Power conversion device and vehicle equipped with power conversion device

Abstract

An objective of the present invention is to provide: a power conversion device (100) that quickly discharges a capacitor (3) while suppressing the application of a high voltage to the power conversion device (100) by stopping a motor (6) when the vehicle is commanded to stop; and a vehicle. A power conversion device (100) includes: a capacitor (3); a discharge switch (5) for discharging residual charge via a discharge resistor (4); a power conversion circuit (22); a drive circuit (13) for controlling the power conversion circuit (22); a drive state determination unit (16) for determining the drive state of the power conversion circuit (22); and a control device (18) for providing a control signal to the drive circuit (13). The control device (18) performs all-phase short-circuit control upon receiving a power conversion stop command, and turns on the discharge switch (5) to discharge the capacitor (3) after determining by means of the drive state determination unit (16) that an all-phase short-circuit state has been entered.

Description

Power conversion device and vehicle equipped with power conversion device

[0001] The present disclosure relates to a power conversion device and a vehicle equipped with the power conversion device.

[0002] Power conversion devices are often used to control motors (electric motors) applied to electrically powered vehicles such as hybrid vehicles and electric vehicles. Examples of power conversion devices include AC / DC (alternate current / direct current) converters that convert AC power to DC power, inverters that convert DC power to AC power, and DC / DC (direct current / direct current) converters that change the input and output voltage levels of DC power. These power conversion devices are often configured with semiconductor switching elements.

[0003] As an example of a power conversion device, an inverter mounted on an electric vehicle converts DC power output from a DC power source into desired AC power and supplies it to the motor to control it. The inverter is composed of a power conversion circuit configured by combining switching elements, a control device that controls the switching elements, a capacitor that counters switching noise, etc.

[0004] For example, when controlling a three-phase synchronous motor, the power conversion circuit is provided with a switching element in each of the upper arm (positive arm) and lower arm (negative arm) of the three phases (U phase, V phase, and W phase).

[0005] By sequentially turning on and off switching elements provided for each phase of the power conversion circuit, AC power with a phase difference of 120 degrees is supplied to each phase of the motor to drive the motor. Power conversion devices for driving motors using high-voltage batteries, such as those in electric vehicles, are equipped with large-capacity capacitors to smooth voltage fluctuations during switching. Power conversion devices for electric vehicles are required by law to rapidly discharge the charge in the capacitor within a predetermined time when the vehicle is stopped.

[0006] When a vehicle comes to a halt due to a collision or other reason, the power conversion device must be disconnected from the battery and the charge stored in the power conversion device's capacitor must be quickly discharged to protect the occupants and emergency personnel from high voltages in the event of a collision.

[0007] A technology has been proposed in which, when a vehicle is commanded to stop, the charge in the capacitor of a power conversion device is discharged by flowing through a discharge resistor. Active discharge is performed by flowing the charge in the capacitor through the discharge resistor via a discharge switch. The amount of voltage drop in the capacitor is then measured, and if the amount of drop is small, an abnormality is determined (see, for example, Patent Document 1).

[0008] Patent No. 7181416

[0009] The technology disclosed in Patent Document 1 measures the amount of voltage drop in the capacitor and determines an abnormality if the amount of drop is small. However, it does not mention the procedure for stopping the power conversion circuit or the procedure for connecting the discharge switch when a command to stop the vehicle is issued. It also does not mention how to respond to the case where a back electromotive force is generated on the motor side and a high voltage is generated when the motor driven by the power conversion device continues to rotate. Even when a command to stop the vehicle is issued, it is possible that the vehicle continues to run and the wheels are spinning.

[0010] The present disclosure provides a power conversion device that stops the motor and prevents high voltage from being applied to the power conversion device while quickly discharging the charge in the capacitor, even if the motor continues to rotate when a command to stop the vehicle is received, causing a back electromotive force to be generated on the motor side, resulting in a high voltage.The present disclosure also provides a vehicle equipped with such a power conversion device.The high voltage applied to the power conversion device can be suppressed, and the charge stored in the capacitor can be quickly discharged, thereby satisfying the performance required by regulations.

[0011] a power conversion circuit having legs for each phase of a motor, the legs being provided with a positive-side switching element connected to the positive-side DC bus, a negative-side switching element connected to the negative-side DC bus, and an external connection point connecting the positive-side switching element and the negative-side switching element in series and supplying a phase current to a coil of the motor; a drive circuit outputting drive signals for controlling the switching elements to operate the power conversion circuit; a drive state determination unit determining the drive state of the switching elements; and a control device giving a control signal to the drive circuit, wherein, when a command to stop power conversion is received, the control device performs all-phase short-circuit control by turning on all positive-side switching elements and turning off all negative-side switching elements, or by turning off all positive-side switching elements and turning on all negative-side switching elements, and after the drive state determination unit determines that an all-phase short-circuit state has occurred, the control device turns on the discharge switch to discharge the charge of the capacitor.

[0012] The power conversion device according to the present disclosure is capable of stopping the motor and preventing the application of high voltage to the power conversion device while rapidly discharging the charge of the capacitor, even if the motor continues to rotate when a command to stop the vehicle is issued and a back electromotive force is generated in the motor, generating a high voltage. Such a power conversion device and a vehicle equipped with the power conversion device can satisfy regulatory requirements by rapidly discharging the charge of the capacitor in the power conversion device.

[0013] FIG. 1 is a configuration diagram of a power conversion device according to a first embodiment. FIG. 2 is a hardware configuration diagram of a control device of the power conversion device according to the first embodiment. FIG. 3 is a first flowchart showing a stop process of the control device of the power conversion device according to the first embodiment. FIG. 4 is a second flowchart showing a stop process of the control device of the power conversion device according to the first embodiment. FIG. 5 is a configuration diagram of a power conversion device according to a second embodiment. FIG. 6 is a first flowchart showing a start process of the control device of the power conversion device according to the second embodiment. FIG. 7 is a configuration diagram of a power conversion device according to a third embodiment. FIG. 8 is a diagram explaining a logic for determining a fault in a discharge circuit of a power conversion device according to the third embodiment. FIG. 9 is a first flowchart showing a stop process of the control device of the power conversion device according to the third embodiment. FIG. 10 is a second flowchart showing a stop process of the control device of the power conversion device according to the third embodiment. FIG. 11 is a second flowchart showing a stop process of the control device of the power conversion device according to the fourth embodiment. FIG. 12 is a third flowchart showing a stop process of the control device of the power conversion device according to the fourth embodiment. FIG. 13 is a first flowchart showing a stop process of the control device of the power conversion device according to the fifth embodiment. FIG. 14 is a third flowchart showing a stop process of the control device of the power conversion device according to the sixth embodiment. 10 is a first time chart showing the discharge of a capacitor of the power conversion device according to embodiment 6. FIG. 11 is a second time chart showing the discharge of a capacitor of the power conversion device according to embodiment 6. FIG. 12 is a third flowchart showing the stop processing of a control device of a power conversion device according to embodiment 7.

[0014] Hereinafter, preferred embodiments of a power conversion device according to the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0015] 1. First Embodiment <Configuration of Power Conversion Device> Fig. 1 is a configuration diagram of a power conversion device 100 according to a first embodiment. The power conversion device 100 is connected to a DC power supply 1 formed of a secondary battery such as a lithium-ion battery mounted on a vehicle via a main power switch 25 and an auxiliary power switch 2. The main power switch 25 is a main switch of the vehicle that may also be called an ignition switch or a key switch. The auxiliary power switch 2 is a switch that may also be called a contactor and is used to supply power to the power conversion device.

[0016] The secondary power switch 2 is connected with a delay after detecting that the main power switch 25 is connected. In FIG. 1 , the power conversion device 100 is capable of recognizing the connected or disconnected state of the main power switch 25. When the power conversion device 100 recognizes that the main power switch 25 is connected, it performs a predetermined initial process and then connects the secondary power switch 2. By connecting the secondary power switch 2, it is possible to supply current from the DC power supply 1 to the positive side DC bus 24a and the negative side DC bus 24b connected to the power conversion circuit 22.

[0017] <Power Conversion Circuit> The power conversion circuit 22 has a positive-side switching circuit 7-9 connected to a positive-side DC bus 24a and a negative-side switching circuit 10-12 connected to a negative-side DC bus 24b. The positive-side switching circuit 7-9 and the negative-side switching circuit 10-12 are connected in series at their respective connection points. The series-connected positive-side and negative-side switching circuits are referred to as legs. Figure 1 shows three legs that supply currents for the U phase, V phase, and W phase.

[0018] The control device 18 receives a torque command from an external device and calculates a target torque and a target current. The control device 18 controls the power conversion circuit 22 so that the output of the motor 6 matches the target torque. By sequentially turning on and off the switching circuits 7-12 provided for each phase of the power conversion circuit 22, AC power with a phase difference of 120 degrees is supplied to each phase of the motor to drive the motor.

[0019] The control device 18 includes a drive state determination unit 16, which can monitor the drive state of the switching circuits 7-12 by the drive circuit 13. The drive state determination unit 16 may monitor the output of the drive circuit 13 to determine whether the drive circuit 13 is outputting an output signal in accordance with the control signal from the signal control unit 15. Alternatively, the drive state determination unit 16 may monitor the voltage at the connection points of the three types of legs of the switching circuit to determine whether the switching circuit is operating in accordance with the control signal.

[0020] The control device 18 includes a fault diagnosis unit 17. The fault diagnosis unit 17 can diagnose faults by monitoring the detected voltage Vc of the capacitor 3 input from the voltage detector 14 and the drive state of the switching circuits 7-12 determined by the drive state determination unit 16. The signal control unit 15 included in the control device 18 can operate the auxiliary power switch 2 and the discharge switch 5 in addition to controlling the drive circuit 13. In FIG. 1, the auxiliary power switch 2 is configured to be operated by the control device 18 of the power conversion device 100, but the auxiliary power switch 2 may also be operated externally by another device. In this case, the auxiliary power switch 2 is turned off when the main power switch 25 is turned off, and is turned on after a predetermined delay time upon detecting that the main power switch 25 is turned on.

[0021] <Capacitor> The capacitor 3 has a function of suppressing ripples in the DC bus voltage. The capacitor 3 also has a function of lowering the power supply impedance of the power conversion circuit 22 to improve the AC current driving capability of the power conversion circuit 22. The capacitor 3 also has a function of absorbing surge voltages.

[0022] The discharge resistor 4 connected to the discharge switch 5 is used to discharge the charge in the capacitor 3. When the control device 18 receives a stop command, it turns off the auxiliary power switch 2 to disconnect the positive DC bus 24a of the power conversion device 100 from the DC power supply 1. Then, it turns on the discharge switch 5 to discharge the charge remaining in the capacitor 3. The power conversion device 100 for an electric vehicle is required by law to rapidly discharge the charge in the capacitor within a predetermined time when the vehicle is stopped.

[0023] 1 shows an example in which each of the switching circuits 7-12 has two switching elements arranged in parallel. Each of the switching circuits 7-12 may be configured with one switching element, or may be configured with three or more switching elements.

[0024] The switching element is often a power transistor, which is a power semiconductor switching element capable of operating at a high switching frequency. Fig. 1 shows an example in which a power transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), is used as the switching element.

[0025] A free wheel diode (FWD) is provided in parallel to each MOSFET of the switching element, with the forward direction being the direction from the negative side to the positive side of the DC power supply. As the power transistor, an IGBT (Insulated Gate Bipolar Transistor) or the like may be used instead of a MOSFET, and the free wheel diode may be provided as a separate component.

[0026] <Hardware Configuration of Control Device> Fig. 2 is a hardware configuration diagram of the control device 18 of the power conversion device 100 according to the first embodiment. In the present embodiment, the control device 18 is a control device that controls the power conversion device 100. Each function of the control device 18 is realized by a processing circuit provided in the control device 18. Specifically, the control device 18 includes, as processing circuits, an arithmetic processing device 90 (computer) such as a CPU (Central Processing Unit), a storage device 91 that exchanges data with the arithmetic processing device 90, an input circuit 92 that inputs external signals to the arithmetic processing device 90, and an output circuit 93 that outputs signals from the arithmetic processing device 90 to the outside.

[0027] The arithmetic processing device 90 may be an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, various signal processing circuits, etc. Furthermore, a plurality of the same or different types of arithmetic processing device 90 may be provided, and each process may be shared and executed.

[0028] The storage device 91 includes a RAM (Random Access Memory) configured to be able to read and write data from and to the arithmetic processing device 90, a ROM (Read Only Memory) configured to be able to read data from and to the arithmetic processing device 90, etc. The input circuit 92 is connected to various sensors and switches including the voltage detector 14, and includes interface circuits such as an AD converter and an input circuit that input output signals from these sensors and switches to the arithmetic processing device 90. The output circuit 93 is connected to electrical loads such as the drive circuit 13, the auxiliary power switch 2, switching elements including the discharge switch 5, and actuators, and includes interface circuits such as a drive circuit and a communication circuit that converts and outputs output signals from the arithmetic processing device 90 to these electrical loads. The control device 18 may also incorporate the function of the drive circuit 13.

[0029] Each function of the control device 18 is realized by the arithmetic processing device 90 executing software (programs) stored in a storage device 91 such as a ROM, and cooperating with other hardware of the control device 18 such as the storage device 91, an input circuit 92, and an output circuit 93. Note that setting data such as thresholds and judgment values ​​used by the control device 18 is stored in the storage device 91 such as a ROM as part of the software (programs).

[0030] Each function installed inside the control device 18 may be configured as a software module, or may be configured as a combination of software and hardware. The entire control device 18 may be a component incorporated into a single package. The control device 18 may be treated as a so-called one-chip microcomputer.

[0031] <All-phase short-circuiting by stop command> When the power conversion device 100 receives a stop command, it stops power conversion and discharges the residual charge in the capacitor 3 via a discharge resistor. At this time, an all-phase short-circuiting operation is performed. In the power conversion device 100 that controls the current to the three-phase coils that control the three-phase motor shown in FIG. 1, the all-phase short-circuiting operation becomes a three-phase short-circuiting operation. The three-phase short-circuiting is performed by turning on all of the positive-side switching circuits 7-9 and turning off all of the negative-side switching circuits 10-12, or by turning off all of the positive-side switching circuits 7-9 and turning on all of the negative-side switching circuits 10-12.

[0032] In this way, the three-phase coils are brought to the same potential, and by short-circuiting, the motor 6 is braked. By short-circuiting the phase current outputs of the power conversion device 100, it is possible to prevent surge voltages due to regenerative currents from being applied. After confirming that the three-phase short-circuit has been performed, the discharge switch is connected, a discharge current is passed through the discharge resistor, and the charge in the capacitor 3 is reduced.

[0033] If an overvoltage is applied to the phase current output of the power conversion device and a large current flows, the life of the discharge switch and discharge resistor may be shortened and performance may be deteriorated. Therefore, the drive state determination unit 16 checks whether the power conversion circuit 22 is in a three-phase short-circuit state.

[0034] The drive state determination unit 16 monitors the gate voltage value to determine whether the gates of the switching circuits 7-12 are operating as instructed. That is, it checks whether the output of the drive circuit 13 is being output as planned. The drive state determination unit 16 may also check the voltage of the phase current output from the external connection points of each leg of the power conversion circuit 22 to check for a three-phase short-circuit state. If a three-phase short-circuit state is detected, the discharge switch is connected to discharge and eliminate the residual charge in the capacitor 3. Possible reasons for a three-phase short-circuit state not being detected include a failure of the drive circuit 13 or a failure of one of the switching circuits 7-12.

[0035] By following this procedure, even if the motor continues to rotate when a command to stop the vehicle is issued and a high voltage is generated due to back electromotive force on the motor side, the motor can be stopped and high voltage can be prevented from being applied to the power conversion device. This also enables the charge in the capacitor to be quickly discharged. Therefore, a power conversion device that satisfies the performance required by regulations and a vehicle equipped with such a power conversion device can be obtained.

[0036] <Stop Processing> Fig. 3 is a first flowchart showing the stop processing of the control device 18 of the power conversion device 100 according to the first embodiment. Fig. 4 is a second flowchart showing the stop processing. Fig. 4 shows the processing continued from Fig. 3. The processing in Figs. 3 and 4 is executed by the arithmetic processing device 90 of the control device 18.

[0037] The processes shown in Figures 3 and 4 are executed at predetermined time intervals (for example, every 1 ms). These processes may be executed for each event, such as each time the motor 6 rotates a predetermined angle or each time an external command is received, instead of at predetermined time intervals.

[0038] 3 starts, and in step S301, it is determined whether a stop command has been received. If a stop command has been received (determination is YES), the process proceeds to step S302. If a stop command has not been received (determination is NO), the process ends.

[0039] In step S302, it is determined whether a discharge prohibition flag is set. The discharge prohibition flag is set when a new discharge should not be started, such as when all phases cannot be short-circuited or when discharge has already ended. If the discharge prohibition flag is set (determined YES), the process ends. If the discharge prohibition flag is not set (determined NO), the process proceeds to step S303.

[0040] In step S303, it is determined whether the discharging flag is set. The discharging flag is set when discharging has already started. If the discharging flag is set (determination is YES), the process proceeds to step S325. If the discharging flag is not set (determination is NO), the process proceeds to step S304.

[0041] In step S304, the auxiliary power switch 2 is turned off to disconnect the power conversion device 100 from the DC power supply 1. Then, the warning light is turned on. In step S305, an all-phase short-circuit operation is performed. In the case of the configuration in FIG. 1, this is a three-phase short-circuit operation. In step S305 in FIG. 3, all positive-side switching circuits are turned on and all negative-side switching circuits are turned off. However, the all-phase short-circuit operation may be performed by turning off all positive-side switching circuits and turning on all negative-side switching circuits.

[0042] In step S306, the drive state of the switching circuit is checked. In practice, the drive state of the switching circuit is checked by the drive state determination unit 16. In step S307, it is determined whether or not an all-phase short-circuit state has occurred. If an all-phase short-circuit state has occurred (determination is YES), the process proceeds to step S321. If an all-phase short-circuit state has not occurred (determination is NO), the process proceeds to step S309.

[0043] In step S309, an all-phase shutoff operation is performed. The all-phase shutoff operation turns off all switching circuits. If all switching circuits are turned off, an overvoltage may be applied to the positive DC bus 24a and the negative DC bus 24b via the free-wheel diodes of each switching circuit while the motor 6 is rotating or if a large voltage surge occurs due to back electromotive force. Therefore, it is decided not to connect the discharge switch here, and the process proceeds to step S350.

[0044] In step S321, the discharge timer TM is cleared. The discharge timer TM is a timer that measures the time during which the capacitor 3 continues to discharge.

[0045] In step S323, the discharging flag is set. In step S324, the discharge switch is closed. Then, the charge in the capacitor 3 starts to be discharged via the discharge resistor 4.

[0046] In step S325, the discharge timer TM is incremented. Since the processes in FIGS. 3 and 4 are executed every 1 ms, the timer is incremented every 1 ms. The timer is clipped at its maximum value. For example, for a 1-byte timer, the maximum value is FFH, and for a 2-byte timer, the maximum value is FFFFH.

[0047] In step S358, it is determined whether the value of the discharge timer TM is equal to or greater than a predetermined termination determination time Te. If the value of the discharge timer TM is equal to or greater than the termination determination time Te (determination is YES), the process proceeds to step S357. If the value of the discharge timer TM is not equal to or greater than the termination determination time Te (determination is NO), the process ends.

[0048] Step S357 is executed after the discharge has continued until the termination determination time has elapsed. In step S357, the warning light is turned off.

[0049] In step S350, the discharge switch 5 is turned off. In step S351, the discharging flag is cleared. In step S352, the discharge prohibition flag is set. Then, the process ends.

[0050] 2. Second Embodiment <Configuration of Power Conversion Apparatus> Fig. 5 is a configuration diagram of a power conversion apparatus 100 according to a second embodiment. Fig. 5 differs from Fig. 1 according to the first embodiment in that a constant current circuit 19 is newly provided. The hardware configuration of Fig. 2 can also be applied to the control device 18 of the power conversion apparatus 100 according to the second embodiment.

[0051] In the power conversion device 100 according to the second embodiment, when the main power switch 25, which is the main switch of the vehicle, is closed, a constant current is supplied from the constant current circuit 19 while the auxiliary power switch 2 is kept closed, and a determination is made as to whether the discharge switch and the discharge resistor are normal or abnormal. After this start-up check is completed, the auxiliary power switch 2 is closed, the power conversion device 100 is connected to the DC power supply 1, and power supply to the motor is started.

[0052] <Check at Startup> The control device 18 keeps the discharge switch 5 connected from the time the main power switch 25 changes from off to on until the auxiliary power switch changes from off to on. Then, a constant current flows through the constant current circuit 19, and the voltage detector 14 detects the detected voltage Vc. If the detected voltage Vc is equal to or lower than a predetermined voltage determination value Vth, it can be determined that the discharge switch 5 is normally connected and that current is normally flowing through the discharge resistor 4. In this case, it can be determined that the connection state of the discharge switch 5 and the resistance value of the discharge resistor 4 are normal.

[0053] A second voltage determination value Vth2 higher than the voltage determination value Vth is set. If the detected voltage is higher than the second voltage determination value Vth2, it can be inferred that the discharge switch 5 cannot be connected or that the discharge resistor 4 is disconnected. This is because it can be inferred that almost no current is flowing through the discharge resistor 4.

[0054] If the detected voltage Vc is higher than the voltage determination value Vth and equal to or lower than the second voltage determination value Vth2, it can be determined that the resistance of the discharge resistor 4 is abnormal. This is because it is possible that the discharge switch 5 is connected normally, and the resistance of the discharge resistor 4 has increased due to aging or performance degradation caused by a large current flow. The resistance of the discharge resistor 4 tends to increase if it heats up beyond the allowable temperature due to an overload. Therefore, the abnormal resistance is determined by whether the resistance value is greater than the threshold value.

[0055] The cases where the discharge switch 5 cannot be connected, or the discharge resistor 4 is broken or has an abnormal resistance value are collectively defined as a discharge voltage abnormality. If the detected voltage Vc is equal to or less than the voltage determination value Vth, it can be determined that the discharge switch 5 and the discharge resistor 4 are normal. If the detected voltage Vc is higher than the voltage determination value Vth, it can be determined that a discharge voltage abnormality has occurred.

[0056] If a discharge voltage abnormality is detected, the power conversion device 100 will not discharge the capacitor 3 even if it receives a stop command while the motor 6 is running after startup. This is because there is a possibility that the discharge switch 5 or the discharge resistor 4 is broken.

[0057] Upon receiving the stop command, the power conversion device 100 stops power conversion and discharges the residual charge in the capacitor 3 via the discharge resistor 4. At this time, under normal conditions, the detected voltage Vc of the voltage detector 14 gradually decreases. If the detected voltage Vc does not decrease, it is possible that there is an abnormality in the discharge switch 5 or the discharge resistor 4, or that the auxiliary power switch 2 cannot be turned off.

[0058] Even in such a case, in the power conversion device 100 according to embodiment 2, when the main power switch 25 is turned on, the discharge switch 5 and the discharge resistor 4 are checked before the secondary power switch 2 is turned on, making it possible to distinguish between an inability to discharge due to a failure of the secondary power switch 2 and an inability to discharge due to an abnormality in the discharge switch 5 or the discharge resistor 4.

[0059] <Start-up process> Fig. 6 is a first flowchart showing the start-up process of the control device 18 of the power conversion device 100 according to embodiment 2. Fig. 7 is a second flowchart showing the start-up process. Fig. 7 shows the process continued from Fig. 6. The processes in Figs. 6 and 7 are executed by the arithmetic processing device 90 of the control device 18.

[0060] 6 and 7 are executed at predetermined time intervals (for example, every 1 ms). These processes may be executed for each event, such as each time the motor 6 rotates a predetermined angle or each time an external command is received.

[0061] 6 starts, and in step S101, the state of the main power switch (on or off) is confirmed. This is then stored in the main power switch state SMSW. In step S102, it is determined whether the main power switch state SMSW is off. If the main power switch state SMSW is off (determination is YES), the process proceeds to step S103. If the main power switch state SMSW is not off (determination is NO), the process proceeds to step S104.

[0062] In step S103, the auxiliary power switch 2 is turned off, and the process then proceeds to step S104.

[0063] In step S104, the previous main power switch state SMSWold is read. Then, in step S105, it is determined whether the previous main power switch state SMSWold was off (OFF) and the main power switch state SMSW was on (ON). If the previous main power switch state SMSWold was off and the main power switch state SMSW was on (determination is YES), this indicates that the current main power switch state SMSW has just been connected. Then, the process proceeds to step S106. If the previous main power switch state SMSWold was off and the main power switch state SMSW was not on (determination is NO), the process proceeds to step S112.

[0064] In step S106, the startup check timer TMig is cleared, in step S107 the startup check flag fig is set, and in step S108 the discharging flag is cleared.

[0065] In step S109, the discharge prohibition flag is cleared, in step S110 the discharge switch is connected, and in step S111 the constant current circuit is turned on.

[0066] In step S112, the main power switch state SMSW is stored in the previous main power switch state SMSWold and updated. In step S113, the startup check timer TMig is incremented. The startup check timer TMig is clipped at its maximum value.

[0067] In step S121, it is determined whether the startup check flag fig is set. If the startup check flag fig is set (determination is YES), the process proceeds to step S122. If the startup check flag fig is not set (determination is NO), the process ends.

[0068] In step S122, it is determined whether the startup check timer TMig has exceeded the startup check determination time TMig1. If the startup check timer TMig has exceeded the startup check determination time TMig1 (determination is YES), the process proceeds to step S126. If the startup check timer TMig has not exceeded the startup check determination time TMig1 (determination is NO), the process proceeds to step S123.

[0069] In step S123, it is determined whether the detected voltage Vc is greater than the second voltage determination value Vth2. If the detected voltage Vc is greater than the second voltage determination value Vth2 (determination is YES), the process proceeds to step S129. In step S129, it is determined that there is an abnormality in the discharge switch 5, and the process ends. If the detected voltage Vc is not greater than the second voltage determination value Vth2 in step S123 (determination is NO), the process proceeds to step S124.

[0070] In step S124, it is determined whether the detected voltage Vc is greater than the voltage determination value Vth. If the detected voltage Vc is greater than the voltage determination value Vth (determination is YES), the process proceeds to step S125. In step S125, an abnormality in the discharge resistor 4 is determined, and the process ends. If the detected voltage Vc is not greater than the voltage determination value Vth (determination is NO) in step S124, the process ends.

[0071] In step S126, the start-up check flag fig is cleared. In step S127, the constant current circuit 19 is turned off. In step S128, the discharge switch 5 is turned off, and the auxiliary power switch 2 is turned on, thereby ending the process.

[0072] 3. Third Embodiment <Configuration of Power Conversion Apparatus> Fig. 8 is a configuration diagram of a power conversion apparatus 100 according to a third embodiment. Fig. 8 differs from Fig. 5 according to the second embodiment in that a discharge state determination unit 21 is newly provided. The hardware configuration of Fig. 2 can also be applied to the control device 18 of the power conversion apparatus 100 according to the third embodiment.

[0073] <Fault detection by discharge state determination unit> Fig. 9 is a diagram illustrating the logic of fault determination for the discharge circuit of the power conversion device 100 according to embodiment 3. In the power conversion device 100 according to embodiment 3, the discharge state can be determined based on a voltage change in the discharge state determination unit 21 when the discharge switch is turned on or off.

[0074] The fault diagnosis unit 17 can determine whether a fault has occurred in the discharge circuit based on the drive state of the discharge switch 5 and the voltage of the discharge state determination unit 21. When the discharge circuit is normal, if the discharge switch is off (disconnected), the capacitor voltage is applied to the discharge state determination unit 21, and the state of the discharge state determination unit 21 becomes H level. When the discharge circuit is normal, if the discharge switch 5 is turned on (connected), the auxiliary power switch 2 is disconnected as a prerequisite, so that a current flows through the discharge resistor, and the state of the discharge state determination unit 21 becomes L level.

[0075] When the auxiliary power switch 2 is turned on and the power conversion device 100 is performing power conversion, the discharge switch is turned off (disconnected). At this time, if the state of the discharge state determination unit 21 is at L level, it can be determined that a discharge circuit failure has occurred. In this case, there is a possibility that the discharge switch 5 is stuck on, the discharge resistor 4 is broken, or the discharge state determination unit 21 is broken. When the discharge switch 5 is turned on (connected), it is assumed that the auxiliary power switch 2 is disconnected, so if the state of the discharge state determination unit 21 is at H level, it can be determined that a discharge circuit failure has occurred. In this case, there is a possibility that the discharge switch 5 has failed to turn off or the discharge state determination unit 21 is broken.

[0076] As described above, the fault diagnosis unit 17 can constantly determine whether a fault has occurred in the discharge circuit based on the drive state of the discharge switch 5 and the voltage of the discharge state determination unit 21. The power conversion device 100 may also determine whether a fault has occurred in the discharge circuit while performing power conversion, store the discharge circuit fault when a fault is detected, and prohibit discharge of the capacitor 3 when a stop command is received. This is because if the discharge switch 5 is connected when a fault has occurred in the discharge circuit, the discharge resistor 4 and the discharge switch 5 may be damaged.

[0077] <Stop Processing> Fig. 10 is a first flowchart showing the stop processing of the control device 18 of the power conversion device 100 according to embodiment 3. Fig. 11 is a second flowchart showing the stop processing. Fig. 11 shows the processing continued from Fig. 10. The processing in Figs. 10 and 11 is executed by the arithmetic processing device 90 of the control device 18.

[0078] 10 and 11 are executed at predetermined time intervals (for example, every 1 ms). These processes may be executed for each event, such as each time the motor 6 rotates a predetermined angle or each time an external command is received.

[0079] The process in Fig. 10 according to the third embodiment differs from the process in Fig. 3 according to the second embodiment in that step S300 is added before step S301, steps S308, S311, and S312 are added after step S307, and step S310 is added after step S309. The process in Fig. 11 according to the third embodiment differs from the process in Fig. 4 according to the second embodiment in that step S326 is added after step S325. The following description will focus on the differences.

[0080] 10 starts, and first in step S300 the level of the input signal to the discharge state determination unit 21 is checked. Then, the on / off state of the discharge switch 5 is compared with the diagram illustrating the logic of fault determination in FIG. 9 to check whether or not there is a fault in the discharge circuit. Note that the presence or absence of a fault in the discharge circuit may be checked constantly even during power conversion, and when a fault is detected, the fault in the discharge circuit may be stored.

[0081] If all phases are short-circuited in step S307 (determination is YES), the process proceeds to step S308. In step S308, it is determined whether all phases are short-circuited successfully. The determination result may be stored. Then, in step S311, the startup discharge check result is read out. The startup discharge check result refers to the result of determining whether or not there is an abnormality in the discharge switch 5 and the discharge resistor 4 through the startup process described in Figures 6 and 7.

[0082] In step S312, it is determined whether or not an abnormality has been detected in the startup discharge check. If an abnormality has been detected in the startup discharge check (determination is YES), the process ends without discharging the capacitor 3. If no abnormality has been detected in the startup discharge check (determination is NO), the process proceeds to step S321.

[0083] After step S309, in step S310, it is determined whether or not the all-phase short circuit has failed. The determination result may be stored. Then, the process proceeds to step S350.

[0084] Following step S325, in step S326, it is determined whether a discharge circuit failure has been detected. A discharge circuit failure is detected by checking the on / off state of the discharge switch 5 and the level of the input signal to the discharge state determination unit 21, and comparing them with the failure determination logic diagram of FIG. 9. If a discharge circuit failure has been detected (determination is YES), the process proceeds to step S350, where the discharge switch 5 is turned off. If a discharge circuit failure has not been detected (determination is NO), the process proceeds to step S358, where it is determined whether the discharge end determination time has elapsed.

[0085] 4. Fourth Embodiment <Configuration of Power Conversion Apparatus> The power conversion apparatus 100 according to the fourth embodiment can be realized by modifying the software of the power conversion apparatus 100 according to the third embodiment. The configuration diagram of the power conversion apparatus 100 according to the fourth embodiment is the same as that shown in Fig. 8, and the configuration shown in Fig. 2 is also applicable.

[0086] After receiving a stop command and entering an all-phase short-circuit state, the power conversion device 100 according to the fourth embodiment connects the discharge switch 5 to start discharging the capacitor 3. Thereafter, the power conversion device 100 differs from the third embodiment in that a process is added to check whether the detected voltage Vc has dropped by a large amount below a predetermined voltage drop threshold ΔVth to determine whether or not the discharge switch has failed.

[0087] The detected voltage Vc at the start of discharge is stored as V0. After a determination time T1 has elapsed from the start of discharge, a voltage drop ΔVc in the detected voltage Vc is calculated as ΔVc = V0 - Vc. If ΔVc is equal to or less than the voltage drop threshold ΔVth, it can be determined that the auxiliary power switch 2 has failed to turn off. It is desirable to set the determination time T1 to 0.3 seconds or less. This is because it is important to avoid passing a large current from the DC power supply 1 through the discharge resistor 4 and discharge switch 5 for a long period of time. This is because a large current can cause an overheating state, which can lead to a disconnection failure and an increase in resistance value. The voltage drop threshold ΔVth is set to a small value of 1 V or less.

[0088] <Stop Processing> Fig. 12 is a second flowchart showing the stop processing of the control device 18 of the power conversion device 100 according to embodiment 4. Fig. 13 is a third flowchart showing the stop processing. The first flowchart showing the stop processing is the same as Fig. 10 according to embodiment 3. Fig. 12 shows a continuation of Fig. 10. Fig. 13 shows a continuation of Fig. 12.

[0089] The processes shown in Figures 10, 12, and 13 are executed at predetermined time intervals (for example, every 1 ms). These processes may be executed for each event, such as each time the motor 6 rotates a predetermined angle or each time an external command is received, instead of at predetermined time intervals.

[0090] 10, 12, and 13 according to the fourth embodiment differ from the processing of the third embodiment in that step S322 is added after step S321, steps S327 to S331 are added after step S326, and step S356 is added after step S358. The following mainly describes the differences.

[0091] 12, in step S322, the value of the detected voltage Vc is stored as the initial voltage V0, in order to set the voltage just before the discharge switch is connected in step S324 as the discharge start voltage.

[0092] If no discharge circuit failure is detected in step S326 (determination: NO), the process proceeds to step S327. In step S327, it is determined whether or not an all-phase short-circuit state exists. If an all-phase short-circuit state exists (determination: YES), the process proceeds to step S328. If an all-phase short-circuit state does not exist (determination: NO), the process proceeds to step S358. Here, if an all-phase short-circuit operation is performed in the process of FIG. 10 and an all-phase short-circuit state does not exist, the process proceeds to step S309 and no discharge process is performed. Therefore, the NO branch is not selected in step S327.

[0093] In step S328, it is determined whether the value of the discharge timer TM is equal to or greater than the determination time T1. If the discharge timer TM is equal to or greater than the determination time T1 (determination is YES), the determination time T1 has elapsed since the start of discharge, and the process proceeds to step S329. If the discharge timer TM is not equal to or greater than the determination time T1 (determination is NO), the process ends.

[0094] In step S329, the difference between the initial voltage V0 and the currently detected voltage Vc is defined as a drop voltage ΔVc, which is calculated using the formula ΔVc = V0 - Vc. In step S330, it is determined whether the drop voltage ΔVc is equal to or less than a voltage drop threshold ΔVth. If the drop voltage ΔVc is equal to or less than the voltage drop threshold ΔVth (determination is YES), the process proceeds to step S331, where a failure of the subsidiary power switch 2 is determined, and the process proceeds to step S350. If the drop voltage ΔVc is not equal to or less than the voltage drop threshold ΔVth (determination is NO) in step S330, the process proceeds to step S358.

[0095] In step S358, it is determined whether the value of the discharge timer TM is equal to or greater than a predetermined termination determination time Te. If the value of the discharge timer TM is equal to or greater than the termination determination time Te (determination is YES), the process proceeds to step S356. If the value of the discharge timer TM is not equal to or greater than the termination determination time Te (determination is NO), the process ends.

[0096] In step S356, it is determined whether the discharge has ended normally, and then the process proceeds to step S357.

[0097] 5. Fifth Embodiment <Configuration of Power Conversion Device> The power conversion device 100 according to the fifth embodiment can be realized by modifying the software of the power conversion device 100 according to the third and fourth embodiments. The configuration diagram of the power conversion device 100 according to the fifth embodiment is the same as that shown in Fig. 8, and is also applicable to Fig. 2.

[0098] The power conversion device 100 according to the fifth embodiment differs from the third and fourth embodiments in that after receiving a stop command and performing an all-phase short-circuit operation, if the all-phase short-circuit state is not established, the power conversion device 100 performs an all-phase interruption operation and then connects the discharge switch 5 to start discharging the capacitor 3. In this manner, even if the all-phase short-circuit state is not established, when the control device 18 receives a stop command, the auxiliary power switch 2 is turned off to disconnect the positive-side DC bus 24a of the power conversion device 100 from the DC power supply 1. Then, the discharge switch 5 is connected, making it possible to discharge the charge remaining in the capacitor 3.

[0099] <Stop Processing> Fig. 14 is a first flowchart showing the stop processing of the control device 18 of the power conversion device 100 according to embodiment 5. The second and third flowcharts are the same as Figs. 12 and 13 according to embodiment 4. Fig. 12 shows the processing continued from Fig. 14. Fig. 13 shows the processing continued from Fig. 12. The processing in Figs. 14, 12, and 13 is executed by the arithmetic processing device 90 of the control device 18.

[0100] The processes shown in Figures 14, 12, and 13 are executed at predetermined time intervals (for example, every 1 ms). These processes may be executed for each event, such as each time the motor 6 rotates a predetermined angle or each time an external command is received, instead of at predetermined time intervals.

[0101] The processing in Figures 14, 12, and 13 according to the fifth embodiment differs from the processing in Figures 10, 12, and 13 according to the fourth embodiment only in that the destination after step S310 in Figure 14 is changed from step S350 to step S311. The following mainly describes the differences.

[0102] 14, if it is determined in step S307 that the all-phase short circuit state is not present (determination is NO), an all-phase shut-off operation is performed in step S309. The all-phase shut-off operation turns off all switching circuits. After determining that the all-phase short circuit state has failed in step S310, the start-up discharge check result is read in step S311, and it is determined in step S312 whether or not an abnormality has been detected in the start-up discharge check.

[0103] In step S327 of Fig. 12, it is determined whether or not an all-phase short-circuit state exists. If an all-phase short-circuit state does not exist (determination is NO), the process skips from step S328 to step S330 and proceeds to step S358.

[0104] If all phases cannot be short-circuited and all phases are shut off, an overvoltage may be applied to the positive DC bus 24a and the negative DC bus 24b via the free-wheel diodes of each switching circuit when the motor 6 is rotating or when a large voltage surge occurs due to back electromotive force. Therefore, the process of calculating the voltage drop ΔVc of the detected voltage Vc as ΔVc = V0 - Vc is skipped after the determination time T1 has elapsed from the start of discharge (T1 is 0.3 seconds or less). This makes it possible to prevent erroneous determination from the start of discharge until the determination time T1 has elapsed.

[0105] 6. Sixth Embodiment <Configuration of Power Conversion Device> The power conversion device 100 according to the sixth embodiment can be realized by modifying the software of the power conversion device 100 according to the third, fourth, or fifth embodiment. The configuration diagram of the power conversion device 100 according to the sixth embodiment is the same as that shown in Fig. 8, and the configuration shown in Fig. 2 is also applicable.

[0106] The power conversion device 100 according to the sixth embodiment differs from the fifth embodiment in that it adds a function of detecting a discharge voltage abnormality by comparing the detected voltage after the second determination time T2 has elapsed since the start of discharge with the discharge voltage threshold Vthcal. In this case, the discharge voltage threshold Vthcal can be expressed as V0×exp(−(T2 / CR)) where V0 is the initial voltage that is the detected voltage when the discharge switch 5 is connected, C is the capacitance of the capacitor, and R is the resistance value R of the discharge resistor 4. Taking into account the range of variation in the capacitance C of the capacitor and the resistance value R of the discharge resistor 4, the maximum value of the discharge voltage threshold Vthcal is calculated.

[0107] If the detected voltage Vc does not become equal to or less than the discharge voltage threshold Vthcal, it is possible that an abnormal resistance value has occurred while the vehicle was running, or that an induced voltage has been generated and the voltage has not decreased due to the continued rotation of the motor 6. This state is determined to be an abnormal discharge voltage, and the discharge switch 5 is turned off to stop the discharge of the capacitor 3.

[0108] An abnormal discharge voltage is a state in which discharge is not occurring as intended, and the discharge must be stopped because a high voltage continues to be applied to the discharge resistor 4, which may cause it to overheat and result in a disconnection or an increase in resistance. Therefore, the second judgment time T2 must be set to a time (within one second) that will not damage the discharge resistor 4 even if an induced voltage is generated with all phases cut off.

[0109] <Stop Processing> Fig. 15 is a third flowchart showing the stop processing according to the sixth embodiment. The first flowchart showing the stop processing is the same as Fig. 14 according to the fifth embodiment. The second flowchart showing the stop processing is the same as Fig. 12 according to the fourth and fifth embodiments. Fig. 12 shows the processing continued from Fig. 14. Fig. 15 shows the processing continued from Fig. 12. The processing in Figs. 14, 12, and 15 is executed by the arithmetic processing device 90 of the control device 18.

[0110] The processes shown in Figures 14, 12, and 15 are executed at predetermined time intervals (for example, every 1 ms). These processes may be executed for each event, such as each time the motor 6 rotates a predetermined angle or each time an external command is received, instead of at predetermined time intervals.

[0111] 15 according to the sixth embodiment differs from the processing of the fifth embodiment in that steps S341 to S344 are added before step S358. The following mainly describes the differences.

[0112] In step S341, it is determined whether the value of the discharge timer TM has exceeded the second determination time T2. If the value of the discharge timer TM has exceeded the second determination time T2 (determination is YES), the process proceeds to step S342. If the value of the discharge timer TM has not exceeded the second determination time T2 (determination is NO), the process ends.

[0113] In step S342, the discharge voltage threshold Vthcal is calculated. Specifically, the maximum value of Vthcal = V0 × exp(-(T2 / CR)) is calculated, taking into consideration variations in the initial voltage V0, which is the voltage detected when the discharge switch 5 is connected, the capacitance C of the capacitor, and the resistance R of the discharge resistor 4.

[0114] In step S343, it is determined whether the detected voltage Vc is higher than the discharge voltage threshold Vthcal. If the detected voltage Vc is higher than the discharge voltage threshold Vthcal (determination is YES), a discharge voltage abnormality is determined in step S344, and the process proceeds to step S350. If the detected voltage Vc is not higher than the discharge voltage threshold Vthcal (determination is NO) in step S343, the process proceeds to step S358.

[0115] Fig. 16 is a first time chart showing the discharge of the capacitor 3 of the power conversion device 100 according to embodiment 6. Fig. 17 is a second time chart showing the discharge of the capacitor 3. Fig. 16 shows a time chart when the discharge circuit is normal. Fig. 17 shows a time chart when the discharge circuit is abnormal.

[0116] When the power conversion device 100 receives a stop command, it performs an all-phase short-circuit operation, then turns on the discharge switch 5 to start discharging the residual charge in the capacitor 3. The voltage of the capacitor 3 decreases over time according to a multiplier determined by the capacitance C of the capacitor 3 and the resistance value R of the discharge resistor 4.

[0117] The voltage drop can be predicted from the initial voltage V0. The voltage after the second determination time T2 from the start of discharge can be expressed as V0 × exp(-(T2 / CR)), where C is the capacitance of the capacitor and R is the resistance of the discharge resistor. The calculation result is defined as the discharge voltage threshold Vthcal.

[0118] The C and R used in the calculation are the maximum values ​​expected for each component. The discharge voltage threshold Vthcal after the second determination time T2 is set to the second voltage determination value Vth2. By comparing the detected voltage Vc of the capacitor 3 after the second determination time T2 with the second voltage determination value Vth2, it can be determined whether the discharge is normal.

[0119] When discharge is performed normally, the capacitor voltage V2 after the second determination time T2 is smaller than the second voltage determination value Vth2, as shown in Figure 16. When the capacitor voltage V2 after the second determination time T2 is larger than the second voltage determination value Vth2, as shown in Figure 17, it is possible that an abnormality in the resistance value has occurred while the vehicle is running, or that an induced voltage has been generated and the voltage has not decreased due to the motor continuing to rotate. This state is determined to be an abnormality in the discharge voltage, and the discharge switch 5 is turned off to stop the discharge.

[0120] Abnormal discharge voltage occurs when the intended discharge is not occurring. If a high voltage continues to be applied to the discharge resistor, it may overheat and cause a disconnection, which may lead to an increase in resistance. This is why it is necessary to stop the discharge. Therefore, the second judgment time T2 is set to a time (within one second) that will not damage the discharge resistor even if an induced voltage is generated with all phases cut off.

[0121] 7. Seventh Embodiment <Configuration of Power Conversion Device> The power conversion device 100 according to the seventh embodiment can be realized by modifying the software of the power conversion device 100 according to the fourth, fifth, or sixth embodiment. The configuration diagram of the power conversion device 100 according to the seventh embodiment is the same as that shown in Fig. 8, and the configuration shown in Fig. 2 is also applicable.

[0122] The power conversion device 100 according to the seventh embodiment has a function of detecting an abnormality in the discharge circuit, an abnormality in the auxiliary power switch 2, etc., based on the detected voltages after the start of discharge, the determination time T1, and the second determination time T2 have elapsed. In addition, the seventh embodiment differs from the sixth embodiment in that a discharge end voltage Vthe is set, and when the detected voltage Vc becomes equal to or lower than the discharge end voltage Vthe, the discharge is normally terminated.

[0123] If the detected voltage Vc does not become equal to or less than the discharge end voltage Vthe even when the termination determination time Te has arrived, it is determined that the discharge has terminated abnormally. In this case, an internal abnormality is considered. One possible internal abnormality is when the motor rotation speed cannot be detected correctly. In this case, if an induced voltage is generated due to the motor rotation being maintained and the voltage does not decrease even when the discharge occurs, it is considered that an abnormality has occurred in the voltage detector 14 that detects the voltage of the capacitor 3.

[0124] The termination determination time Te is set to a time defined by regulations or a time longer than that. The discharge termination voltage Vthe is a voltage defined by regulations and is set taking into consideration the detection error of the voltage detector 14 that detects the voltage of the capacitor 3.

[0125] <Stop Processing> Fig. 18 is a third flowchart showing the stop processing according to the seventh embodiment. The first flowchart showing the stop processing is the same as Fig. 14 according to the fifth and sixth embodiments. The second flowchart showing the stop processing is the same as Fig. 12 according to the fourth to sixth embodiments. Fig. 12 shows the processing continued from Fig. 14. Fig. 18 shows the processing continued from Fig. 12. The processing in Figs. 14, 12, and 18 is executed by the arithmetic processing device 90 of the control device 18.

[0126] The processes shown in Figures 14, 12, and 18 are executed at predetermined time intervals (for example, every 1 ms). These processes may be executed for each event, such as each time the motor 6 rotates a predetermined angle or each time an external command is received, instead of at predetermined time intervals.

[0127] 18 according to the seventh embodiment differs from the processing of the sixth embodiment in that step S343, followed by step S358, is replaced by step S345, step S348, and step S349. The following description will focus on the differences.

[0128] If the detected voltage Vc is not higher than the discharge voltage threshold Vthcal (determination is NO) in step S343, the process proceeds to step S345. In step S345, it is determined whether the detected voltage Vc is lower than the discharge end voltage Vthe. If the detected voltage Vc is lower than the discharge end voltage Vthe (determination is YES), the process proceeds to step S346. If the detected voltage Vc is not lower than the discharge end voltage Vthe (determination is NO), the process proceeds to step S348.

[0129] In step S348, it is determined whether the value of the discharge timer TM is equal to or greater than a predetermined termination determination time Te. If the value of the discharge timer TM is equal to or greater than the termination determination time Te (determination is YES), the process proceeds to step S349, where it is determined that discharge has terminated abnormally, and the process proceeds to step S350. If the value of the discharge timer TM is not equal to or greater than the termination determination time Te (determination is NO) in step S348, the process ends.

[0130] The electric vehicle described above is equipped with the above-described power conversion device 100. To comply with regulations, the electric vehicle needs to discharge the charge stored in the capacitor 3 within a predetermined time.

[0131] Furthermore, since there is a risk of problems if the capacitor 3 is not completely discharged, it is desirable to detect whether the discharge is being carried out correctly. The vehicle can determine the discharge state based on information from the power conversion device 100, and if it is determined that the discharge is not being carried out in accordance with regulations, a warning light on the vehicle is turned on.

[0132] The electric vehicle may be any of an electric vehicle (BEV: Battery Electric Vehicle), a hybrid vehicle (HEV: Hybrid Electric Vehicle), a plug-in hybrid electric vehicle (PHEV: Plug-in Hybrid Electric Vehicle), and a fuel cell electric vehicle (FCEV: Fuel Cell Electric Vehicle).

[0133] Although various exemplary embodiments and examples are described in this disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are anticipated within the scope of the technology disclosed herein. For example, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0134] 2 Sub-power switch, 3 Capacitor, 4 Discharge resistor, 5 Discharge switch, 6 Motor, 13 Drive circuit, 14 Voltage detector, 16 Drive state determination unit, 18 Control device, 19 Constant current circuit, 21 Discharge state determination unit, 24a Positive side DC bus, 24b Negative side DC bus, 25 Main power switch, 100 Power conversion device

Claims

1. A power conversion circuit having, for each phase of the motor, a capacitor connected between a positive DC bus and a negative DC bus, a discharge switch that discharges the charge of the capacitor through a discharge resistor, a positive switching element connected to the positive DC bus, a negative switching element connected to the negative DC bus, and a leg provided with an external connection point that connects the positive switching element and the negative switching element in series and supplies a phase current to the motor coil, a drive circuit that outputs a drive signal to control the switching element to operate the power conversion circuit, a drive state determiner that determines the drive state of the switching element, and a control device that gives a control signal to the drive circuit, When the control device receives a command to stop power conversion, the control device performs all-phase short-circuit control by turning on all of the positive electrode side switching elements and turning off all of the negative electrode side switching elements, or by turning off all of the positive electrode side switching elements and turning on all of the negative electrode side switching elements, and after determining that an all-phase short-circuit state has occurred using the drive state determiner, turns on the discharge switch to discharge the charge in the capacitor.

2. The power conversion device according to claim 1, wherein the control device performs the all-phase short-circuit control when it receives the stop command from outside, and turns off all of the switching elements and then turns on the discharge switch if the drive state determiner does not determine that an all-phase short-circuit state has occurred.

3. A power conversion device according to claim 1 or 2, further comprising: a voltage detector that detects the voltage of the capacitor; and a constant current circuit that passes a constant current through the discharge resistor, wherein the positive DC bus is connected to the positive side of an external DC power supply via a secondary power switch, and the negative DC bus is connected to the negative side of the external DC power supply, and wherein the control device turns on the discharge switch and passes a constant current through the constant current circuit during a period of time until the secondary power supply switch changes from off to on after a delay after the main power switch changes from off to on, and determines that a discharge voltage abnormality has occurred if the detected voltage detected by the voltage detector is higher than a predetermined voltage determination value.

4. The power conversion device according to claim 3, wherein the control device turns on the discharge switch and causes a constant current to flow through the constant current circuit during the period from when the main power switch changes from off to on until when the auxiliary power switch changes from off to on, and determines that there is an abnormality in the discharge switch or the discharge resistor if the detected voltage detected by the voltage detector is higher than a predetermined second voltage judgment value that is higher than the voltage judgment value, determines that there is an abnormality in the discharge resistor if the detected voltage is equal to or lower than the second voltage judgment value and higher than the voltage judgment value, and determines that the discharge switch and the discharge resistor are normal if the detected voltage is equal to or lower than the voltage judgment value.

5. A power conversion device according to claim 3 or 4, wherein one end of the discharge resistor is connected to the positive side of the capacitor, the other end of the discharge resistor is connected to the negative DC bus via the discharge switch, and the other end of the discharge resistor is connected to a discharge state determiner, and the control device determines whether the discharge circuit is faulty or normal based on the presence or absence of the stop command and the state determined by the discharge state determiner.

6. The power conversion device according to claim 5, wherein, when the control device receives the stop command from outside, if it determines that the discharge switch and the discharge resistor are normal and that the discharge circuit is normal, it performs the all-phase short-circuit control, and after determining that an all-phase short-circuit state has occurred using the drive state determiner, it turns on the discharge switch to discharge the charge in the capacitor.

7. The power conversion device according to claim 6, wherein when the control device receives the stop command from the outside, if the voltage to which the detected voltage drops from the time the discharge switch is turned on until a predetermined judgment time has elapsed is smaller than a predetermined voltage drop threshold, the control device turns off the discharge switch and determines that the auxiliary power switch has failed.

8. A power conversion device as described in claim 6 or 7, wherein when the control device receives the stop command from the outside, if the detected voltage after a predetermined second judgment time has elapsed since the discharge switch was turned on is greater than a discharge voltage threshold value calculated from the initial voltage, which is the detected voltage when the discharge switch was turned on, the capacitance of the capacitor, the resistance value of the discharge resistor, and the second judgment time, the control device turns off the discharge switch and judges that a discharge voltage drop abnormality has occurred.

9. A power conversion device as claimed in any one of claims 1 to 8, further comprising a voltage detector for detecting the voltage of the capacitor, wherein the control device, upon receiving the stop command from outside, turns off the discharge switch and determines that the discharge has ended normally if the detected voltage detected by the voltage detector after turning on the discharge switch becomes equal to or lower than a predetermined discharge end voltage.

10. The power conversion device according to claim 9, wherein the control device, upon receiving a stop command from outside, turns off the warning light if it determines that the discharge has ended normally, and turns on the warning light if it does not determine that the discharge has ended normally.

11. A power conversion device as claimed in any one of claims 1 to 10, further comprising a voltage detector for detecting the voltage of the capacitor, wherein the control device, upon receiving the stop command from outside, turns off the discharge switch and determines that discharge has abnormally terminated if the detected voltage detected by the voltage detector after a predetermined termination determination time has elapsed since the discharge switch was turned on is greater than a predetermined discharge termination voltage.

12. A vehicle equipped with the power conversion device according to any one of claims 1 to 11.