Power conversion unit

Abstract

The present application provides a kind of in the power conversion unit with the switch of the electrical connection between power conversion circuit and electric storage device can be switched, determine whether the switch is abnormal technology.Power conversion unit as the diagnosis processing of reverse flow prevention switch (#10), at least one of ON fault determination processing (#20) and OFF fault determination processing (#30) is executed, in ON fault determination processing (#20), in the difference (ΔV1) of first reference voltage value (Vr1) and first voltage detection value (Vd1), and the difference of second reference voltage value and second voltage detection value, in any one exceeds ON fault determination value (Ts), it is determined that ON fault is generated, in OFF fault determination processing (#30), in the difference (ΔV3) of third reference voltage value (Vr3) and first voltage detection value (Vd1), and the difference of fourth reference voltage value and second voltage detection value, in any one exceeds OFF fault determination value (To), it is determined that OFF fault is generated.

Description

Technical Field

[0001] This invention relates to an electric power conversion unit. Background Technology

[0002] Japanese Patent Application Publication No. 2018-68035 discloses a power system circuit in which a load switch (42) is provided between a power supply circuit (51) that generates a power supply voltage (VCC3) for a driver circuit (52) that drives a power converter (10) including a DC-DC boost converter (11) and an inverter (20), and an energy storage device (auxiliary device battery (95)) that supplies power to the power supply circuit (51). (In the background art, the reference numerals in parentheses are reference numerals of the document referred to.) The electrical connection between the power supply circuit (51) and the energy storage device (95) can be switched on and off by the load switch (42). For example, if it is determined that the current flowing to the DC-DC boost converter (11) and the inverter (20) is not within the normal range, the load switch (42) is controlled to be open, the power supply to the driver circuit (52) is cut off, and the driving of the DC-DC boost converter (11) and the inverter (20) is stopped. By setting up such a load switch (42), the safety of the power converter (10) can be ensured. However, this is based on the premise that the load switch (42) is functioning normally, and it does not mention whether the load switch (42) itself is abnormal.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2018-68035

[0004] Such switches, like load switches, can also be used to limit the extraction of unnecessary power from the energy storage device. For example, when the device supporting the energy storage device is equipped with a charging circuit for charging the energy storage device, a switch can be configured between the charging circuit and the energy storage device. When the energy storage device is being charged from the charging circuit, the switch is controlled to the closed state, electrically connecting the charging circuit and the energy storage device. When the charging circuit is not charging the energy storage device and is not in operation, the electrical connection between the charging circuit and the energy storage device can be cut off by controlling the switch to the open state. This prevents the backflow of current from the energy storage device to the charging circuit in the non-operational state, thus suppressing the consumption of power from the energy storage device. That is, in this case, the switch functions as a backflow prevention switch. Preferably, it is also possible to appropriately determine whether the switch is functioning correctly. Summary of the Invention

[0005] In view of the above background, it is desirable to provide a technique for determining whether a switch is malfunctioning in a power conversion unit that has a switch capable of switching the electrical connection between a power conversion circuit and an energy storage device.

[0006] The power conversion unit, given the above situation, has the following features:

[0007] The first terminal pair is connected to the DC terminal pair of the power conversion circuit;

[0008] The second terminal pair is connected to the energy storage device;

[0009] A DC link capacitor, which is connected to both ends of the first terminal pair mentioned above;

[0010] A reverse current prevention switch is disposed between the first terminal pair and the second terminal pair. In the closed state, it allows current to flow between the first terminal pair and the second terminal pair. In the open state, it at least cuts off the current from the second terminal pair toward the first terminal pair.

[0011] The first voltage detection unit detects the voltage between the terminals of the first terminal pair.

[0012] The second voltage detection unit detects the voltage between the terminals of the second terminal pair; and

[0013] The control unit controls the aforementioned power conversion circuit and the aforementioned reverse current prevention switch.

[0014] The aforementioned control unit is capable of performing diagnostic processing to determine whether the aforementioned backflow prevention switch is normal or abnormal.

[0015] In the above diagnostic process, at least one of the ON fault determination process and the OFF fault determination process is performed. In the ON fault determination process, it is determined whether an ON fault has occurred, in which the reverse current prevention switch is in the closed state. In the OFF fault determination process, it is determined whether an OFF fault has occurred, in which the reverse current prevention switch is in the open state.

[0016] In the above ON fault determination and processing,

[0017] Set the aforementioned backflow prevention switch to the open position.

[0018] If either the difference between the voltage between the terminals of the first terminal pair (i.e., the first reference voltage value) and the detection value of the first voltage detection unit (i.e., the first voltage detection value) when the reverse current prevention switch is in the open state and the reverse current prevention switch is normal, or the difference between the voltage between the terminals of the second terminal pair (i.e., the second reference voltage value) and the detection value of the second voltage detection unit (i.e., the second voltage detection value) when the reverse current prevention switch is in the open state and the reverse current prevention switch is normal, exceeds a preset ON fault determination value, then an ON fault is determined to have occurred.

[0019] In the above OFF fault determination and processing,

[0020] Set the aforementioned backflow prevention switch to the off state.

[0021] If any one of the following exceeds a preset OFF fault determination value: the difference between the terminal voltage of the first terminal pair (i.e., the third reference voltage value) and the first voltage detection value when the reverse current prevention switch is in the closed state and the reverse current prevention switch is normal, or the difference between the terminal voltage of the second terminal pair (i.e., the fourth reference voltage value) and the second voltage detection value when the reverse current prevention switch is in the closed state and the reverse current prevention switch is normal, the aforementioned OFF fault is determined to have occurred.

[0022] According to this structure, by using reference voltage values ​​based on the inter-terminal voltage of the first terminal pair and the inter-terminal voltage of the second terminal pair when the reverse current prevention switch is functioning normally, and the voltage detection values ​​of the first and second terminal pairs, it is possible to perform appropriate diagnostic processing to determine whether the reverse current prevention switch is normal or abnormal. Furthermore, although abnormalities of the reverse current prevention switch include ON and OFF faults, both types of faults can be determined as abnormal. Thus, according to this structure, a technique can be provided to determine whether a power conversion unit equipped with a switch capable of switching the electrical connection between a power conversion circuit and an energy storage device is abnormal.

[0023] Further features and advantages of the power conversion unit will become clear from the following description of illustrative and non-limiting embodiments illustrated with reference to the accompanying drawings. Attached Figure Description

[0024] Figure 1 This is a schematic circuit block diagram representing an example of the on-board circuitry of a power conversion unit.

[0025] Figure 2 This is a schematic circuit block diagram representing an example of a power conversion unit.

[0026] Figure 3 This is a flowchart illustrating an example of diagnostic procedures (the first of two sub-graphs).

[0027] Figure 4 This is a flowchart illustrating an example of diagnostic procedures (the second of two sub-graphs).

[0028] Figure 5 It means Figure 4 A flowchart of an example of the first preprocessing and the second preprocessing.

[0029] Figure 6 It means Figure 4 The flowcharts for the first preprocessing and other examples of the second preprocessing are shown.

[0030] Description of the attached text

[0031] 1: Power conversion unit, 2: Control unit, 4: DC link capacitor, 6: Reverse current prevention switch, 7: Power conversion circuit, 11: First terminal pair, 12: Second terminal pair, 41: Capacitive load, 61: First switch (multiple reverse current prevention switches), 62: Second switch (multiple reverse current prevention switches), 66: Temperature sensor, 77: DC terminal pair, 91: First voltage detection unit, 92: Second voltage detection unit, BL: Low-voltage battery (energy storage device), To: OFF fault judgment value, Ts: ON fault judgment value, V1: First voltage, V2: Second voltage, V41: Terminal voltage of capacitive load, Vb: Battery voltage ( The voltage values ​​between the terminals of the energy storage device are as follows: Vd1: first voltage detection value, Vd2: second voltage detection value, Vdc: DC link voltage (voltage between the terminals of the DC link capacitor), Vr1: first reference voltage value, Vr2: second reference voltage value, Vr3: third reference voltage value, Vr4: fourth reference voltage value, ΔV1: first deviation (difference between the first reference voltage value and the first voltage detection value), ΔV2: second deviation (difference between the second reference voltage value and the second voltage detection value), ΔV3: third deviation (difference between the third reference voltage value and the first voltage detection value), and ΔV4: fourth deviation (difference between the fourth reference voltage value and the second voltage detection value). Detailed Implementation

[0032] The following describes the implementation of the power conversion unit 1, illustrating its use in electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs). Figure 1 The schematic circuit block diagram shows an example of an on-board circuit including the power conversion unit 1. Figure 2 The schematic circuit block diagram shows an example of power conversion unit 1. Figure 1 The on-board circuit shown is a power system electrical circuit, which includes: an inverter 50 that converts power between an AC rotary motor 8 (traction motor) that serves as the driving force source for the vehicle's wheels and a DC high-voltage battery BH; an onboard charger circuit (OBC) that charges the high-voltage battery BH with power supplied from an external AC power source (not shown); a DC-DC converter that steps down the voltage of the high-voltage battery BH and supplies it to on-board auxiliary equipment, etc.; and a low-voltage battery charger circuit that charges the low-voltage battery BL with power supplied from the high-voltage battery BH, etc.

[0033] The rotating electric motor 8 is electrically connected via an inverter 50 to a DC power source, namely a high-voltage battery BH, which consists of a secondary battery such as a lithium battery and an energy storage device such as a double-layer capacitor. The rated voltage of the high-voltage battery BH is, for example, around 200 volts to 800 volts. The rotating electric motor 8 functions as both a motor (electric motor) that receives power from the high-voltage battery BH and generates power, and an engine (generator) that receives power transmitted from the wheel side and generates electricity.

[0034] Sometimes, in addition to a traction motor (rotary motor 8), a vehicle may also have an auxiliary rotating motor M, such as an air conditioning compressor or an electric pump that circulates oil, coolant, and refrigerant for the air conditioning system. In vehicles that only use the existing internal combustion engine as the driving force for the wheels, the internal combustion engine is always running when the vehicle is stationary (when the wheels are not rotating), and its power can power the compressor and pump. However, the traction motor usually stops when the vehicle is stationary, making it difficult to power the compressor and pump. Furthermore, even when power can be utilized by having a clutch or other means to switch the power transmission path to the wheels, over-driving the traction motor can reduce the vehicle's energy efficiency. Additionally, while vehicles that only use the existing internal combustion engine as the driving force for the wheels can utilize the engine's waste heat for air conditioning, hybrid and electric vehicles cannot rely on the same waste heat as internal combustion engines and require temperature regulation by heat pumps, leading to a trend of increasing the output required for the compressor and electric pump. Therefore, there is a trend of increasing the output required for the auxiliary rotating motor M.

[0035] In order to output a larger driving force to the auxiliary equipment rotary motor M, the auxiliary equipment rotary motor M is also configured to be powered by the high-voltage battery BH, similar to the traction motor. On the other hand, there is a trend that the output of the traction motor needs to be increased, and the rated voltage of the high-voltage battery BH needs to be higher. In the case where the rated voltage of the high-voltage battery BH is too high due to the auxiliary equipment rotary motor M, a voltage conversion circuit is often provided to step down the DC power supplied from the high-voltage battery BH. In this embodiment, a structure with a first DC-DC converter 75 is shown as such a voltage conversion circuit.

[0036] As described above, the rotary motor 8 functions not only as a traction motor but also as a generator to charge the high-voltage battery BH. For example, in a PHEV, the rotary motor 8 can be powered by the internal combustion engine to generate electricity, but sometimes the opportunity to generate electricity is limited, and the high-voltage battery BH cannot be fully charged. Furthermore, in a BEV where the rotary motor 8 is the only driving force source, the electricity generated is limited to mechanical energy from the wheels, such as inertial driving, and often cannot fully charge the high-voltage battery BH. Additionally, in a PHEV, the energy efficiency of externally supplied power is sometimes better than when the rotary motor 8 generates electricity. Therefore, when the high-voltage battery BH is mounted on the vehicle, an on-board charging circuit (a function of the power conversion circuit 7) is provided to charge the high-voltage battery BH using power supplied from an external power source.

[0037] The high-voltage battery BH is configured to be charged by power (ACIN) supplied by an external AC power source (not shown), such as a commercial AC power supply with a rated voltage of approximately 100 volts to 240 volts. Therefore, the high-voltage battery BH is configured to be connected to an external AC power source via a power conversion circuit 7 equipped with an on-board charging circuit.

[0038] Furthermore, in recent years, there has been a growing advocacy for using batteries in electric and hybrid vehicles as emergency power sources during disasters. In this embodiment, the power conversion circuit 7 is configured to not only charge the high-voltage battery BH, but also supply commercial frequency alternating current (ACOUT) from the high-voltage battery BH. Of course, the power conversion circuit 7 may also be configured to have only a charging function.

[0039] The power conversion circuit 7 of this embodiment includes a dual active bridge (DAB) circuit with a transformer T, which converts the alternating current (AC IN) supplied from the external AC power source into a first direct current and a second direct current. Viewed from the AC side, the transformer T has a primary winding and two secondary windings. Alternatively, the two secondary windings can be referred to as a secondary winding and a tertiary winding, respectively. For example, a full-bridge circuit formed by switching elements is connected to the primary winding, forming a primary winding circuit 71. Similarly, a full-bridge circuit is also connected to the first secondary winding (secondary winding), forming a first secondary winding circuit (secondary winding circuit 72), and a full-bridge circuit is also connected to the second secondary winding (tertiary winding), forming a second secondary winding circuit (tertiary winding circuit 73).

[0040] The secondary-side circuit 72 generates a first DC current for charging the high-voltage battery BH. A smoothing capacitor is provided at the output of the secondary-side circuit 72 to smooth the voltage of the first DC current. The tertiary-side circuit 73 generates a second DC current with a lower voltage than the first DC current. A smoothing capacitor is provided at the output of the tertiary-side circuit 73 to smooth the voltage of the second DC current (equivalent to a reference capacitor). Figure 2 (The DC link capacitor 4 of the power conversion unit 1 is described).

[0041] like Figure 1 As shown, in addition to the high-voltage battery BH, the vehicle also has a low-voltage battery BL with a rated voltage lower than that of the high-voltage battery BH. The rated power supply voltage of the low-voltage battery BL is, for example, about 12 to 50 volts. In existing vehicles that use only an internal combustion engine as the driving force source for the wheels, such a low-voltage battery BL is charged by using the power of the internal combustion engine and the electricity generated by the alternator. In the vehicle of this embodiment that has a high-voltage battery BH, it is configured to be able to charge the low-voltage battery BL by the power supplied from the high-voltage battery BH. The low-voltage battery BL can be charged from the high-voltage battery BH via the secondary side circuit 72, the transformer T, and the tertiary side circuit 73. In addition, in terms of circuit structure, the low-voltage battery BL can also be charged from an external AC power source via the primary side circuit 71, the transformer T, and the tertiary side circuit 73. In this embodiment, a voltage conversion circuit that further reduces the voltage of the second DC power is shown, which includes a second DC-DC converter 76 (see reference). Figure 2 The chopper circuit 3) described later has the following configuration. Additionally, the low-voltage battery BL can be the same as in existing vehicles that use an internal combustion engine as the driving force source for the wheels, such as a lead-acid battery.

[0042] In this embodiment, as referred to Figure 1 As described above, by using a transformer T to construct the power conversion circuit 7, insulation of the external AC power supply, the high-voltage battery BH, and the low-voltage battery BL can be ensured.

[0043] Furthermore, the external AC power supply and the power conversion circuit 7 are connected via an EMI filter 79 to reduce EMI (Electro Magnetic Interference) noise. When the power conversion circuit 7 functions as a power supply circuit, AC power (AC OUT) is also output from the power conversion circuit 7 via the EMI filter 79. Thus, in this embodiment, the power conversion circuit 7 is configured to include a charging circuit, a power supply circuit, and a voltage conversion circuit. The power conversion circuit 7 is not limited to this configuration and may be configured to include at least one of the charging circuit, power supply circuit, and voltage conversion circuit. Additionally, the power conversion circuit 7 may also include an inverter 50.

[0044] The rotary motor 8 is driven and controlled by the rotary motor control unit based on the target torque set according to instructions from a higher-level control device, namely a vehicle control device (not shown). The rotary motor control unit controls the switching of the inverter 50, which is composed of multiple switching elements, so that the inverter 50 converts power between DC and multiphase (three-phase) AC. In this embodiment, the rotary motor control unit, together with the charging and power supply control unit that controls the power conversion circuit 7, the first voltage conversion control unit that controls the first DC-DC converter 75, and the second voltage conversion control unit that controls the second DC-DC converter 76, constitutes an ECU (control unit 2). The control unit 2 is constructed with logic circuits such as microcomputers as its core components, and the various functions of the control unit 2 are realized through the cooperation of hardware such as microcomputers and software (programs).

[0045] Figure 2 A schematic circuit block diagram illustrates an example of power conversion unit 1. In this embodiment, power conversion unit 1 is illustrated as an example corresponding to the reference... Figure 1 The above-mentioned power system electrical circuit is a circuit configuration in which the low-voltage battery BL is charged by power supplied from the high-voltage battery BH.

[0046] like Figure 2 As shown, the power conversion unit 1 includes: a first terminal pair 11 connected to the DC terminal pair 77 of the power conversion circuit 7 (here, the tertiary side circuit 73), a second terminal pair 12 connected to the low-voltage battery BL (energy storage device), a DC link capacitor 4 connected to both ends of the first terminal pair 11 (synonymous with the DC terminal pair 77), and a reverse current prevention switch 6 disposed between the first terminal pair 11 and the second terminal pair 12. Although in Figure 1 The details are omitted, but the third-side circuit 73 is configured with a rectifier circuit 78 that has a power factor correction (PFC) function, and the DC-side terminals of the rectifier circuit 78 are equivalent to DC terminal pairs 77. In this embodiment, it is shown that a [missing information - likely a device or component] is also provided between the rectifier circuit 78 and the low-voltage battery BL. Figure 1 It can be in the form of a chopper circuit 3 that functions as a second DC-DC converter 76, but it can also be in the form of not having a second DC-DC converter 76 (chopper circuit 3).

[0047] The reverse current prevention switch 6 is a switch that electrically connects the first terminal pair 11 and the second terminal pair 12 in the closed state, allowing current to flow between the first terminal pair 11 and the second terminal pair 12, and at least cuts off the current from the second terminal pair 12 to the first terminal pair 11 in the open state. While the reverse current prevention switch 6 can be constructed using an on / off switch that can be electrically controlled by the control unit 2, such as a relay, in this embodiment, a form constructed using a semiconductor switching element (e.g., a power MOSFET (Power Metal Oxide Semiconductor Field Effect Transistor)) is shown. In most cases, the semiconductor switching element has a diode portion 6d connected in parallel with the transistor portion 6s, so even when the transistor portion 6s is in the off state, current sometimes flows through the diode portion 6d. Thus, when the reverse current prevention switch 6 is constructed using a semiconductor switching element, the reverse current prevention switch 6 allows current to flow between the first terminal pair 11 and the second terminal pair 12 in the closed state, at least cuts off the current from the second terminal pair 12 to the first terminal pair 11 in the open state, and allows current from the first terminal pair 11 to the second terminal pair 12.

[0048] Furthermore, the power conversion unit 1 includes a first voltage detection unit 91 that detects the inter-terminal voltage of the first terminal pair 11, i.e., the first voltage V1 (which is synonymous with the inter-terminal voltage of the DC link capacitor 4, i.e., the DC link voltage Vdc), and a second voltage detection unit 92 that detects the inter-terminal voltage of the second terminal pair 12, i.e., the second voltage V2. The aforementioned ECU is also included in the power conversion unit 1 as a control unit 2 that sets the power conversion unit 1 as the controlled object. The detection result of the first voltage detection unit 91, i.e., the first voltage detection value Vd1, and the detection result of the second voltage detection unit 92, i.e., the second voltage detection value Vd2, are provided to the control unit 2, and the control unit 2 obtains the aforementioned detection results.

[0049] The control unit 2 controls at least the power conversion circuit 7 and the reverse current prevention switch 6. Furthermore, when functioning as the control unit of the power conversion unit 1, the control unit 2 is not limited to controlling the tertiary side circuit 73 (rectifier circuit 78) included in the power conversion unit 1; it may also control the secondary side circuit 72 and the primary side circuit 71. Additionally, when the power conversion unit 1 is equipped with a chopper circuit 3 (second DC-DC converter 76), the control unit also controls the chopper circuit 3.

[0050] The chopper circuit 3 comprises a control branch 30, a choke coil 33, and an energy storage capacitor 34, which are connected in series with an upper-side switching element 31 connected to the positive DC terminal and a lower-side switching element 32 connected to the negative DC terminal. One end of the energy storage capacitor 34 is connected to the negative DC terminal, and the choke coil 33 is connected between the other end of the energy storage capacitor 34 and the midpoint of the control branch 30. Although the chopper circuit 3 is a bidirectional chopper, it functions as a buck chopper when power is supplied from the power conversion circuit 7 to the low-voltage battery BL (when the low-voltage battery BL is being charged). When power is supplied from the low-voltage battery BL to the power conversion circuit 7, the chopper circuit 3 functions as a boost chopper.

[0051] In addition, such as Figure 2 As shown, a filter circuit 40 is provided at the connection point between the power conversion unit 1 and the low-voltage battery BL, and at the output point of the low-voltage battery BL as viewed from the power conversion unit 1. The filter circuit 40 is positioned between the reverse current prevention switch 6 and the second terminal pair 12. The filter circuit 40 can use various known circuit types (T-type, π-type, L-type, etc.). Figure 2 A T-type filter is illustrated. The filter circuit 40 includes at least a capacitive filter element (capacitor) that serves as a capacitive load 41. Furthermore, the power conversion unit 1 and the low-voltage battery BL are connected to the power conversion unit 1 via a detachable connector 19. Alternatively, although not shown in the figure, the power conversion unit 1 and the low-voltage battery BL can also be connected via a switch (not shown) such as a relay capable of disconnecting the electrical connection between the power conversion unit 1 and the low-voltage battery BL. Preferably, this switch is disposed, for example, between the connector 19 and the low-voltage battery BL.

[0052] like Figure 2 As shown, a discharge resistor 4r is connected in parallel with the DC link capacitor 4. After the power conversion circuit 7 (third-side circuit 73) stops operating and there is no power supply from the power conversion circuit 7, the charge remaining in the DC link capacitor 4 is discharged through the discharge resistor 4r. The resistance value of the discharge resistor 4r is often relatively large when considering the losses during normal operation. Therefore, in applications where it is required to discharge the DC link capacitor 4 quickly, the discharge resistor 4r can be replaced, or a discharge switch 4s connected in parallel with the DC link capacitor 4 can be connected in addition to the discharge resistor 4r. If the discharge switch 4s is in the closed state, the two ends of the DC link capacitor 4 are short-circuited, the charge is discharged quickly, and the DC link voltage Vdc can drop to approximately zero. In addition, as in this embodiment, when the chopper circuit 3 is provided, the DC link capacitor 4 can also be discharged by controlling both switching elements (31, 32) of the control branch 30 to the on state.

[0053] The reverse current prevention switch 6 is controlled to be in the closed state when the low-voltage battery BL is being charged from the power conversion circuit 7. This allows power to be supplied from the first terminal pair 11 to the second terminal pair 12, thus charging the low-voltage battery BL. When a larger charging current is desired, it is preferable to configure multiple switches in parallel, considering the rated current of a single reverse current prevention switch 6. In this embodiment, a configuration where the reverse current prevention switch 6 is configured by connecting the first switch 61 and the second switch 62 in parallel is shown. Of course, the reverse current prevention switch 6 can also be configured by connecting three or more switches in parallel, or it can be a single switch, depending on the required charging current.

[0054] When multiple backflow prevention switches 6 are connected in parallel, it is preferable to have at least one temperature sensor 66 that detects the temperature of the multiple backflow prevention switches 6. In this embodiment, the temperature sensor 66 is shown as having a thermistor, and the voltage between the terminals of the thermistor, i.e., the thermistor voltage Vt, is provided to the control unit 2.

[0055] For example, as in this embodiment, when the first switch 61 and the second switch 62 are connected in parallel, a temperature sensor 66 can be provided between the first switch 61 and the second switch 62, or two temperature sensors 66 can be provided, one for the first switch 61 and one for the second switch 62. Even when only one temperature sensor 66 is provided between the first switch 61 and the second switch 62, the temperature of that switch will be higher when current flows only in one of the switches compared to when current flows in both switches. Therefore, the temperature detected by the temperature sensor 66 is higher, and an abnormality can be detected.

[0056] For example, in the event of an OFF fault (not limited to a fault that becomes fully ON, but also includes a state that maintains a high resistance value) in one switch, as described later, another switch can be used to achieve both the function of the reverse current prevention switch 6 being in the OFF state and the function of being in the OFF state. Therefore, even if the control unit 2 performs the diagnostic process #10 described later, it may not be able to determine the occurrence of an OFF fault. However, when current flows to the reverse current prevention switch 6, for example when charging the low-voltage battery BL from the power conversion circuit 7, the current flows only through the normal switch. Therefore, the temperature of the normal switch is more likely to be higher than when both switches are normal. The control unit 2 can determine the occurrence of such an OFF fault based on the detection result of the temperature sensor 66.

[0057] Furthermore, the chopper circuit 3 can be configured in parallel according to the required charging current. For example, two control branches 30, two choke coils 33, and two energy storage capacitors 34 can be provided, and the energy storage capacitors 34 can be connected to the midpoint of each control branch 30 via the choke coils 33, thus dualizing the chopper circuit 3.

[0058] Furthermore, when the reverse current prevention switch 6 is constructed from a semiconductor switching element, as described above, a diode section 6d is typically connected in parallel with the transistor section 6s. In the semiconductor switching element, the diode section 6d is positioned so that the direction from the first terminal pair 11 toward the second terminal pair 12 is positive. Therefore, when charging the low-voltage battery BL from the power conversion circuit 7, even if the reverse current prevention switch 6 is in the open state, power can still be supplied from the first terminal pair 11 to the second terminal pair 12.

[0059] When the low-voltage battery BL is not being charged, the reverse current prevention switch 6 is controlled to be in the open state. This cuts off the current flowing from the second terminal pair 12 side (i.e., the low-voltage battery BL side) to the first terminal pair 11 side. Therefore, unnecessary current consumption from the low-voltage battery BL is suppressed. If the operation of the power conversion circuit 7 is stopped, the inflow of charge from the power conversion circuit 7 to the DC link capacitor 4 also disappears. When the discharge of the DC link capacitor 4 ends, the DC link voltage Vdc and the first voltage V1 become approximately 0 volts.

[0060] Here, when the reverse current prevention switch 6 malfunctions, such as an ON fault (not limited to a complete short circuit, but also including a state with extremely low resistance), even if the reverse current prevention switch 6 is controlled to the open state, current flows between the first terminal pair 11 and the second terminal pair 12. As a result, even in the presence of the chopper circuit 3, current flows from the low-voltage battery BL through the choke coil 33 of the chopper circuit 3 and the freewheeling diode of the upper-side switching element 31 to the DC link capacitor 4, charging the DC link capacitor 4. That is, the current drawn from the low-voltage battery BL to charge the DC link capacitor 4 may reduce the charge capacity of the low-voltage battery BL.

[0061] Conversely, when the reverse current prevention switch 6 malfunctions (e.g., fails to close and maintains a high resistance value (impedance)), even if the reverse current prevention switch 6 is controlled to close, current is unlikely to flow between the first terminal pair 11 and the second terminal pair 12. As in this embodiment, when the reverse current prevention switch 6 is a semiconductor switching element and includes a diode portion 6d, current flows through the diode portion 6d. However, the diode portion 6d also has a resistive component, and a voltage drop of approximately 0.6 to 0.7 volts is generated when current flows through the diode portion 6d. Therefore, power loss during charging of the low-voltage battery BL may increase, or charging time may become longer.

[0062] Therefore, in this embodiment, the control unit 2 is configured to perform diagnostic processing #10 (see reference) to determine whether the backflow prevention switch 6 is normal or abnormal. Figures 3-6 The control unit 2 is configured as diagnostic processing #10, capable of executing at least one of ON fault determination processing #20 and OFF fault determination processing #30. In ON fault determination processing #20, it determines whether an ON fault has occurred, where the reverse current prevention switch 6 is in the closed state. In OFF fault determination processing #30, it determines whether an OFF fault has occurred, where the reverse current prevention switch 6 is in the open state. As in this embodiment, when the reverse current prevention switch 6 is configured as a switching element with a diode section 6d, since the low-voltage battery BL can still be charged even if an OFF fault occurs, at least ON fault determination processing #20 can be executed. Of course, it is preferable that the control unit 2 can execute both ON fault determination processing #20 and OFF fault determination processing #30. In this embodiment, the control unit 2 can execute both, so that even if the reverse current prevention switch 6 malfunctions, it can distinguish between ON and OFF faults for determination. In addition, since the reverse current prevention switch 6 is configured as a switching element with a diode section 6d, a fault in which both the transistor section 6s and the diode section 6d are OFF is referred to as an "open circuit fault" in this embodiment.

[0063] The following also refers to Figures 3-6The details of diagnostic process #10 will be explained, but in this embodiment, the control unit 2 can execute the first diagnostic process #11 when the low-voltage battery BL is connected to the power conversion unit 1, and the second diagnostic process #15 when the low-voltage battery BL is not connected to the power conversion unit 1. Furthermore, in the first diagnostic process #11, ON fault determination process #20 and OFF fault determination process #30 can be executed, and in the second diagnostic process #15, both ON fault determination process #20 and OFF fault determination process #30 can be executed. The control unit 2 may execute only one of ON fault determination process #20 and ON fault determination process #30, or it may execute both ON fault determination process #20 and ON fault determination process #30 by executing the illustrated flowchart twice. Additionally, if the control unit 2 has predetermined the execution of both processes, for example, if it determines that an abnormality exists in either ON fault determination process #20 or ON fault determination process #30 that was executed first, the execution of the process scheduled to be executed later can be suspended.

[0064] Furthermore, the first diagnostic process #11 is a process that determines whether the backflow prevention switch 6 is abnormal when the vehicle is already completed as a finished product. This diagnostic process can be performed even when the energy storage device (target energy storage device) connected to the backflow prevention switch 6 is in use (not charging, but supplying power to the load). On the other hand, the second diagnostic process #15 is performed not only when the switch is controlled to be in the open state and the target energy storage device is separated from the power conversion unit 1, but also during vehicle manufacturing, maintenance at repair shops, when the target energy storage device is removed from the vehicle, or during component manufacturing. Figure 1 This process can also be performed when inspecting the power system electrical circuit board shown. If the energy storage device that supplies power to the control system circuit (control unit 2, etc.) is the target energy storage device, it is preferable to perform the second diagnostic process #15 by supplying additional power to the control system circuit from another power source.

[0065] Although details will be described later, in the ON fault determination process #20, the control unit 2 controls the reverse current prevention switch 6 to the open state and obtains the detection value of the first voltage detection unit 91, i.e., the first voltage detection value Vd1, and the detection value of the second voltage detection unit 92, i.e., the second voltage detection value Vd2. Furthermore, if either of the following exceeds the preset ON fault determination value Ts (refer to the following parameters): "the difference between the voltage between the terminals of the first terminal pair 11 (first voltage V1), i.e., the first reference voltage value Vr1, and the first voltage detection value Vd1 when the reverse current prevention switch 6 is in the open state and the reverse current prevention switch 6 is normal, i.e., the first deviation ΔV1") or "the difference between the voltage between the terminals of the second terminal pair 12 (second voltage V2), i.e., the second reference voltage value Vr2, and the second voltage detection value Vd2, i.e., the second deviation ΔV2) when the reverse current prevention switch 6 is in the open state and the reverse current prevention switch 6 is normal," the control unit 2 will determine the ON fault determination value Ts (refer to the following parameters). Figure 3 , Figure 4 In the event that the first deviation ΔV1 exceeds the ON fault determination value Ts, the control unit 2 determines that an ON fault has occurred. Specifically, in the first diagnostic process #11, "if the first deviation ΔV1 exceeds the ON fault determination value Ts", and in the second diagnostic process #15, "if the second deviation ΔV2 exceeds the ON fault determination value Ts", the control unit 2 determines that an ON fault has occurred. For details, please refer to [link to relevant documentation]. Figure 3 as well as Figure 4 This will be discussed later.

[0066] Furthermore, in the OFF fault determination process #30, the control unit 2 controls the backflow prevention switch 6 to the closed state and obtains the first voltage detection value Vd1 and the second voltage detection value Vd2. Moreover, if any of the following exceeds the preset OFF fault determination value To: "the difference between the voltage between the terminals of the first terminal pair 11 (first voltage V1), i.e., the third reference voltage value Vr3, and the first voltage detection value Vd1 when the backflow prevention switch 6 is in the closed state and the backflow prevention switch 6 is normal, i.e., the third deviation ΔV3", or "the difference between the voltage between the terminals of the second terminal pair 12 (second voltage V2), i.e., the fourth reference voltage value Vr4, and the second voltage detection value Vd2, i.e., the fourth deviation ΔV4) when the backflow prevention switch 6 is in the closed state and the backflow prevention switch 6 is normal", the control unit 2 determines that an OFF fault has occurred. Specifically, in the first diagnostic process #11, "when the third deviation ΔV3 exceeds the OFF fault determination value To", and in the second diagnostic process #15, "when the fourth deviation ΔV4 exceeds the OFF fault determination value To", the control unit 2 determines that an OFF fault has occurred. For details, please refer to [link to relevant documentation]. Figures 3-6 This will be discussed later.

[0067] Figure 3 as well as Figure 4 These are two separate diagrams illustrating an example of diagnostic procedure #10. Generally speaking... Figure 3 This indicates the first diagnostic treatment #11. Figure 4 This indicates the second diagnostic treatment #15. Additionally... Figure 5 express Figure 4 Details of the first preprocessing #25 and the second preprocessing #35 are shown. Figure 6 express Figure 5 In another embodiment of the first preprocessing #25 shown, a pre-diagnostic process is performed as described below.

[0068] like Figure 3 As shown, if the control unit 2 starts diagnostic process #10, it first determines whether the energy storage device (here, the low-voltage battery BL) is connected to the power conversion unit 1 (#1). If the low-voltage battery BL is connected to the power conversion unit 1, the control unit 2 executes the first diagnostic process #11; if the low-voltage battery BL is not connected to the power conversion unit 1, it executes the second diagnostic process #15.

[0069] In the first diagnostic process #11, control unit 2 first outputs an on / off command (#41) to the reverse current prevention switch 6. When executing diagnostic process #10, if sufficient time has elapsed since charging the low-voltage battery BL, the DC link capacitor 4 discharges, and the terminal voltage (DC link voltage Vdc) is approximately zero. Even if sufficient time has elapsed since charging the low-voltage battery BL, if the power conversion unit 1 is equipped with the aforementioned discharge switch 4s, control unit 2 can discharge the DC link capacitor 4 by controlling the discharge switch 4s before executing step #41, thereby setting the DC link voltage Vdc to approximately zero. Of course, regardless of the elapsed time since charging the low-voltage battery BL, control unit 2 can also execute step #41 after discharging the DC link capacitor 4 by controlling the discharge switch 4s.

[0070] Furthermore, to illustrate the scenario where the "first reference voltage value Vr1" described later is a fixed value and is set to approximately zero (Vr1≈0), the condition where the DC link voltage Vdc is approximately zero is shown. However, it is also possible for the first voltage detection unit 91 to detect the value of the DC link voltage Vdc during the execution of the first diagnostic process #11, and to variably set the first reference voltage value Vr1 based on the detection result (first voltage detection value Vd1). In this scenario, the value of the DC link voltage Vdc may not be approximately zero.

[0071] Next, it is determined whether the target of diagnostic processing #10 is ON fault determination processing #20 or OFF fault determination processing #30. As described above, controlling the reverse current prevention switch 6 to the open state is the case of executing ON fault determination processing #20. Therefore, control unit 2 determines whether the opening / closing command output in step #41 is an opening command (OPEN) (#51). In addition, after executing step #41, and before executing step #61 or step #62 described later, control unit 2 obtains the first voltage detection value Vd1 and the second voltage detection value Vd2. In addition, since only the first voltage detection value Vd1 is used in the first diagnostic processing #11, it is also possible to obtain only the first voltage detection value Vd1.

[0072] In step #51, if the opening / closing command is determined to be an OPEN command, then step #61 is entered, where control unit 2 determines whether the absolute value (difference) between the first voltage detection value Vd1 and the first reference voltage value Vr1, i.e., the first deviation ΔV1, is below the ON fault determination value Ts (#61). Since this is merely a matter of logical expression, it is equivalent to determining whether the first deviation ΔV1 exceeds the ON fault determination value Ts. As described above, when the DC link capacitor 4 discharges, the voltage between terminals (DC link voltage Vdc) is zero. Therefore, the first voltage V1 is ideally also zero, and the first reference voltage value Vr1 is also zero. If the reverse current prevention switch 6 is normal, the detection value of the first voltage V1, i.e., the first voltage detection value Vd1, is also zero, so the first deviation ΔV1 also becomes zero. That is, step #61 is equivalent to determining whether the first voltage V1 is zero. The ON fault determination value Ts can also be zero, but it is preferable to set it to a value close to zero (e.g., about 0.5 to 1 volt) taking into account the possibility of generating a small amount of leakage current, the possibility of residual charge in the DC link capacitor 4, and the possibility of detection error in the first voltage detection unit 91.

[0073] If the determination condition of step #61 is met, control unit 2 sets the on / off state of the backflow prevention switch 6 to the open state (#71); if the determination condition of step #61 is not met, it sets the on / off state to the closed state (#72). Next, control unit 2 determines whether the on / off command output in step #41 is consistent with the on / off state (#81) set in step #71 or step #72. If the on / off command is consistent with the on / off state (#91), control unit 2 determines that the backflow prevention switch 6 is normal; if they are inconsistent, it determines that the backflow prevention switch 6 is abnormal. In this case, since the abnormality occurs when the on / off command is an open command, it is determined that an abnormality has occurred where the on / off command is an open command but the state is closed, i.e., an "ON fault" (#92).

[0074] If the opening / closing command is determined to be a closing command (CLOSE) in step #51, then proceed to step #62, where the control unit 2 determines whether the difference (absolute value) between the first voltage detection value Vd1 and the third reference voltage value Vr3, i.e., the third deviation ΔV3, is below the OFF fault determination value To (#62). Since this is merely a matter of logical operation, it is equivalent to determining whether the third deviation ΔV3 exceeds the OFF fault determination value To. As described above, the DC link capacitor 4 discharges, and the inter-terminal voltage (DC link voltage Vdc) is zero. Here, if the reverse current prevention switch 6 is in the closed state, the DC link capacitor 4 is charged by the power from the low-voltage battery BL. The inter-terminal voltage (DC link voltage Vdc) of the DC link capacitor 4 rises to a maximum of the inter-terminal voltage of the low-voltage battery BL (battery voltage Vb) (ignoring the forward voltage drop of the diode in the chopper circuit 3). However, the outflow of charge from the low-voltage battery BL also increases, so it is preferable to also limit the time for which the reverse current prevention switch 6 is kept in the closed state. In this case, the DC link voltage Vdc becomes a value greater than zero and less than the battery voltage Vb. The theoretical value of the DC link voltage Vdc corresponding to the time it is in the off state can be calculated using the time constant corresponding to the capacitance of the DC link capacitor 4.

[0075] The first voltage V1 is the DC link voltage Vdc (e.g., battery voltage Vb), and the third reference voltage value Vr3 is also the DC link voltage Vdc (e.g., battery voltage Vb). If the reverse current prevention switch 6 is normal, the detected value of the first voltage V1, i.e., the first voltage detection value Vd1, is also the DC link voltage Vdc (e.g., battery voltage Vb), so the third deviation ΔV3 becomes zero. That is, step #62 is equivalent to determining whether the first voltage V1 is not zero (e.g., whether it is the battery voltage Vb). Although the OFF fault determination value To can also be zero, considering the wiring resistance, voltage drop of circuit components (diode, choke coil 33), time constant error, detection error of the first voltage detection unit 91, etc., it is preferable to set it to a value close to zero (e.g., about 1 to 2 volts).

[0076] If the determination condition of step #62 is met, control unit 2 sets the on / off state of the backflow prevention switch 6 to the closed state (CLOSE) (#73); if the determination condition of step #62 is not met, it sets the on / off state to the open state (OPEN) (#74). Next, control unit 2 determines whether the on / off command output in step #41 is consistent with the on / off state (State) set in step #73 or step #74 (#82). If the on / off command is consistent with the on / off state (State), control unit 2 determines that the backflow prevention switch 6 is normal (#93); if they are inconsistent, it determines that the backflow prevention switch is abnormal. In this case, since the abnormality occurs when the on / off command is a closed command, it is determined that an abnormality has occurred where the closed command is actually an open state, i.e., an "OFF fault" (#94).

[0077] Control Unit 2 Figure 3 In step #1 shown, if it is determined that the power conversion unit 1 is not connected to the low-voltage battery BL, then the following steps are executed. Figure 4 The second diagnostic process #15 ($1 → #15 → $2) is shown. Since the low-voltage battery BL is not connected, and the power conversion circuit 7 does not need to operate, the DC link capacitor 4 is discharged in order to charge the low-voltage battery BL. In the second diagnostic process #15, the control unit 2 first executes the first preprocessing #25.

[0078] like Figure 5 As shown, in the first pre-processing #25, the control unit 2 drives the power conversion circuit 7 in a state where the reverse current prevention switch 6 allows current to flow from the DC link capacitor 4 to the second terminal pair 12, in order to output voltage to the second terminal pair 12. This charges the DC link capacitor 4 (pre-charging process #23). As in this embodiment, when the reverse current prevention switch 6 is composed of a semiconductor switching element, a diode 6d is connected in the positive direction from the DC link capacitor 4 to the second terminal pair 12, allowing current to flow from the DC link capacitor 4 to the second terminal pair 12. If the reverse current prevention switch 6 does not have such a diode 6d, the reverse current prevention switch 6 can be controlled to be in the closed state (#22) only during the execution of the first pre-processing #25. That is, before the pre-charging process #23, the control unit 2 determines whether the reverse current prevention switch 6 is a switching element (#21), and if the reverse current prevention switch 6 is not a switching element, sets the on / off command to the closed state (CLOSE) (#22).

[0079] Furthermore, since it is known whether the backflow prevention switch 6 of the diagnostic object is a switching element or a switch, it can also be in the following form: without setting step #21, a first preprocessing #25 for the switching element and a first preprocessing #25 for the switch are set respectively, and the program to be executed is selected.

[0080] Furthermore, as in this embodiment, when the chopper circuit 3 is provided, the control unit 2 controls the upper-side switching element 31 of the control branch 30 to be in a conducting state and directly connects the chopper circuit 3 to output voltage to the second terminal pair 12. Alternatively, the control unit 2 may cause the chopper circuit 3 to perform a voltage reduction operation to output any voltage to the second terminal pair 12. In addition, the first preprocessing #25 may be continued until the DC link voltage Vdc becomes the same value as when charging the low-voltage battery BL, or it may be limited to continuing until it becomes any voltage lower than that (a preset pre-charge voltage). The control unit 2 may also control the duration of the first preprocessing #25 based on the detection result (first voltage detection value Vd1) of the first voltage detection unit 91.

[0081] If the control unit 2 raises the inter-terminal voltage (DC link voltage Vdc) of the DC link capacitor 4 to an arbitrary voltage through the first preprocessing, it executes the second preprocessing #35. At the beginning of the second preprocessing #35, the control unit 2 sets the opening / closing command to the open state (OPEN) (#32). Although the open / closed state of the reverse current prevention switch 6 does not change without step #22, the reverse current prevention switch 6 needs to be in the open state (OPEN) in the next step #33. Therefore, it is preferable to determine the control state of the reverse current prevention switch 6 to the open state (OPEN) through the execution of step #32. Under the normal state where the reverse current prevention switch 6 does not allow current to flow from the second terminal pair 12 toward the DC link capacitor 4, the control unit 2 stops the power conversion circuit 7 and discharges the DC link capacitor 4 via the discharge resistor 4r or the discharge switch 4s (#33).

[0082] Since the direction from the second terminal pair 12 toward the DC link capacitor 4 is reversed (from the cathode toward the anode), the diode portion 6d of the reverse current prevention switch 6 does not allow current flow. The reverse current prevention switch 6 does not have a diode portion 6d. During the pre-charging process #23, even though the reverse current prevention switch 6 is controlled to the closed state via step #22, it is controlled to the open state in the initial step #32 of the second pre-processing #35, thus cutting off current flow. Furthermore, as in this embodiment, when the chopper circuit 3 is provided, it is preferable that the switching elements of the control branch 30 are all controlled to the cut-off state.

[0083] After the execution of the first preprocessing #25 and the second preprocessing #35, the control unit 2 outputs an on / off command (#45) to the reverse current prevention switch 6. Additionally, when discharging the DC link capacitor 4 via the discharge resistor 4r, a standby time is preferably provided before proceeding to step #45. Furthermore, steps #33 and #45 can also be executed in reverse order.

[0084] Next, it is determined whether the target of diagnostic processing #10 is ON fault determination processing #20 or OFF fault determination processing #30. As described above, when ON fault determination processing #20 is executed, the reverse current prevention switch 6 is controlled to the open state. Therefore, the control unit 2 determines whether the opening / closing command output in step #45 is an opening command (OPEN) (#55). In the second diagnostic processing #15, after executing the second preprocessing #35 and before executing step #65 or step #66 (described later), the control unit 2 obtains the first voltage detection value Vd1 and the second voltage detection value Vd2. In addition, since only the second voltage detection value Vd2 is used in the second diagnostic processing #15, it is also possible to obtain only the second voltage detection value Vd2.

[0085] If the opening / closing command is determined to be an OPEN command in step #55, then step #65 is entered, where control unit 2 determines whether the difference (absolute value) between the second voltage detection value Vd2 and the second reference voltage value Vr2, i.e., the second deviation ΔV2, is below the ON fault determination value Ts (#65). Since this is merely a matter of logical operation, it is equivalent to determining whether the second deviation ΔV2 exceeds the ON fault determination value Ts. Furthermore, when distinguishing between the ON fault determination value Ts of step #61 and the ON fault determination value Ts of step #65, the ON fault determination value Ts of step #61 can be referred to as the first ON fault determination value (e.g., "Ts1"), and the ON fault determination value Ts of step #65 can be referred to as the second ON fault determination value (e.g., "Ts2"). "Ts1" and "Ts2" can be the same value or different values.

[0086] As described above, in the first preprocessing #25, the DC link capacitor 4 is charged while allowing current to flow from the DC link capacitor 4 via the reverse current prevention switch 6 towards the second terminal pair 12. Additionally, as referred to... Figure 2As described above, a capacitive load 41 (e.g., a capacitor) of a filter circuit 40 is connected in parallel to the second terminal pair 12. This capacitive load 41 is charged by the charge stored in the DC link capacitor 4. The inter-terminal voltage "V41" of the capacitive load 41 rises to a maximum of the DC link voltage Vdc (when the upper-side switching element 31 of the control branch 30 of the chopper circuit 3 is controlled to be in the on state, and the forward voltage drop of the diode section 6d of the reverse current prevention switch 6 is ignored). In addition, when the control unit 2 causes the chopper circuit 3 to perform a voltage reduction operation, an arbitrary voltage can be output to the second terminal pair 12, and the inter-terminal voltage "V41" of the capacitive load 41 can be set to this arbitrary voltage.

[0087] The inter-terminal voltage (second voltage V2) of the second terminal pair 12 connected to the capacitive load 41 is the inter-terminal voltage "V41" of the capacitive load 41 charged in the first pre-processing #25 (e.g., the DC link voltage Vdc in the first pre-processing #25). Here, the second reference voltage value Vr2 can also be a value corresponding to the DC link voltage Vdc. If the reverse current prevention switch 6 is normal, the detected value of the second voltage V2, that is, the second voltage detection value Vd2, is also the DC link voltage Vdc in the first pre-processing #25, so the second deviation ΔV2 becomes zero. That is, step #65 is equivalent to determining whether the second voltage V2 is not zero (e.g., whether it is the DC link voltage Vdc in the first pre-processing #25). Although the ON fault determination value Ts can be zero, considering the wiring resistance, voltage drop of circuit elements (diode, choke coil 33), time constant error, detection error of the first voltage detection unit 91, etc., it is set to a value close to zero (e.g., about 1 to 2 volts).

[0088] When the reverse current prevention switch 6 malfunctions, i.e., when the reverse current prevention switch 6 is in an ON fault state, current flows between the DC link capacitor 4 and the capacitive load 41 via the reverse current prevention switch 6. Since the DC link capacitor 4 is discharged in the second preprocessing step #35, charge moves from the capacitive load 41 to the DC link capacitor 4. Because the capacitance of the capacitive load 41 is smaller than the capacitance of the DC link capacitor 4, the capacitive load 41 discharges, and the inter-terminal voltage "V41" is approximately zero. Therefore, when the reverse current prevention switch 6 is in an ON fault state, the determination condition of step #65 is not met.

[0089] If the determination condition of step #65 is met, control unit 2 sets the on / off state of the backflow prevention switch 6 to the open state (#75); if the determination condition of step #65 is not met, it sets the on / off state to the closed state (#76). Next, control unit 2 determines whether the on / off command output in step #45 is consistent with the on / off state (#85) set in step #75 or step #76. If the on / off command is consistent with the on / off state (#95), control unit 2 determines that the backflow prevention switch 6 is normal; if they are inconsistent, it determines that the backflow prevention switch 6 is abnormal. In this case, since the abnormality occurs when the on / off command is an open command, it is determined that an abnormality has occurred where the state is closed even though the command is open, i.e., an "ON fault" (#96).

[0090] If the on / off command is determined to be a CLOSE command in step #55, then step #66 is entered, where control unit 2 determines whether the difference (absolute value) between the second voltage detection value Vd2 and the fourth reference voltage value Vr4, i.e., the fourth deviation ΔV4, is below the OFF fault determination value To (#66). Since this is merely a matter of logical operation, it is equivalent to determining whether the fourth deviation ΔV4 exceeds the OFF fault determination value To. Furthermore, when distinguishing between the OFF fault determination value To in step #62 and the OFF fault determination value To in step #66, the OFF fault determination value To in step #62 can be referred to as the first OFF fault determination value (e.g., "To1"), and the OFF fault determination value To in step #66 can be referred to as the second OFF fault determination value (e.g., "To2"). "To1" and "To2" can be the same value or different values.

[0091] As described above, in the first preprocessing #25, the capacitive load 41 is charged by the charge stored in the DC link capacitor 4. Furthermore, the DC link capacitor 4 is discharged in the second preprocessing #35, so if the reverse current prevention switch 6 is controlled to the closed state, charge moves from the capacitive load 41 to the DC link capacitor 4. Since the electrostatic capacitance of the capacitive load 41 is smaller than that of the DC link capacitor 4, the capacitive load 41 discharges, and the inter-terminal voltage "V41" is approximately zero.

[0092] Therefore, the second voltage V2 is ideally zero, and the fourth reference voltage value Vr4 is also zero. If the reverse current prevention switch 6 is normal, the detected value of the second voltage V2, i.e., the second voltage detection value Vd2, is also zero, so the second deviation ΔV2 also becomes zero. That is, step #66 is equivalent to determining whether the second voltage V2 is zero. Although the OFF fault determination value To can also be zero, it is preferable to set it to a value close to zero (for example, about 0.5 to 1 volt) considering the possibility of generating a small amount of leakage current, the possibility of residual charge in the capacitive load 41, and the possibility of detection error in the second voltage detection unit 92.

[0093] When the reverse current prevention switch 6 malfunctions, i.e., when the reverse current prevention switch 6 is in an OFF state, current does not flow from the capacitive load 41 to the DC link capacitor 4. Therefore, the capacitive load 41 does not discharge, and the terminal voltage "V41" does not become zero, maintaining approximately the DC link voltage Vdc of the first preprocessing step #25. Therefore, when the reverse current prevention switch 6 is in an OFF state, the determination condition of step #66 is not met.

[0094] If the determination condition of step #66 is met, control unit 2 sets the on / off state of the backflow prevention switch 6 to the closed state (CLOSE) (#77); if the determination condition of step #66 is not met, it sets the on / off state to the open state (OPEN) (#78). Next, control unit 2 determines whether the on / off command output in step #45 is consistent with the on / off state (State) set in step #77 or step #78 (#86). If the on / off command is consistent with the on / off state (State), control unit 2 determines that the backflow prevention switch 6 is normal (#97); if they are inconsistent, it determines that the backflow prevention switch 6 is abnormal. In this case, since the abnormality occurs when the on / off command is a closed command, it is determined that an abnormality has occurred where the on / off state is open even though the command is closed, i.e., an "OFF fault" (#98).

[0095] However, when the reverse current prevention switch 6 is composed of a switching element that connects a transistor section 6s and a diode section 6d in parallel, and the direction of the diode section 6d from the DC link capacitor 4 side toward the second terminal pair 12 is set to positive, and the reverse current prevention switch 6 is connected, current is allowed to flow in the direction from the DC link capacitor 4 side toward the second terminal pair 12 regardless of the control state of the reverse current prevention switch 6. Therefore, the control unit 2 can perform the first preprocessing #25 without the opening and closing control of the reverse current prevention switch 6. That is, the control unit 2 can refer to Figure 4 The above steps determine whether the transistor section 6s of the reverse current prevention switch 6 is in an OFF fault.

[0096] However, when the backflow prevention switch 6 is composed of a relay or other switch, the same steps cannot determine an OFF fault without the on / off control of the backflow prevention switch 6. For example, if the backflow prevention switch 6 is not controlled to the closed state by the control unit 2, then in the first preprocessing #25, current cannot flow from the DC link capacitor 4 toward the second terminal pair 12. Therefore, when the backflow prevention switch 6 is composed of a relay or other switch, as referred to... Figure 5 As described above, in step #22 of the first pre-processing #25, after controlling the reverse current prevention switch 6 to the closed state, the control unit 2 performs a pre-charging process (#23). Therefore, if the reverse current prevention switch 6 is functioning correctly, the first pre-processing #25 is performed to charge the DC link capacitor 4 by activating the power conversion circuit 7, while allowing current flow from the DC link capacitor 4 to the second terminal pair 12. Furthermore, after the first pre-processing #25, the control unit 2 controls the reverse current prevention switch 6 to the open state. If the reverse current prevention switch 6 is functioning correctly, the second pre-processing #35 is performed to stop the operation of the power conversion circuit 7 and discharge the DC link capacitor 4, while preventing current flow from the second terminal pair 12 to the DC link capacitor 4.

[0097] At this time, if the switch is in an OFF fault state, in the first preprocessing step #25, the current does not flow from the DC link capacitor 4 towards the second terminal pair 12, and the inter-terminal voltage "V41" of the capacitive load 41, i.e., the second voltage V2, is approximately zero. If the processing below step #45 continues and the OFF fault determination process #30 is executed, then in step #66, it is determined that the reverse current prevention switch 6 is in the closed state, and in step #77, "State = CLOSE" is set. Furthermore, in the subsequent step #86, the opening / closing command of the OFF fault determination process #30 is consistent with "State," and the determination result of the OFF fault determination process #30 becomes "normal" (#97). That is, the OFF fault situation cannot be detected. Additionally, if the ON fault determination process #20 is executed, in step #65, it is determined that the reverse current prevention switch 6 is in the closed state, and the determination result of the ON fault determination process #20 becomes an ON fault indicating an abnormality (#96). Although the reverse current prevention switch 6 is determined to be abnormal, the type of abnormality is incorrectly determined.

[0098] Furthermore, the reverse current prevention switch 6 is not limited to the case where it is composed of a relay or other switching device. When the reverse current prevention switch 6 is composed of a switching element, refer to... Figure 4 as well as Figure 5In the above steps, even if the diode section 6d fails, it is sometimes impossible to determine if the reverse current prevention switch 6 is not in a state of conducting current. As mentioned above, although it is at least determined to be an abnormality, the type of abnormality cannot be correctly determined. Furthermore, in distinguishing between a fault in which the diode section 6d of the switching element is normal and only the transistor section 6s is not in a state of conducting current (the OFF fault as the object of judgment mentioned above), and a fault in which the diode section 6d is not in a state of conducting current according to specifications, the latter can be called an "open circuit fault". An "open circuit fault" can also be called a special mode of "OFF fault". In the construction of the switching element, if the diode section 6d fails, the transistor section 6s will also fail, so an "open circuit fault" can be called a fault in which both the diode section 6d and the transistor section 6s are not in a state of conducting current according to specifications, regardless of the flow direction and control state. In addition, in this embodiment, at least the fault in which the diode section 6d is not in a state of conducting current according to specifications is also included in the "open circuit fault".

[0099] Therefore, control unit 2 preferably performs the same determination process as step #65 in the first preprocessing #25. Figure 6 : Pre-fault determination processing #24 (in Figure 4 and Figure 6 In this case, since the destination of the "yes" branch becomes the opposite record through "normal" and "fault", the decision logic also becomes the opposite logic. That is, in the first preprocessing #25, it can be confirmed that the inter-terminal voltage of the DC link capacitor 4 (DC link voltage Vdc) and the inter-terminal voltage "V41" (second voltage V2) of the capacitive load 41 are approximately the same (when the chopper circuit 3 is in the direct connection operation state, the forward voltage drop of the diode section 6d is ignored). This decision can also use the fifth reference voltage value Vr5 and the second voltage detection value Vd2 corresponding to the second reference voltage value Vr2 in step #65, or it can use the first voltage detection value Vd1 and the second voltage detection value Vd2. The fifth reference voltage value Vr5 is the value corresponding to the inter-terminal voltage of the DC link capacitor 4 in the pre-charge processing #23, that is, the DC link voltage Vdc (first voltage detection value Vd1). When the chopper circuit 3 is in direct connection operation, if the forward voltage drop of the diode section 6d is ignored, the fifth reference voltage value Vr5 can be approximately set as the DC link voltage Vdc (the first voltage detection value Vd1). When the chopper circuit 3 is performing a step-down operation, the fifth reference voltage value Vr5 can be set as the voltage of the step-down command for the chopper circuit 3.

[0100] For example, if the difference (absolute value) between the fifth reference voltage value Vr5 (or the first voltage detection value Vd1) and the second voltage detection value Vd2, i.e., the fifth deviation ΔV5, exceeds the pre-fault determination value Tp, the control unit 2 determines that the reverse current prevention switch 6 is not in a state of conducting current (OFF fault or open circuit fault). Figure 6 (#24 → #28, #29). As mentioned above, an open-circuit fault can also be considered a special mode of an OFF fault, so step #28 can also be considered an "OFF fault (open-circuit fault)". Although the pre-fault determination value Tp can also be zero, it is the same as the second reference voltage value Vr2. Taking into account wiring resistance, voltage drop of circuit elements (diode, choke coil 33), time constant error, detection error of the first voltage detection unit 91, etc., it is preferable to set it to a value close to zero (for example, about 1 to 2 volts).

[0101] Furthermore, during the execution of the second diagnostic process #15, the capacitive load 41 connected to the energy storage device is not discharged, and the inter-terminal voltage "V41", i.e., the second voltage V2, is approximately zero. If a fault (OFF fault or open circuit fault) occurs when the reverse current prevention switch 6 is in a state of cutting off the current toward the second terminal pair 12, even if the first pre-process #25 is executed, the second voltage V2 will not rise and will remain approximately zero. Therefore, the control unit 2 can also determine that a fault has occurred in the pre-fault determination process #24 when the second voltage V2 is approximately zero.

[0102] Figure 6 Examples are shown for Figure 5 A flowchart for the pre-fault determination process #24 has been added. Although the determination content is the same, the determination result will be different depending on whether the backflow prevention switch 6 is a switching element or a relay or other switch. Therefore, two steps, "#24a" and "#24b", are set up. In addition, along with this, two steps, "#23a" and "#23b", are also set up for the pre-charge process #23. That is, after the first pre-processing #25 of the pre-fault determination process #24 is in step #21, there are two systems: one for entering steps #23a (#23) and #24a (#24), and the other for entering steps #23b (#23) and #24b (#24).

[0103] In the pre-fault determination process #24, if no fault is determined, the control unit 2 determines that the first pre-processing #25 was successful and proceeds to step #35. That is, when the backflow prevention switch 6 is composed of a switching element, after step #45, by executing the OFF fault determination process #30, it is possible to determine whether the transistor unit 6s is in an OFF fault state. When the backflow prevention switch 6 is composed of an on / off switch, it can be confirmed in the pre-fault determination process #24 that no OFF fault has occurred, so the OFF fault determination process #30 may not need to be executed.

[0104] In the pre-fault determination process #24, if an OFF fault is determined to have occurred (#23b→#24b→#29), proceed to $2, and control unit 2 ends diagnostic process #10. That is, if the reverse current prevention switch 6 is composed of an on / off switch, diagnostic process #10 ends here. In the pre-fault determination process #24, if an open circuit fault is determined to have occurred (#23b→#24b→#29), it is known that at least diode section 6d has failed. In the construction of the switching element, it is almost impossible for only diode section 6d to fail while transistor section 6s is normal. If diode section 6d fails, the switching element is also abnormal, so the process can end here in the same way as when the reverse current prevention switch 6 is composed of an on / off switch.

[0105] Furthermore, even though the illustration is omitted, when it is necessary to definitively determine whether a fault exists in transistor section 6s, control unit 2 can, for example, treat the faulty switching element in diode section 6d as an on / off switch and, after step #29, perform the same process as "#22→#23b→#24b" in the first preprocessing #25 (assuming it is set to "#22c→#23c→#24c"). Here, if the determination is normal (if the determination result of step #24c is "no"), transistor section 6s is normal, so control unit 2 can determine that the fault is only that diode section 6d is not in a state of conducting current. If the determination result of step #24c is "yes", control unit 2 can determine that the fault is that neither diode section 6d nor transistor section 6s is in a state of conducting current.

[0106] That is, when the control unit 2 of the power conversion unit 1, which has a capacitive load 41 connected to the second terminal pair 12, is not connected to the energy storage device (low-voltage battery BL) to the second terminal pair 12 (step #1 → No: $1), it can perform diagnostic processing #10 as follows. If the reverse current prevention switch 6 is normal, the control unit 2 executes a first pre-processing #25, which includes a pre-charging process #23 that charges the DC link capacitor 4 by activating the power conversion circuit 7, and a pre-fault determination process #24 that is executed after the pre-charging process #23, while allowing current to flow from the DC link capacitor 4 to the second terminal pair 12. In the pre-fault determination process #24, if the difference between the fifth reference voltage value Vr5 corresponding to the inter-terminal voltage (DC link voltage Vdc) of the DC link capacitor 4 in the pre-charging process #23 and the second voltage detection value Vd2 (e.g., the fifth deviation ΔV5) exceeds the pre-fault determination value Tp, it is determined that an OFF fault has occurred. Following the first preprocessing step #25, if the reverse current prevention switch 6 is functioning normally, and current is not allowed to flow from the second terminal pair 12 toward the DC link capacitor 4, the control unit 2 executes the second preprocessing step #35 to stop the operation of the power conversion circuit 7 and discharge the DC link capacitor 4. Furthermore, in the ON fault determination process #20, the control unit 2 sets the value corresponding to the inter-terminal voltage (DC link voltage Vdc) of the DC link capacitor 4 from the pre-charging process #23 to the second reference voltage value Vr2 for determination processing (#65). In the OFF fault determination process #30, the control unit 2 sets the value corresponding to the inter-terminal voltage "V41" of the capacitive load 41 in the discharged state to the fourth reference voltage value Vr4 for determination processing (#66).

[0107] Furthermore, the above example illustrates a method of distinguishing between ON and OFF faults for determination. However, it is also possible to determine that the reverse current prevention switch 6 is "abnormal" if either an ON or OFF fault occurs, without distinguishing between them. That is, if either the ON fault determination process #20 or the OFF fault determination process #30 determines "abnormal (ON fault or OFF fault)," then it is determined that "the reverse current prevention switch 6 is abnormal." In such a case, the pre-fault determination process #24 may not be executed in the second diagnostic process #15.

[0108] Furthermore, although the application of a low-voltage battery BL as an energy storage device has been illustrated and explained above, a high-voltage battery BH can also be used as an energy storage device. This will be easily understood by anyone skilled in the art, so detailed explanation is omitted.

[0109] As one embodiment, the power conversion unit (1) includes: a first terminal pair (11) connected to a DC terminal pair (77) of the power conversion circuit (7); a second terminal pair (12) connected to an energy storage device (BL); a DC link capacitor (4) connected to both ends of the first terminal pair (11); a reverse current prevention switch (6) disposed between the first terminal pair (11) and the second terminal pair (12), which allows current to flow between the first terminal pair (11) and the second terminal pair (12) in a closed state, and at least cuts off the current from the second terminal pair (12) to the first terminal pair (11) in an open state; a first voltage detection unit (91) that detects the inter-terminal voltage (V1) of the first terminal pair (11); and a second voltage detection unit (92) that detects the inter-terminal voltage (V2) of the second terminal pair (12).The control unit (2) controls the power conversion circuit (7) and the reverse current prevention switch (6). The control unit (2) can perform a diagnostic process (#10) to determine whether the reverse current prevention switch (6) is normal or abnormal. In the diagnostic process (#10), at least one of the ON fault determination process (#20) and the OFF fault determination process (#30) is performed. In the ON fault determination process (#20), it is determined whether an ON fault has occurred, in which the reverse current prevention switch (6) becomes closed. In the OFF fault determination process (#30), it is determined whether an ON fault has occurred. In response to the OFF fault of the reverse current prevention switch being in the open state, in the ON fault determination process (#20), the reverse current prevention switch (6) is controlled to be in the open state. The difference between the voltage (V1) between the terminals of the first terminal pair (11), i.e., the first reference voltage value (Vr1), and the detection value (Vd1) of the first voltage detection unit (91), i.e., the first voltage detection value (Vd1), when the reverse current prevention switch (6) is in the open state and the reverse current prevention switch (6) is normal (first deviation ΔV1), and the voltage between the terminals of the first terminal pair (11) and the reverse current prevention switch (6) is in the open state and the reverse current prevention switch (6) is normal (first deviation ΔV1), and the voltage between the terminals of the first terminal pair (11) and the reverse current prevention switch (6) is in the open state and the reverse current prevention switch (6) is normal (first deviation ΔV1). (6) If either the voltage (V2) between the terminals of the second terminal pair (12) under normal conditions, i.e., the second reference voltage value (Vr2), or the difference (second deviation ΔV2) between the detection value of the second voltage detection unit (92), i.e., the second voltage detection value (Vd2), exceeds the preset ON fault determination value (Ts), an ON fault is determined to have occurred. In the OFF fault determination process (#30), the reverse current prevention switch (6) is controlled to be in the closed state. When the reverse current prevention switch (6) is in the closed state and the reverse current prevention switch (6) is normal, the above-mentioned ON fault is determined to have occurred. If any one of the following exceeds a preset OFF fault determination value (To), it is determined that an OFF fault has occurred: the difference between the inter-terminal voltage (V1) of the first terminal pair (11), i.e., the third reference voltage value (Vr3), and the first voltage detection value (Vd1) (third deviation ΔV3); or the difference between the inter-terminal voltage (V2) of the second terminal pair (12), i.e., the fourth reference voltage value (Vr4), and the second voltage detection value (Vd2) (fourth deviation ΔV4), when the reverse current prevention switch (6) is in the closed state and the reverse current prevention switch (6) is normal.

[0110] Based on this structure, using the reference voltage values ​​(Vr1, Vr2) of the inter-terminal voltage (V1) of the first terminal pair (11) and the inter-terminal voltage (V2) of the second terminal pair (12) when the reverse current prevention switch (6) is normal, and the voltage detection values ​​(Vr1, Vr2) of the first terminal pair (11) and the second terminal pair (12), it is possible to perform a diagnostic process (#10) to determine whether the reverse current prevention switch (6) is normal or abnormal. In addition, although the abnormality of the reverse current prevention switch (6) includes ON fault and OFF fault, it can be determined to be abnormal regardless of the type of fault.

[0111] In addition, as an embodiment, the power conversion unit (1) preferably performs the diagnostic process (#10) when the control unit (2) connects the energy storage device (BL) to the second terminal pair (12) and the discharge of the DC link capacitor (4) has ended. In the ON fault determination process (#20), the value corresponding to the inter-terminal voltage (Vdc) of the DC link capacitor (4) in the discharged state is set as the first reference voltage value (Vr1). In the OFF fault determination process (#30), the value corresponding to the inter-terminal voltage (Vdc) of the DC link capacitor (4) charged by the charge from the energy storage device (BL) is set as the third reference voltage value (Vr3).

[0112] According to this structure, when the power conversion unit (1) is connected to the energy storage device (BL), the relationship between the first reference voltage value (Vr1) and the third reference voltage value (Vr3) of the first terminal pair (11) when the reverse current prevention switch (6) is normal and the first voltage detection value (Vd1) can be used to perform appropriate diagnostic processing to determine whether the reverse current prevention switch (6) is normal or abnormal, even if either an ON fault or an OFF fault occurs.

[0113] In addition, as an embodiment, it is preferable that the power conversion unit (1) has a capacitive load (41) connected to the second terminal pair (12). When the control unit (2) performs the diagnostic process (#10) without the energy storage device (BL) connected to the second terminal pair (12), if the reverse current prevention switch (6) is normal, then in a state where current is allowed to flow from the DC link capacitor (4) toward the second terminal pair (12), after performing the first pre-processing (#25) to charge the DC link capacitor (4) by activating the power conversion circuit (7), if the reverse current prevention switch (6) is normal, then in a state where current is not allowed to flow, after performing the first pre-processing (#25) to charge the DC link capacitor (4) by activating the power conversion circuit (7), if the reverse current prevention switch (6) is normal, then in a state where current is not allowed to flow, In the state where the flow from the second terminal pair (12) toward the DC link capacitor (4) is in progress, a second preprocessing (#35) is performed to stop the operation of the power conversion circuit (7) and discharge the DC link capacitor (4). In the ON fault determination process (#20), the value corresponding to the inter-terminal voltage (Vdc) of the DC link capacitor (4) in the first preprocessing (#25) is set to the second reference voltage value (Vr2). In the OFF fault determination process (#30), the value corresponding to the inter-terminal voltage (V41) of the capacitive load (41) in the discharge end state is set to the fourth reference voltage value (Vr4).

[0114] When the DC link capacitor (4) is electrically connected to the second terminal pair (12) via the reverse current prevention switch (6), the inter-terminal voltage (Vdc) of the DC link capacitor (4) and the inter-terminal voltage (V2) of the second terminal pair (12) are approximately the same. In this state, for example, the inter-terminal voltage (Vdc) of the DC link capacitor (4) in the first preprocessing (#25) and the inter-terminal voltage (V2) of the second terminal pair (12) are approximately the same. Therefore, according to this structure, even when the energy storage device (BL) is not connected to the power conversion unit (1), by using the second reference voltage value (Vr2) and the fourth reference voltage value (Vr4) of the inter-terminal voltage of the second terminal pair (12) when the reverse current prevention switch (6) is normal, and the relationship with the second voltage detection value (Vd2), it is possible to perform appropriate diagnostic processing to determine whether the reverse current prevention switch (6) is normal or abnormal, even if either an ON fault or an OFF fault occurs.

[0115] In addition, as an embodiment, the power conversion unit (1) preferably has multiple reverse current prevention switches (6) connected in parallel (61, 62) and has at least one temperature sensor (66) for detecting the temperature of the multiple reverse current prevention switches (6 (61, 62)).

[0116] According to this structure, if either of the two reverse current prevention switches (61, 62) malfunctions, current flows through the other. As a result, the temperature of the reverse current prevention switch through which current flows is easily raised. By detecting that the temperature of the reverse current prevention switch (6) is higher than the specified temperature by a temperature sensor (66), it is possible to detect that either reverse current prevention switch (6) has malfunctioned.

Claims

1. A power conversion unit, characterized in that, have: The first terminal pair is connected to the DC terminal pair of the power conversion circuit; The second terminal pair is connected to the energy storage device; A DC link capacitor, which is connected to both ends of the first terminal pair mentioned above; A reverse current prevention switch is disposed between the first terminal pair and the second terminal pair. In the closed state, it allows current to flow between the first terminal pair and the second terminal pair. In the open state, it at least cuts off the current from the second terminal pair toward the first terminal pair. The first voltage detection unit detects the voltage between the terminals of the first terminal pair. The second voltage detection unit detects the voltage between the terminals of the second terminal pair; and The control unit controls the aforementioned power conversion circuit and the aforementioned reverse current prevention switch. The aforementioned control unit is capable of performing diagnostic processing to determine whether the aforementioned backflow prevention switch is normal or abnormal. In the above diagnostic process, at least one of the ON fault determination process and the OFF fault determination process is performed. In the ON fault determination process, it is determined whether an ON fault has occurred, in which the reverse current prevention switch is in the closed state. In the OFF fault determination process, it is determined whether an OFF fault has occurred, in which the reverse current prevention switch is in the open state. In the above ON fault determination and processing, Set the aforementioned backflow prevention switch to the open position. If either the difference between the voltage between the terminals of the first terminal pair (i.e., the first reference voltage value) and the detection value of the first voltage detection unit (i.e., the first voltage detection value) when the reverse current prevention switch is in the open state and the reverse current prevention switch is normal, or the difference between the voltage between the terminals of the second terminal pair (i.e., the second reference voltage value) and the detection value of the second voltage detection unit (i.e., the second voltage detection value) when the reverse current prevention switch is in the open state and the reverse current prevention switch is normal, exceeds a preset ON fault determination value, then an ON fault is determined to have occurred. In the above OFF fault determination and processing, Set the aforementioned backflow prevention switch to the off state. If any one of the following exceeds a preset OFF fault determination value: the difference between the terminal voltage of the first terminal pair (i.e., the third reference voltage value) and the first voltage detection value when the reverse current prevention switch is in the closed state and the reverse current prevention switch is normal, or the difference between the terminal voltage of the second terminal pair (i.e., the fourth reference voltage value) and the second voltage detection value when the reverse current prevention switch is in the closed state and the reverse current prevention switch is normal, the aforementioned OFF fault is determined to have occurred.

2. The power conversion unit according to claim 1, characterized in that, When the control unit begins performing the diagnostic process from the state where the energy storage device is connected to the second terminal pair and the discharge of the DC link capacitor has ended, In the above-mentioned ON fault determination process, the value corresponding to the inter-terminal voltage of the DC link capacitor in the discharged state is set as the first reference voltage value. In the above-mentioned OFF fault determination process, the value corresponding to the inter-terminal voltage of the DC link capacitor that is charged by the charge from the above-mentioned energy storage device is set as the third reference voltage value.

3. The power conversion unit according to claim 1, characterized in that, have: A capacitive load, which is connected to the second terminal pair mentioned above. When the control unit performs the diagnostic process without connecting the energy storage device to the second terminal pair, If the aforementioned reverse current prevention switch is functioning correctly, then, in a state where current is allowed to flow from the aforementioned DC link capacitor toward the aforementioned second terminal pair, after performing the first pre-processing to charge the aforementioned DC link capacitor by activating the aforementioned power conversion circuit, If the aforementioned reverse current prevention switch is functioning correctly, then, in a state where current flow from the second terminal pair towards the DC link capacitor is not permitted, a second pre-processing step is performed to stop the operation of the power conversion circuit and discharge the DC link capacitor. In the above-mentioned ON fault determination process, the value corresponding to the inter-terminal voltage of the DC link capacitor in the first preprocessing is set as the second reference voltage value. In the above-mentioned OFF fault determination process, the value corresponding to the inter-terminal voltage of the above-mentioned capacitive load in the discharge end state is set as the above-mentioned fourth reference voltage value.

4. The power conversion unit according to any one of claims 1 to 3, characterized in that, Multiple backflow prevention switches are connected in parallel as described above. It has at least one temperature sensor that detects the temperature of multiple backflow prevention switches mentioned above.

Images