Discharge control circuit and power conversion device

Abstract

The present invention aims to provide a power conversion device capable of determining in detail the fault location of an inverter when active discharge fails. The device comprises an operation circuit (102) for outputting a discharge instruction for controlling a discharge operation based on a voltage across a discharge circuit; and an output circuit (203) for outputting a drive signal based on the control signal. The operation circuit (102) monitors the decrease in the voltage across the discharge circuit, the output of the operation circuit (102), i.e., an LV readback signal, and the output of the output circuit (203), i.e., an HV readback signal, to determine the fault location.

Description

Technical Field

[0001] The present invention relates to a fast active discharge control circuit for a high voltage capacitor in a power conversion device suitable for use in driving systems of hybrid vehicles, electric vehicles, etc., and in particular to a method for diagnosing a fault location of the discharge control circuit. Background Art

[0002] In systems such as hybrid and electric vehicles that use high-voltage batteries to drive motors, there's a requirement to quickly disconnect the inverter from the battery or quickly discharge any residual charge within the inverter. For example, US FMVSS 305 (Prevention of Electrolyte Discharge and Electric Shock in Electric Vehicles) stipulates that within five seconds of a vehicle coming to a stop due to a collision or other factors, the residual charge in the smoothing capacitor connected to the input stage must be quickly discharged to a specified value in order to reduce the inverter output voltage to a specified value or below.

[0003] This discharge control function is implemented to protect the driver and emergency personnel from electric shock in the event of a collision. A representative technology is active discharge. Active discharge dissipates the charge accumulated in the inverter circuit's smoothing capacitors through a discharge resistor, rapidly reducing the inverter's output voltage.

[0004] As a conventional example of discharge control, for example, there is Patent Document 1. To prevent excessive power consumption in the discharge resistor during discharge control, the on / off duty cycle of the discharge control switching element is controlled at high voltages, while the on-state of the discharge control switching element is fixed at low voltages to increase the discharge rate.

[0005] However, the discharge control performed in an emergency for the purpose of transferring the inverter to a safe state needs to be frequently verified for normal operation from the perspective of functional safety. Since the discharge control described above causes the inverter to operate according to instructions different from those of normal control, the soundness of the discharge control cannot be verified during normal control. Therefore, a diagnostic function is generally installed, for example, the diagnostic function shown in Patent Document 2. When the discharge control is executed, if the contactor of the battery is in a closed state for some reason, an excessive current flows through the discharge resistor for a long time, and the discharge resistor may be damaged due to heat. In order to avoid this situation, when the terminal voltage of the capacitor exceeds a preset voltage drop characteristic, the switching element used for the discharge control is cut off to stop the discharge of the discharge resistor.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: International Publication No. 2019 / 039047 Pamphlet

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2011-041363 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] The diagnostic function described above is designed to detect active discharge while the contactors are closed, thereby preventing damage to the discharge resistors caused by heat. However, since it cannot distinguish between abnormalities in the inverter and those in peripheral equipment, there is a problem of inability to perform appropriate control in the event of a fault. For example, due to the discrepancy between instructions to the contactors and the actual timing of their operation, if active discharge is executed while the contactors remain closed, the diagnostic function may mistakenly detect an abnormality as an active discharge failure, even though there is no fault in the inverter.

[0012] The object of the present invention is to provide a power conversion device and a control method thereof, which can determine the fault location of the inverter in detail when active discharge fails, perform appropriate control according to the fault mode, and enable the inverter to be transferred to a safe state more reliably.

[0013] Technical means to solve problems

[0014] To achieve the above-mentioned objectives, the discharge control circuit of the present invention comprises: a discharge circuit connecting a discharge resistor and a switching element in series; and a control circuit controlling the discharge of the discharge resistor by turning on / off the switching element, the control circuit comprising: an operation circuit outputting a control signal for controlling the switching element based on the voltage across the discharge circuit; and an output circuit outputting a drive signal for driving the switching element based on the control signal, the operation circuit comprising: a detection circuit monitoring unit detecting a decrease in the voltage across the discharge circuit; an operation circuit monitoring unit monitoring the output of the operation circuit; and an output circuit monitoring unit monitoring the output of the output circuit.

[0015] Furthermore, the discharge control circuit of the present invention has the following function: after the operation circuit outputs the control signal instructing discharge, if the voltage across the discharge circuit does not fall below a specified threshold within a specified time, based on the first signal as the monitoring result of the operation circuit monitoring unit and the second signal as the monitoring result of the output circuit monitoring unit, it is determined which of the discharge circuit, the operation circuit, and the output circuit has an abnormality.

[0016] Effects of the Invention

[0017] According to the present invention, by combining multiple diagnostic functions, the fault location can be precisely identified in the event of active discharge failure. Appropriate control can be implemented based on the nature of the fault, allowing the inverter to more reliably transition to a safe state. Furthermore, diagnostic results are stored as a fault history, and analysis of this history can be used to identify inverter fault-prone areas, contributing to safer product design. Furthermore, by quickly identifying the fault location, vehicle maintainability can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the configuration of a power conversion device according to an embodiment of the present invention.

[0019] Figure 2 This is a functional block diagram of a discharge control circuit according to an embodiment of the present invention.

[0020] Figure 3 This is a graph for normal discharge.

[0021] Figure 4 This is a flow chart of the discharge time diagnosis.

[0022] Figure 5 This is a flowchart for diagnosing the voltage drop amount.

[0023] Figure 6 This is a flowchart of the diagnosis of HV output results.

[0024] Figure 7 This is a flow chart of the diagnosis of LV output results.

[0025] Figure 8 It is a metric diagram used to combine multiple diagnostic results to determine the fault location.

[0026] Figure 9 This is a graph when the discharge amount is insufficient.

[0027] Figure 10 This is the diagram when the contactor is closed.

[0028] Figure 11 This graph shows the change in resistance value due to a short-circuit failure of the discharge resistor.

[0029] Figure 12 This is a diagram for when the discharge resistor fails due to an open circuit.

[0030] Figure 13 This is a diagram showing a stuck-off fault in the sub-CPU output.

[0031] Figure 14 This is a graph showing a stuck-on fault of the sub-CPU output. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the power conversion device of the present invention will be described with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0033] Figure 1 This is a schematic diagram of a power conversion device 101 according to an embodiment of the present invention. The power conversion device 101 includes a main control unit (CPU) 102, a first switching element 110 controlled by the main control unit 102, a sub-control unit (sub-CPU) 103, a second switching element 107 controlled by the sub-control unit 103, a capacitor 109 for accumulating charge, and a discharge resistor 108 for consuming charge. The power conversion device 101 receives DC power supplied from a battery 105 via a contactor 106 and outputs AC power to drive a motor 104.

[0034] Figure 2 yes Figure 1 The example configuration of the functional blocks of a power conversion device shown in the figure specifically shows the control system (discharge control circuit) for the discharge circuit composed of the second switching element 107 and the discharge resistor 108. On the low voltage (LV) side, a main control unit 102 and a sub-control unit 103 are configured, along with a power supply circuit that supplies power to them. On the high voltage (HV) side, an output circuit 203, a voltage fluctuation detection circuit 204, and a voltage detection circuit 205 are configured, which drives the second switching element 107 based on a discharge instruction and causes the discharge resistor 108 to perform a discharge operation. Signal transmission between the LV and HV sides is performed using a photocoupler, etc.

[0035] The main control unit 102 and the sub-control unit 103 operate by receiving power from the main power supply 201. A discharge instruction output from the main control unit 102 is input to the output circuit 203 via the sub-control unit 103, where the charge is consumed by the discharge resistor 108. The discharge instruction output from the sub-control unit 103 is input to the sub-control unit 103 as an LV read back signal and then transmitted to the main control unit 102.

[0036] The terminal voltage of the discharge resistor 108 is detected by a shunt resistor connected in series with the switching element 107 and input to the main control device 102 as an HVreadback signal. The voltage fluctuation detection circuit 204 detects whether the voltage decreases as expected during the discharge of the charge. The voltage fluctuation detected by the voltage fluctuation detection circuit 204 is input to the sub-control device 103 and then transmitted to the main control device 102. The HV voltage detection circuit 205 detects the terminal voltage of the capacitor 109 and inputs it to the main control device 102.

[0037] Before describing the active discharge diagnosis method in the present embodiment, the control of active discharge in the present embodiment will be described. Figure 3The purpose of discharge control is to start the discharge control from the state where the HVDC is at the value V_ini and reduce the voltage to below V_lo within a predetermined time.

[0038] During the period when the discharge instruction from the main control device 102 is output as AD_CMD, AD_OUT is output from the output circuit 203 to the discharge resistor. In this embodiment, AD_OUT, which is the period during which the charge is consumed by the discharge resistor, changes the pulse pattern before and after the HV voltage falls below the threshold value V_th. Specifically, when the HV voltage is above the threshold value V_th (time t30-t31), the pulsed power supply of the second switching element 107 is alternately switched on / off by indicating that an excessive current does not flow through the discharge resistor 108. When the discharge is in progress and the HV voltage is lower than the threshold value V_th (time t31-t32), the second switching element 107 is always controlled to be on, and the charge of the capacitor 109 is quickly discharged through the discharge resistor 108.

[0039] If the voltage fluctuation detected by the voltage fluctuation detection circuit 204 is greater than a specified value, the voltage drop per unit time is considered as expected, and the value of AD_dvdt is set to 1. Furthermore, if the HV voltage is lower than the threshold value V_th, the value of AD_V_th is set to 1, and if the HV voltage is lower than the threshold value V_lo, the value of AD_V_lo is set to 1. Threshold V_lo is the target voltage for discharge and serves as a threshold for determining whether the voltage has dropped to a safe state. Here, at time t32, the HV voltage falls below V_lo, and AD_V_lo = 1, ending the discharge operation at this time.

[0040] As will be described later, the discharge control circuit of this embodiment compares the read back signal AD_Diag_LV on the LV side and the read back signal AD_Diag_HV on the HV side with AD_OUT. Figure 3 In the embodiment described below, only AD_Diag_HV becomes an inverted signal.

[0041] Active discharge diagnosis is primarily performed by the main controller 102. By comparing discharge instructions from the main controller 102 with the LV and HV readback signals, the region where undesired output occurs is identified, and abnormality is detected. Furthermore, using voltage fluctuations and voltage signals, the voltage behavior caused by discharge can be understood.

[0042] The following describes a method for combining multiple diagnostic results to identify the fault location in detail when active discharge fails and to perform appropriate control according to the fault. Figures 4 to 7 The flowchart shown explains the respective diagnostic steps of (1) diagnosis of discharge time, (2) diagnosis of voltage drop amount, (3) diagnosis of HV output result, and (4) diagnosis of LV output result.

[0043] Figure 4 This is a flow chart for the diagnosis of discharge time (1). In the diagnosis of discharge time, if the HV voltage value after a certain time has passed since the start of discharge is higher than the prescribed diagnostic threshold value V_lo, it is determined to be NG as the diagnostic result. As an example, if the discharge can be reduced to 60V or less within 5 seconds from the start of discharge, it is determined to be OK, and if not, it is determined to be NG. Here, if the diagnosis is OK, AD_Time is set to 0, and if the diagnosis is NG, it is set to AD_Time = 1. The HV voltage uses the detection value of the HV voltage detection circuit 205.

[0044] Figure 5 This is a flowchart of the diagnosis of the voltage drop (2). The diagnosis of the voltage drop is performed when the value of the HV voltage is sufficiently high. Here, the diagnosis is performed when the value of the HV voltage is higher than the diagnostic threshold value V_lo as an example. In the diagnosis of the voltage drop, when the change in the voltage variation of the HV voltage during discharge (the reduction per unit time) is smaller than the specified threshold value dVth, it is determined to be NG as the diagnostic result. The voltage variation of the HV voltage uses the detection value of the voltage variation detection circuit 204. When the reduction of the HV voltage per unit time is greater than the specified value dVth, it is determined to be OK for normal discharge and set to AD_dvdt=1. When the reduction of the HV voltage per unit time is less than the specified value dVth, it is determined to be NG for diagnosis as failure to discharge as expected and set to AD_dvdt=0.

[0045] If the voltage drop diagnosis is determined to be NG, discharge is temporarily suspended and the device transitions to a retry state. This configuration involves suspending discharge and then waiting for a predetermined time before resuming discharge. While the voltage drop diagnosis is primarily determined to be NG when contactor 106 is in a closed state, it is expected that the temporary contactor closed state will be released over time, returning to an open state, and a predetermined number of retries will be performed. The number of retries can be arbitrarily set, and a configuration in which no retries are performed is also possible.

[0046] Figure 6This is a flowchart of the diagnosis of HV output results (3). The diagnosis of HV output results is performed based on the HV read back signal AD_Diag_HV received by the main control device 102 from the discharge circuit. The diagnosis of HV output results is classified into PWM check diagnosis, conduction fixed diagnosis, and disconnection fixed diagnosis. The diagnosis of abnormality is different depending on the situation shown in the flow chart. Figure 6 , the following method is described: that is, instead of directly comparing the AD_OUT signal and the AD_DIAG_HV signal, the specified frequency and duty cycle used when generating AD_OUT are stored as diagnostic thresholds in the main control device 102, and these diagnostic thresholds are used to diagnose the HV output results.

[0047] However, in Figure 5 In the diagnosis of the voltage drop amount, if there is no voltage fluctuation and the discharge is continued during the retry, since the discharge is temporarily stopped, it is not determined as a diagnosis NG. Therefore, the diagnosis pending information AD_PEND is set to 1 while the retry is continued.

[0048] In the diagnosis of the HV output result, the frequency and duty cycle of the HV read back signal are first calculated. Each of these is compared with a diagnostic threshold. The diagnostic threshold compared with the frequency of the HV read back signal is Figure 3 The PWM frequency of AD_OUT in time t30-t31. In addition, the diagnostic threshold value compared with the duty cycle of the HV read back signal is Figure 3 The duty cycle of AD_OUT is set at the time t30 to t31 or t31 to t32. Figure 3 In the embodiment, the duty ratio of AD_OUT during time t31 to t32 is 100%.

[0049] Thus, in this embodiment, the AD_OUT pulse used as the comparison target differs depending on whether the HV voltage is V_th or above or below V_th. Therefore, in the diagnosis of the HV output result, the situation is also divided according to whether the HV voltage is V_th or above.

[0050] When the HV voltage is above V_th, that is, when Figure 3In the region corresponding to time t30 to t31, both the frequency and the duty cycle are compared with the diagnostic threshold. First, in step 601, the frequency of the HV read back signal is compared with the diagnostic threshold. At this time, if the frequency is different from the expected value, it is determined that the PWM check diagnosis on the HV side is NG. Next, in step 602, the duty cycle is compared, and if it is different from the expected value, it can be determined as diagnostic NG. In particular, if the duty cycle of the detected HV read back signal is 0%, it is determined as a disconnection fixed diagnosis NG on the HV side, and if the duty cycle is 100%, it is determined as a conduction fixed diagnosis NG on the HV side.

[0051] On the other hand, when the HV voltage is smaller than V_th, as shown in FIG. Figure 3 As shown, AD_OUT is always on, so frequency comparison is not performed, only duty cycle comparison is performed. Since the AD_OUT duty cycle is 100%, a diagnosis failure can be determined if the HV readback signal duty cycle is anything other than 100%. In particular, a duty cycle of 0% indicates a diagnosis failure for the HV disconnection and fixation. In all other cases, a diagnosis failure for the HV PWM check is determined.

[0052] Figure 7 This is a flowchart of the LV output result diagnosis (4). The LV output result diagnosis is performed based on the LV read back signal received by the main control device 102 from the sub-control device 103, that is, AD_Diag_LV. Figure 7 The flow chart of the flow chart is similar to the flow chart except that the type of read back signal is different. Figure 6 The process is roughly the same, so the detailed description is omitted here.

[0053] Figure 8 It is a metric diagram used to combine multiple diagnostic results to determine the fault location. Figures 4 to 7 The diagnostic results for (1) discharge time, (2) voltage drop, (3) HV output, and (4) LV output described above are combined and evaluated to identify the fault location. The diagnostic results for (3) HV output and (4) LV output are classified into three types: on-state diagnosis, off-state diagnosis, and PWM check diagnosis.

[0054] Below, use Figures 9 to 14The timing diagram corresponding to each failure mode is described. By identifying the failure location, for example, in the design phase, it can be used to re-evaluate the design value or change the control method. Understanding the location where failures are prone to occur helps improve and develop technology and can play a role in subsequent product design. Alternatively, by identifying the failure location, it is possible to appropriately transfer to a safe state. Figure 3 Repeated descriptions are given while describing the characteristic parts.

[0055] Figure 9 This is a graph when the discharge capacity is insufficient. Figure 9 In the example, after discharge begins at time t90, the HV voltage does not drop below V_lo until time t92, a predetermined time later. Therefore, the AD_V_lo value remains at 0. Therefore, at time t92, the discharge time diagnosis AD_Time fails. The discharge control circuit performs discharge using duty control when the HV voltage is higher than V_th (times t90 to t91). This behavior occurs when the duty is low or when the charge consumed by discharge resistor 108 is low.

[0056] In this case, since there is a problem with the design value of discharge, it is necessary to re-evaluate the design value and reduce the HV voltage to the threshold value V_lo within a specified time. Figure 9 Although the voltage drop is slightly smaller than normal, the charge consumption itself is properly performed, so during discharge execution (AD_CMD = 1), AD_dvdt continues to output the normal value of 1. In addition, the read back signals on the HV side and LV side also show normal values.

[0057] Figure 10 This is a diagram when the contactor is closed. When the contactor 106 is closed, even if discharge starts at time t100, the HV voltage will not drop because the capacitor 109 is connected to the battery 105. The HV voltage will not fall below V_lo, so the diagnosis of the discharge time is judged to be NG (AD_Time = 1). In addition, since the voltage drop per unit time is also lower than the threshold, the diagnosis of the voltage drop is judged to be NG (AD_dvdt = 0). Then, a retry action is performed after a certain period of time. During the retry standby, in order to avoid detecting other diagnostic NGs, the diagnostic pending information AD_PEN is set.

[0058] When the contactor is temporarily in a closed state due to the mechanical action moment of the contactor, discharge begins during the retry, and HVDC drops to V_lo within the specified time. Preferably, multiple retries are performed during the period from time t100 to t103. However, even in the case of a closing failure of the contactor 106, if the HV circuit such as the discharge resistor or the LV circuit such as the main control device or the sub-control device is normal, the charge consumption can be normally performed by the discharge resistor 108 as long as the voltage of the capacitor 109 does not decrease, so the diagnosis of the HV output and the diagnosis of the LV output are judged to be normal (OK). In the discharge control circuit of this embodiment, by monitoring the read back signals on the HV side and the LV side, it can be confirmed that the control circuit on the LV side and the output circuit on the HV side have no faults and are operating normally.

[0059] Figure 11 This is a graph showing a change in resistance due to a short-circuit in the discharge resistor. Specifically, this is a graph showing a change in resistance due to a short-circuit in the discharge resistor. As the resistance decreases, the charge consumed during discharge decreases, and the HV voltage decreases less than expected. Because the HV voltage does not drop below V_lo within the specified time, the discharge time diagnosis AD_Time detects a NG error at time t116. Figure 9 The situation is similar, but Figure 11 At time t112, the voltage drop per unit time is lower than the expected value, and the voltage drop diagnosis is determined to be NG. The retry function then activates after a certain period of time. In this case, although the discharge amount varies due to changes in the resistance value, the readback signals on the LV and HV sides operate as expected, confirming that there are no problems in the control circuit or output circuit.

[0060] Figure 12 This graph shows an open-circuit failure in the discharge resistor. In the event of an open-circuit failure, charge cannot be dissipated through discharge resistor 108. Therefore, the HV voltage drop is due solely to passive discharge caused by power consumption within the internal circuitry. Consequently, the HV voltage cannot be discharged below V_lo within the specified time, and at time t124, AD_Time is diagnosed as NG. Furthermore, because the amount of discharge through passive discharge alone is insufficient, the voltage drop per unit time is less than expected. Therefore, the voltage drop detection is diagnosed as NG, and the retry operation is repeated after a certain period of time.

[0061] In the case of an open-circuit failure in the discharge resistor, the HV readback signal (AD_Diag_HV) is detected as a diagnostic failure indicating a fixed disconnection because the discharge resistor remains permanently disconnected. Furthermore, since the disconnection remains fixed in the region where duty-cycle-controlled discharge should have begun at time t120, the PWM pulse check diagnostic is also detected as a failure. As a result, at time t121, AD_HV-OFF ​​and AD_HV-PWM are determined to be diagnostic failures. Furthermore, in the case of an open-circuit failure in the discharge resistor, the LV control circuit operates normally, so the LV readback signal (AD_Diag_LV) matches the discharge indication AD_OUT.

[0062] Figure 13 This is a diagram of a disconnection fixed fault of the sub-CPU output. The diagram shows the action when a fault occurs in any one of the output section of the sub-control unit (sub-CPU) on the LV side, the output circuit on the HV side, and the path containing the switch element that controls the on / off of the discharge. Here, for convenience, the situation where any one of the output circuit and the path containing the switch element fails is also collectively referred to as "disconnection fixed of the sub-CPU". Since the second switch element 107 cannot be turned on due to the disconnection fixed fault, the charge in the discharge resistor 108 cannot be consumed, and the reduction in the HV voltage is only caused by the passive discharge caused by the power consumption in the internal circuit. As a result, the HV voltage cannot be discharged to below V_lo within the specified time, and at time t134, AD_Time is diagnosed as NG. In addition, since the discharge amount through passive discharge alone is insufficient, the voltage drop per unit time is smaller than the expected value. Therefore, the diagnosis of the voltage drop is NG, and the retry action is repeated after a certain period of time.

[0063] When only focusing on the HV voltage and its voltage drop, Figure 12 and Figure 13 Looks the same. However, Figure 12 Unlike an open-circuit fault in the discharge resistor, in the case of a stuck-off fault in the sub-CPU, not only the HV readback signal (AD_Diag_HV) but also the LV readback signal (AD_Diag_LV) exhibits behavior different from AD_OUT. As a result, both the HV output diagnosis (AD_Diag_HV) and the LV output diagnosis (AD_Diag_LV) detect a stuck-off diagnosis failure and a PWM check diagnosis failure. Monitoring the HV readback signal (AD_Diag_HV) and the LV readback signal (AD_Diag_LV) in this way allows for the location of the fault to be determined.

[0064] Figure 14This is a diagram for the case of a fixed conduction failure of the sub-CPU output. This diagram shows the operation when a failure occurs in any of the output section of the sub-CPU on the LV side, the output circuit on the HV side, or the path including the switching element that controls the on / off of the discharge. Figure 14 In particular, it shows the action when a fixed conduction fault occurs at the moment when the discharge start is indicated. Depending on the moment when the fault occurs, the same action as in the diagram may not necessarily be performed. In the case of a fixed conduction fault output by the sub-CPU, although the charge can be consumed by the discharge resistor, the discharge based on the duty cycle control cannot be performed, and the discharge is always carried out by the conduction. Therefore, the discharge is carried out at a faster speed than normal. The HV voltage can be lower than V_lo within the specified time, and the voltage reduction amount is also discharged at a speed exceeding the specified threshold. Therefore, in the diagnosis of the discharge time and the diagnosis of the voltage reduction amount, it is detected as OK. However, since both the LV read back signal (AD_Diag_LV) and the HVread back signal (AD_Diag_HV) are always on, the detection of the fixed conduction diagnosis on the LV side and the HV side is NG. Furthermore, since the conduction is always on in the area where the discharge based on the duty cycle control should be carried out, the PWM check diagnosis on the LV side and the HV side is NG.

[0065] Summarizing the embodiments of the present invention described above, the discharge control circuit of the present invention includes: a discharge circuit connecting a discharge resistor 108 and a switching element 107 in series; and a control circuit that controls the discharge of the discharge resistor 108 by turning the switching element 107 on and off. The control circuit includes an output circuit 203 that outputs a drive signal for turning the switching element 107 on and off; and a main control circuit 102 and / or a sub-control circuit 103 (calculation circuit) that outputs a discharge instruction based on the voltage across the discharge circuit to the output circuit 203. The calculation circuit includes detection circuits 204 and 205 that detect the amount of voltage drop across the discharge circuit. The output of the calculation circuit is monitored as an LV readback signal, and the output of the output circuit 203 is monitored as an HV readback signal. By monitoring the HV and LV readback signals, it is possible to identify a fault location in the discharge control circuit.

[0066] This discharge control circuit, by combining multiple diagnostic functions, can pinpoint the fault location in detail if active discharge fails. Appropriate control can be implemented based on the nature of the fault, enabling the inverter to more reliably transition to a safe state. Furthermore, rapid fault location identification contributes to improved vehicle maintainability.

[0067] For example, if the discharge amount is determined to be insufficient, the design value of the discharge amount can be re-evaluated. Alternatively, if the voltage cannot be reduced sufficiently due to differences in the capacitor capacity of peripheral equipment depending on the vehicle type, passive discharge can be used to continue the discharge.

[0068] If the contactor is determined to be in the closed state, the system transitions to a discharge retry. This is because, although mechanical delays prevent discharge in the closed state during the initial discharge, discharge may be possible after a certain period of time. However, the discharge retry function is not essential, and an arbitrary upper limit can be set.

[0069] Furthermore, if discharge cannot be performed normally, a function can be provided to notify the driver of the abnormality. Furthermore, the notification method or the power conversion device control method can be modified based on the diagnosis results of the discharge abnormality. For example, if a short circuit fault in the discharge resistor is detected, active discharge can be performed while the resistance value (i.e., discharge amount) is changed, and the residual charge after active discharge can be released through passive discharge.

[0070] Furthermore, by storing diagnostic results as a fault history, it is possible to analyze the fault history to identify the most vulnerable parts of the inverter, contributing to safer product design. In this case, non-volatile memory can also be provided to record the fault history.

[0071] For example, if an open-circuit fault is detected in a discharge resistor, there's a risk of damage due to heat generation, so the discharge pattern design will be reevaluated. If a sub-CPU is detected as permanently disconnected or permanently connected, the hardware will be investigated from the perspective of circuit damage caused by overcurrent, with research to improve durability.

[0072] While the embodiments of the present invention have been described in detail above using the drawings, the specific configuration is not limited to the embodiments, and design changes and the like within the scope of the present invention are also encompassed by the present invention.

[0073] For example, by having the sub-controller 103 execute part of the diagnosis performed by the main control device 102, the computational load of the main control device 102 can be reduced. Furthermore, in the above embodiment, AD_OUT is output at a fixed duty cycle until the HV voltage falls below V_th, but a multi-step duty cycle may also be employed.

[0074] Explanation of symbols

[0075] 101…Power conversion device, 102…Main control device, 103…Sub-control device, 104…Motor, 105…Battery, 106…Contactor, 107…Second switching element, 108…Discharge resistor for consuming charge, 109…Capacitor for accumulating charge, 110…First switching element, 201…Main power supply, 202…Sub-power supply, 203…Output circuit, 204…Voltage variation detection circuit, 205…HV voltage detection circuit.

Claims

1. A discharge control circuit comprising: a discharge circuit connecting a discharge resistor and a switching element in series; and a control circuit that controls the switching element to turn on / off to control the discharge of the discharge resistor; The discharge control circuit is characterized in that: The control circuit has: an operation circuit that outputs a control signal for controlling the switching element based on a voltage across the discharge circuit; and an output circuit that outputs a drive signal for driving the switching element based on the control signal, The operation circuit has: a detection circuit monitoring unit configured to detect a decrease in voltage across the discharge circuit; an arithmetic circuit monitoring unit that monitors an output of the arithmetic circuit; and an output circuit monitoring unit that monitors the output of the output circuit, After the arithmetic circuit outputs the control signal instructing discharge, if the voltage across the discharge circuit does not fall below a predetermined threshold within a predetermined time, the arithmetic circuit determines which of the discharge circuit, the arithmetic circuit, and the output circuit has an abnormality based on a comparison between the control signal and a first signal, which is a monitoring result of the arithmetic circuit monitoring unit, and a comparison between the control signal and a second signal, which is a monitoring result of the output circuit monitoring unit. determining whether an abnormality occurs in the arithmetic circuit based on the frequency or duty cycle of the first signal; Based on the frequency or duty ratio of the second signal, it is determined whether an abnormality has occurred in the output circuit or the discharge circuit.

2. The discharge control circuit according to claim 1, wherein: The control signal is outputted so as to control the switching element to be alternately turned on / off at a predetermined frequency.

3. The discharge control circuit according to claim 1 or 2, characterized in that: A nonvolatile memory is provided for recording information on the occurrence of a failure detected by the arithmetic circuit as a failure history.

4. A power conversion device, characterized in that: have: A discharge control circuit according to any one of claims 1 to 3, and a smoothing capacitor and an inverter circuit connected in parallel to the discharge circuit.

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