeover switch QHb and a negative-side changeover switch QLb. Each of the changeover switches QHb and QLb is a normally-on switch. For example, each of the changeover switches QHb and QLb is a semiconductor switching element such as a normally-closed mechanical relay or a depletion-mode N-channel MOSFET. Each of the changeover switches QHb and QLb is controlled by a switch control unit 83.

[0076] The power conversion system 100 includes a discharge resistor 71 and a series switch Kb. The discharge resistor 71 is electrically connected in parallel with only the second capacitor 15b of the first capacitor 15a and the second capacitor 15b. Specifically, a first end of the discharge resistor 71 is electrically connected between a connection point of the positive bus 11 with the second upper arm switches SUHb, SVHa, and SWHa of each phase and a first end of the second capacitor 15b. A second end of the discharge resistor 71 is electrically connected between a connection point of the negative bus 12 with the second lower arm switches SULb, SVLb, and SWLb of each phase and a second end of the second capacitor 15b.

[0077] In this embodiment, the changeover switches QHb and QLb correspond to a "switch unit." The buses 11 and 12, the first inverter 20, the second inverter 30, the rotating electric machine 40, the discharge resistor 71, the power switches MH and ML, and the changeover switches QHb and QLb constitute a "power conversion device."

[0078] The series switch Kb is connected in series to the discharge resistor 71 on the high potential side of the discharge resistor 71. The series switch Kb is electrically connected between a connection point of the positive pole side bus 11 with the second upper arm switches SUHb, SVHa, SWHa of each phase and a first end of the second capacitor 15b. The series switch Kb is a normally-on switch. The series switch Kb is controlled by the switch control unit 83.

[0079] In this embodiment, when each of the changeover switches QHb, QLb and the series switch Kb is turned on and each of the power switches MH, ML is turned off, it is possible to flow current through a closed circuit including the first capacitor 15a and the discharge resistor 71.

[0080] 8, a description will be given of the operation when an abnormality occurs in power conversion system 100. Here, it is assumed that a vehicle collision occurs at time t1, and the drive signals for switches SUHa-SWLa and SUHb-SWLb controlled by inverter control unit 80 and the control signals for switches MH, ML, QHb, QLb, and Kb controlled by switch control unit 83 are interrupted.

[0081] 8, (a) shows the transition of the voltages VC1 and VC2 of the capacitors 15a and 15b, (b) shows the transition of the currents IQH and IQL flowing through the switches QHb and QLb, (c) shows the on / off state of the positive-side switch QHb, (d) shows the on / off state of the negative-side switch QLb, (e) shows the on / off state of the series switch Kb, and (f) shows the on / off state of the power switches MH and ML. The signs of the currents IQH and IQL flowing through the switches QHb and QLb are positive when the current flows from the first inverter 20 to the second inverter 30 in each bus 11 and 12, and negative when the current flows from the second inverter 30 to the first inverter 20.

[0082] Before time t1, the selector 82 selects Y-drive control. In this case, the switch controller 83 turns on the power switches MH, ML and the negative-side selector switch QLb, and turns off the positive-side selector switch QHb and the series switch Kb. The inverter controller 80 fixes the second upper-arm switches SUHb, SVHb, SWHb for each phase on and fixes the second lower-arm switches SULb, SVLb, SWLb for each phase off, and controls the switching of the switches SUHa to SWLa in the first inverter 20.

[0083] After time t1, the drive signal from the inverter control unit 80 is discontinued, turning off the switches SUHa-SWLa and SUHb-SWLb. The control signal from the switch control unit 83 is discontinued, turning off the normally-off power switches MH and ML. Furthermore, the normally-on switches QHb and QLb and the series switch Kb are turned on. In this state, current flows through the closed circuit including the second capacitor 15b, the buses 11 and 12, and the discharge resistor 71. This gradually reduces the voltage VC2 of the second capacitor 15b. Furthermore, the discharge current from the first capacitor 15a conducts through the switches QHb and QLb, so that current flows through the closed circuit including the first capacitor 15a, the buses 11 and 12, the switches QHb and QLb, and the discharge resistor 71. This gradually reduces the voltage VC1 of the first capacitor 15a. In this embodiment, the first capacitor 15a corresponds to the "specific capacitor."

[0084] In this embodiment, the changeover switches QHb and QLb are normally-on switches. This allows the first capacitor 15a and the second capacitor 15b to be discharged by the discharge resistor 71 when an abnormality occurs in the power conversion system 100. Therefore, compared to a comparative example in which resistors are provided corresponding to the capacitors 15a and 15b, an increase in the number of components in the power conversion system 100 can be suppressed. As a result, the power conversion system 100 can be appropriately configured to discharge the first capacitor 15a and the second capacitor 15b when an abnormality occurs.

[0085] When normally-on type switches are used as the changeover switches QHb and QLb, the configuration is not limited to that shown in Fig. 7 , and even in the configuration shown in Fig. 1 in which the discharge resistor 70 is provided, the capacitors 15a and 15b can be discharged by the discharge resistor 70. This increases the degree of freedom in designing the power conversion system 100.

[0086] Third Embodiment A third embodiment will now be described with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, as shown in FIG. 9 , a power conversion system 100 includes a discharge resistor 71, a series switch Kb, a positive-side parallel switch JH, and a negative-side parallel switch JL. The positive-side parallel switch JH is connected in parallel with the positive-side changeover switch QHa. The negative-side parallel switch JL is connected in parallel with the negative-side changeover switch QLa. Each of the parallel switches JH, JL is a normally-on switch. Here, each of the parallel switches JH, JL is a normally-closed mechanical relay.

[0087] In this embodiment, the changeover switches QHb, QLb and the parallel switches JH, JL correspond to a "switch unit." The buses 11, 12, the first inverter 20, the second inverter 30, the rotating electric machine 40, the discharge resistor 71, the power switches MH, ML, the changeover switches QHb, QLb, and the parallel switches JH, JL constitute a "power conversion device."

[0088] 10 , the switch control unit 83 controls the changeover switches QHa and QLa, the power switches MH and ML, the series switch Kb, and the parallel switches JH and JL. If the switch control unit 83 determines that no abnormality has occurred in the power conversion system 100, it turns off the parallel switches JH and JL. On the other hand, if the switch control unit 83 determines that an abnormality has occurred in the power conversion system 100, it turns on the parallel switches JH and JL.

[0089] In this embodiment, when the parallel switches JH, JL and the series switch Kb are turned on and the power switches MH, ML and the changeover switches QHa, QLa are turned off, it is possible to pass current through the closed circuit including the first capacitor 15a and the discharge resistor 71.

[0090] 11, a description will be given of the operation when an abnormality occurs in the power conversion system 100. Here, it is assumed that a vehicle collision occurs at time t1, and the drive signals for the switches SUHa-SWLa and SUHb-SWLb controlled by the inverter control unit 80 and the control signals for the switches MH, ML, QHa, QLa, Kb, JH, and JL controlled by the switch control unit 83 are interrupted.

[0091] 11, (a) shows the transition of the voltages VC1 and VC2 of the capacitors 15a and 15b, (b) shows the transition of the currents IJH and IJL flowing through the parallel switches JH and JL, (c) shows the on / off states of the changeover switches QHa and QLa, (d) shows the on / off states of the series switch Kb, (e) shows the on / off states of the power switches MH and ML, and (f) shows the on / off states of the parallel switches JH and JL. The signs of the currents IJH and IJL flowing through the parallel switches JH and JL are positive when the current flows from the first inverter 20 to the second inverter 30 in each bus 11 and 12, and negative when the current flows from the second inverter 30 to the first inverter 20.

[0092] Before time t1, the selector 82 selects H drive control. In this case, the switch controller 83 turns on the power switches MH and ML and the changeover switches QHa and QLa, and turns off the series switch Kb and the parallel switches JH and JL. The inverter controller 80 controls the switching of the switches SUHa to SWLa and SUHb to SWLb.

[0093] After time t1, the drive signal from the inverter control unit 80 is discontinued, turning off the switches SUHa-SWLa and SUHb-SWLb. The control signal from the switch control unit 83 is discontinued, turning off the normally-off power switches MH and ML and the selector switches QHa and QLa. Furthermore, the normally-on series switch Kb and the parallel switches JH and JL are turned on. In this state, current flows through the closed circuit including the second capacitor 15b, the buses 11 and 12, and the discharge resistor 71. This gradually reduces the voltage VC2 of the second capacitor 15b. Furthermore, the discharge current from the first capacitor 15a conducts through the parallel switches JH and JL, so that current flows through the closed circuit including the first capacitor 15a, the buses 11 and 12, the parallel switches JH and JL, and the discharge resistor 71. This gradually reduces the voltage VC1 of the first capacitor 15a. In this embodiment, the first capacitor 15a corresponds to the "specific capacitor."

[0094] In this embodiment, the normally-on parallel switches JH, JL are connected in parallel to the changeover switches QHb, QLb. This allows the first capacitor 15a and the second capacitor 15b to be discharged by the discharge resistor 71 when an abnormality occurs in the power conversion system 100. Therefore, compared to the comparative example in which resistors are provided corresponding to the capacitors 15a, 15b, an increase in the number of components in the power conversion system 100 can be suppressed. As a result, the power conversion system 100 can be appropriately configured to discharge the first capacitor 15a and the second capacitor 15b when an abnormality occurs.

[0095] In a configuration in which the parallel switches JH, JL, which are normally-on switches, are provided, the configuration is not limited to the configuration shown in Fig. 9 above, and even in a configuration in which the discharge resistor 70 shown in Fig. 1 above is provided, the capacitors 15a, 15b can be discharged by the discharge resistor 70. This increases the degree of freedom in designing the power conversion system 100.

[0096] When it is determined that no abnormality has occurred in the power conversion system 100, the switch control unit 83 controls the on / off states of the changeover switches QHa, QLa and the parallel switches JH, JL while the power switches MH, ML are turned on. Specifically, the changeover switches QHa, QLa are controlled to be on or off based on the operating point of the rotating electric machine 40. The parallel switches JH, JL are turned off. On the other hand, when it is determined that an abnormality has occurred in the power conversion system 100, the parallel switches JH, JL are turned on. That is, the changeover switches QHa, QLa are used to switch between Y-drive control and H-drive control, and the parallel switches JH, JL are used to discharge the capacitors 15a, 15b. In this case, it is possible to select switches suitable for the applications of the changeover switches QHa, QLa and the parallel switches JH, JL. As a result, in the power conversion system 100, it is possible to realize a configuration suitable for driving the rotating electrical machine 40 by Y drive control or H drive control while enabling each of the capacitors 15a, 15b to be discharged when an abnormality occurs.

[0097] For example, the switches QHa and QLa may be semiconductor switching elements that are more responsive to control signals than mechanical relays, assuming that they will be turned on and off more frequently than the parallel switches JH and JL. Also, the switches JH and JL may be mechanical relays, assuming that they will be turned on and off less frequently than the switches QHa and QLa.

[0098] Other Embodiments The above-described embodiments may be modified as follows.

[0099] The power conversion system 100 may be provided with snubber capacitors for absorbing surge voltages that occur when the switches SUHa to SWLa, SUHb to SWLb, QHa, QHb, QLa, and QLb interrupt current. The snubber capacitors have a smaller capacitance than the first and second capacitors 15a and 15b, which serve as smoothing capacitors. For example, in a power conversion system 100 in which the voltage of the battery 10 is 300 V or higher and 800 V or lower, the first and second capacitors 15a and 15b may have a capacitance of 100 μF or higher, 150 μF or higher, 200 μF or higher, 250 μF or higher, or 300 μF or higher, while the snubber capacitors may have a capacitance of 100 nF or higher and 1 μF or lower.

[0100] In the above embodiments, the snubber capacitors may or may not be discharged as long as the capacitors 15a, 15b are discharged by the discharge resistors when the power switches MH, ML are turned off. In other words, it is sufficient that the capacitors 15a, 15b, which are smoothing capacitors, are discharged when the power switches MH, ML are turned off.

[0101] The resistance values ​​of the discharge resistors 70, 71 are determined taking into consideration at least one of the following (1) to (4) so ​​as to enable discharge of the first and second capacitors 15a, 15b. For example, the discharge resistors 70, 71 may be any of the following: a resistor of 10 Ω or more and 10 kΩ or less, a resistor of 10 Ω or more and 100 Ω or less, a resistor of 100 Ω or more and 1 kΩ or less, or a resistor of 1 kΩ or more and 10 kΩ or less.

[0102] (1) The voltage of the battery 10. (2) The capacitance of the first and second capacitors 15a and 15b. (3) The discharge time of the first and second capacitors 15a and 15b required for the power conversion system 100. (4) The presence or absence of a series switch. In addition, the power conversion system 100 may be provided with an RC snubber circuit instead of a snubber capacitor.

[0103] The series switch may be connected in series to the low potential side of the discharge resistor, instead of being connected in series to the high potential side of the discharge resistor.

[0104] The series switches may be normally-off switches instead of normally-on switches.

[0105] The power conversion system 100 does not need to be provided with a series switch.

[0106] In the first and third embodiments, an enhancement type N-channel MOSFET or a normally open type mechanical relay may be used as the changeover switch.

[0107] In the third embodiment, semiconductor switching elements such as depletion-type N-channel MOSFETs may be used as the parallel switches.

[0108] In the first embodiment, the power conversion system 100 may be provided with either one of the changeover switches QHa and QLa. In the second embodiment, the power conversion system 100 may be provided with either one of the changeover switches QHb and QLb. In the third embodiment, the power conversion system 100 may be provided with either one of the changeover switches QHa and QLa. In this case, the parallel switch may be connected in parallel to the changeover switch provided in the power conversion system 100.

[0109] The power conversion system 100 may be provided with either one of the power switches MH and ML.

[0110] The DC power source is not limited to a battery, and may be, for example, a fuel cell.

[0111] The rotating electric machine is not limited to a three-phase one, but may be a two-phase one or a four-phase or more phase one.

[0112] The semiconductor switches constituting the first inverter and the second inverter are not limited to IGBTs, but may be, for example, N-channel MOSFETs. In this case, the high-potential terminal of the switch is the drain, and the low-potential terminal is the source. Each switch also has a body diode.

[0113] The inverter, rotating electric machine, and control device may be installed in a mobile body other than a vehicle, such as an aircraft or a ship. If the mobile body is an aircraft, the rotating electric machine serves as a power source for the aircraft's flight, and if the mobile body is a ship, the rotating electric machine serves as a power source for the ship's navigation. Furthermore, the inverter, rotating electric machine, and control device may be installed in a mobile body other than a vehicle.

[0114] The control device and method described herein may be implemented by a special-purpose computer configured with a processor and memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control device and method described herein may be implemented by a special-purpose computer configured with a processor comprising one or more dedicated hardware logic circuits. Alternatively, the control device and method described herein may be implemented by one or more special-purpose computers configured with a combination of a processor and memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions to be executed by a computer.

[0115] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A rotating electric machine (40) having multiple phase windings (51U, 51V, 51W), A first inverter (20) has a number of first upper arm switches (SUHa, SVHa, SWHa) and first lower arm switches (SULa, SVLa, SWLa) connected in series for each phase, and the series connection of the first upper arm switches and the first lower arm switches is connected in parallel to a DC power supply (10) and a first capacitor (15a), A second inverter (30) has a number of second upper arm switches (SUHb, SVHb, SWHb) and second lower arm switches (SULb, SVLb, SWLb) connected in series for each phase, and the series connection of the second upper arm switches and the second lower arm switches is connected in parallel to a second capacitor (15b), In each phase, a positive-side busbar (11) connects the high-potential terminal of the first upper arm switch and the high-potential terminal of the second upper arm switch, In each phase, a negative-side busbar (12) connects the low-potential terminal of the first lower arm switch and the low-potential terminal of the second lower arm switch, Power switches (MH, ML) provided in the path connecting the first inverter and the DC power supply, In a power conversion device equipped with, In each phase, the low-potential terminal of the first upper arm switch and the high-potential terminal of the first lower arm switch are connected to the first end of the winding. In each phase, the low-potential terminal of the second upper arm switch and the high-potential terminal of the second lower arm switch are connected to the second end of the winding. A discharge resistor (70) connected in parallel to only the first capacitor among the first and second capacitors, A changeover switch (QHa, QLa) is provided on the target bus, which is at least one of the positive and negative buses, Diodes (DH, DL) connected in parallel to the aforementioned changeover switch, Equipped with, A power conversion device in which the anode and cathode of the diode are oriented in such a way that the discharge current of the second capacitor can flow through the discharge resistor.

2. A rotating electric machine (40) having multiple phase windings (51U, 51V, 51W), A first inverter (20) has a number of first upper arm switches (SUHa, SVHa, SWHa) and first lower arm switches (SULa, SVLa, SWLa) connected in series for each phase, and the series connection of the first upper arm switches and the first lower arm switches is connected in parallel to a DC power supply (10) and a first capacitor (15a), A second inverter (30) has a number of second upper arm switches (SUHb, SVHb, SWHb) and second lower arm switches (SULb, SVLb, SWLb) connected in series for each phase, and the series connection of the second upper arm switches and the second lower arm switches is connected in parallel to a second capacitor (15b), In each phase, a positive-side busbar (11) connects the high-potential terminal of the first upper arm switch and the high-potential terminal of the second upper arm switch, In each phase, a negative-side busbar (12) connects the low-potential terminal of the first lower arm switch and the low-potential terminal of the second lower arm switch, Power switches (MH, ML) provided in the path connecting the first inverter and the DC power supply, In a power conversion device equipped with, In each phase, the low-potential terminal of the first upper arm switch and the high-potential terminal of the first lower arm switch are connected to the first end of the winding. In each phase, the low-potential terminal of the second upper arm switch and the high-potential terminal of the second lower arm switch are connected to the second end of the winding. A discharge resistor (70, 71) connected in parallel to only one of the first capacitor and the second capacitor, A normally-off type changeover switch (QHa, QLa) is provided on the target bus, which is at least one of the positive-side bus and the negative-side bus, A power conversion device comprising normally-on type parallel switches (JH, JL) connected in parallel to the aforementioned changeover switch.

3. A rotating electric machine (40) having multiple phase windings (51U, 51V, 51W), A first inverter (20) has a number of first upper arm switches (SUHa, SVHa, SWHa) and first lower arm switches (SULa, SVLa, SWLa) connected in series for each phase, and the series connection of the first upper arm switches and the first lower arm switches is connected in parallel to a DC power supply (10) and a first capacitor (15a), A second inverter (30) has a number of second upper arm switches (SUHb, SVHb, SWHb) and second lower arm switches (SULb, SVLb, SWLb) connected in series for each phase, and the series connection of the second upper arm switches and the second lower arm switches is connected in parallel to a second capacitor (15b), In each phase, a positive-side busbar (11) connects the high-potential terminal of the first upper arm switch and the high-potential terminal of the second upper arm switch, In each phase, a negative-side busbar (12) connects the low-potential terminal of the first lower arm switch and the low-potential terminal of the second lower arm switch, Power switches (MH, ML) provided in the path connecting the first inverter and the DC power supply, In a power conversion device equipped with, In each phase, the low-potential terminal of the first upper arm switch and the high-potential terminal of the first lower arm switch are connected to the first end of the winding. In each phase, the low-potential terminal of the second upper arm switch and the high-potential terminal of the second lower arm switch are connected to the second end of the winding. A discharge resistor (70, 71) connected in parallel to only one of the first capacitor and the second capacitor, A switch provided on a target busbar which is at least one of the positive-side busbar and the negative-side busbar, comprising a normally-on type changeover switch (QHb, QLb), A power conversion device equipped with the following features.

4. The power conversion device according to any one of claims 1 to 3, further comprising a series switch (Ka, Kb) connected in series with the discharge resistor on the high-potential side or the low-potential side with respect to the discharge resistor.

5. The power conversion device according to claim 4, wherein the series switch is a normally-on type switch.