JP2026023601A - Power Conversion Device - Google Patents

Abstract

The present invention is directed to a power conversion device that can be made smaller, lighter, and less expensive by determining whether or not a voltage detector is abnormal without providing a dedicated voltage detector and improving the reliability of the power conversion device.
[Solution] The power conversion device includes a power conversion circuit having multiple legs in which a positive-side switching element and a negative-side switching element are connected in series and each leg has an external connection point connected to the field winding of a rotating electric machine, a charging terminal connected to at least one of the external connection points, a power supply voltage detector, a power conversion circuit voltage detector, a charging terminal voltage detector, and a control unit that controls the power conversion circuit and, when diagnosing a fault, turns on the positive-side switching element of the leg having the external connection point to which the charging switch is connected, turns off all other switching elements of the power conversion circuit, and compares two each of the power supply voltage, power conversion circuit voltage, and charging terminal voltage to determine whether or not there is an abnormality.
[Selected Figure] Figure 1

Description

This disclosure relates to a power conversion device.

In recent years, plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs) have become popular. These electric vehicles run by converting the power stored in a DC power source (also called a battery) into the rotational force of a rotating electric machine using a power conversion device. Electric motors and generators are collectively called rotating electric machines. Common power conversion devices that convert the power output form and control rotating electric machines include an AC/DC (Alternating Current/Direct Current) converter, which converts AC power to DC power, and an inverter, which converts DC power to AC power. The power conversion devices that control these rotating electric machines often include semiconductor switching elements.

Electric vehicles need to be charged using a DC power supply installed on the vehicle. Charging is typically done by connecting the charger directly to the DC power supply. However, if the rated voltage of the DC power supply is higher than the supply voltage of the charger, a problem occurs in which the DC power supply cannot be charged. This problem also arises when high-performance vehicles with higher-voltage DC power supplies appear, causing a mismatch with the specifications of existing charging equipment.

In such cases, a technology has been disclosed that uses the coil of a rotating electrical machine connected to a power conversion device to boost the charger's output and charge a DC power source with high voltage (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2021-175363

In the technology disclosed in Patent Document 1, when the coils of each phase of a rotating electric machine are driven by a power conversion device, it is essential to detect the DC voltage applied to the power conversion circuit. Detecting the DC voltage applied to the power conversion circuit is extremely important in order to control the rotating electric machine according to the required torque, required rotation speed, required current, etc.

Assuming that the voltage detector that detects the DC voltage applied to the power conversion circuit is normal, the power conversion device drives the coil of the rotating electric machine and boosts the charger voltage to charge the vehicle's DC power supply. However, Patent Document 1 does not disclose a method for determining whether or not there is an abnormality in this voltage detector. One way to determine whether or not there is an abnormality in the voltage detector is to install a new voltage detector and verify the reliability of voltage detection, but this method leads to an increase in the size, weight, and cost of the power conversion device.

The present disclosure has been made to solve the above-mentioned problems. It aims to provide a new voltage detector in a rechargeable electric vehicle to determine whether or not there is an abnormality in the voltage detector that detects the DC voltage applied to the power conversion circuit, and to determine whether or not there is an abnormality in the voltage detector without providing new wiring for this purpose, thereby improving the reliability of the power conversion device while also improving the maintainability, size, weight, and cost of the power conversion device.

The power conversion device according to the present disclosure comprises:
a positive busbar connected to the positive side of the DC power supply;
a negative busbar connected to the negative side of the DC power supply;
a power conversion circuit having a plurality of legs each provided with a positive-side switching element connected to a positive-side bus and having an anti-parallel-connected diode, a negative-side switching element connected to a negative-side bus and having an anti-parallel-connected diode, and an external connection point connecting the positive-side switching element and the negative-side switching element in series and connected to a field winding of a rotating electric machine;
a positive-side charging terminal connected to at least one of the external connection points of the power conversion circuit via a charging switch;
a negative charging terminal connected to the negative bus;
a power supply voltage detector for detecting the voltage of a DC power supply;
a power conversion circuit voltage detector for detecting a voltage between the positive and negative poles of the power conversion circuit;
a charging terminal voltage detector for detecting the voltage between the positive charging terminal and the negative charging terminal;
The power conversion circuit is controlled to drive or stop the rotating electric machine, and when performing a fault diagnosis, the control unit turns on the positive side switching element of the leg having the external connection point to which the charging switch is connected, turns off all other switching elements of the power conversion circuit, turns on the charging switch, compares two by two of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector, and if the difference between the two compared voltages is within a predetermined voltage difference, determines that both of the two voltage detectors that detected the two compared voltages are normal, if the difference between the two compared voltages is greater than the predetermined voltage difference, determines that one of the two voltage detectors that detected the two compared voltages is abnormal, and if none of the voltage detectors is determined to be abnormal, determines that all three voltage detectors are normal, and if any of the voltage detectors is determined to be abnormal, determines that the voltage detector that was not determined to be normal is abnormal.

The power conversion device disclosed herein makes it possible to determine whether or not there is an abnormality in the voltage detector that detects the DC voltage applied to the power conversion circuit, using the detected value of a charging terminal voltage detector provided on the charging terminal side to which a charger is connected to charge the DC power source, or a power supply voltage detector provided on the DC power source side. This makes it possible to determine whether or not there is an abnormality in the voltage detector that detects the DC voltage applied to the power conversion circuit in a rechargeable electric vehicle, without having to provide a new voltage detector to determine whether there is an abnormality, and without providing new wiring for that purpose. This makes it possible to improve the reliability of the power conversion device, while also improving its maintainability, making it smaller, lighter, and less expensive.

1 is a configuration diagram of a power conversion device according to a first embodiment; 2 is a hardware configuration diagram of a control unit of the power conversion device according to the first embodiment. FIG. FIG. 10 is a configuration diagram of a power conversion device according to a second embodiment. FIG. 10 is a configuration diagram of a power conversion device according to a third embodiment. FIG. 10 is a configuration diagram of a power conversion device according to a fourth embodiment. FIG. 10 is a configuration diagram of a power conversion device according to a fifth embodiment.

A power conversion device according to an embodiment of the present disclosure will be described using the drawings. The drawings are schematic, and for the sake of convenience, some components have been omitted or simplified. Furthermore, the relative sizes and positions of components shown in different drawings are not necessarily accurately depicted and may be changed as appropriate. In the following description, similar components will be denoted with the same reference numerals, and their names and functions will also be similar. Therefore, detailed descriptions of these components may be omitted to avoid duplication.

1. First Embodiment
<Configuration of power conversion device>
Fig. 1 is a configuration diagram of a power conversion device 100 according to the present disclosure. The power conversion device 100 shown in Fig. 1 is mounted on a chargeable electric vehicle and includes an inverter 2, a control unit 20, a switch 4, and a capacitor 22. The inverter 2 is also referred to as a power conversion circuit. The power conversion device 100 is connected to a DC power source 1, a rotating electric machine 3, and a charger 5. The inverter 2 may include the capacitor 22.

A power switch 30 called a contactor may be connected between the DC power source 1 and the inverter 2. When the power conversion device 100 is driving or stopping the rotating electric machine 3, or when the DC power source 1 is charging, the power switch 30 is in the on (conducting) state. A charging switch or the like may also be connected before the positive charging terminal 44a of the switch 4. In this case, the charging switch is in the on (conducting) state when the DC power source 1 is charging. The power switch 30 may be omitted, and the DC power source 1 and inverter 2 may be directly connected.

<Rotating electric machines>
The rotating electric machine 3 is a concept that includes an electric motor (motor) and a generator (electric power generator). The rotating electric machine 3 connected to the power conversion device 100 according to the first embodiment may be interpreted as an electric motor or a generator. The rotating electric machine 3 having the functions of both an electric motor and a generator can convert electric power into driving force for power running, and can also convert the driving force back into electric power for regenerative operation with the same structure. The electric motor and the generator have basically the same structure, and both can be operated in power running and regenerative operation.

In Figure 1, the rotating electric machine 3 is shown as a three-phase AC rotating electric machine having a U-phase coil 17, a V-phase coil 18, and a W-phase coil 19 as field windings. A rotating electric machine with two phases or more than three phases may also be used. While Figure 1 shows the rotating electric machine 3 as being star-connected, it may also be delta-connected.

Normally, the power conversion device 100 converts the power supplied from the DC power source 1 into the rotational force of the rotating electric machine 3 to drive the electric vehicle. Furthermore, when the vehicle decelerates, the regenerative power generated by the rotating electric machine 3 is fed into the DC power source 1 to charge it.

<Switch>
To charge the DC power supply 1 mounted on an electric vehicle, the electric vehicle is parked at a charging station and a charger 5 is connected (the charger 5 is not shown in FIG. 1 but is shown in FIG. 3). When charging, the charger 5 is connected to the positive charging terminal 44a and negative charging terminal 44b of the switch 4. The negative charging terminal 44b is connected to the negative bus 1b. The switch 4 is equipped with a capacitor 23 connected to the positive charging terminal 44a and negative charging terminal 44b, a charging terminal voltage detector 7 that detects the charging terminal voltage V3 between the positive charging terminal 44a and negative charging terminal 44b, and a charging switch 29 that switches between connection and disconnection of the positive charging terminal 44a.

When charging the DC power supply 1 of an electric vehicle, it is important to monitor the charging terminal voltage V3. This is because there is a concern that supplying charging power exceeding the rated capacity may cause deterioration of the charger, that rapid charging is not possible unless sufficient current is supplied, and that excessive charging of a saturated DC power supply 1 may cause deterioration of the DC power supply 1. Therefore, the charging terminal voltage detector 7 is an essential detector when charging an electric vehicle.

Information about the charging terminal voltage V3 detected by the charging terminal voltage detector 7 is input to the control unit 20. The charging terminal voltage detector 7 does not need to be built into the switch 4. It is sufficient if it can detect the voltage applied to the line section between the positive charging terminal 44a and the charging switch 29, or the line section between the charging switch 29 and the inverter 2, and the negative bus.

By operating the inverter 2 and the switch 4, the current supplied from the charger 5 flows into the DC power supply 1, causing it to charge. When the charger 5 is not connected, power is supplied from the DC power supply 1 to the rotating electric machine 3 via the inverter 2. At that time, the switch 4 is not operating and is open.

In Figure 1, the switch 4 is connected to the connection wire connecting the inverter 2 and the W-phase coil of the rotating electric machine 3. However, this connection does not have to be the connection wire connecting the W-phase coil, and it may be connected to the connection wire connecting the U-phase and V-phase coils. Furthermore, the connection wire between the switch 4 and the inverter 2 does not have to be one, but may be two or three. Furthermore, if the number of phases of the coils of the rotating electric machine 3 is more than three, the number of connection wires from the switch 4 may also be more than three.

<DC power supply>
The DC power supply 1 is provided with a power supply voltage detector 21 that detects a power supply voltage V1 of the DC power supply 1. The DC power supply 1 may be provided with a power supply current detector 24. The power supply current detector 24 detects, as a power supply current Ib, an outflow current when a current is supplied from the DC power supply 1 and an inflow current when the DC power supply 1 is charged (the power supply current detector 24 and the power supply current Ib are not shown).

When charging the DC power supply 1, rapid charging may be required in a short period of time, so it is also possible to monitor the power supply voltage V1 and power supply current Ib. Rapid charging is not possible without sufficient current supply, and excessive charging of a saturated DC power supply 1 may cause deterioration of the DC power supply 1. Furthermore, since the driving distance of an electric vehicle varies depending on the remaining amount of DC power, it is useful to monitor the power supply voltage V1 and power supply current Ib of the DC power supply 1. For this reason, a power supply current detector 24 and a power supply voltage detector 21 are often provided in rechargeable electric vehicles.

Information about the power supply current Ib detected by the power supply current detector 24 and the power supply voltage V1 detected by the power supply voltage detector 21 is input to the control unit 20. The power supply voltage detector 21 does not need to be provided in the DC power supply 1. It may be provided so that it can detect the voltage applied to the line section between the DC power supply 1 and the inverter 2 and the negative busbar. Also, a shunt resistor may be provided in each switching element to detect the current. Furthermore, the information detected by the power supply current detector 24 and the power supply voltage detector 21 does not need to be input directly to the control unit 20, but may be input via another control device or communication device.

<Power conversion circuit>
The power conversion device 100 includes a capacitor 22 connected between a positive bus 1a and a negative bus 1b on the input side of an inverter 2, and a power conversion circuit voltage detector 6 that detects a power conversion circuit voltage V2 applied to the inverter 2. The inverter 2 is a power conversion circuit including a plurality of switching elements 8 to 13. The inverter 2 performs DC/AC power conversion. Phase currents flow through three connection lines connecting the inverter 2 to the coils of a rotating electric machine 3. Phase current detectors 14, 15, and 16 that detect the phase currents detect phase currents Iu, Iv, and Iw of the U, V, and W phases (phase currents Iu, Iv, and Iw are not shown). Information on the phase currents Iu, Iv, and Iw of each phase detected by the phase current detectors 14, 15, and 16 is input to a control unit 20.

The control unit 20 performs drive control to switch the switching elements 8 to 13 on (conducting) and off (blocking). The phase current detectors 14, 15, and 16 may be provided outside the power conversion device. Alternatively, the phase current detectors 14, 15, and 16 may be provided within the rotating electric machine 3. The phase current detectors that detect the phase currents Iu, Iv, and Iw are configured using, for example, shunt resistors. The phase current detectors 14 to 16 may also be phase current detectors that use Hall elements, etc.

The power conversion circuit voltage detector 6, which detects the power conversion circuit voltage V2 applied to the inverter 2, and the phase current detectors 14 to 16, which detect the phase currents Iu, Iv, and Iw, are extremely important for controlling the rotating electric machine 3 according to the required torque, required rotation speed, required current, etc. The power conversion device 100 drives the inverter 2 based on the power conversion circuit voltage V2 applied to the inverter 2. Therefore, it is necessary to verify the validity of the detected value of the power conversion circuit voltage detector 6. One way to determine whether the power conversion circuit voltage detector 6 is normal or abnormal is to install an additional voltage detector and verify the reliability of the voltage detection. However, this approach leads to an increase in the size, weight, and cost of the device.

We therefore investigated a method for determining abnormalities in the power conversion circuit voltage detector 6 using a power supply voltage detector 21 and a charging terminal voltage detector 7 installed in a rechargeable electric vehicle. This will improve the reliability of the power conversion device while also enabling it to be easier to maintain, smaller, lighter, and less expensive.

<Switching element>
The inverter 2 is a power conversion circuit in which six switching elements 8 to 13 are connected in a full bridge configuration. The inverter 2 is provided with positive-side switching elements 8, 9, and 10 connected to a positive-side bus 1a of the DC power supply 1 and having positive-side diodes connected in anti-parallel. The inverter 2 is provided with negative-side switching elements 11, 12, and 13 connected to a negative-side bus 1b of the DC power supply 1 and having negative-side diodes connected in anti-parallel. The switching elements 8, 11, the switching elements 9, 12, and the switching elements 10, 13 form three legs in which a positive-side (upper-stage) switching element and a negative-side (lower-stage) switching element are connected in series, and are connected in parallel to the DC power supply 1. The positive-side switching elements 8, 9, and 10 and the negative-side switching elements 11, 12, and 13 are connected in series via external connection points, respectively.

The external connection points of switching elements 8 and 11 are connected to the U-phase coil 17 of the rotating electric machine 3. The external connection points of switching elements 9 and 12 are connected to the V-phase coil 18 of the rotating electric machine 3. The external connection points of switching elements 10 and 13 are connected to the W-phase coil 19 of the rotating electric machine 3.

Switching elements 8 to 13 are each semiconductors. For example, switching elements 8 to 13 may be configured with an IGBT (Insulated Gate Bipolar Transistor) and a diode connected in anti-parallel between the emitter and collector of the IGBT. The type and number of switching elements are not limited to this. In addition to the combination of an IGBT and an anti-parallel diode, one or more switching elements may be used, such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) with a built-in parasitic diode between the source and drain, or a SiC-MOSFET using SiC (Silicon Carbide).

Figure 1 shows an example in which only the W phase of the three-phase connection wires (U, V, and W phases) that run from the inverter 2 to the coils 17, 18, and 19 of the rotating electric machine 3 is connected to the switch 4. After the charging terminal voltage detector 7 detects that the charger 5 has been connected to the positive charging terminal 44a and the negative charging terminal 44b, the control unit 20 operates the charging switch 29 of the switch 4 to turn it on. The U, V, and W phase coils of the rotating electric machine 3 are star-connected, with the neutral point floating.

The charging switch 29 of the switch 4 may be a diode, a semiconductor such as an IGBT, or a relay. A capacitor 23 is provided at the positive charging terminal 44a and the negative charging terminal 44b to which the charger is connected, to reduce the ripple voltage of the charger and to prevent momentary power outages.

By providing a charging switch 29 for the switch 4, when the rotating electric machine 3 is in power running or regenerative operation, the charging switch 29 can be turned off to disconnect the capacitor 23 and the positive charging terminal 44a from the external connection point of the inverter 2. This prevents current from flowing through the capacitor 23 for the switch 4, thereby reducing power loss caused by this current flow.

<Hardware configuration of the control unit>
2 is a hardware configuration diagram of the control unit 20 of the power conversion device 100 according to the first embodiment. In this embodiment, the control unit 20 is a control device that controls the power conversion device 100. Each function of the control unit 20 is realized by a processing circuit provided in the control unit 20. Specifically, the control unit 20 includes, as processing circuits, an arithmetic processing device 90 (computer) such as a CPU (Central Processing Unit), a storage device 91 that exchanges data with the arithmetic processing device 90, an input circuit 92 that inputs external signals to the arithmetic processing device 90, and an output circuit 93 that outputs signals from the arithmetic processing device 90 to the outside.

The arithmetic processing device 90 may be an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, various signal processing circuits, etc. Furthermore, multiple arithmetic processing devices 90 of the same or different types may be provided, with each device sharing the responsibility of executing various processes. The storage device 91 may be a RAM (Random Access Memory) configured to be able to read and write data from the arithmetic processing device 90, or a ROM (Read Only Memory) configured to be able to read data from the arithmetic processing device 90. The input circuit 92 is connected to various sensors and switches, and includes interface circuits such as an AD conversion unit and input circuit that inputs output signals from these sensors and switches to the arithmetic processing device 90. The input circuit 92 may be connected to a power supply voltage detector 21, a power conversion circuit voltage detector 6, a charging terminal voltage detector 7, a charging voltage detector 32, phase current detectors 14 to 16, switch temperature detectors 41 and 42, and switching element temperature detectors 49 to 52. The output circuit 93 is connected to electrical loads such as switching elements and actuators, and includes interface circuits such as a drive circuit and a communication circuit that converts and outputs output signals from the arithmetic processing unit 90 to these electrical loads. The output circuit 93 may also be connected to switching elements 8 to 13, charging switches 28 and 29, a power switch 30, a charging current limit switch 62, and the like.

The functions of the control unit 20 are realized by the arithmetic processing device 90 executing software (programs) stored in a storage device 91 such as a ROM, and working in cooperation with other hardware of the control unit 20, such as the storage device 91, input circuitry 92, and output circuitry 93. Setting data such as thresholds and judgment values used by the control unit 20 is stored in the storage device 91 such as a ROM as part of the software (programs).

Each function implemented within the control unit 20 may be configured as a software module. Each function may also be configured as a combination of software and hardware.

<Normal power conversion operation>
Consider a normal case where the rotating electric machine 3 is driven or stopped by the power conversion device 100. This is the case where the charger 5 is not connected to the positive charging terminal 44a and the negative charging terminal 44b of the switch 4, and charging is not being performed.

In this case, the power switch 30 is on (conducting) and the charging switch 29 is off (shutoff). The inverter 2 receives power from the DC power supply 1 and turns on, off, or stops driving the switching elements 8 to 13. At this time, the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6 is approximately equal to the power supply voltage V1 detected by the power supply voltage detector 21. By comparing the power conversion circuit voltage V2 with the power supply voltage V1, if the voltage difference is less than a predetermined voltage difference ΔV, it can be determined that both the power conversion circuit voltage detector 6 and the power supply voltage detector 21 are normal (voltage difference ΔV is not shown). If the voltage difference is greater than the predetermined voltage difference ΔV, it can be determined that either the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is abnormal. In other words, it is possible to determine whether the power conversion circuit voltage detector 6 is normal or abnormal, i.e., to perform a fault diagnosis, without installing a new voltage detector.

<Charging control>
Consider a case where charger 5 is connected to positive charging terminal 44a and negative charging terminal 44b of switch 4, and charging of DC power supply 1 is initiated. Depending on the magnitude relationship between power supply voltage V1 and charging terminal voltage V3, the charging can be classified into boost charging and direct charging.

<Direct charging (when V1≦V3)>
The power supply voltage V1 detected by the power supply voltage detector 21 is compared with the charging terminal voltage V3 detected by the charging terminal voltage detector 7. When the charger 5 is connected to the switch 4, the charging switch 29 is on, and V1≦V3, current flows through the diode of the positive-side switching element 10, bypassing the coil of the rotating electric machine 3. Therefore, the DC power supply 1 is charged by the charging terminal voltage V3 transmitted from the charger 5. This is referred to as direct charging. Whether direct charging is currently being performed can also be determined by the current flowing through the phase current detector 16 connected to the leg to which the charging switch 29 is connected (the W-phase leg in FIG. 1 ). If current flows from the external connection point to which the charging switch 29 is connected (to which the coil 19 of the rotating electric machine 3 is connected) toward the leg, it can be determined that direct charging is being performed. If current does not flow from the external connection point to which the charging switch 29 is connected toward the leg, it can be determined that direct charging is not being performed.

In this case, if a MOSFET is used as the switching element, the positive side switching element 10 can be turned on to allow current to flow without passing through the diode connected inversely in parallel to the switching element. This prevents current from concentrating in the diode. Furthermore, when a MOSFET is used, the on-resistance is small, so the voltage drop is smaller than the forward voltage drop when current flows through the diode. As a result, the accuracy of abnormality detection can be improved when comparing the charging terminal voltage V3 and the power conversion circuit voltage V2. Furthermore, by preventing current from concentrating in the diode, overheating of semiconductor components can be prevented.

Let's consider a case where a MOSFET is used as the switching element, the charging switch 29 of the switch 4 is turned on, the positive side switching element 10 is conductive, and charging is performed from the charger 5 to the DC power supply 1. Current flows from the charger 5 to the DC power supply 1 via the positive side charging terminal 44a, the charging switch 29, and the positive side switching element 10. At this time, the charging terminal voltage V3 is detected by the charging terminal voltage detector 7.

<<Comparison of V1, V2, and V3>>
At this time, comparison is performed after the current flowing from the charger 5 to the DC power supply 1 has stabilized and the voltage values of the charging terminal voltage V3, the power conversion circuit voltage V2, and the power supply voltage V1 have stabilized. Comparison of each voltage may be started after the voltage changes ΔV3, ΔV2, and ΔV1, which represent the changes per unit time of the charging terminal voltage V3, the power conversion circuit voltage V2, and the power supply voltage V1, have become smaller than a predetermined voltage change threshold ΔVth (the voltage changes ΔV1, ΔV2, ΔV3, and the voltage change threshold ΔVth are not shown). The power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6, the power supply voltage V1 detected by the power supply voltage detector 21, and the charging terminal voltage V3 detected by the charging terminal voltage detector 7 are compared with each other. Two of the three voltage values are compared, and if the voltage difference is within the predetermined voltage difference ΔV, both of the two voltage detectors that detected the two compared voltages are determined to be normal. If the difference between the two compared voltages is greater than a predetermined voltage difference ΔV, it is determined that one of the two voltage detectors that detected the two compared voltages is abnormal.

Two of the three voltage detectors are compared, and if none of the voltage detectors are judged to be abnormal, it is determined that all three voltage detectors are normal. If any voltage detector is judged to be abnormal, it is possible to identify the voltage detector that is not judged to be normal as being abnormal.

Since the on-voltage of the positive-side switching element 10 is smaller than the forward voltage of the anti-parallel diode of the positive-side switching element 10 in the off state, it is thought that current flows only through the positive-side switching element 10. However, when all positive-side switching elements are off, current flows through the diode of the positive-side switching element 10. Therefore, the voltage difference between the power conversion circuit voltage V2 and the charging terminal voltage V3 is affected by the diode voltage drop due to changes in the conductive/cut-off state of the positive-side switching element 10. This effect can be eliminated by setting the specified voltage difference ΔV taking into account the effect of the diode voltage drop.

In this way, an abnormal current detector can be identified by majority rule. When charging the DC power supply 1 of a rechargeable electric vehicle from the charger 5, the charging current Ic, charging terminal voltage V3, power supply current Ib, and power supply voltage V1 are often mutually monitored and their integrity is confirmed. Therefore, if it is determined that there is an abnormality in either the power supply voltage V1 or the power conversion circuit voltage V2, or if it is determined that there is an abnormality in either the power conversion circuit voltage V2 or the charging terminal voltage V3, it may be determined that there is an abnormality in the power conversion circuit voltage detector 6 that detects the power conversion circuit voltage V2.

<Boost charging (when V1 >V3)>
The power supply voltage V1, which is the value detected by the power supply voltage detector 21, is compared with the charging terminal voltage V3, which is the value detected by the charging terminal voltage detector 7. If the charger 5 is connected to the switch 4 via the positive charging terminal 44a and the negative charging terminal 44b, the charging switch 29 is on, and the power supply voltage V1 is greater than the charging terminal voltage V3, boost charging is performed.

<<On/Off of Negative-Side Switching Element 11>>
The control unit 20 turns on, for example, the switching element 11 on the negative electrode side of the inverter 2. Current flows through the coils 17 and 19 of the rotating electric machine 3, and magnetic energy is accumulated. Next, when the switching element 11 on the negative electrode side of the inverter 2 is turned off, current flows through the diode of the switching element 8 on the positive electrode side of the inverter 2. Therefore, the voltage of the charger 5 is boosted by the magnetic energy accumulated in the coils 17 and 19 of the rotating electric machine 3, and is smoothed by the capacitor 22. By continuing to turn on and off the switching element 11 on the negative electrode side, the DC power supply 1 is charged from the charger 5.

This process of repeatedly energizing and de-energizing the coil of the rotating electric machine 3 to boost the voltage of the charger 5 and charge the DC power source 1 is called boost charging. When boost charging is being performed, no current flows through the leg to which the charging switch 29 is connected (the W-phase leg in Figure 1). Therefore, the detected current of the phase current detector 16 to which the charging switch 29 is connected is zero. Current flows through the negative-side switching element 11, which is repeatedly energized and de-energized, from the U-phase coil 17 of the rotating electric machine 3 toward the leg (the U-phase leg in Figure 1). Therefore, the U-phase phase current detector 14 can detect the current flowing from the coil 17 toward the U-phase leg. In this way, it is possible to determine whether boost charging is currently being performed based on the current detected by the phase current detector 16 of the leg to which the charging switch 29 is connected and the phase current detector 14 to which the negative-side switching element 11, which is repeatedly energized and de-energized, is connected. The same applies when the negative-side switching element 12, instead of the negative-side switching element 11, repeatedly turns on and off.

At this time, the boosted voltage becomes the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6, and if the power conversion circuit voltage detector 6 is normal, it will be approximately equal to the power supply voltage V1 detected by the power supply voltage detector 21. By comparing the power conversion circuit voltage V2 with the power supply voltage V1, if the voltage difference is less than a predetermined voltage difference ΔV, it can be determined that both the power conversion circuit voltage detector 6 and the power supply voltage detector 21 are normal. If the voltage difference is greater than the predetermined voltage difference ΔV, it can be determined that either the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is abnormal.

<<Turning ON/OFF the negative pole side switching element 12>>
In contrast to the above, when the control unit 20 turns on the negative-side switching element 12 of the inverter 2, current flows through the coils 18 and 19 of the rotating electric machine, and magnetic energy is accumulated. Next, when the negative-side switching element 12 of the inverter 2 is turned off, current flows through the diode of the positive-side switching element 9 of the inverter 2. Therefore, the voltage of the charger 5 is boosted by the magnetic energy accumulated in the coils 18 and 19 of the rotating electric machine 3, and is smoothed by the capacitor 22. By continuing to turn on and off the negative-side switching element 12, the DC power supply 1 is charged from the charger 5.

At this time, the boosted voltage becomes the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6, and if the power conversion circuit voltage detector 6 is normal, it will be approximately equal to the power supply voltage V1 detected by the power supply voltage detector 21. By comparing the power conversion circuit voltage V2 with the power supply voltage V1, if the voltage difference is less than a predetermined voltage difference ΔV, it can be determined that both the power conversion circuit voltage detector 6 and the power supply voltage detector 21 are normal. If the voltage difference is greater than the predetermined voltage difference ΔV, it can be determined that either the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is abnormal.

In this way, by controlling the switching of the negative-side switching element 11 or 12 of the inverter 2, a boost circuit can be formed using the coil of the rotating electric machine 3. The above example shows the case where the switching of the negative-side switching element 11 or 12 of the inverter 2 is independently controlled.

<<Driving a plurality of negative-side switching elements>>
However, the switching elements on the negative side of the phase not connected to the switch 4, specifically the switching elements 11 and 12, may be simultaneously switched. In this way, the current is shunted, thereby reducing the heat generated by the switching elements.

Furthermore, taking into account the temperature rise caused by energizing the switching elements and the coils, it is possible to implement interleaved control, in which the switching elements 11 and 12 of the inverter 2 are alternately switched. In this way, the switching elements 11 and 12 and the coils 17 and 18 of the rotating electric machine are alternately energized, thereby reducing the temperature rise.

Even in this case, the boosted voltage becomes the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6, and if the power conversion circuit voltage detector 6 is normal, it will be approximately equal to the power supply voltage V1 detected by the power supply voltage detector 21. By comparing the power conversion circuit voltage V2 with the power supply voltage V1, if the voltage difference is less than or equal to a predetermined voltage difference ΔV, it can be determined that both the power conversion circuit voltage detector 6 and the power supply voltage detector 21 are normal. If the voltage difference is greater than the predetermined voltage difference ΔV, it can be determined that either the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is abnormal.

<Identifying the voltage detector with a malfunction>
As described above, it is possible to determine whether the power conversion circuit voltage detector 6 is normal or abnormal, i.e., to perform a fault diagnosis, without providing a new voltage detector or new wiring for that purpose. During normal power conversion operation and when boost charging is being performed, the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6 can be compared with the power supply voltage V1 detected by the power supply voltage detector 21, and by comparing the voltage difference with a predetermined voltage difference ΔV, it is possible to determine whether both are normal or whether one is abnormal. However, if the voltage difference is greater than the predetermined voltage difference ΔV, it is only possible to determine that either the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is abnormal, and it is not possible to identify which voltage detector is abnormal.

Therefore, if either of these is abnormal, the charging switch 29 of the switch 4 is turned on and the positive side switching element 10 is turned on, regardless of the magnitude relationship between the power supply voltage V1 and the charging terminal voltage V3. When the charging switch 29 is turned on, the negative side switching elements of all phases are turned off, resulting in the direct charging state described above. At this time, consider the case where the charger 5 is not connected to the positive side charging terminal 44a and the negative side charging terminal 44b of the switch 4.

<Fault diagnosis when the charger is not connected>
The procedure for determining whether the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is malfunctioning when the charger 5 is not connected will be described. It is possible to determine whether the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is malfunctioning by using the charging terminal voltage V3, which is the detected value of the charging terminal voltage detector 7. By turning on the charging switch 29 and the positive-side switching element 10 of the W-phase leg to which the charging switch 29 is connected, the positive bus 1a and the positive-side charging terminal 44a of the switch 4 can be electrically connected. As a result, after the capacitor 23 is discharged or charged, the power supply voltage V1, the power conversion circuit voltage V2, and the charging terminal voltage V3 become approximately the same value. Comparison of the voltages may be started after a voltage change ΔV3, which represents the change in the charging terminal voltage V3 per unit time, becomes smaller than a predetermined voltage change threshold ΔVth (voltage change ΔV3 is not shown).

<<Comparison of V1, V2, and V3>>
At this time, the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6, the power supply voltage V1 detected by the power supply voltage detector 21, and the charging terminal voltage V3 detected by the charging terminal voltage detector 7 are compared with each other. Two of the three voltage values are compared, and if the difference between the two compared voltages is within a predetermined voltage difference ΔV, both of the two voltage detectors that detected the two compared voltages are determined to be normal. If the difference between the two compared voltages is greater than the predetermined voltage difference ΔV, one of the two voltage detectors that detected the two compared voltages is determined to be abnormal.

Two of the three voltage detectors are compared, and if none of the voltage detectors are judged to be abnormal, it is determined that all three voltage detectors are normal. If any voltage detector is judged to be abnormal, it is possible to identify the voltage detector that is not judged to be normal as being abnormal.

This makes it possible to determine whether the power conversion circuit voltage detector 6, which detects the DC voltage applied to the inverter 2 in a chargeable electric vehicle, is abnormal without providing a new voltage detector to determine whether it is abnormal. This improves the reliability of the power conversion device 100, while also improving the maintainability, size, weight, and cost of the power conversion device 100. Furthermore, when the charging terminal voltage detector 7 detects the charging terminal voltage V3, there is no need to energize the coils 17 to 19 of the rotating electric machine 3. Therefore, the coils 17 to 19 do not heat up, and power consumption does not increase. Furthermore, there is no need to provide a rotating electric machine with a switch and connection terminal at the neutral point of the coil.

<Transient current detection>
Here, we will explain a method for more quickly determining whether the power conversion circuit voltage detector 6 is normal or abnormal. In this method, the voltage of the capacitor 22 is estimated based on the phase current Iw detected by the phase current detector 16, and is compared with the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6.

During normal power conversion operation and when boost charging is being performed, the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6 can be compared with the power supply voltage V1 detected by the power supply voltage detector 21. The voltage difference can then be compared with a predetermined voltage difference ΔV to determine whether both are normal or whether one is abnormal.

If the voltage difference between the power conversion circuit voltage V2 and the power supply voltage V1 is greater than the predetermined voltage difference ΔV, either the power conversion circuit voltage V2 or the power supply voltage V1 is abnormal. In this case, the power switch 30 is turned off to disconnect the DC power supply 1 from the power conversion device 100. Then, the charge switch 29 is turned on, the positive-side switching element 10 of the inverter 2 is turned on, and all other switching elements 8, 9, 11-13 are turned off. In this way, the phase current Iw passes through the phase current detector 16 so that the potential of capacitor 23 and the potential of capacitor 22 are balanced.

Therefore, the predicted voltage change value ΔVPC22 of capacitor 22 can be calculated based on the phase current Iw, the elapsed time, and the capacitance of capacitor 22. The voltage change measured value ΔVC22 obtained from the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6 is compared with the voltage change predicted value ΔVPC22. By comparing the voltage change measured value ΔVC22 with the voltage change predicted value ΔVPC22, if the difference in the voltage change is greater than a predetermined voltage change difference ΔVCd22, it can be determined that the power conversion circuit voltage detector 6 is abnormal. If the difference in the voltage change is equal to or less than the predetermined voltage change difference ΔVCd22, it may be determined that the power conversion circuit voltage detector 6 is normal (the voltage change measured value ΔVC22, voltage change predicted value ΔVPC22, and voltage change difference ΔVCd22 are not shown). Furthermore, if the voltage difference between the power conversion circuit voltage V2 and the power supply voltage V1 is greater than the predetermined voltage difference ΔV, then either the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is abnormal, and in this case, it is possible to identify the abnormality in the power supply voltage detector 21.

In this way, the transient voltage change of capacitor 22 can be confirmed, and the normality of the power conversion circuit voltage detector 6 can be quickly determined. That is, the transient change of the power conversion circuit voltage V2, which is the voltage of capacitor 22, is calculated as a predicted voltage change value ΔVPC22, and compared with the measured voltage change value ΔVC22, which is the change in the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6. It is then possible to determine whether the difference in voltage change is greater than a predetermined voltage change difference ΔVCd22 before the power conversion circuit voltage V2 and the charging terminal voltage V3 are balanced. This shortens the time required to determine whether the power conversion circuit voltage detector 6 is normal or abnormal.

2. Second Embodiment
<Configuration of power conversion device>
3 is a configuration diagram of a power conversion device 100 according to the second embodiment. The power conversion device 100 according to the second embodiment differs from the power conversion device 100 according to the first embodiment in that a charger 5 is connected to the positive-side charging terminal 44a and the negative-side charging terminal 44b. The hardware configuration of the power conversion device 100 according to the second embodiment is substantially the same as that of the power conversion device 100 according to the first embodiment, and can be realized by adding input signals such as a charging voltage detector 32 and modifying the software. The hardware configuration of the control unit 20 in FIG. 2 can also be applied to the second embodiment.

<Charger>
The charger 5 has a built-in DC power supply for charging. The charger 5 is provided with a charging voltage detector 32 that detects the charging power supply voltage V4 and a charging current detector 25 that detects the charging current Ic (the charging current detector 25 and the charging current Ic are not shown). The charger 5 is also provided with a backflow prevention diode 26 that prevents a reverse current flow when the voltage of the charging power supply of the charger 5 is lower than the voltage of the DC power supply 1 to which the power conversion device 100 is connected.

When charging the DC power supply 1 of an electric vehicle, it is necessary to supply a large current for rapid charging. For this reason, it is also possible to detect the charging current Ic and the charging power supply voltage V4.

This is because supplying charging power exceeding the rated capacity may cause deterioration of the charger 5, rapid charging is not possible unless sufficient current is supplied, and excessive charging of a saturated DC power supply 1 may cause deterioration of the DC power supply 1. Therefore, the charging voltage detector 32 and charging current detector 25 are useful when charging electric vehicles.

<Comparison between V3 and V4>
With the charger 5 connected, both the power switch 30 and the charging switch 29 are on (conducting) during charging. The charging terminal voltage V3 detected by the charging terminal voltage detector 7 is approximately equal to the charging power supply voltage V4 detected by the charging voltage detector 32. This is because current flows from the charger 5 toward the power conversion device 100, and power is transmitted to the DC power supply 1 by direct charging or boost charging. In this case, current flows from the charger 5 to the switch 4 of the power conversion device 100.

At this time, the charging terminal voltage V3 and the charging power supply voltage V4 are compared, and if the voltage difference is greater than a predetermined voltage difference ΔV, it can be determined that either the charging terminal voltage V3 or the charging power supply voltage V4 is abnormal. In this case, which voltage detector is abnormal is identified.

During fault diagnosis, the positive-side switching element 10 of the inverter 2 is turned on. The other switching elements 8, 9, 11-13 are turned off.

<Direct charging (when V1≦V4)>
The power supply voltage V1, which is the value detected by the power supply voltage detector 21, is compared with the charging power supply voltage V4, which is the value detected by the charging voltage detector 32. When the charger 5 is connected to the switch 4, the charging switch 29 is on, and V1≦V4, current flows through the diode of the positive-side switching element 10, not through the coil of the rotating electrical machine 3. Therefore, the DC power supply 1 is charged by the current transmitted from the connected charger 5.

In this case, if a MOSFET is used as the switching element, the positive switching element 10 can be turned on to allow current to flow without passing through the diode connected in anti-parallel to the switching element. This prevents current from concentrating in the diode. Furthermore, the voltage drop due to the on-resistance of the MOSFET is smaller than the forward voltage of the diode. This helps prevent overheating of semiconductor components. It also contributes to improving the accuracy of the comparison between the power conversion circuit voltage V2 and the charging terminal voltage V3.

Consider the case where a MOSFET is used as the switching element, the charging switch 29 of the switch 4 is turned on, the positive-side switching element 10 is conductive, and charging is performed from the charger 5 to the DC power supply 1. Current flows from the charger 5 to the DC power supply 1 via the positive-side charging terminal 44a, the charging switch 29, and the positive-side switching element 10. At this time, the charging power supply voltage V4, the charging terminal voltage V3, the power conversion circuit voltage V2, and the power supply voltage V1 balance and stabilize over time. Comparison of each voltage may begin once the voltage change amounts ΔV4, ΔV3, ΔV2, and ΔV1, which represent the change per unit time of the charging power supply voltage V4, the charging terminal voltage V3, the power conversion circuit voltage V2, and the power supply voltage V1, become smaller than a predetermined voltage change amount threshold ΔVth (voltage change amount ΔV4 is not shown).

<<Comparison of V1, V2, V3, and V4>>
At this time, the charging power supply voltage V4, charging terminal voltage V3, power conversion circuit voltage V2, and power supply voltage V1 are compared with one another. Two of the four voltage values are compared, and if the difference between the two compared voltages is within a predetermined voltage difference ΔV, both of the two voltage detectors that detected the two compared voltages are determined to be normal. If the difference between the two compared voltages is greater than the predetermined voltage difference ΔV, one of the two voltage detectors that detected the two compared voltages is determined to be abnormal.

If two of the four voltage detectors are compared and none of the voltage detectors are judged to be abnormal, it is determined that all four voltage detectors are normal. If any voltage detector is judged to be abnormal, it is possible to identify the voltage detector that is not judged to be normal as being abnormal.

In this way, an abnormal voltage detector can be identified by majority rule. Furthermore, when charging the DC power supply 1 of a rechargeable electric vehicle from the charger 5, the charging current Ic, charging power supply voltage V4, power supply current Ib, and power supply voltage V1 are often mutually monitored and their integrity is confirmed. Therefore, if the difference between the charging power supply voltage V4 or power supply voltage V1 and the power conversion circuit voltage V2 is greater than a predetermined voltage difference ΔV, it may be determined that there is an abnormality in the power conversion circuit voltage V2. Furthermore, when the charging terminal voltage detector 7 detects the charging terminal voltage V3, it is not necessary to energize the coils 17 to 19 of the rotating electric machine 3. As a result, the coils 17 to 19 do not heat up and power consumption does not increase. Furthermore, there is no need to provide a rotating electric machine with a switch and connection terminal at the coil's neutral point.

<Boost charging (when V1 >V4)>
The power supply voltage V1, which is the value detected by the power supply voltage detector 21, is compared with the charging power supply voltage V4, which is the value detected by the charging voltage detector 32. When the charger 5 is connected to the switch 4, the charging switch 29 is on, and V1>V4, the charger 5 is connected to the switch 4 via the positive charging terminal 44a and the negative charging terminal 44b, the charging switch 29 is turned on, and, for example, the negative switching element 11 is controlled on and off to perform boost charging.

Alternatively, the negative side switching element 11 is turned off and the negative side switching element 12 is controlled to be turned on and off. Alternatively, the negative side switching element 11 and the negative side switching element 12 are controlled to be turned on and off simultaneously or alternately.

As a result, the voltage of the charger 5 is boosted by the magnetic energy stored in coils 17 and 19, or coils 18 and 19, of the rotating electric machine 3, and smoothed by capacitor 22. By continuously turning on and off the negative-side switching element 11 or 12, or switching elements 11 and 12, the charger 5 charges the DC power supply 1.

At this time, the boosted voltage becomes the power conversion circuit voltage V2 detected by the power conversion circuit voltage detector 6, and if the power conversion circuit voltage detector 6 is normal, it will be approximately equal to the power supply voltage V1 detected by the power supply voltage detector 21. By comparing the power conversion circuit voltage V2 with the power supply voltage V1, if the voltage difference is less than a predetermined voltage difference ΔV, it can be determined that both the power conversion circuit voltage detector 6 and the power supply voltage detector 21 are normal. If the voltage difference is greater than the predetermined voltage difference ΔV, it can be determined that either the power conversion circuit voltage detector 6 or the power supply voltage detector 21 is abnormal.

Furthermore, when charging the DC power supply 1 of a rechargeable electric vehicle from the charger 5, the charging current Ic, charging power supply voltage V4, power supply current Ib, and power supply voltage V1 are often mutually monitored and their integrity is confirmed. Therefore, if the difference between power supply voltage V1 and power conversion circuit voltage V2 is greater than a predetermined voltage difference ΔV, it may be determined that there is an abnormality in the power conversion circuit voltage detector 6 that detects the power conversion circuit voltage V2. Similarly, it may also be determined that there is an abnormality in the charging terminal voltage detector 7 that detects the charging terminal voltage V3 by comparing the charging terminal voltage V3 with the charging power supply voltage V4 and finding that the voltage difference is greater than a predetermined voltage difference ΔV.

This eliminates the need to install a new voltage detector or new wiring to determine whether the power conversion circuit voltage detector 6, which detects the DC voltage applied to the inverter 2, or the charging terminal voltage detector 7, which detects the voltage between the positive charging terminal 44a and the negative charging terminal 44b, is malfunctioning in a chargeable electric vehicle. This makes it possible to determine whether the power conversion circuit voltage detector 6 or the charging terminal voltage detector 7 is malfunctioning. This improves the reliability of the power conversion device 100, while also enabling the device to be easier to maintain, smaller, lighter, and less expensive.

<Identifying an abnormal voltage detector during boost charging (when V1>V4)>
When the power supply voltage V1 is greater than the charging power supply voltage V4, in order to identify the voltage detector having an abnormality, the positive side switching element 10 of the inverter 2 is turned on (on), and the other switching elements 8, 9, 11 to 13 are turned off (off), and the charging switch 29 is turned on (on).

At this time, the current from the DC power supply 1 flows into the capacitor 23 of the switch 4 via the switching element 10. The power supply voltage V1, power conversion circuit voltage V2, and charging terminal voltage V3 are balanced, stabilizing the voltage. The charger 5 is equipped with a backflow prevention diode 26, so the charging power supply voltage V4 detected by the charging voltage detector 32 is not affected.

Two of the three voltage values (power supply voltage V1, power conversion circuit voltage V2, and charging terminal voltage V3) are compared, and if the voltage difference is within a specified voltage difference ΔV, both voltage detectors are determined to be normal. If the voltage difference is greater than the specified voltage difference ΔV, one of the voltage detectors whose voltage values were compared is determined to be abnormal.

Two of the three voltage detectors are compared, and if none of the voltage detectors are judged to be abnormal, it is determined that all three voltage detectors are normal. If any voltage detector is judged to be abnormal, it is possible to identify the voltage detector that is not judged to be normal as being abnormal.

If it is determined that all three voltage detectors are normal, and it is first determined that either the charging terminal voltage V3 or the charging power supply voltage V4 is abnormal, it may be determined that the charging voltage detector 32 that detected the charging power supply voltage V4 is abnormal. Also, if only one of the three voltage detectors, power supply voltage detector 21, power conversion circuit voltage detector 6, and charging terminal voltage detector 7, indicates a different voltage value, it can be determined that that voltage detector is abnormal.
<Transient current detection>
Here, we will explain a method for more quickly determining whether the power conversion circuit voltage detector 6 is normal or abnormal. The presence or absence of an abnormality in the charging terminal voltage detector 7 is determined only when the charging power supply voltage V4 detected by the charging voltage detector 32 is lower than the power supply voltage V1 detected by the power supply voltage detector 21. In this method, the voltage of the capacitor 23 is estimated based on the phase current Iw detected by the phase current detector 16, and is compared with the charging terminal voltage V3 detected by the charging terminal voltage detector 7.

During normal power conversion operation and when boost charging is being performed, the charging terminal voltage V3 detected by the charging terminal voltage detector 7 can be compared with the charging power supply voltage V4 detected by the charging voltage detector 32. The voltage difference can then be compared with a predetermined voltage difference ΔV to determine whether both are normal or whether one is abnormal.

<For V1 and V4>
If the voltage difference between charging terminal voltage V3 and charging power supply voltage V4 is greater than a predetermined voltage difference ΔV, either charging terminal voltage V3 or charging power supply voltage V4 is abnormal. In this case, if charging power supply voltage V4 is lower than power supply voltage V1, i.e., if boost charging is required, positive side switching element 10 of inverter 2 is turned on and all other switching elements 8, 9, 11-13 are turned off. In this manner, phase current Iw passes through phase current detector 16 so that the potentials of capacitors 23 and 22 are balanced. Since V1 > V4, the influence of charger 5 can be eliminated by backflow prevention diode 26.

At this time, the predicted voltage change value ΔVPC23 of capacitor 23 can be calculated based on the phase current Iw, the elapsed time, and the capacitance of capacitor 23. The measured voltage change value ΔVC23 calculated from the charging terminal voltage V3 detected by charging terminal voltage detector 7 is compared with the predicted voltage change value ΔVPC23. By comparing the measured voltage change value ΔVC23 with the predicted voltage change value ΔVPC23, if the difference in the voltage change is greater than a predetermined voltage change difference ΔVCd23, it can be determined that charging terminal voltage detector 7 is abnormal. If the difference in the voltage change is equal to or less than the predetermined voltage change difference ΔVCd23, it can be determined that charging terminal voltage detector 7 is normal (measured voltage change value ΔVC23, predicted voltage change value ΔVPC23, and voltage change difference ΔVCd23 are not shown). If either charging terminal voltage V3 or charging power source voltage V4 is abnormal, it can be determined that charging voltage detector 32 is abnormal if charging terminal voltage detector 7 is normal.

In this way, the transient voltage change of capacitor 23 can be confirmed, and the normality of the charging terminal voltage detector 7 can be quickly determined. Specifically, the transient change of the charging terminal voltage V3, which is the voltage of capacitor 23, is calculated as a predicted voltage change value ΔVPC23, and this is compared with the measured voltage change value ΔVC23 obtained from the charging terminal voltage V3 detected by the charging terminal voltage detector 7. It is then possible to determine whether the difference in voltage change is greater than a predetermined voltage change difference ΔVCd23 before the power conversion circuit voltage V2 and the charging terminal voltage V3 are balanced. This shortens the time required to determine whether the charging terminal voltage detector 7 is normal or abnormal.

3. Third Embodiment
<Configuration of power conversion device>
4 is a configuration diagram of a power conversion device 100 according to embodiment 3. The power conversion device 100 according to embodiment 3 differs from the power conversion device 100 according to embodiment 2 in that switching element temperature detectors 49, 50, 51, and 52 are provided on the positive-side switching elements 9 and 10 and the negative-side switching elements 11 and 12 of the inverter 2, and that the positive-side charging terminal 44a is connected to a plurality of external connection points of the inverter 2 via charging switches 28 and 29, respectively.

The hardware configuration of the power conversion device 100 according to embodiment 3 is substantially the same as that of the power conversion device 100 according to embodiment 2, and can be realized by adding input signals such as switching element temperature detectors 49 to 51, adding output signals such as the charging switch 28, and modifying the software. The hardware configuration of the control unit 20 in FIG. 2 can also be applied to embodiment 3.

<Preventing overheating of switching elements during direct charging (when V1≦V4)>
The overheating state of the switching elements of inverter 2 may be estimated by calculating the current flowing therethrough, and the switching element on the positive side to be driven for direct charging may be switched. The overheating state of each element may be detected by switching element temperature detectors 49, 50 provided in switching elements 9, 10.

In FIG. 4, the positive-side charging terminal 44a is connected to multiple external connection points of the inverter 2 via charging switches 28, 29, respectively. The positive-side switching elements 9, 10 of the arms connected to the charging switches 28, 29 of the inverter 2 each have a switching element temperature detector 49, 50 that detects the temperature of the switching element. When performing fault diagnosis, the control unit 20 turns on only the positive-side switching element 9, 10 that has the lowest temperature detected by the switching element temperature detector and turns off the other positive-side switching elements among the positive-side switching elements 9, 10 that can be connected to the positive-side charging terminal 44a. In this case, the charging switch connected to the positive-side switching element with the lowest temperature is turned on, and the other charging switches are turned off. This prevents overheating of the switching elements when charging and fault diagnosis are performed, making it possible to perform direct charging and fault diagnosis.

<Preventing overheating of switching elements during boost charging (when V1 >V4)>
The overheating state of the negative-side switching element of the inverter 2 and the overheating state of the coils of the rotating electric machine 3 may be estimated by calculating the current flow, and the negative-side switching element to be driven for boosting may be switched. As described in the first embodiment, in order to boost the power received from the charger 5 and charge the DC power supply 1, the negative-side switching element 11 or the negative-side switching element 12 is on/off controlled. In this case, the negative-side switching element that can be estimated to have a lower temperature may be selected and on/off controlled. Furthermore, for the coils of the rotating electric machine 3 that are repeatedly subjected to current flow and interruption, the combination of coils with a lower temperature may be used.

In this case, switching element temperature detectors 51, 52 may be provided on the negative-side switching elements 11, 12, and the negative-side switching element with the lower detected temperature may be controlled on and off. Temperature detectors may also be provided on each of the coils 17 to 19 of the rotating electric machine 3 to detect the temperature, and the coil with the lower temperature may be used.

This prevents overheating of the switching elements and coils and allows for efficient voltage boosting. Temperature detectors may be provided for all switching elements of the inverter 2. Also, all external connection lines of the inverter 2 may be connected to the positive charging terminal 44a via a charging switch. This increases the number of options for selecting switching elements and coils.

4. Fourth Embodiment
<Configuration of power conversion device>
5 is a configuration diagram of a power conversion device 100 according to embodiment 4. The power conversion device 100 according to embodiment 4 differs from the power conversion device 100 according to embodiment 3 in that switch temperature detectors 41 and 42 are provided on the charging switches 28 and 29 instead of the switching element temperature detectors 49, 50, 51, and 52 provided on the positive side switching elements 9 and 10 and the negative side switching elements 11 and 12 of the inverter 2.

The hardware configuration of the power conversion device 100 according to embodiment 4 is substantially the same as that of the power conversion device 100 according to embodiment 3, and can be realized by adding input signals from switch temperature detectors 41 and 42 instead of the input signals from switching element temperature detectors 49 to 51, and by modifying the software. The hardware configuration of the control unit 20 in Figure 2 can also be applied to embodiment 4.

The positive charging terminal 44a is connected to multiple external connection points of the power conversion device 100 via charging switches 28 and 29, each equipped with switch temperature detectors 41 and 42. The control unit 20 controls the switch with the lowest temperature detected by the switch temperature detectors 41 and 42. This is to prevent current from flowing through the charging switch 28 or 29, causing the switch to overheat and fail.

By configuring in this manner, the power conversion device 100 according to embodiment 4 can prevent heat generation in the charging switches 28 and 29 when charging and performing fault diagnosis, thereby contributing to improved reliability of the power conversion device 100. Similar to the prevention of overheating of the switching elements and coils described in embodiment 3, preventing overheating of the charging switches can achieve both efficient charging and prevention of switch degradation.

5. Fifth Embodiment
<Configuration of power conversion device>
6 is a configuration diagram of a power conversion device 100 according to embodiment 5. The power conversion device 100 according to embodiment 5 differs from the power conversion device 100 according to embodiment 2 in that a charge current limiting unit is provided in the charger 5a. The charge current limiting unit is made up of a charge current limiting switch 62, a current limiting resistor 63, and backflow prevention diodes 26a and 26b.

When the charging current limiting switch 62 is in the OFF (shut-off) state, the charging current is limited by the current limiting resistor 63. When the charging current limiting switch 62 is in the ON (conducting) state, the charging current is not limited. Backflow prevention diodes 26a and 26b prevent current from flowing into the charger.

The hardware configuration of the power conversion device 100 according to embodiment 5 is substantially the same as that of the power conversion device 100 according to embodiment 2, and can be realized by adding the output of the charging current limit switch 62 and modifying the software. The hardware configuration of the control unit 20 in Figure 2 can also be applied to embodiment 5.

In the power conversion device 100 according to embodiment 5, the control unit 20 instructs the charger 5 to limit the charging current when performing a fault diagnosis. Specifically, it instructs the charger 5 to turn the charging current limit switch 62 off.

The power conversion device 100 compares the power conversion circuit voltage V2 with the power supply voltage V1, and if the voltage difference is greater than a predetermined voltage difference ΔV, it determines that one of the voltage detectors is abnormal and begins fault diagnosis. It also compares the charging power supply voltage V4 with the charging terminal voltage V3, and if the voltage difference is greater than a predetermined voltage difference ΔV, it determines that one of the voltage detectors is abnormal and begins fault diagnosis.

The predetermined voltage difference ΔV, which indicates the difference between the detected voltages of the two voltage detectors, is set taking into account voltage drop in wiring, etc. By limiting the charging current flowing from the charger 5 to the DC power source 1 to a value lower than normal, it is possible to reduce voltage drop in wiring, etc. Therefore, limiting the charging current can improve the accuracy of voltage detector abnormality detection.

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

The various aspects of this disclosure are summarized below as appendices.

(Appendix 1)
a positive busbar connected to the positive side of the DC power supply;
a negative busbar connected to the negative side of the DC power supply;
a power conversion circuit having a plurality of legs each provided with a positive-side switching element connected to the positive-side bus and having an anti-parallel-connected diode, a negative-side switching element connected to the negative-side bus and having an anti-parallel-connected diode, and an external connection point connecting the positive-side switching element and the negative-side switching element in series and connected to a field winding of a rotating electric machine;
a positive-side charging terminal connected to at least one of the external connection points of the power conversion circuit via a charging switch;
a negative charging terminal connected to the negative bus;
a power supply voltage detector that detects the voltage of the DC power supply;
a power conversion circuit voltage detector for detecting a voltage between the positive and negative poles of the power conversion circuit;
a charging terminal voltage detector for detecting a voltage between the positive charging terminal and the negative charging terminal; and
a control unit that controls the power conversion circuit to drive or stop the rotating electric machine, and when performing a fault diagnosis, turns on a positive-side switching element of a leg having an external connection point to which the charging switch is connected, turns off all other switching elements of the power conversion circuit, turns on the charging switch, compares two by two of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector, and determines that both of the two voltage detectors that detected the two compared voltages are normal if the difference between the two compared voltages is within a predetermined voltage difference, and determines that one of the two voltage detectors that detected the two compared voltages is abnormal if the difference between the two compared voltages is greater than the predetermined voltage difference, and determines that all three voltage detectors are normal if none of the voltage detectors are determined to be abnormal, and determines that the voltage detector that was not determined to be normal is abnormal if any of the voltage detectors is determined to be abnormal.
(Appendix 2)
The power conversion device described in Appendix 1, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine, compares the power supply voltage detected by the power supply voltage detector with the power conversion circuit voltage detected by the power conversion circuit voltage detector, and performs the fault diagnosis if the voltage difference is greater than the voltage difference.
(Appendix 3)
3. The power conversion device according to claim 1, wherein the control unit starts a comparison of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector when a voltage change amount representing a change amount per unit time of the charging terminal voltage detected by the charging terminal voltage detector becomes smaller than a predetermined voltage change amount threshold.
(Appendix 4)
the positive charging terminal is connected to the positive side of a charging DC power supply via a backflow prevention diode;
the negative charging terminal is connected to the negative side of the charging DC power supply,
The power conversion device according to any one of appendixes 1 to 3, wherein, when performing the fault diagnosis, the control unit turns on a positive-side switching element of a leg having an external connection point to which the charging switch is connected, turns off all other switching elements of the power conversion circuit, turns on the charging switch, and compares two each of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector.
(Appendix 5)
a charging voltage detector for detecting the voltage of the charging DC power supply;
The power conversion device described in Appendix 4, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine or when charging the DC power supply, compares the charging terminal voltage detected by the charging terminal voltage detector with the charging voltage detected by the charging voltage detector, and performs the fault diagnosis if the voltage difference is greater than the voltage difference.
(Appendix 6)
The power conversion device according to claim 4 or 5, wherein the control unit starts a comparison of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector when each of the voltage change amounts representing the change per unit time of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector becomes smaller than a predetermined voltage change amount threshold.
(Appendix 7)
a charging voltage detector for detecting the voltage of the charging DC power supply;
the positive charging terminal is connected to the positive side of the charging DC power supply via a backflow prevention diode;
the negative charging terminal is connected to the negative side of the charging DC power supply,
4. The power conversion device according to any one of appendices 1 to 3, wherein, when performing a fault diagnosis during direct charging in which the voltage of the charging DC power supply is directly supplied to the DC power supply for charging, the control unit turns off all of the switching elements of the power conversion circuit except for a positive-side switching element of a leg having an external connection point to which the charging switch is connected, turns on the charging switch, compares two by two of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, the charging terminal voltage detected by the charging terminal voltage detector, and the charging voltage detected by the charging voltage detector, and determines that both of the two voltage detectors that detected the two compared voltages are normal if a difference between the two compared voltages is within the voltage difference, and determines that one of the two voltage detectors that detected the two compared voltages is abnormal if the difference between the two compared voltages is greater than the voltage difference, and determines that all four voltage detectors are normal if none of the voltage detectors are determined to be abnormal, and determines that the voltage detector that is not determined to be normal if any of the voltage detectors is determined to be abnormal.
(Appendix 8)
a phase current detector is provided in a leg having an external connection point to which the charging switch is connected;
The power conversion device according to claim 7, wherein the control unit determines that direct charging is being performed by detecting, with the phase current detector, that a current is flowing from an external connection point to which the charging switch is connected toward the leg.
(Appendix 9)
The power conversion device according to claim 7 or 8, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine or when charging the DC power supply, compares the charging terminal voltage detected by the charging terminal voltage detector with the charging voltage detected by the charging voltage detector, and performs the fault diagnosis if the voltage difference is greater than the voltage difference.
(Appendix 10)
The power conversion device according to any one of appendices 7 to 9, wherein the control unit starts a comparison of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, the charging terminal voltage detected by the charging terminal voltage detector, and the charging voltage detected by the charging voltage detector when each of the voltage change amounts representing the change per unit time of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, the charging terminal voltage detected by the charging terminal voltage detector, and the charging voltage detected by the charging voltage detector becomes smaller than a predetermined voltage change amount threshold.
(Appendix 11)
a phase current detector provided for each leg to detect a phase current flowing between the external connection point for each leg and a field winding of the rotating electric machine;
a charging voltage detector for detecting the voltage of the charging DC power supply;
a charging terminal capacitor connected between the positive charging terminal and the negative charging terminal;
the positive charging terminal is connected to the positive side of the charging DC power supply via a backflow prevention diode;
the negative charging terminal is connected to the negative side of the charging DC power supply,
4. The power conversion device according to claim 1, wherein, when diagnosing a fault while performing boost charging to boost the voltage of the charging DC power supply and charge the DC power supply, the control unit turns on the positive-side switching element of the leg having the external connection point to which the charging switch is connected among the switching elements of the power conversion circuit and turns off all other switching elements, turns on the charging switch, compares a voltage rise prediction value calculated based on the phase current detected by the phase current detector, the elapsed time, and the capacitance of the charging terminal capacitor with a voltage rise value of the charging terminal voltage detected by the charging terminal voltage detector, and determines that the charging terminal voltage detector is abnormal if the difference in voltage rise value is greater than a predetermined rise value difference.
(Appendix 12)
The power conversion device described in Appendix 11, wherein the control unit determines that boost charging is being performed by detecting, using the phase current detector, that no current is flowing from the external connection point to which the charging switch is connected toward the leg, and that a current is flowing from a field winding of the rotating electric machine toward another leg.
(Appendix 13)
The power conversion device according to claim 11 or 12, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine or when charging the DC power supply, compares the charging terminal voltage detected by the charging terminal voltage detector with the charging voltage detected by the charging voltage detector, and performs the fault diagnosis if the voltage difference is greater than the voltage difference.
(Appendix 14)
a phase current detector provided for each leg to detect a phase current flowing between the external connection point for each leg and a field winding of the rotating electric machine;
a power conversion circuit capacitor connected between the positive bus and the negative bus; and
a charging terminal capacitor connected between the positive charging terminal and the negative charging terminal;
the positive busbar is connected to the DC power supply via a power switch;
When performing a fault diagnosis, the control unit turns off the power switch, turns on a positive-side switching element of a leg having an external connection point to which the charging switch is connected, turns off all other switching elements of the power conversion circuit, turns on the charging switch, compares a voltage change prediction value calculated based on the phase current detected by the phase current detector, the elapsed time, and the capacitance of the power conversion circuit capacitor with a voltage change amount of the power conversion circuit voltage detected by the power conversion circuit voltage detector, and determines an abnormality in the power conversion circuit voltage detector if the difference in the voltage change amount is greater than a predetermined difference in change amount.
(Appendix 15)
The power conversion device according to claim 14, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine or when charging the DC power supply, compares the power supply voltage detected by the power supply voltage detector with the power conversion circuit voltage detected by the power conversion circuit voltage detector, and performs the fault diagnosis if the difference between the power supply voltage detected by the power supply voltage detector and the power conversion circuit voltage detected by the power conversion circuit voltage detector is greater than a predetermined voltage difference.
(Appendix 16)
the charging DC power supply has a charging current limiting unit,
14. The power conversion device according to claim 4, wherein the control unit instructs the charge current limiting unit to limit the charge current when performing the fault diagnosis.
(Appendix 17)
the positive charging terminal is connected to a plurality of external connection points of the power conversion circuit via charging switches respectively provided thereto;
a switching element temperature detector for detecting the temperature of each of the positive-side switching elements of the arm connected to the charging switch in the power conversion circuit;
17. The power conversion device according to any one of appendices 1 to 16, wherein, when performing the fault diagnosis, the control unit conducts a positive-side switching element that has the lowest temperature detected by the switching element temperature detector among the positive-side switching elements connectable to the positive-side charging terminal.
(Appendix 18)
the positive charging terminal is connected to a plurality of external connection points of the power conversion circuit via charging switches each having a switch temperature detector;
18. The power conversion device according to any one of appendices 1 to 17, wherein, when performing the fault diagnosis, the control unit conducts electricity to a charging switch among the charging switches whose temperature detected by the switch temperature detector is the lowest.
(Appendix 19)
Supplementary notes 1 to 18, wherein a positive-side switching element having an anti-parallel-connected diode of the power conversion circuit and a negative-side switching element having an anti-parallel-connected diode are MOS-FETs. The power conversion device according to any one of claims 1 to 18.

1 DC power supply, 1a Positive busbar, 1b Negative busbar, 3 Rotating electric machine, 5, 5a Charger, 6 Power conversion circuit voltage detector, 7 Charging terminal voltage detector, 8, 9, 10, 11, 12, 13 Switching element, 14, 15, 16 Phase current detector, 17, 18, 19 Coil, 20 Control unit, 21 Power supply voltage detector, 22, 23 Capacitor, 26, 26a, 26b Backflow prevention diode, 28, 29 Charging switch, 30 Power switch, 32 Charging voltage detector, 41, 42 Switch temperature detector, 44a Positive charging terminal, 44b Negative charging terminal, 49, 50, 51, 52 Switching element temperature detector, 62 Charging current limiting switch, 63 Current limiting resistor, 100 Power conversion device

Claims (19)

a positive busbar connected to the positive side of the DC power supply;
a negative busbar connected to the negative side of the DC power supply;
a power conversion circuit having a plurality of legs each provided with a positive-side switching element connected to the positive-side bus and having an anti-parallel-connected diode, a negative-side switching element connected to the negative-side bus and having an anti-parallel-connected diode, and an external connection point connecting the positive-side switching element and the negative-side switching element in series and connected to a field winding of a rotating electric machine;
a positive-side charging terminal connected to at least one of the external connection points of the power conversion circuit via a charging switch;
a negative charging terminal connected to the negative bus;
a power supply voltage detector that detects the voltage of the DC power supply;
a power conversion circuit voltage detector for detecting a voltage between the positive and negative poles of the power conversion circuit;
a charging terminal voltage detector for detecting a voltage between the positive charging terminal and the negative charging terminal; and
a control unit that controls the power conversion circuit to drive or stop the rotating electric machine, and when performing a fault diagnosis, turns on a positive-side switching element of a leg having an external connection point to which the charging switch is connected, turns off all other switching elements of the power conversion circuit, turns on the charging switch, compares two by two of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector, and determines that both of the two voltage detectors that detected the two compared voltages are normal if the difference between the two compared voltages is within a predetermined voltage difference, and determines that one of the two voltage detectors that detected the two compared voltages is abnormal if the difference between the two compared voltages is greater than the predetermined voltage difference, and determines that all three voltage detectors are normal if none of the voltage detectors are determined to be abnormal, and determines that the voltage detector that was not determined to be normal is abnormal if any of the voltage detectors is determined to be abnormal. The power conversion device described in claim 1, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine, compares the power supply voltage detected by the power supply voltage detector with the power conversion circuit voltage detected by the power conversion circuit voltage detector, and performs the fault diagnosis if the voltage difference is greater than the voltage difference. The power conversion device described in claim 1, wherein the control unit begins comparing the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector when a voltage change amount representing the change per unit time of the charging terminal voltage detected by the charging terminal voltage detector becomes smaller than a predetermined voltage change amount threshold. the positive charging terminal is connected to the positive side of a charging DC power supply via a backflow prevention diode;
the negative charging terminal is connected to the negative side of the charging DC power supply,
2. The power conversion device according to claim 1, wherein, when performing the fault diagnosis, the control unit turns on a positive-side switching element of a leg having an external connection point to which the charging switch is connected, turns off all other switching elements of the power conversion circuit, turns on the charging switch, and compares two of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector. a charging voltage detector for detecting the voltage of the charging DC power supply;
5. The power conversion device according to claim 4, wherein, when the control unit is controlling the power conversion circuit to drive or stop the rotating electric machine or when the DC power supply is being charged, the control unit compares the charging terminal voltage detected by the charging terminal voltage detector with the charging voltage detected by the charging voltage detector, and performs the fault diagnosis if the voltage difference is greater than the voltage difference. The power conversion device described in claim 4, wherein the control unit begins comparing the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector with each other when the respective voltage change amounts representing the change per unit time of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, and the charging terminal voltage detected by the charging terminal voltage detector become smaller than predetermined voltage change amount thresholds. a charging voltage detector for detecting the voltage of the charging DC power supply;
the positive charging terminal is connected to the positive side of the charging DC power supply via a backflow prevention diode;
the negative charging terminal is connected to the negative side of the charging DC power supply,
2. The power conversion device according to claim 1, wherein, when performing a fault diagnosis during direct charging in which the voltage of the charging DC power supply is directly supplied to the DC power supply for charging, the control unit turns off all of the switching elements of the power conversion circuit except for a positive-side switching element of a leg having an external connection point to which the charging switch is connected, turns on the charging switch, compares two by two of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, the charging terminal voltage detected by the charging terminal voltage detector, and the charging voltage detected by the charging voltage detector, and determines that both of the two voltage detectors that detected the two compared voltages are normal if a difference between the two compared voltages is within the voltage difference, determines that one of the two voltage detectors that detected the two compared voltages is abnormal if the difference between the two compared voltages is greater than the voltage difference, determines that all four voltage detectors are normal if none of the voltage detectors are determined to be abnormal, and determines that the voltage detector that is not determined to be normal if any of the voltage detectors is determined to be abnormal. a phase current detector is provided in a leg having an external connection point to which the charging switch is connected;
8. The power conversion device according to claim 7, wherein the control unit determines that direct charging is being performed by detecting, with the phase current detector, that a current is flowing from an external connection point to which the charging switch is connected toward the leg. The power conversion device described in claim 7, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine or when charging the DC power supply, compares the charging terminal voltage detected by the charging terminal voltage detector with the charging voltage detected by the charging voltage detector, and performs the fault diagnosis if the voltage difference is greater than the voltage difference. The power conversion device described in claim 7, wherein the control unit begins comparing the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, the charging terminal voltage detected by the charging terminal voltage detector, and the charging voltage detected by the charging voltage detector with each other when the respective voltage change amounts representing the change per unit time of the power supply voltage detected by the power supply voltage detector, the power conversion circuit voltage detected by the power conversion circuit voltage detector, the charging terminal voltage detected by the charging terminal voltage detector, and the charging voltage detected by the charging voltage detector become smaller than predetermined voltage change amount thresholds. a phase current detector provided for each leg to detect a phase current flowing between the external connection point for each leg and a field winding of the rotating electric machine;
a charging voltage detector for detecting the voltage of the charging DC power supply;
a charging terminal capacitor connected between the positive charging terminal and the negative charging terminal;
the positive charging terminal is connected to the positive side of the charging DC power supply via a backflow prevention diode;
the negative charging terminal is connected to the negative side of the charging DC power supply,
2. The power conversion device according to claim 1, wherein, when diagnosing a fault while performing boost charging in which the voltage of the charging DC power supply is boosted to charge the DC power supply, the control unit turns on a positive-side switching element of a leg having an external connection point to which the charging switch is connected among the switching elements of the power conversion circuit and turns off all other switching elements, turns on the charging switch, compares a voltage rise prediction value calculated based on the phase current detected by the phase current detector, the elapsed time, and the capacitance of the charging terminal capacitor with a voltage rise value of the charging terminal voltage detected by the charging terminal voltage detector, and determines that the charging terminal voltage detector is abnormal if a difference in voltage rise value is greater than a predetermined rise value difference. The power conversion device described in claim 11, wherein the control unit determines that boost charging is being performed by detecting, using the phase current detector, that no current is flowing from the external connection point to which the charging switch is connected toward the leg, and that current is flowing from the field winding of the rotating electric machine toward another leg. The power conversion device described in claim 11, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine or when charging the DC power supply, compares the charging terminal voltage detected by the charging terminal voltage detector with the charging voltage detected by the charging voltage detector, and performs the fault diagnosis if the voltage difference is greater than the voltage difference. a phase current detector provided for each leg to detect a phase current flowing between the external connection point for each leg and a field winding of the rotating electric machine;
a power conversion circuit capacitor connected between the positive bus and the negative bus; and
a charging terminal capacitor connected between the positive charging terminal and the negative charging terminal;
the positive busbar is connected to the DC power supply via a power switch;
2. The power conversion device according to claim 1, wherein, when performing a fault diagnosis, the control unit turns off the power switch, turns on a positive-side switching element of a leg having an external connection point to which the charging switch is connected, turns off all other switching elements of the power conversion circuit, turns on the charging switch, compares a voltage change prediction value calculated based on the phase current detected by the phase current detector, the elapsed time, and the capacitance of the power conversion circuit capacitor with a voltage change amount of the power conversion circuit detected by the power conversion circuit voltage detector, and determines an abnormality in the power conversion circuit voltage detector if a difference in the voltage change amount is larger than a predetermined difference in change amount. The power conversion device described in claim 14, wherein the control unit, when controlling the power conversion circuit to drive or stop the rotating electric machine or when charging the DC power supply, compares the power supply voltage detected by the power supply voltage detector with the power conversion circuit voltage detected by the power conversion circuit voltage detector, and performs the fault diagnosis if the difference is greater than a predetermined voltage difference. the charging DC power supply has a charging current limiting unit,
The power conversion device according to claim 4 , wherein the control unit instructs the charge current limiting unit to limit the charge current when performing the fault diagnosis. the positive charging terminal is connected to a plurality of external connection points of the power conversion circuit via charging switches respectively provided thereto;
a switching element temperature detector for detecting the temperature of each of the positive-side switching elements of the arm connected to the charging switch in the power conversion circuit;
16. The power conversion device according to claim 1, wherein, when performing the fault diagnosis, the control unit conducts a positive-side switching element that has the lowest temperature detected by the switching element temperature detector among the positive-side switching elements connectable to the positive-side charging terminal. the positive charging terminal is connected to a plurality of external connection points of the power conversion circuit via charging switches each having a switch temperature detector;
16. The power conversion device according to claim 1, wherein when performing the fault diagnosis, the control unit conducts the charging switch having the lowest temperature detected by the switch temperature detector among the charging switches. The power conversion device described in any one of claims 1 to 15, wherein the positive-side switching element having an anti-parallel-connected diode and the negative-side switching element having an anti-parallel-connected diode of the power conversion circuit use MOS-FETs.