Power Conversion Device

Abstract

To provide a power conversion apparatus for preventing the discharge resistance of a smoothing capacitor from deteriorating.SOLUTION: A power conversion device 1 includes a power conversion part 2, a capacitor C1 for smoothing DC power supplied from a DC power supply 60 to the power conversion unit 2, a voltage detection part 3 for detecting voltage between terminals of the capacitor C1, a discharge part 9 for discharging charge of the capacitor C1, and a discharge control part 10 for controlling the discharge part 9. The discharge part 9 includes a resistor R1 and a switch element SW connected in series, forms an active discharge circuit when the switch element SW is in an on state, and forms a passive discharge circuit when the switch element SW is in an off state. The discharge control part 10 controls the switch element SW in the off state when the voltage between the terminals is equal to or more than a threshold, and controls the switch element SW in the on state when the voltage between the terminals is less than the threshold in the case where power supply from the DC power supply 60 to the capacitor C1 is stopped to decrease the voltage between the terminals.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] Conventionally, power conversion devices that convert power between a DC power source and a load have been known. For example, vehicles such as hybrid vehicles, electric vehicles, and fuel cell vehicles are equipped with power conversion devices that convert DC power supplied from the vehicle's DC power source into AC power and supply it to the load. Such power conversion devices include a capacitor that smoothes the DC power supplied from the DC power source. In the event of an abnormality, such as a vehicle collision, it is necessary to quickly discharge the residual charge in the capacitor.

[0003] Japanese Patent No. 6874499 discloses a power conversion device including a capacitor that smooths DC power supplied from a vehicle's DC power supply, a discharge resistor that discharges the capacitor, a switching element connected in series to the discharge resistor, and a discharge control unit that drives and controls the switching element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6874499 Summary of the Invention [Problem to be solved by the invention]

[0005] In the power conversion device disclosed in Patent Document 1, in an emergency such as when a vehicle crashes, the discharge control unit turns on the switching element, thereby discharging the capacitor using the discharge resistor.

[0006] However, even though DC power is being supplied from the DC power source to the power conversion device, if the discharge control unit turns on the switching element, the DC power supplied from the DC power source will cause a continuous current to flow through the discharge resistor, which may cause problems such as the discharge resistor deteriorating due to the rated power of the discharge resistor being exceeded.

[0007] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a technology for preventing deterioration of a discharge resistor that discharges a smoothing capacitor in a power conversion device. [Means for solving the problem]

[0008] A power conversion device according to an aspect of the present disclosure includes a power conversion unit, a capacitor, a voltage detection unit, a discharge unit, and a discharge control unit. The power conversion unit converts power between a DC power source and a load. The capacitor smoothes DC power supplied from the DC power source to the power conversion unit. The voltage detection unit detects a terminal voltage of the capacitor. The discharge unit is connected in parallel with the capacitor and includes a plurality of resistors and a switch element for discharging the charge of the capacitor. The discharge control unit controls discharge by the discharge unit based on the terminal voltage detected by the voltage detection unit. The discharge unit forms an active discharge circuit in which at least one resistor of the plurality of resistors and the switch element are in a conductive state when the switch element is in an on state, and forms a passive discharge circuit in which at least one resistor and the switch element are in a non-conductive state when the switch element is in an off state. The active discharge circuit has a faster discharge rate of the capacitor than the passive discharge circuit. When the power supply from the DC power source to the capacitor is stopped and the terminal voltage drops, the discharge control unit controls the switch element to the off state if the terminal voltage is equal to or greater than a threshold, and controls the switch element to the on state if the terminal voltage is less than the threshold.

[0009] According to the above configuration, when the power supply from the DC power source to the smoothing capacitor is stopped and the terminal voltage of the capacitor drops, the power conversion device controls the switch element to the off state to form a passive discharge circuit when the terminal voltage is equal to or higher than the threshold, and controls the switch element to the on state to form an active discharge circuit when the terminal voltage is less than the threshold, thereby preventing deterioration of the active discharge resistor that discharges the smoothing capacitor.

[0010] Preferably, the DC power supply is mounted on a vehicle. The power conversion device further includes a control command unit that outputs a signal to the discharge control unit to switch the switch element from an on state to an off state. When the control command unit receives a signal indicating that the control command unit is normal from the control command unit, the discharge control unit controls the switch element to an on state or an off state based on whether or not the control command unit has received a signal indicating that the vehicle is abnormal, and when the control command unit receives a signal indicating that the control command unit is abnormal from the control command unit, the discharge control unit controls the switch element to an off state when the terminal voltage is equal to or greater than a threshold, regardless of whether or not the control command unit has received a signal indicating that the vehicle is abnormal from the control command unit,

[0011] According to the above configuration, when the control instruction unit is abnormal, the power conversion device controls the switch element to the off state when the terminal voltage of the smoothing capacitor detected by the voltage detection unit is equal to or greater than a threshold value, regardless of whether the vehicle is abnormal, and controls the switch element to the on state when the terminal voltage is less than the threshold value, thereby preventing the active discharge resistor from deteriorating.

[0012] Preferably, the discharge control unit controls the switch element to the off state when it receives a signal from the control command unit indicating that the control command unit is normal and a signal from the control command unit indicating that the vehicle is normal, controls the switch element to the on state when it receives a signal from the control command unit indicating that the control command unit is normal and a signal from the control command unit indicating that the vehicle is abnormal, controls the switch element to the off state when it receives a signal from the control command unit indicating that the control command unit is abnormal and the voltage between the terminals is equal to or greater than a threshold, and controls the switch element to the on state when it receives a signal from the control command unit indicating that the control command unit is abnormal and the voltage between the terminals is less than the threshold.

[0013] According to the above configuration, the power conversion device controls the switch element to the off state when the control instruction unit is abnormal and the inter-terminal voltage is equal to or greater than the threshold, thereby preventing the switch element from being turned on when the control instruction unit is abnormal, thereby preventing current from continuously flowing through the active discharge resistor and causing deterioration of the active discharge resistor.On the other hand, the power conversion device controls the switch element to the on state when the control instruction unit is abnormal and the inter-terminal voltage is less than the threshold, thereby allowing the discharge unit to discharge the smoothing capacitor even when the control instruction unit is abnormal.

[0014] Preferably, when the discharge control unit receives a signal from the control command unit indicating that the control command unit is normal and a signal from the control command unit indicating that the vehicle is normal, the discharge control unit controls the switch element to the off state; when the discharge control unit receives a signal from the control command unit indicating that the control command unit is normal and a signal from the control command unit indicating that the vehicle is abnormal, the discharge control unit controls the switch element to the off state if the terminal voltage is equal to or greater than a threshold, and controls the switch element to the on state if the terminal voltage is less than the threshold; when the discharge control unit receives a signal from the control command unit indicating that the control command unit is abnormal and the terminal voltage is equal to or greater than the threshold, the discharge control unit controls the switch element to the off state; and when the discharge control unit receives a signal from the control command unit indicating that the control command unit is abnormal and the terminal voltage is less than the threshold, the discharge control unit controls the switch element to the on state.

[0015] According to the above configuration, when the control instruction unit is normal and the vehicle is abnormal, the power conversion device turns the switch element off when the terminal voltage is equal to or higher than the threshold, and turns the switch element on when the terminal voltage is less than the threshold.Therefore, even if the control instruction unit is normal, the smoothing capacitor can be discharged by the discharge unit while preventing current from continuing to flow through the active discharge resistor and causing the active discharge resistor to deteriorate.

[0016] Preferably, the plurality of resistors includes a first resistor connected in series with the switch element, and a second resistor connected in parallel with the first resistor and the switch element connected in series. The first resistor and the switch element connected in series are connected in parallel with the capacitor. The second resistor is connected in parallel with the capacitor.

[0017] According to the above configuration, the power conversion device can switch the resistance value of the discharge unit connected in parallel with the capacitor by switching the switch element between the on state and the off state.

[0018] Preferably, the plurality of resistors include a first resistor and a second resistor connected in series, the first resistor connected in parallel with the switch element, the second resistor connected in series with the switch element, and the first and second resistors connected in series are connected in parallel with the capacitor.

[0019] According to the above configuration, the power conversion device can switch the flow path of the discharge current from the capacitor in the discharge unit connected in parallel with the capacitor by switching the switch element between the on state and the off state.

[0020] Preferably, the load is an electric motor used in an electric compressor for a vehicle. According to the above configuration, the power conversion device can convert DC power supplied from the DC power supply into AC power and supply the AC power to an electric motor used in an electric compressor for a vehicle. [Effects of the Invention]

[0021] According to the present disclosure, it is possible to prevent deterioration of a discharge resistor that discharges a smoothing capacitor in a power conversion device. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a circuit diagram showing a configuration of a power conversion device according to a first embodiment. [Figure 2] FIG. 3 is a diagram for explaining passive discharge control executed by the power conversion device according to the first embodiment. [Figure 3] FIG. 2 is a diagram for explaining active discharge control executed by the power conversion device according to the first embodiment. [Figure 4] 10A and 10B are diagrams for explaining discharge control executed for each state by a power conversion device according to a comparative example. [Figure 5] 4 is a diagram for explaining discharge control that the power conversion device according to the first embodiment executes for each state. FIG. [Figure 6] 10 is a graph showing a change in the voltage between the terminals of a capacitor over time when the power conversion device 1 according to the first embodiment executes discharge control. [Figure 7] 3 is a circuit diagram showing the configuration of a logic circuit of a discharge control unit according to the first embodiment. FIG. [Figure 8] 4 is a diagram showing a truth table of the discharge control unit according to the first embodiment. FIG. [Figure 9] FIG. 10 is a diagram for explaining discharge control that is executed for each state by the power conversion device according to the second embodiment. [Figure 10] FIG. 10 is a circuit diagram showing the configuration of a logic circuit of a discharge control unit according to a second embodiment. [Figure 11] FIG. 10 is a diagram showing a truth table of a discharge control unit according to the second embodiment. [Figure 12] FIG. 10 is a circuit diagram showing a configuration of a power conversion device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0024] <First Embodiment> [Configuration of power conversion device] The configuration of a power conversion device 1 according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a circuit diagram showing the configuration of a power conversion device 1 according to the first embodiment.

[0025] The power conversion device 1 according to the first embodiment converts DC power supplied from a battery 60 of a vehicle 6 into AC power and supplies it to a load device 8, which is a load. In the present disclosure, an electric motor used in an electric compressor for the vehicle 6 is exemplified as the load device 8. That is, the power conversion device 1 according to the first embodiment is configured integrally with the load device 8 to form the electric compressor for the vehicle 6. Note that the power conversion device 1 is not limited to being used in an electric motor used in an electric compressor, and may also be used in an electric motor for other auxiliary equipment or an electric motor for a main equipment in the vehicle 6.

[0026] 1, the load device 8 is a so-called three-phase AC motor, and includes a U-phase coil 8U, a V-phase coil 8V, and a W-phase coil 8W. The coils 8U, 8V, and 8W are connected in a Y-connection, for example. When power is supplied to the coils 8U, 8V, and 8W, the load device 8 rotates a rotor (not shown) and a rotating shaft connected to the rotor.

[0027] The power conversion device 1 can be connected to a vehicle system via connection points T1 to T5. The connection points T1 to T5 are attached as connectors (not shown) to a housing of the power conversion device 1. The vehicle 6 includes a battery 60, a system main relay (hereinafter also referred to as "SMR") 65, a battery 70, a control relay 75, and a host ECU (Electronic Control Unit) 200.

[0028] Battery 60 is a DC power supply that is configured by a rechargeable secondary battery such as a lithium-ion secondary battery, a nickel-metal hydride battery, or a lead-acid battery and is capable of outputting DC power. In vehicles 6 such as hybrid vehicles, electric vehicles, or fuel cell vehicles, a secondary battery of 200V to 800V may be applied as battery 60. In FIG. 1, the voltage of the power supplied from battery 60 is indicated by "HV." The positive terminal of battery 60 is connected to connection point T1 via SMR 65. The negative terminal of battery 60 is connected to connection point T2 via SMR 65.

[0029] SMR 65 is configured by a switch such as an electromagnetic contactor or an electromagnetic switch, and electrically connects or disconnects the path between battery 60 and power conversion device 1 under the control of host ECU 200. When SMR 65 is in the on state (conductive state), power supplied from battery 60 is supplied to positive line PL. When SMR 65 is in the off state (non-conductive state), power supplied from battery 60 is not supplied to positive line PL.

[0030] The battery 70 is a 12V or 24V power supply provided in the vehicle 6. In FIG. 1, the voltage of the power supplied from the battery 70 is indicated by "LV." The positive terminal of the battery 70 is connected to a connection point T4 via a control relay 75. The negative terminal of the battery 70 is connected to a connection point T5. The battery 60 and the battery 70 may be integrated into a single battery. In this case, the control instruction unit 5, which will be described later, is supplied with power converted to, for example, 12V.

[0031] The control relay 75 is configured by a switch such as an electromagnetic contactor or an electromagnetic switch, and electrically connects or disconnects the path between the battery 70 and the power conversion device 1. When the control relay 75 is in the on state (conductive state), power supplied from the battery 70 is supplied to a power supply circuit 52 of the power conversion device 1, which will be described later. When the SMR 65 is in the off state (non-conductive state), power supplied from the battery 70 is not supplied to the power supply circuit 52.

[0032] The upper ECU 200 includes a processor such as a CPU (Central Processing Unit), FPGA (Field-Programmable Gate Array), and GPU (Graphics Processing Unit), and a memory such as RAM (Random Access Memory) or ROM (Read-Only Memory), and is configured so that the processor controls the system on the vehicle 6 side based on the data stored in the memory.

[0033] The host ECU 200 outputs an ECU signal indicating whether or not an abnormality such as a collision has occurred in the vehicle 6 to a control command unit 5 of the power conversion device 1, which will be described later. Specifically, when no abnormality has occurred in the vehicle 6, the host ECU 200 outputs a Lo signal to the control command unit 5 as an ECU signal indicating that the vehicle 6 is normal. On the other hand, when an abnormality has occurred in the vehicle 6, the host ECU 200 outputs a Hi signal to the control command unit 5 as an ECU signal indicating that the vehicle 6 is abnormal, and further switches the SMR 65 to an OFF state to cut off the power supply from the battery 60 to the power conversion device 1.

[0034] The power conversion device 1 includes a positive electrode line PL, a negative electrode line NL, an inverter circuit 2, a smoothing capacitor C1, a discharge unit 9, a voltage detection unit 3, a discharge power supply unit 4, a discharge control unit 10, and a control command unit 5.

[0035] The positive electrode line PL is connected to the positive terminal of the battery 60 via a connection point T1. The negative electrode line NL is connected to the negative terminal of the battery 60 via a connection point T2. The negative electrode line NL is also connected to the ground terminal GND.

[0036] The inverter circuit 2 constitutes a so-called three-phase inverter. In the power conversion device 1 according to the first embodiment, the inverter circuit 2 is an example of a "power conversion unit." The inverter circuit 2 includes switching elements TU1 and TU2 connected in series between a positive electrode line PL and a negative electrode line NL, switching elements TV1 and TV2 connected in series between a positive electrode line PL and a negative electrode line NL, and switching elements TW1 and TW2 connected in series between a positive electrode line PL and a negative electrode line NL. Hereinafter, any or all of the switching elements TU1, TU2, TV1, TV2, TW1, and TW2 will also be simply referred to as "switching elements."

[0037] Each switching element is configured by a semiconductor transistor such as an insulated gate bipolar transistor (IGBT) or a field effect transistor (FET). In the first embodiment, each switching element is configured by an IGBT.

[0038] Switching element TU1 constitutes the U-phase upper arm. Switching element TU2 constitutes the U-phase lower arm. Switching element TV1 constitutes the V-phase upper arm. Switching element TV2 constitutes the V-phase lower arm. Switching element TW1 constitutes the W-phase upper arm. Switching element TW2 constitutes the W-phase lower arm.

[0039] Specifically, the collector of switching element TU1 is connected to the positive electrode line PL, and the emitter of switching element TU1 is connected to the collector of switching element TU2. The emitter of switching element TU2 is connected to the negative electrode line NL. The collector of switching element TV1 is connected to the positive electrode line PL, and the emitter of switching element TV1 is connected to the collector of switching element TV2. The emitter of switching element TV2 is connected to the negative electrode line NL. The collector of switching element TW1 is connected to the positive electrode line PL, and the emitter of switching element TW1 is connected to the collector of switching element TW2. The emitter of switching element TW2 is connected to the negative electrode line NL.

[0040] A node N1 between the emitter of switching element TU1 and the collector of switching element TU2 is connected to a coil 8U. A node N2 between the emitter of switching element TV1 and the collector of switching element TV2 is connected to a coil 8V. A node N3 between the emitter of switching element TW1 and the collector of switching element TW2 is connected to a coil 8W.

[0041] Furthermore, the inverter circuit 2 includes a diode DU1 connected in parallel with the switching element TU1, a diode DU2 connected in parallel with the switching element TU2, a diode DV1 connected in parallel with the switching element TV1, a diode DV2 connected in parallel with the switching element TV2, a diode DW1 connected in parallel with the switching element TW1, and a diode DW2 connected in parallel with the switching element TW2.

[0042] The anode of diode DU1 is connected to the emitter of switching element TU1, and the cathode of diode DU1 is connected to the collector of switching element TU1. The anode of diode DU2 is connected to the emitter of switching element TU2, and the cathode of diode DU2 is connected to the collector of switching element TU2. The anode of diode DV1 is connected to the emitter of switching element TV1, and the cathode of diode DV1 is connected to the collector of switching element TV1. The anode of diode DV2 is connected to the emitter of switching element TV2, and the cathode of diode DV2 is connected to the collector of switching element TV2. The anode of diode DW1 is connected to the emitter of switching element TW1, and the cathode of diode DW1 is connected to the collector of switching element TW1. The anode of diode DW2 is connected to the emitter of switching element TW2, and the cathode of diode DW2 is connected to the collector of switching element TW2.

[0043] Capacitor C1 is disposed on the input side of power conversion device 1 and has the function of smoothing the DC power supplied from battery 60 to inverter circuit 2. One end of capacitor C1 is connected to positive electrode line PL, and the other end of capacitor C1 is connected to negative electrode line NL.

[0044] The discharge unit 9 is connected in parallel to the capacitor C1 and has a function of discharging the capacitor C1. The discharge unit 9 includes discharge resistors R1 and R2 and a discharge switch SW. In the power conversion device 1 according to the first embodiment, the resistor R1 is an example of a "first resistor," and the resistor R2 is an example of a "second resistor." Preferably, the resistance value of the resistor R1 is smaller than the resistance value of the resistor R2.

[0045] The resistor R1 and the discharge switch SW are connected in series and disposed between the positive electrode line PL and the negative electrode line NL. Specifically, one end of the resistor R1 is connected to the positive electrode line PL, and the other end of the resistor R1 is connected to one end of the discharge switch SW. One end of the discharge switch SW is connected to the other end of the resistor R1, and the other end of the discharge switch SW is connected to the negative electrode line NL. In other words, the resistor R1 and the discharge switch SW connected in series are connected in parallel with the capacitor C1 between the positive electrode line PL and the negative electrode line NL.

[0046] The discharge switch SW is configured by, for example, a semiconductor transistor such as an IGBT or an FET. In the power conversion device 1 according to the first embodiment, the discharge switch SW is an example of a "switch element." The discharge switch SW is configured by, for example, an FET. A source (one end) of the discharge switch SW is connected to a resistor R1. A drain (the other end) of the discharge switch SW is connected to the negative electrode line NL. A gate of the discharge switch SW is connected to the discharge control unit 10. The discharge switch SW is controlled to an on state (conductive state) or an off state (non-conductive state) according to the control of the discharge control unit 10.

[0047] The resistor R2 is disposed between the positive electrode line PL and the negative electrode line NL. Specifically, one end of the resistor R2 is connected to the positive electrode line PL, and the other end of the resistor R2 is connected to the negative electrode line NL. That is, the resistor R2 is connected in parallel with the capacitor C1 between the positive electrode line PL and the negative electrode line NL. The path connecting the positive electrode line PL through the resistor R2 to the negative electrode line NL is electrically connected at all times.

[0048] The voltage detection unit 3 is disposed between the positive electrode line PL and the negative electrode line NL. Specifically, one end of the voltage detection unit 3 is connected to the positive electrode line PL, and the other end of the voltage detection unit 3 is connected to the negative electrode line NL. That is, the voltage detection unit 3 is connected in parallel with the capacitor C1 between the positive electrode line PL and the negative electrode line NL. The voltage detection unit 3 detects the voltage between the terminals of the capacitor C1, and outputs the detection result to the discharge control unit 10.

[0049] The discharge power supply unit 4 is connected to the battery 60 via a positive line PL. The discharge power supply unit 4 converts the power supplied from the battery 60 to about 10 V and supplies it to the discharge control unit 10.

[0050] The discharge control unit 10 switches the discharge switch SW between an ON state and an OFF state by controlling the discharge switch SW based on the terminal voltage of the capacitor C1 detected by the voltage detection unit 3, using power supplied from the discharge power supply unit 4. Hereinafter, the switching control of the discharge switch SW by the discharge control unit 10 is also referred to as "discharge control."

[0051] The control command unit 5 controls each switching element of the inverter circuit 2 and outputs a signal for executing discharge control to the discharge control unit 10. The control command unit 5 includes a control circuit 51, a power supply circuit 52, and an interface 53.

[0052] The control circuit 51 includes a processor such as a CPU, FPGA, or GPU, and a memory such as a RAM or ROM, and is configured so that the processor controls the inverter circuit 2 based on data stored in the memory.

[0053] The control circuit 51 is connected to the gates of each switching element of the inverter circuit 2 and to nodes N1, N2, and N3. The control circuit 51 outputs a PWM signal to each switching element to control each switching element, thereby switching each switching element between an ON state (conducting state) and an OFF state (non-conducting state). As a result, DC power supplied from the battery 60 is converted into AC power by the inverter circuit 2 and supplied to the load device 8. The control circuit 51 is connected to a power supply path from the inverter circuit 2 to the load device 8 via nodes N1, N2, and N3. In other words, the control circuit 51 and the load device 8 are connected to the inverter circuit 2 so as to branch off from the nodes N1, N2, and N3.

[0054] Furthermore, the control circuit 51 outputs a control signal indicating whether the control command unit 5 is normal or not to the discharge control unit 10. Specifically, if the control command unit 5 is normal, the control circuit 51 outputs a signal indicating that the control command unit 5 is normal to the discharge control unit 10. On the other hand, if the control command unit 5 is abnormal, the control circuit 51 outputs a signal indicating that the control command unit 5 is abnormal to the discharge control unit 10.

[0055] The power supply circuit 52 is an internal power supply for the control command unit 5. The power supply circuit 52 supplies power from a 12V battery 70 provided in the vehicle system to the interface 53 and the control circuit 51. When the control relay 75 is in the on state, the control command unit 5 can be driven by the power supplied from the battery 70, but when the control relay 75 is in the off state, the control command unit 5 cannot be driven because no power is supplied from the battery 70.

[0056] The interface 53 acquires the ECU signal output from the host ECU 200 and outputs the ECU signal to the discharge control unit 10 and the control circuit 51. For example, when no abnormality occurs in the vehicle 6, the host ECU 200 outputs a Lo signal to the interface 53 as an ECU signal indicating that the vehicle 6 is normal, and when an abnormality occurs in the vehicle 6, the host ECU 200 outputs a Hi signal to the interface 53 as an ECU signal indicating that the vehicle 6 is abnormal. The interface 53 acquires the ECU signal output from the host ECU 200 and outputs the acquired ECU signal to the discharge control unit 10 and the control circuit 51.

[0057] [Discharge control] 2 to 6, the discharge control executed by the power conversion device 1 according to the first embodiment will be described. When the SMR 65 is in the on state and power is being supplied from the battery 60, the power conversion device 1 discharges the capacitor C1 while minimizing power consumption in the discharge unit 9, while when the SMR 65 is in the off state and power is not being supplied from the battery 60, the discharge unit 9 is required to increase the amount of discharge of the capacitor C1 to rapidly discharge the capacitor C1.

[0058] Here, the greater the resistance value of the discharge unit 9, the smaller the value of the current flowing from capacitor C1 to the discharge unit 9, thereby reducing power consumption in the discharge unit 9. On the other hand, the smaller the resistance value of the discharge unit 9, the larger the value of the current flowing from capacitor C1 to the discharge unit 9, allowing capacitor C1 to be discharged more quickly, but increasing power consumption in the discharge unit 9 accordingly. In other words, in the power conversion device 1, the discharge control unit 10 performs discharge control in which the discharge switch SW is switched between the on state and the off state, thereby increasing the resistance value of the discharge unit 9 to discharge capacitor C1 while reducing power consumption in the discharge unit 9, or decreasing the resistance value of the discharge unit 9 to allow capacitor C1 to be rapidly discharged in the discharge unit 9. Below, passive discharge control and active discharge control will be specifically described as examples of discharge control.

[0059] FIG. 2 is a diagram illustrating passive discharge control executed by power conversion device 1 according to the first embodiment. As shown in FIG. 2, when SMR 65 is in the ON state and power from battery 60 is supplied to positive line PL, a charge corresponding to the voltage applied by battery 60 is accumulated in smoothing capacitor C1. In this case, discharge control unit 10 controls discharge switch SW to the OFF state, thereby electrically interrupting the path passing through resistor R1 between positive line PL and negative line NL. As a result, the resistance value of discharge unit 9 connected in parallel to capacitor C1 becomes the same as the resistance value of resistor R2. The current of the power supplied from battery 60 flows to resistor R2. Furthermore, the charge accumulated in capacitor C1 is discharged via resistor R2 as a result of a current flowing from capacitor C1 to resistor R2.

[0060] In this way, the discharge control unit 10 can discharge the capacitor C1 using only the resistor R2 by turning the discharge switch SW off. Since the resistance of the discharge unit 9 connected in parallel to the capacitor C1 is the same as that of the resistor R2, increasing the resistance of the resistor R2 allows the capacitor C1 to be discharged while minimizing power consumption. Hereinafter, this type of discharge control, in which the discharge switch SW is turned off and the capacitor C1 is discharged using only the resistor R2, will be referred to as "passive discharge control," and this type of discharge will also be referred to as "passive discharge." As shown in FIG. 2, the circuit of the discharge unit 9 in which the discharge switch SW is turned off and the resistor R1 and the discharge switch SW are not electrically connected will also be referred to as a "passive discharge circuit."

[0061] 3 is a diagram illustrating the active discharge control executed by the power conversion device 1 according to the first embodiment. As shown in FIG. 3, when the SMR 65 is in the off state and the power supply from the battery 60 is interrupted, the discharge control unit 10 controls the discharge switch SW to the on state, thereby electrically connecting the path passing through the resistor R1 between the positive electrode line PL and the negative electrode line NL. As a result, the resistance value of the discharge unit 9 connected in parallel to the capacitor C1 becomes the combined resistance value of the resistors R1 and R2 connected in parallel.

[0062] As described above, the resistance value of resistor R1 is smaller than the resistance value of resistor R2. Therefore, a larger current flows through resistor R1 than through resistor R2, and the time required for discharge is shortened. Furthermore, because resistors R1 and R2 are connected in parallel, the resistance value of the discharge unit 9 when the discharge switch SW is in the on state (the combined resistance value of resistors R1 and R2) is smaller than the resistance value of the discharge unit 9 when the discharge switch SW is in the off state (the resistance value of resistor R1 alone). Therefore, when the discharge switch SW is controlled to the on state as shown in FIG. 3, a larger current flows through the discharge unit 9 than when the discharge switch SW is controlled to the off state as shown in FIG. 2, and the time required for discharge is shortened.

[0063] The charge stored in capacitor C1 is discharged through resistor R2 as current flows from capacitor C1 to resistor R2, and is also discharged through resistor R1 as current flows from capacitor C1 to resistor R1.

[0064] In this way, the discharge control unit 10 can rapidly discharge the capacitor C1 using the resistors R1 and R2 by turning on the discharge switch SW. Hereinafter, this type of discharge control in which the discharge switch SW is turned on and the capacitor C1 is discharged using the resistors R1 and R2 will also be referred to as "active discharge control," and this type of discharge will also be referred to as "active discharge." Note that, as shown in FIG. 3, the circuit of the discharge unit 9 in which the discharge switch SW is turned on and the resistor R1 and the discharge switch SW are in a conductive state will also be referred to as an "active discharge circuit."

[0065] As described above, when the SMR 65 is in the ON state and power is being supplied from the battery 60, the discharge control unit 10 of the power conversion device 1 turns the discharge switch SW to the OFF state to perform passive discharge, and when the SMR 65 is in the OFF state and power supply from the battery 60 is cut off, the discharge control unit 10 turns the discharge switch SW to the ON state to perform active discharge. However, the discharge control unit 10 cannot directly know whether the SMR 65 on the vehicle 6 side is controlled to the ON state or the OFF state. For this reason, the discharge control unit 10 switches the discharge switch SW by performing discharge control based on an ECU signal input from the host ECU 200.

[0066] Specifically, when no abnormality occurs in the vehicle 6, the host ECU 200 turns on the SMR 65 to continue the supply of power from the battery 60 to the power conversion device 1. Furthermore, the host ECU 200 outputs a Lo signal indicating that the vehicle 6 is normal to the discharge control unit 10 via the interface 53 of the control command unit 5. When the Lo signal is input from the host ECU 200, the discharge control unit 10 turns off the discharge switch SW through passive discharge control, thereby passively discharging the capacitor C1. This allows the power conversion device 1 to passively discharge the capacitor C1 while power is being supplied to the power conversion device 1 from the battery 60.

[0067] On the other hand, if an abnormality occurs in the vehicle 6, the host ECU 200 turns the SMR 65 off to prevent damage, thereby cutting off the power supply from the battery 60 to the power conversion device 1. Furthermore, the host ECU 200 outputs a Hi signal indicating that the vehicle 6 is abnormal to the discharge control unit 10 via the interface 53 of the control command unit 5. When the Hi signal is input from the host ECU 200, the discharge control unit 10 turns on the discharge switch SW by active discharge control, thereby actively discharging the capacitor C1. As a result, when an abnormality occurs in the vehicle 6, the power conversion device 1 can actively discharge the capacitor C1 in a state where power is not supplied from the battery 60 to the power conversion device 1.

[0068] [Discharge control for each state of the power conversion device according to the comparative example] Discharge control performed by a power conversion device according to a comparative example for each state will be described with reference to Fig. 4. Fig. 4 is a diagram for explaining discharge control performed by a power conversion device according to a comparative example for each state. As shown in Fig. 4, states 1 to 4 can be cited as states in which discharge control can be performed by the power conversion device.

[0069] State 1 is a state in which control relay 75 is in the ON state, a control signal indicating that control command unit 5 is normal is input from control command unit 5, and a Lo signal indicating that vehicle 6 is normal is input from host ECU 200. That is, in state 1, power is supplied to control command unit 5 from battery 70, and it is assumed that control command unit 5 and vehicle 6 are normal. State 1 is further divided into state 1-A in which SMR 65 is in the ON state and state 1-B in which SMR 65 is in the OFF state.

[0070] In state 1-A, it is assumed that the discharge control unit 10 executes passive discharge control to turn off the discharge switch SW. In this case, power is supplied to the power conversion device from the battery 60, but passive discharge is performed in the discharge unit 9, so no current flows through the resistor R1 in the discharge unit 9, and no particular problem occurs.

[0071] In state 1-B, it is assumed that the discharge control unit 10 executes passive discharge control to turn off the discharge switch SW. In this case, no power is supplied from the battery 60 to the power conversion device, and passive discharge is also performed in the discharge unit 9. Therefore, no current flows through the resistor R1 in the discharge unit 9, and no particular problem occurs.

[0072] State 2 is a state in which control relay 75 is in the ON state, a control signal indicating that control command unit 5 is normal is input from control command unit 5, and a Hi signal indicating that vehicle 6 is abnormal is input from host ECU 200. That is, in state 2, power is supplied to control command unit 5 from battery 70, control command unit 5 is normal, but it is assumed that vehicle 6 is abnormal. State 2 is further divided into state 2-A in which SMR 65 is in the ON state and state 2-B in which SMR 65 is in the OFF state.

[0073] In state 2-A, it is assumed that the discharge control unit 10 executes active discharge control to turn on the discharge switch SW based on the Hi signal input from the host ECU 200. Normally, when the Hi signal is input from the host ECU 200 to the discharge control unit 10, the SMR 65 is controlled to the off state. However, in this example, the SMR 65 is unexpectedly controlled to the on state, and power is supplied from the battery 60 to the power conversion device. In this case, current continues to flow through the active discharge resistor R1 in the discharge unit 9, which may exceed the rated power of the resistor R1 and cause the resistor R1 to deteriorate. However, this is avoided by controlling the host system on the host ECU 200 side to discharge the capacitor C1, for example.

[0074] In state 2-B, it is assumed that the discharge control unit 10 executes active discharge control to turn on the discharge switch SW based on the Hi signal input from the host ECU 200. In this case, active discharge is performed in the discharge unit 9 while no power is being supplied from the battery 60 to the power conversion device, so no current flows through the resistor R1 in the discharge unit 9, and no particular problem occurs.

[0075] As in states 1 and 2, when the discharge control unit 10 receives a signal from the control command unit 5 indicating that the control command unit 5 is normal, the discharge control unit 10 is configured to perform discharge control based on whether or not it receives an ECU signal from the control command unit 5 indicating that the vehicle 6 is abnormal.

[0076] State 3 is a state in which control relay 75 is in the ON state and a control signal indicating that control command unit 5 is abnormal is input from control command unit 5. That is, in state 3, power is supplied to control command unit 5 from battery 70, but it is assumed that control command unit 5 is abnormal. State 3 is further divided into state 3-A in which SMR 65 is in the ON state and state 3-B in which SMR 65 is in the OFF state.

[0077] In state 3-A, assume that the discharge control unit 10 executes active discharge control to turn on the discharge switch SW. In this case, active discharge is performed while power is being supplied from the battery 60 to the power conversion device. This causes a current to continuously flow through the active discharge resistor R1, possibly exceeding the rated power of the resistor R1 and degrading the resistor R1. Because the discharge control unit 10 cannot directly determine whether the SMR 65 on the vehicle 6 is controlled to the on state or the off state, a situation like state 3-A can occur.

[0078] In state 3-B, it is assumed that the discharge control unit 10 executes active discharge control to turn on the discharge switch SW. In this case, active discharge is performed in the discharge unit 9 while no power is being supplied from the battery 60 to the power conversion device, so no current flows through the resistor R1 in the discharge unit 9, and no particular problem occurs.

[0079] In state 4, the control relay 75 is in the off state. That is, in state 4, power is not supplied from the battery 70 to the control command unit 5, and therefore the control command unit 5 cannot operate. State 4 is further divided into state 4-A in which the SMR 65 is in the on state and state 4-B in which the SMR 65 is in the off state.

[0080] In state 4-A, assume that the discharge control unit 10 executes active discharge control to turn on the discharge switch SW. In this case, active discharge is performed while power is being supplied from the battery 60 to the power conversion device. This causes a current to continuously flow through the active discharge resistor R1 in the discharge unit 9, possibly exceeding the rated power of the resistor R1 and degrading the resistor R1. Because the discharge control unit 10 cannot directly know whether the SMR 65 on the vehicle 6 is controlled to the on state or the off state, a situation like state 4-A can occur.

[0081] In state 4-B, it is assumed that the discharge control unit 10 executes active discharge control to turn on the discharge switch SW. In this case, active discharge is performed in the discharge unit 9 while no power is being supplied from the battery 60 to the power conversion device, so no current flows through the resistor R1 in the discharge unit 9, and no particular problem occurs.

[0082] As described above, in the power conversion device according to the comparative example, when the discharge control unit 10 executes active discharge control while power is being supplied from the battery 60, a problem occurs in that a current continuously flows through the active discharge resistor R1 due to the DC power supplied from the battery 60, exceeding the rated power of the resistor R1 and degrading the resistor R1. In particular, the discharge control unit 10 cannot directly know whether the SMR 65 on the vehicle 6 is controlled to the ON state or the OFF state. For this reason, when the control command unit 5 is abnormal as in state 3-A, or when the control command unit 5 is inoperable as in state 4-A, the discharge control unit 10 may execute active discharge control even though power is being supplied to the power conversion device from the battery 60.

[0083] Therefore, the power conversion device 1 according to the first embodiment is configured so that the discharge control unit 10 executes discharge control based on the inter-terminal voltage of the capacitor C1 detected by the voltage detection unit 3. Hereinafter, the discharge control in the power conversion device 1 according to the first embodiment will be described.

[0084] [Discharge control for each state of the power conversion device according to the first embodiment] Discharge control performed by the power conversion device 1 according to the first embodiment for each state will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining discharge control performed by the power conversion device 1 according to the first embodiment for each state. Note that, in the power conversion device 1 according to the first embodiment shown in Fig. 5, only the parts that are different from the power conversion device according to the comparative example will be described, and the parts that are the same as those of the power conversion device according to the comparative example will not be described.

[0085] 5, the discharge control unit 10 of the power conversion device 1 executes discharge control depending on whether the terminal voltage of the capacitor C1 detected by the voltage detection unit 3 is equal to or greater than a predetermined threshold in each of state 3-A in which the control command unit 5 is abnormal and state 4-A in which the control command unit 5 is inoperable. Note that the threshold may be set to a value at which a current does not continue to flow through the resistor R1 for active discharge in the discharge unit 9 to such an extent that the resistor R1 deteriorates when the terminal voltage of the capacitor C1 is less than the threshold even when active discharge is performed in the discharge unit 9.

[0086] 5, State 3 is a state in which control relay 75 is in the on state and a control signal indicating that control command unit 5 is abnormal is input from control command unit 5. State 3 is further divided into State 3-A in which the detection value of voltage detection unit 3 is equal to or greater than the threshold value, and State 3-B in which the detection value of voltage detection unit 3 is less than the threshold value.

[0087] In State 3-A, when the detection value of the voltage detection unit 3 is equal to or greater than the threshold, the discharge control unit 10 turns off the discharge switch SW and performs passive discharge in the discharge unit 9, regardless of whether the state is State 3-Aa, in which the SMR 65 is on and power is being supplied from the battery 60, or State 3-Ab, in which the SMR 65 is off and power is not being supplied from the battery 60. In this way, when the voltage between the terminals of capacitor C1 is equal to or greater than the threshold, passive discharge control is performed by the discharge control unit 10, so no current flows through resistor R1 in the discharge unit 9, and no particular problem occurs. Note that in State 3-Ab, the voltage between the terminals of capacitor C1 decreases over time, causing a transition from State 3-Ab to State 3-Bb, which will be described later.

[0088] In state 3-B, when the detection value of voltage detection unit 3 is less than the threshold, discharge control unit 10 turns on discharge switch SW and performs active discharge in discharge unit 9, regardless of whether the state is state 3-Ba in which SMR 65 is on and power is being supplied from battery 60, or state 3-Bb in which SMR 65 is off and power is not being supplied from battery 60. In this way, because the voltage between the terminals of capacitor C1 is less than the threshold, even if active discharge control is performed by discharge control unit 10, the rated power of resistor R1 is not exceeded, and no particular problem occurs.

[0089] In state 4, the control relay 75 is in the off state. State 4 is further divided into state 4-A in which the detection value of the voltage detection unit 3 is equal to or greater than the threshold value, and state 4-B in which the detection value of the voltage detection unit 3 is less than the threshold value.

[0090] In state 4-A, when the detection value of the voltage detection unit 3 is equal to or greater than the threshold, the discharge control unit 10 turns off the discharge switch SW and performs passive discharge in the discharge unit 9, regardless of whether the state is state 4-Aa, in which the SMR 65 is on and power is being supplied from the battery 60, or state 4-Ab, in which the SMR 65 is off and power is not being supplied from the battery 60. In this way, when the voltage between the terminals of capacitor C1 is equal to or greater than the threshold, passive discharge control is performed by the discharge control unit 10, so no current flows through resistor R1 in the discharge unit 9, and no particular problem occurs. Note that in state 4-Ab, the voltage between the terminals of capacitor C1 decreases over time, causing a transition from state 4-Ab ​​to state 4-Bb, which will be described later.

[0091] In state 4-B, when the detection value of the voltage detection unit 3 is less than the threshold value, the discharge control unit 10 turns on the discharge switch SW and performs active discharge in the discharge unit 9, regardless of whether the state is state 4-Ba in which the SMR 65 is on and power is being supplied from the battery 60, or state 4-Bb in which the SMR 65 is off and power is not being supplied from the battery 60. In this way, because the voltage between the terminals of the capacitor C1 is less than the threshold value, even if the discharge control unit 10 executes active discharge control, the rated power of the resistor R1 is not exceeded, and no particular problem occurs.

[0092] Fig. 6 is a graph showing a change in the inter-terminal voltage of the capacitor C1 over time when the power conversion device 1 according to embodiment 1 executes discharge control. In the graph shown in Fig. 6, the horizontal axis represents the elapsed time, and the vertical axis represents the inter-terminal voltage of the capacitor C1 detected by the voltage detection unit 3.

[0093] 6, it is assumed that the SMR 65 is turned off at timing t0. As shown in state 2-B, when the control relay 75 is on, a control signal indicating that the control command unit 5 is normal is input from the control command unit 5, and a Hi signal indicating that the vehicle 6 is abnormal is input from the host ECU 200 at timing t0, the discharge control unit 10 executes active discharge control to turn on the discharge switch SW. This allows the power conversion device 1 to rapidly discharge the capacitor C1.

[0094] As shown in state 3-Ab, even when the control relay 75 is in the ON state and a control signal indicating that the control command unit 5 is abnormal is input from the control command unit 5, the discharge control unit 10 does not immediately turn the discharge switch SW ON, but keeps the discharge switch SW OFF and performs passive discharge in the discharge unit 9 until the voltage between the terminals of the capacitor C1 detected by the voltage detection unit 3 falls below the threshold value V2. As shown by the dashed line, if passive discharge control is continued thereafter, it will take a long time for the voltage between the terminals of the capacitor C1 to fall below the target voltage Va.

[0095] In contrast, as in state 3-Bb, if the discharge control unit 10 turns on the discharge switch SW to perform active discharge in the discharge unit 9 at time t1 when the terminal voltage of capacitor C1 detected by the voltage detection unit 3 falls below the threshold value V2, the time until the terminal voltage of capacitor C1 falls below the target voltage Va can be shortened as much as possible. As a result, even if the control instruction unit 5 is abnormal, the power conversion device 1 can rapidly discharge capacitor C1 based on the terminal voltage of capacitor C1 without allowing current to continue to flow through the active discharge resistor R1. As a result, the power conversion device 1 can reduce the terminal voltage of capacitor C1 to below voltage Va by the time the target timing ta is reached.

[0096] Even when the control relay 75 is in the OFF state and the control command unit 5 is in an inoperable state as in state 4-Ab, the discharge control unit 10 does not immediately turn on the discharge switch SW, but keeps the discharge switch SW in the OFF state and performs passive discharge in the discharge unit 9 until the voltage between the terminals of the capacitor C1 detected by the voltage detection unit 3 falls below the threshold value V2. As indicated by the dashed line, if passive discharge control is continued thereafter, it will take a long time for the voltage between the terminals of the capacitor C1 to fall below the target voltage Va.

[0097] In contrast, as in state 4-Bb, if the discharge control unit 10 turns on the discharge switch SW to perform active discharge in the discharge unit 9 at time t1 when the terminal voltage of capacitor C1 detected by the voltage detection unit 3 falls below the threshold value V2, the time until the terminal voltage of capacitor C1 falls below the target voltage Va can be shortened as much as possible. As a result, even when the control instruction unit 5 is inoperable, the power conversion device 1 can rapidly discharge capacitor C1 based on the terminal voltage of capacitor C1 without allowing current to continue to flow through the active discharge resistor R1. As a result, the power conversion device 1 can reduce the terminal voltage of capacitor C1 to below voltage Va by the time the target timing ta is reached.

[0098] [Logic circuit of discharge control unit] The configuration of the logic circuit of the discharge control unit 10 according to embodiment 1 will be described with reference to Fig. 7. Fig. 7 is a circuit diagram showing the configuration of the logic circuit of the discharge control unit 10 according to embodiment 1. As shown in Fig. 7, the discharge control unit 10 includes NOT circuits 15 to 17, AND circuits 11 to 14, and an OR circuit 18.

[0099] The NOT circuits 15 to 17 invert and output the input signal. For example, when a signal indicating "1" is input to the NOT circuits 15 to 17, the NOT circuits output a signal indicating "0", and when a signal indicating "0" is input to the NOT circuits 15 to 17, the NOT circuits output a signal indicating "1".

[0100] AND circuits 11 to 14 output a signal indicating "1" when all input signals indicate "1", and output a signal indicating "0" when the input signals include a signal indicating "0".

[0101] The OR circuit 18 outputs a signal indicating "0" when all input signals indicate "0", and outputs a signal indicating "1" when the input signals include a signal indicating "1".

[0102] An ECU signal output from the host ECU 200 is input to the AND circuit 11 and the NOT circuit 15. A control signal output from the control circuit 51 is input to the AND circuit 12, the AND circuit 13, and the NOT circuit 16. A detection signal output from the voltage detection unit 3 is input to the AND circuit 12 and the NOT circuit 17. A signal output from the NOT circuit 15 is input to the AND circuit 12, the AND circuit 13, and the AND circuit 14. A signal output from the NOT circuit 16 is input to the AND circuit 11, the AND circuit 13, and the AND circuit 14. A signal output from the NOT circuit 17 is input to the AND circuit 11 and the AND circuit 14. The signals output from each of the AND circuits 11 to 14 are input to the OR circuit 18. The signal output from the OR circuit 18 is input to the discharge switch SW.

[0103] The signal input from the host ECU 200 to the AND circuit 11 is indicated by "IN11." The signal input from the NOT circuit 16 to the AND circuit 11 is indicated by "IN12." The signal input from the NOT circuit 17 to the AND circuit 11 is indicated by "IN13."

[0104] The signal input from the NOT circuit 15 to the AND circuit 12 is indicated by "IN21." The signal input from the control circuit 51 to the AND circuit 12 is indicated by "IN22." The signal input from the voltage detection unit 3 to the AND circuit 12 is indicated by "IN23."

[0105] The signal input from the NOT circuit 15 to the AND circuit 13 is indicated by "IN31." The signal input from the control circuit 51 to the AND circuit 13 is indicated by "IN32." The signal input from the NOT circuit 16 to the AND circuit 13 is indicated by "IN33."

[0106] The signal input from the NOT circuit 15 to the AND circuit 14 is indicated by "IN41." The signal input from the NOT circuit 16 to the AND circuit 14 is indicated by "IN42." The signal input from the NOT circuit 17 to the AND circuit 14 is indicated by "IN43."

[0107] The signal input from the AND circuit 11 to the OR circuit 18 is indicated by "OUT1." The signal input from the AND circuit 12 to the OR circuit 18 is indicated by "OUT2." The signal input from the AND circuit 13 to the OR circuit 18 is indicated by "OUT3." The signal input from the AND circuit 14 to the OR circuit 18 is indicated by "OUT4."

[0108] The input value is "1" when an ECU signal (Lo signal) indicating that the vehicle 6 is normal is input from the upper ECU 200. The input value is "0" when an ECU signal (Hi signal) indicating that the vehicle 6 is abnormal is input from the upper ECU 200. The input value is "1" when a control signal indicating that the control instruction unit 5 is normal is input from the control circuit 51. The input value is "0" when a control signal indicating that the control instruction unit 5 is abnormal is input from the control circuit 51. The input value is "1" when a detection signal indicating that the terminal voltage of the capacitor C1 is equal to or greater than the threshold is input from the voltage detection unit 3. The input value is "0" when a detection signal indicating that the terminal voltage of the capacitor C1 is less than the threshold is input from the voltage detection unit 3.

[0109] When the value of the signal output from the OR circuit 18 to the discharge switch SW is "1", the discharge switch SW is controlled to be in the ON state. When the value of the signal output from the OR circuit 18 to the discharge switch SW is "0", the discharge switch SW is controlled to be in the OFF state.

[0110] [Truth table for discharge control unit] A truth table of the discharge control unit 10 according to the first embodiment will be described with reference to Fig. 8. Fig. 8 is a diagram showing the truth table of the discharge control unit 10 according to the first embodiment. As shown in Fig. 8, the discharge control unit 10 outputs a signal for executing discharge control that switches the discharge switch SW, based on an ECU signal input from the host ECU 200, a control signal input from the control command unit 5, and a detection signal input from the voltage detection unit 3.

[0111] Specifically, when the discharge control unit 10 receives a control signal (control signal = 1) from the control instruction unit 5 indicating that the control instruction unit 5 is normal, such as in state 1-A, state 1-B, state 2-A, or state 2-B, the discharge control unit 10 performs discharge control based on whether or not it receives an ECU signal from the control instruction unit 5 indicating that the vehicle 6 is abnormal.

[0112] For example, as in state 1-A or state 1-B, when the discharge control unit 10 receives a control signal (control signal = 1) from the control command unit 5 indicating that the control command unit 5 is normal, and also receives an ECU signal (ECU signal = 1) from the control command unit 5 indicating that the vehicle 6 is normal, it outputs a signal (OUT = 0) to execute passive discharge control so that the discharge unit 9 performs passive discharge, regardless of the detection signal from the voltage detection unit 3.

[0113] Furthermore, as in state 2-A or state 2-B, when the discharge control unit 10 receives a control signal (control signal = 1) from the control command unit 5 indicating that the control command unit 5 is normal, and also receives an ECU signal (ECU signal = 0) from the control command unit 5 indicating that the vehicle 6 is abnormal, it outputs a signal (OUT = 1) to perform active discharge control so that the discharge unit 9 performs active discharge, regardless of the detection signal from the voltage detection unit 3.

[0114] When the discharge control unit 10 receives a control signal (control signal = 0) from the control instruction unit 5 indicating that the control instruction unit 5 is abnormal, such as in state 3-A, state 3-B, state 4-A, or state 4-B, the discharge control unit 10 performs discharge control based on the detection signal from the voltage detection unit 3, regardless of whether it receives an ECU signal from the control instruction unit 5 indicating that the vehicle 6 is abnormal.

[0115] Specifically, when the discharge control unit 10 receives a control signal (control signal = 0) from the control command unit 5 indicating that the control command unit 5 is abnormal, and also receives a detection signal (detection signal = 1) from the voltage detection unit 3 indicating that the terminal voltage of the capacitor C1 is above a threshold, such as in state 3-Aa, state 4-Aa, state 3-Ba, or state 4-Ba, the discharge control unit 10 outputs a signal (OUT = 0) to execute passive discharge control so that the discharge unit 9 performs passive discharge, regardless of the ECU signal.

[0116] Furthermore, when the discharge control unit 10 receives a control signal (control signal = 0) from the control instruction unit 5 indicating that the control instruction unit 5 is abnormal, and also receives a detection signal (detection signal = 0) from the voltage detection unit 3 indicating that the terminal voltage of the capacitor C1 is below the threshold, as in state 3-Ab, state 4-Ab, state 3-Bb, or state 4-Bb, it outputs a signal (OUT = 1) to perform active discharge control so that the discharge unit 9 becomes active, regardless of the ECU signal.

[0117] In this way, when the control instruction unit 5 is abnormal, the power conversion device 1 switches the discharge unit 9 between passive discharge control and active discharge control based on the terminal voltage of the capacitor C1 detected by the voltage detection unit 3, regardless of whether the vehicle 6 is abnormal or not, thereby preventing current from continuously flowing through the resistor R1 that discharges the capacitor C1.

[0118] Furthermore, when the control instruction unit 5 is abnormal and the terminal voltage of the capacitor C1 is equal to or greater than the threshold, the power conversion device 1 performs passive discharge control on the discharge unit 9, thereby preventing a continuous current flow through the resistor R1 by performing active discharge control on the discharge unit 9 when the control instruction unit 5 is abnormal. On the other hand, when the control instruction unit 5 is abnormal and the terminal voltage of the capacitor C1 is less than the threshold, the power conversion device 1 performs active discharge control on the discharge unit 9, thereby allowing the discharge unit 9 to actively discharge the capacitor C1 even when the control instruction unit 5 is abnormal.

[0119] <Embodiment 2> A power conversion device according to embodiment 2 will be described with reference to Figures 9 to 11. Note that in the power conversion device according to embodiment 2, only the parts that are different from the power conversion device 1 according to embodiment 1 will be described, and a description of the parts that are the same as those in power conversion device 1 will be omitted.

[0120] [Discharge control for each state of the power conversion device according to the second embodiment] Discharge control performed by the power conversion device according to the second embodiment for each state will be described with reference to Fig. 9. Fig. 9 is a diagram for explaining discharge control performed by the power conversion device according to the second embodiment for each state.

[0121] As shown in FIG. 9, in state 2 in which the control relay 75 is in the on state, a control signal indicating that the control instruction unit 5 is normal is input from the control instruction unit 5, and a Hi signal indicating that the vehicle 6 is abnormal is input from the upper ECU 200, the power conversion device of embodiment 2 performs discharge control depending on whether the terminal voltage of the capacitor C1 detected by the voltage detection unit 3 is equal to or greater than a predetermined threshold value.

[0122] Specifically, as shown in state 2-A, when the detection value of the voltage detection unit 3 is equal to or greater than the threshold value, the discharge control unit 20 of the power conversion device according to embodiment 2 turns the discharge switch SW to the OFF state and performs passive discharge in the discharge unit 9, regardless of whether the state is state 2-Aa, in which the SMR 65 is in the ON state and power is being supplied from the battery 60, or state 2-Ab, in which the SMR 65 is in the OFF state and power is not being supplied from the battery 60. In this way, when the voltage between the terminals of the capacitor C1 is equal to or greater than the threshold value, the discharge control unit 20 executes passive discharge control, so that no current flows through the resistor R1 in the discharge unit 9, and no particular problem occurs. Note that in state 2-Ab, the voltage between the terminals of the capacitor C1 decreases over time, causing a transition from state 2-Ab to state 2-Bb, which will be described later.

[0123] When the detection value of the voltage detection unit 3 is less than the threshold value as in state 2-B, the discharge control unit 20 turns on the discharge switch SW and performs active discharge in the discharge unit 9, regardless of whether the state is state 2-Ba in which the SMR 65 is on and power is being supplied from the battery 60, or state 2-Bb in which the SMR 65 is off and power is not being supplied from the battery 60. In this way, because the voltage between the terminals of the capacitor C1 is less than the threshold value, even if the discharge control unit 20 executes active discharge control, the rated power of the resistor R1 is not exceeded, and no particular problem occurs.

[0124] [Logic circuit of discharge control unit] The configuration of the logic circuit of the discharge control unit 20 according to embodiment 2 will be described with reference to Fig. 10. Fig. 10 is a circuit diagram showing the configuration of the logic circuit of the discharge control unit 20 according to embodiment 2. As shown in Fig. 10, the discharge control unit 20 includes NOT circuits 25 to 27, AND circuits 21 to 23, and an OR circuit .

[0125] The NOT circuits 25 to 27 invert the input signal and output the inverted signal. For example, when a signal indicating "1" is input to the NOT circuits 25 to 27, the NOT circuits 25 to 27 output a signal indicating "0", and when a signal indicating "0" is input to the NOT circuits 25 to 27, the NOT circuits 25 to 27 output a signal indicating "1".

[0126] The AND circuits 21 to 23 output a signal indicating "1" when all input signals indicate "1", and output a signal indicating "0" when the input signals include a signal indicating "0".

[0127] The OR circuit 28 outputs a signal indicating "0" when all input signals indicate "0", and outputs a signal indicating "1" when the input signals include a signal indicating "1".

[0128] An ECU signal output from the upper ECU 200 is input to the AND circuit 21 and the NOT circuit 25. A control signal output from the control circuit 51 is input to the AND circuit 22 and the NOT circuit 26. A detection signal output from the voltage detection unit 3 is input to the NOT circuit 27. A signal output from the NOT circuit 25 is input to the AND circuit 22 and the AND circuit 23. A signal output from the NOT circuit 26 is input to the AND circuit 21 and the AND circuit 23. A signal output from the NOT circuit 27 is input to the AND circuit 21, the AND circuit 22, and the AND circuit 23. The signals output from each of the AND circuits 21 to 23 are input to the OR circuit 28. The signal output from the OR circuit 28 is input to the discharge switch SW.

[0129] The signal input from the host ECU 200 to the AND circuit 21 is indicated by "IN11." The signal input from the NOT circuit 26 to the AND circuit 21 is indicated by "IN12." The signal input from the NOT circuit 27 to the AND circuit 21 is indicated by "IN13."

[0130] The signal input from the NOT circuit 25 to the AND circuit 22 is indicated by "IN21." The signal input from the control circuit 51 to the AND circuit 22 is indicated by "IN22." The signal input from the NOT circuit 27 to the AND circuit 22 is indicated by "IN23."

[0131] The signal input from the NOT circuit 25 to the AND circuit 23 is indicated by "IN31." The signal input from the NOT circuit 26 to the AND circuit 23 is indicated by "IN32." The signal input from the NOT circuit 27 to the AND circuit 23 is indicated by "IN33."

[0132] The signal input from the AND circuit 21 to the OR circuit 28 is indicated by "OUT1." The signal input from the AND circuit 22 to the OR circuit 28 is indicated by "OUT2." The signal input from the AND circuit 23 to the OR circuit 28 is indicated by "OUT3."

[0133] The input value is "1" when an ECU signal (Lo signal) indicating that the vehicle 6 is normal is input from the upper ECU 200. The input value is "0" when an ECU signal (Hi signal) indicating that the vehicle 6 is abnormal is input from the upper ECU 200. The input value is "1" when a control signal indicating that the control instruction unit 5 is normal is input from the control circuit 51. The input value is "0" when a control signal indicating that the control instruction unit 5 is abnormal is input from the control circuit 51. The input value is "1" when a detection signal indicating that the terminal voltage of the capacitor C1 is equal to or greater than the threshold is input from the voltage detection unit 3. The input value is "0" when a detection signal indicating that the terminal voltage of the capacitor C1 is less than the threshold is input from the voltage detection unit 3.

[0134] When the value of the signal output from the OR circuit 28 to the discharge switch SW is "1," the discharge switch SW is controlled to be in the ON state. When the value of the signal output from the OR circuit 28 to the discharge switch SW is "0," the discharge switch SW is controlled to be in the OFF state.

[0135] [Truth table for discharge control unit] A truth table of the discharge control unit 20 according to the second embodiment will be described with reference to Fig. 11. Fig. 11 is a diagram showing the truth table of the discharge control unit 20 according to the second embodiment. As shown in Fig. 11, the discharge control unit 20 outputs a signal for executing discharge control that switches the discharge switch SW, based on an ECU signal input from the host ECU 200, a control signal input from the control command unit 5, and a detection signal input from the voltage detection unit 3.

[0136] Specifically, as in state 1-A or state 1-B, when the discharge control unit 10 receives a control signal (control signal = 1) from the control command unit 5 indicating that the control command unit 5 is normal, and also receives an ECU signal (ECU signal = 1) from the control command unit 5 indicating that the vehicle 6 is normal, the discharge control unit 10 outputs a signal (OUT = 0) to execute passive discharge control so that the discharge unit 9 performs passive discharge.

[0137] As in state 2-A, when the discharge control unit 10 receives a control signal (control signal = 1) from the control instruction unit 5 indicating that the control instruction unit 5 is normal and also receives an ECU signal (ECU signal = 0) from the control instruction unit 5 indicating that the vehicle 6 is abnormal, if the discharge control unit 10 receives a detection signal (detection signal = 1) from the voltage detection unit 3 indicating that the terminal voltage of the capacitor C1 is above the threshold, it outputs a signal (OUT = 0) to execute passive discharge control so that the discharge unit 9 performs passive discharge, and if the discharge control unit 10 receives a detection signal (detection signal = 0) from the voltage detection unit 3 indicating that the terminal voltage of the capacitor C1 is below the threshold, it outputs a signal (OUT = 1) to execute active discharge control so that the discharge unit 9 becomes active.

[0138] In this way, in the power conversion device of embodiment 2, when the control instruction unit 5 is normal and the vehicle 6 is abnormal, if the terminal voltage of capacitor C1 is above the threshold, the discharge unit 9 is passively discharged, and if the terminal voltage of capacitor C1 is below the threshold, the discharge unit 9 is actively discharged.Therefore, even if the control instruction unit 5 is normal, the discharge unit 9 can actively discharge capacitor C1 while preventing current from continuously flowing through the resistor for active discharge.

[0139] <Third Embodiment> A power conversion device 100 according to the third embodiment will be described with reference to Fig. 12. Note that, in the power conversion device 100 according to the third embodiment, only the parts that are different from the power conversion device 1 according to the first embodiment will be described, and the parts that are the same as those of the power conversion device 1 will not be described.

[0140] FIG. 12 is a circuit diagram showing a configuration of a power conversion device 100 according to a third embodiment. As shown in FIG. 12, the power conversion device 100 includes a discharge unit 90 connected in parallel to a smoothing capacitor C1. The discharge unit 90 has a function of discharging the capacitor C1. The discharge unit 90 includes discharge resistors R3 and R4, and a discharge switch SW. In the power conversion device 100 according to the third embodiment, the resistor R3 is an example of a "first resistor," and the resistor R4 is an example of a "second resistor."

[0141] Resistors R3 and R4 are connected in series and are disposed between the positive electrode line PL and the negative electrode line NL. The path connecting the positive electrode line PL through resistors R4 and R3 to the negative electrode line NL is electrically connected at all times. Resistors R3 and R4 connected in series are connected in parallel with capacitor C1. Resistor R4 and a discharge switch SW are also connected in series and are disposed between the positive electrode line PL and the negative electrode line NL. Resistor R4 and the discharge switch SW connected in series are connected in parallel with capacitor C1. Resistor R3 and the discharge switch SW are connected in parallel. That is, resistor R3 and the discharge switch SW connected in parallel are connected in series with resistor R4.

[0142] Specifically, one end of resistor R4 is connected to the positive electrode line PL, and the other end of resistor R4 is connected to resistor R3 and one end of discharge switch SW. The other end of resistor R3 is connected to the negative electrode line NL. The other end of discharge switch SW is connected to the negative electrode line NL.

[0143] The source (one end) of the discharge switch SW is connected to resistors R3 and R4. The drain (the other end) of the discharge switch SW is connected to the negative electrode line NL. The gate of the discharge switch SW is connected to the discharge control unit 10. The discharge switch SW is controlled to an on state (conductive state) or an off state (non-conductive state) under the control of the discharge control unit 10.

[0144] In the power conversion device 100 configured in this manner, the discharge control unit 10 uses power supplied from the discharge power supply unit 4 to control the discharge switch SW based on the terminal voltage of the capacitor C1 detected by the voltage detection unit 3, thereby switching the discharge switch SW between an on state and an off state.

[0145] First, the passive discharge performed by the discharge unit 90 will be described. The discharge control unit 10 controls the discharge switch SW to the off state, thereby electrically blocking the path between the positive electrode line PL and the negative electrode line NL that passes through the resistor R4 and the discharge switch SW. As a result, the resistance value of the discharge unit 90, which is connected in parallel with the capacitor C1, becomes the combined resistance value of the resistors R3 and R4 connected in series. The charge stored in the capacitor C1 is discharged through the resistors R4 and R3 as a current flows from the capacitor C1 to the resistors R4 and R3.

[0146] In this way, the discharge control unit 10 can discharge the capacitor C1 using the resistors R3 and R4 by turning off the discharge switch SW through passive discharge control. Because the resistance value of the discharge unit 90 connected in parallel to the capacitor C1 is the combined resistance value of the resistors R3 and R4 connected in series, the resistance value of the discharge unit 90 is greater than the resistance value of resistor R4 alone. This allows the capacitor C1 to be discharged while minimizing power consumption.

[0147] Next, the active discharge performed by the discharge unit 90 will be described. The discharge control unit 10 electrically connects the path through resistor R4 and the discharge switch SW between the positive electrode line PL and the negative electrode line NL by controlling the discharge switch SW to the on state. As a result, the charge stored in capacitor C1 does not flow through the path through resistors R4 and R3, but current flows through the path through resistor R4 and the discharge switch SW. Because the resistance value of resistor R4 alone is smaller than the combined resistance value of resistors R3 and R4 connected in series, when the discharge current of capacitor C1 flows from capacitor C1 to the path through resistor R4 and the discharge switch SW, the time required for discharge is shorter than when the discharge current of capacitor C1 flows through the path through resistors R4 and R3. In other words, when the discharge switch SW is controlled to the on state, the current flowing through the discharge unit 90 is larger than when the discharge switch SW is controlled to the off state, and therefore the time required for discharge is shorter.

[0148] In this way, the discharge control unit 10 can rapidly discharge the capacitor C1 using only the resistor R4 by turning on the discharge switch SW through active discharge control.

[0149] [Aspect] It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0150] (Item 1) A power conversion device according to one embodiment includes an inverter circuit 2 that performs power conversion between a battery 60 and a load device 8, a capacitor C1 that smooths DC power supplied from the battery 60 to the inverter circuit 2, a voltage detection unit 3 that detects the terminal voltage of the capacitor C1, a discharge unit 9 that is connected in parallel with the capacitor C1 and includes a plurality of resistors R1 and R2 and a discharge switch SW for discharging the charge of the capacitor C1, and a discharge control unit 10 that controls discharge by the discharge unit 9 based on the terminal voltage detected by the voltage detection unit 3. The discharge unit 9 forms an active discharge circuit in which at least one resistor R1 of the plurality of resistors R1 and R2 is conductive with the discharge switch SW when the discharge switch SW is in an on state, and forms a passive discharge circuit in which at least one resistor R1 is non-conductive with the discharge switch SW when the discharge switch SW is in an off state. The active discharge circuit discharges the capacitor C1 at a faster rate than the passive discharge circuit. When the power supply from the battery 60 to the capacitor C1 is stopped and the terminal voltage drops, the discharge control unit 10 controls the discharge switch SW to the off state if the terminal voltage is equal to or greater than a threshold, and controls the discharge switch SW to the on state if the terminal voltage is less than the threshold.

[0151] According to the above configuration, when the power supply from the battery 60 to the smoothing capacitor C1 is stopped and the terminal voltage of the capacitor C1 drops, the power conversion device 1 controls the discharge switch SW to the off state to form a passive discharge circuit when the terminal voltage is equal to or higher than the threshold, and controls the discharge switch SW to the on state to form an active discharge circuit when the terminal voltage is less than the threshold, thereby preventing deterioration of the discharge resistor that discharges the smoothing capacitor C1.

[0152] (Item 2) In the power conversion device according to item 1, the battery 60 is mounted on a vehicle. The power conversion device further includes a control command unit 5 that outputs a signal to the discharge control unit 10 to switch the discharge switch SW from an on state to an off state. When the control command unit 5 has received a signal indicating that the control command unit 5 is normal, the discharge control unit 10 controls the discharge switch SW to an on state or an off state based on whether the control command unit 5 has received a signal indicating that the vehicle 6 is abnormal. When the control command unit 5 has received a signal indicating that the vehicle 6 is abnormal from the control command unit 5, the discharge control unit 10 controls the discharge switch SW to an off state when the inter-terminal voltage is equal to or greater than a threshold, regardless of whether the control command unit 5 has received a signal indicating that the vehicle 6 is abnormal. When the control command unit 5 has received a signal indicating that the vehicle 6 is abnormal from the control command unit 5, the discharge control unit 10 controls the discharge switch SW to an off state when the inter-terminal voltage is equal to or greater than a threshold, and controls the discharge switch SW to an on state when the inter-terminal voltage is less than the threshold.

[0153] According to the above configuration, when the control instruction unit 5 is abnormal, regardless of whether the vehicle 6 is abnormal or not, the power conversion device controls the discharge switch SW to the off state when the terminal voltage of the smoothing capacitor C1 detected by the voltage detection unit 3 is equal to or higher than a threshold, and controls the discharge switch SW to the on state when the terminal voltage is less than the threshold, thereby preventing the active discharge resistor from deteriorating.

[0154] (Clause 3) In the power conversion device according to paragraph 2, when the discharge control unit 10 receives a signal from the control command unit 5 indicating that the control command unit 5 is normal and a signal from the control command unit 5 indicating that the vehicle 6 is normal, the discharge control unit 10 controls the discharge switch SW to the off state; when the discharge control unit 10 receives a signal from the control command unit 5 indicating that the control command unit 5 is normal and a signal from the control command unit 5 indicating that the vehicle 6 is abnormal, the discharge control unit 10 controls the discharge switch SW to the on state; when the discharge control unit 10 receives a signal from the control command unit 5 indicating that the control command unit 5 is abnormal and the inter-terminal voltage is equal to or greater than a threshold, the discharge control unit 10 controls the discharge switch SW to the off state; when the discharge control unit 10 receives a signal from the control command unit 5 indicating that the control command unit 5 is abnormal and the inter-terminal voltage is less than the threshold, the discharge control unit 10 controls the discharge switch SW to the on state.

[0155] According to the above configuration, the power conversion device controls the discharge switch SW to the OFF state when the control command unit 5 is abnormal and the inter-terminal voltage is equal to or greater than the threshold, thereby preventing deterioration of the active discharging resistor due to a current continuously flowing through the active discharging resistor caused by the discharge switch SW being turned ON when the control command unit 5 is abnormal. On the other hand, the power conversion device 1 turns the discharge switch SW to the ON state when the control command unit 5 is abnormal and the inter-terminal voltage is less than the threshold, thereby allowing the discharge unit 9 to discharge the smoothing capacitor C1 even when the control command unit 5 is abnormal.

[0156] (4) In the power conversion device according to 2, when the discharge control unit 20 receives a signal from the control command unit 5 indicating that the control command unit 5 is normal and a signal from the control command unit 5 indicating that the vehicle 6 is normal, the discharge control unit 20 controls the discharge switch SW to the off state; when the discharge control unit 20 receives a signal from the control command unit 5 indicating that the control command unit 5 is normal and a signal from the control command unit 5 indicating that the vehicle 6 is abnormal, the discharge control unit 20 controls the discharge switch SW to the off state if the inter-terminal voltage is equal to or greater than a threshold, and controls the discharge switch SW to the on state if the inter-terminal voltage is less than the threshold; when the discharge control unit 20 receives a signal from the control command unit 5 indicating that the control command unit 5 is abnormal and the inter-terminal voltage is equal to or greater than the threshold, the discharge control unit 20 controls the discharge switch SW to the off state; when the discharge control unit 20 receives a signal from the control command unit 5 indicating that the control command unit 5 is abnormal and the inter-terminal voltage is less than the threshold, the discharge control unit 20 controls the discharge switch SW to the on state.

[0157] According to the above configuration, when the control instruction unit 5 is normal and the vehicle 6 is abnormal, the power conversion device turns the discharge switch SW off when the terminal voltage is equal to or higher than the threshold, and turns the discharge switch SW on when the terminal voltage is less than the threshold. Therefore, even if the control instruction unit 5 is normal, the discharge unit 9 can discharge the smoothing capacitor C1 while preventing current from continuously flowing through the active discharge resistor and causing the active discharge resistor to deteriorate.

[0158] (5) In the power conversion device according to any one of paragraphs 1 to 4, the plurality of resistors include a resistor R1 connected in series with the discharge switch SW, and a resistor R2 connected in parallel with the resistor R1 and the discharge switch SW connected in series. The resistor R1 and the discharge switch SW connected in series are connected in parallel with the capacitor C1. The resistor R2 is connected in parallel with the capacitor C1.

[0159] According to the above configuration, the power conversion device can switch the resistance value of the discharge unit 9 connected in parallel with the capacitor C1 by switching the discharge switch SW between the on state and the off state.

[0160] (Item 6) In the power conversion device according to any one of items 1 to 4, the plurality of resistors include resistors R3 and R4 connected in series. Resistor R3 is connected in parallel with discharge switch SW. Resistor R4 is connected in series with discharge switch SW. Resistors R3 and R4 connected in series are connected in parallel with capacitor C1.

[0161] According to the above configuration, the power conversion device can switch the flow path of the discharge current from the capacitor C1 in the discharge unit 90 connected in parallel with the capacitor C1 by switching the discharge switch SW between the on state and the off state.

[0162] (7th paragraph) In the power conversion device according to any one of paragraphs 1 to 6, the load device 8 is an electric motor used in an electric compressor for the vehicle 6.

[0163] According to the above configuration, the power conversion device can convert DC power supplied from the battery 60 of the vehicle 6 into AC power and supply it to the electric motor used in the electric compressor for the vehicle 6.

[0164] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0165] 1,100 power conversion device, 2 inverter circuit, 3 voltage detection section, 4 discharge power supply section, 5 control command section, 6 vehicle, 8 load device, 8U, 8V, 8W coils, 9, 90 discharge section, 10, 20 discharge control section, 11, 12, 13, 14, 21, 22, 23 AND circuit, 15, 16, 17, 25, 26, 27 NOT circuit, 18, 28 OR circuit, 51 control circuit, 52 power supply circuit, 53 interface, 60, 70 battery, 75 control relay, C1 capacitor, DU1, DU2, DV1, DV2, DW1, DW2 diodes, 200 upper ECU, GND ground terminal, N1, N2, N3 node, NL negative pole line, PL positive pole line, R1, R2, R3, R4 resistor, SW discharge switch, T1, T2, T4, T5 Connection points, TU1, TU2, TV1, TV2, TW1, TW2 switching elements.

Claims

1. A power conversion device, a power conversion unit that converts power between a DC power source mounted on the vehicle and a load; a capacitor that smoothes the DC power supplied from the DC power supply to the power conversion unit; a voltage detection unit that detects a voltage between the terminals of the capacitor; a discharge unit connected in parallel with the capacitor and including a plurality of resistors and switch elements for discharging the charge of the capacitor; a discharge control unit that controls discharge by the discharge unit based on the inter-terminal voltage detected by the voltage detection unit; a control command unit that outputs a signal to the discharge control unit to switch the switch element from an on state to an off state, The discharge unit is an active discharge circuit is configured such that, when the switch element is in the on state, at least one resistor among the plurality of resistors is in a conductive state with the switch element; a passive discharge circuit is configured such that the at least one resistor and the switch element are in a non-conductive state when the switch element is in the off state; The active discharge circuit discharges the capacitor at a faster rate than the passive discharge circuit, The discharge control unit When the power supply from the DC power source to the capacitor is stopped and the inter-terminal voltage drops, if the inter-terminal voltage is equal to or higher than a threshold value, the switch element is controlled to the off state, and if the inter-terminal voltage is less than the threshold value, the switch element is controlled to the on state; When a signal indicating that the control command unit is normal is received from the control command unit, the switch element is controlled to the on state or the off state based on whether a signal indicating that the vehicle is abnormal is received from the control command unit; When the control instruction unit receives a signal indicating an abnormality from the control instruction unit, regardless of whether the control instruction unit receives a signal indicating an abnormality in the vehicle, the power conversion device controls the switch element to the off state when the inter-terminal voltage is equal to or greater than the threshold, and controls the switch element to the on state when the inter-terminal voltage is less than the threshold.

2. The discharge control unit controlling the switch element to the off state when receiving from the control command unit a signal indicating that the control command unit is normal and when receiving from the control command unit a signal indicating that the vehicle is normal; controlling the switch element to the on state when receiving from the control command unit a signal indicating that the control command unit is normal and a signal indicating that the vehicle is abnormal, When a signal indicating that the control instruction unit is abnormal is received from the control instruction unit and the inter-terminal voltage is equal to or greater than a threshold value, the switch element is controlled to the off state; The power conversion device according to claim 1 , wherein the power conversion device controls the switch element to the on state when the control command unit receives a signal indicating that the control command unit is abnormal and the inter-terminal voltage is less than the threshold value.

3. The discharge control unit controlling the switch element to the off state when receiving from the control command unit a signal indicating that the control command unit is normal and when receiving from the control command unit a signal indicating that the vehicle is normal; When a signal indicating that the control instruction unit is normal is received from the control instruction unit and a signal indicating that the vehicle is abnormal is received from the control instruction unit, if the inter-terminal voltage is equal to or greater than a threshold value, the switch element is controlled to the off state, and if the inter-terminal voltage is less than the threshold value, the switch element is controlled to the on state; When a signal indicating that the control instruction unit is abnormal is received from the control instruction unit and the inter-terminal voltage is equal to or greater than a threshold value, the switch element is controlled to the off state; The power conversion device according to claim 1 , wherein the power conversion device controls the switch element to the on state when the control command unit receives a signal indicating that the control command unit is abnormal and the inter-terminal voltage is less than the threshold value.

4. the plurality of resistors include a first resistor connected in series with the switch element, and a second resistor connected in parallel with the first resistor connected in series and the switch element; the first resistor and the switch element connected in series are connected in parallel with the capacitor; The power conversion device according to any one of claims 1 to 3, wherein the second resistor is connected in parallel with the capacitor.

5. the plurality of resistors includes a first resistor and a second resistor connected in series; the first resistor is connected in parallel with the switch element; the second resistor is connected in series with the switch element; 4. The power conversion device according to claim 1, wherein the first resistor and the second resistor connected in series are connected in parallel with the capacitor.

6. 2. The power conversion device according to claim 1, wherein the load is an electric motor used in an electric compressor for a vehicle.

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