Power converter

Abstract

The present invention provides a power conversion device capable of detecting relay malfunctions. [Solution] The power conversion device comprises first and second inverters, first and second capacitors, a voltage detection unit for detecting the voltage between both terminals of the second capacitor, a relay interposed in the wiring connecting one end of the second capacitor and one pole of the second battery, and a control unit. The control unit acquires a first detection value from the voltage detection unit when the relay is closed, controls the relay to open after acquiring the first detection value, controls the first and second inverters to charge the second capacitor from the first capacitor through the windings of each phase after controlling the first and second inverters, acquires a second detection value from the voltage detection unit, and detects a relay malfunction if the second detection value is substantially equal to the first detection value.

Description

[Technical Field]

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

[0002] Regarding power conversion devices, for example, Patent Document 1 discloses two inverters connected to each other via windings of each phase of a motor mounted on a vehicle, and smoothing capacitors connected to the input side of each inverter. The power conversion device converts DC power supplied from a power source to the motor into AC power. Power from the power source is supplied or cut off by a System Main Relay (SMR) interposed in each power line connecting the power source and the power conversion device. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2022-165651 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] The smoothing capacitor is precharged via a power supply line connected to the power line. Precharging the smoothing capacitor reduces the voltage difference between the power source and the inverter compared to before precharging, so inrush current flowing from the power source to the inverter when the power supply device is started is suppressed. Energization between the smoothing capacitor and the power source is turned on and off by a power supply relay (for example, a semiconductor relay) interposed in the power supply line.

[0005] For example, in an end sequence of a power conversion device, the power supply relay is controlled to be open from the viewpoint of ensuring safety. However, the power supply relay may seize due to aging degradation or the like and remain in a closed state.

[0006] Therefore, the present invention has been made in view of the above problems, and aims to provide a power conversion device that can detect abnormalities in relays. [Means for solving the problem]

[0007] The power conversion device of the present invention is a power conversion device that converts DC power from a first battery and a second battery supplied to a motor into AC power, comprising: a first inverter connected to both poles of the first battery and one end of each phase winding of the motor, a second inverter connected to both poles of the second battery and the other end of each phase winding of the motor, a first capacitor connected in parallel to the first battery between the first inverter and the first battery, a second capacitor connected in parallel to the second battery between the second inverter and the second battery, a voltage detection unit that detects the voltage between both terminals of the second capacitor, and one end of the second capacitor and the The system includes a relay interposed in the wiring connecting one pole of the second battery, the first inverter, the second inverter, and a control unit that controls the relay. The control unit acquires a first detection value from the voltage detection unit when the relay is closed, controls the relay to open after acquiring the first detection value, controls the first inverter and the second inverter to charge the second capacitor from the first capacitor through the windings of each phase after controlling the first inverter and the second inverter, acquires a second detection value from the voltage detection unit, and detects an abnormality in the relay if the second detection value is substantially equal to the first detection value.

[0008] In the power converter described above, if the value obtained by subtracting the first detection value from the second detection value is greater than or equal to a predetermined value greater than 0, the abnormality of the relay may not be detected. However, if the value obtained by subtracting the first detection value from the second detection value is less than the predetermined value, the abnormality of the relay may be detected.

[0009] In the power conversion device described above, there is a current detection unit that detects the current value flowing through the windings of each phase, and the control unit may control the first inverter and the second inverter based on the current value detected by the current detection unit so that the voltage between both terminals of the second capacitor becomes a predetermined target value. [Effects of the Invention]

[0010] According to the present invention, it is possible to detect abnormalities in the relays of a power conversion device. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a diagram illustrating an example of a power supply unit. [Figure 2] Figure 2(A) illustrates the pre-charge operation of the smoothing capacitor on one inverter side. Figure 2(B) illustrates the pre-charge operation of the smoothing capacitor on the other inverter side. [Figure 3] Figure 3 illustrates the diagnostic process for a relay. [Figure 4] Figure 4(A) illustrates the time variation of the smoothing capacitor voltage when the relay is in the open position. Figure 4(B) illustrates the time variation of the smoothing capacitor voltage when the relay is in the closed position. [Figure 5] Figure 5 is a diagram illustrating the functionality of a PWM (Pulse Width Modulation) controller. [Figure 6] Figure 6 is a flowchart illustrating the operation of the power supply unit. [Modes for carrying out the invention]

[0012] (Power supply unit configuration) Figure 1 is a diagram illustrating the configuration of a power supply unit S. The power supply unit S is installed in vehicles such as electric vehicles and hybrid vehicles. The power supply unit S includes a power supply PWR, a relay device RL, a power converter U, a motor M, relays RLd and RLe, an inlet 83, and a vehicle control unit 2.

[0013] Motor M drives the vehicle. Motor M comprises a rotor and a stator (not shown). The stator has u-phase, v-phase, and w-phase windings Lu, Lv, and Lw. The stator generates a rotating magnetic field when a three-phase alternating current flows through the windings Lu, Lv, and Lw. The rotor has, for example, permanent magnets and rotates according to the rotating magnetic field of the stator.

[0014] The power supply PWR supplies power to the motor M via power lines VDDa, VDDb and ground line SG within the relay device RL. The power supply PWR has batteries Eu and Ed, relays RLa and RLb, and terminals T1a to T3a. Batteries Eu and Ed are, for example, lithium-ion batteries. Batteries Eu and Ed are connected in series with each other via relay RLa. The negative terminal of battery Eu is connected to one end of relay RLa. The positive terminal of battery Ed is connected to the other end of relay RLa.

[0015] The power supply PWR is connected to inverters 6 and 7 via terminals T1a to T3a. Terminals T1a and T3a are connected to power lines VDDa and VDDb, respectively. Terminal T2a is connected to the ground line SG. Terminal T1a is drawn from the positive terminal of battery Eu. Terminal T2a is drawn from the negative terminal of battery Ed. Terminal T3a is drawn from the contact between one end of relay RLa and the positive terminal of battery Ed.

[0016] One end of relay RLb is connected to the wiring between one end of relay RLa and the negative terminal of battery Eu. The other end of relay RLb is connected to the wiring between the negative terminal of battery Ed and terminal T2a. When relay RLa is closed and relay RLb is open, batteries Eu and Ed are connected in series. When relay RLa is open and relay RLb is closed, batteries Eu and Ed are connected in parallel.

[0017] The power conversion device U is connected to a power source PWR via a relay device RL. The power conversion device U converts DC power of batteries Eu and Ed into AC power. The power conversion device U includes a control unit 1, inverters 6 and 7, current sensors 9u to 9w, smoothing capacitors 21 and 22, voltage sensors 23 and 24, and relays RL1m to RL3m.

[0018] A motor M is connected between the inverters 6 and 7. The inverter 6 is respectively connected to one end of each of windings Lu, Lv and Lw. The inverter 7 is respectively connected to the other end of each of the windings Lu, Lv and Lw.

[0019] The current sensors 9u, 9v and 9w are respectively connected in series with the windings Lu, Lv and Lw. The current sensors 9u, 9v and 9w respectively detect current values of a u-phase, a v-phase and a w-phase. Each of the current sensors 9u, 9v and 9w outputs a detected current value to the control unit 1.

[0020] Further, the inverter 6 is connected to terminals T1a and T2a of the power source PWR via a power supply line VDDa and a ground line SG. The inverter 7 is connected to terminals T3a and T2a of the power source PWR via a power supply line VDDb and the ground line SG. With this configuration, the inverters 6 and 7 convert DC current from the power source PWR into three-phase AC current and output the three-phase AC current to the motor M. Note that the inverters 6 and 7 are an example of a first inverter and a second inverter.

[0021] The inverter 6 includes switching elements 61 to 66. The switching elements 61 to 66 are connected between a high-potential side wiring H1v and a low-potential side wiring Hs. The inverter 7 includes switching elements 71 to 76. The switching elements 71 to 76 are connected between a high-potential side wiring H2v and the low-potential side wiring Hs. The high-potential side wiring H1v and the low-potential side wiring Hs are power supply lines in the inverter 6, and the high-potential side wiring H2v and the low-potential side wiring Hs are power supply lines in the inverter 7. The potential of the high-potential side wirings H1v and H2v is higher than the potential of the low-potential side wiring Hs.

[0022] Inverters 6 and 7 have input terminals T1b to T3b. Input terminal T1b is drawn from the high-potential side wiring H1v of inverter 6 and connected to the power line VDDa. Input terminal T2b is drawn from the low-potential side wiring Hs of inverters 6 and 7 and connected to the ground line SG. Input terminal T3b is drawn from the high-potential side wiring H2v of inverter 7 and connected to the power line VDDb.

[0023] Each switching element 61-66, 71-76 has a freewheeling diode connected between its two input / output terminals. The switching elements 61-66, 71-76 are, for example, IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), but other electronic components may also be used.

[0024] In the inverter 6, one input / output terminal of the upper arm switching elements 61-63 is connected to the high-potential wiring H1v, and one input / output terminal of the lower arm switching elements 64-66 is connected to the low-potential wiring Hs. The upper arm switching elements 61-63 and the lower arm switching elements 64-66 are connected in series with each other. The contacts of the upper arm switching elements 61-63 and the lower arm switching elements 64-66 are connected to one end of the windings Lu, Lv, and Lw, respectively.

[0025] In the inverter 7, one input / output terminal of the upper arm switching elements 71-73 is connected to the high-potential wiring H2v, and one input / output terminal of the lower arm switching elements 74-76 is connected to the low-potential wiring Hs. The upper arm switching elements 71-73 and the lower arm switching elements 74-76 are connected in series with each other. The contacts of the upper arm switching elements 71-73 and the lower arm switching elements 74-76 are connected to the other ends of the windings Lu, Lv, and Lw, respectively. In addition, the control terminals of each switching element 61-66 and 71-76 are connected to the control unit 1.

[0026] The contacts of switching elements 61 and 64, and the contacts of switching elements 71 and 74 are connected to the u-phase winding Lu. The contacts of switching elements 62 and 65, and the contacts of switching elements 72 and 75 are connected to the v-phase winding Lv. The contacts of switching elements 63 and 66, and the contacts of switching elements 73 and 76 are connected to the w-phase winding Lw.

[0027] The smoothing capacitor 21 is connected between the inverter 6 and the relay device RL, between the high-potential wiring H1v and the low-potential wiring Hs. The smoothing capacitor 21 smooths the voltage between the high-potential wiring H1v and the low-potential wiring Hs. The voltage sensor 23 is connected in parallel to the smoothing capacitor 21. The voltage sensor 23 detects the voltage VH between both terminals of the smoothing capacitor 21. The voltage sensor 23 outputs the detected value to the control unit 1. Note that the smoothing capacitor 21 is an example of a first capacitor.

[0028] The smoothing capacitor 22 is connected between the inverter 7 and the relay device RL, between the high-potential wiring H2v and the low-potential wiring Hs. The smoothing capacitor 22 smooths the voltage between the high-potential wiring H2v and the low-potential wiring Hs. The voltage sensor 24 is connected in parallel to the smoothing capacitor 22. The voltage sensor 24 detects the voltage VL between both terminals of the smoothing capacitor 22. The voltage sensor 24 outputs the detected value to the control unit 1. Note that the smoothing capacitor 22 is an example of a second capacitor.

[0029] Relays RL1m to RL3m are, for example, semiconductor relays. Relays RL1m and RL2m are connected between the high-potential wiring H1v and the high-potential wiring H2v. Relays RL1m and RL2m are connected in series with each other. Relay RL3m is interposed in the high-potential wiring H2v between the input terminal T3b and the voltage sensor 24. Note that the high-potential wiring H2v is an example of wiring connecting one end of the smoothing capacitor 22 and one pole of the battery Ed. Relays RL1m to RL3m are controlled to be open or closed by the control unit 1.

[0030] The relay device RL comprises power lines VDDa and VDDb, a ground line SG, relays RL1s to RL4s, and a resistor r. The connection configuration between the power supply PWR and inverters 6 and 7 is switched by the open / closed state of relays RL1s to RL4s.

[0031] Relay RL1s is connected to the power line VDDa. Relay RL2s is connected to the ground line SG. Relay RL3s is connected to the power line VDDb. Relay RL4s is connected in series with resistor r. The ends of the series circuit of relay RL4s and resistor r are connected to the ends of relay RL2s.

[0032] Relay RL4s is a pre-charge relay. When relay RL2s is open, relay RL4s closes when the smoothing capacitors 21 and 22 are pre-charged from the power supply PWR. At this time, the inrush current is reduced by flowing through resistor r, thus suppressing welding of relay RL4s due to the inrush current.

[0033] The inlet 83 is connected to an external DC charger 9. The DC charger 9 charges batteries Eu and Ed via the inlet 83. Batteries Eu and Ed can also supply power to the DC charger 9 via the inlet 83. The inlet 83 is connected to the power line VDDa and the ground line SG, respectively, via relays RLd and RLe. When batteries Eu and Ed are being charged or powered, relays RLd and RLe are closed.

[0034] Control unit 1 controls inverters 6 and 7 and relays RL1m to RL3m. Control unit 1 includes a PWM controller (PWM-CNT) 10, a relay controller (RL-CNT) 11, and a diagnostic controller (DIAG-CNT) 12. Note that control unit 1 is an example of a control unit.

[0035] The PWM controller 10 controls the switching operation of inverters 6 and 7 by outputting PWM signals to them. While the vehicle is running, the PWM controller 10 controls the duty cycle of the PWM signal based on the detected values ​​of current sensors 9u to 9w and voltage sensors 23 and 24, for example, according to the required output torque of motor M.

[0036] The relay controller 11 controls the opening and closing of relays RL1m to RL3m. The diagnostic controller 12 diagnoses the status of relay RL3m. Details of the diagnostic process will be described later. The PWM controller 10, relay controller 11, and diagnostic controller 12 operate in coordination with each other according to the instructions of the vehicle control unit 2.

[0037] The vehicle control unit 2 controls the power supply PWR, the relay device RL, and the control unit 1 according to the operating status of the vehicle. The control unit 1 and the vehicle control unit 2 are each implemented by, for example, one or more ECUs or IC (Integrated Circuit) chips.

[0038] (Pre-charge operation) When the power supply unit S is started, the vehicle control unit 2 performs a pre-charge operation of the smoothing capacitors 21 and 22. As described above, the voltage difference between the inverters 6 and 7 and the power supply PWR is reduced by the pre-charging of the smoothing capacitors 21 and 22, thereby suppressing the inrush current that flows when the two are connected.

[0039] Figure 2(A) illustrates the pre-charge operation of the smoothing capacitor 21 on one side of inverter 6. In Figure 2(A), components common to Figure 1 are indicated by the same reference numerals as in Figure 1. Furthermore, explanations of components common to Figure 1 in Figure 2(A) are omitted here. It is assumed that before the pre-charge operation, relays RLa, RLb, RL1s~RL4s, RLd, RLe, RL1m~RL3m are in the open state (OFF).

[0040] The vehicle control unit 2 controls relays RL1s, RL4s, and RLb to be closed (ON). As a result, the smoothing capacitor 21 and the battery Eu are connected in parallel. Consequently, the smoothing capacitor 21 is precharged from the battery Eu along the path Ka, so that the voltage VH becomes substantially equal to the voltage between the two electrodes of the battery Eu.

[0041] Furthermore, the vehicle control unit 2 can also perform a pre-charge operation such that the voltage VH across the smoothing capacitor 22 is substantially equal to the sum of the voltages of batteries Eu and Ed. In this case, relay RLa is closed and relay RLb is opened. Therefore, batteries Eu and Ed are connected in series with each other, and the smoothing capacitor 21 is connected in parallel with the series circuit of batteries Eu and Ed. The following examples will show the case where the voltage VH after pre-charging is substantially equal to the voltage between the two poles of battery Eu.

[0042] Figure 2(B) illustrates the pre-charge operation of the smoothing capacitor 22 on the other inverter 7 side. In Figure 2(B), components common to Figure 1 are indicated by the same reference numerals as in Figure 1. Furthermore, explanations of components common to Figure 1 in Figure 2(B) are omitted here. Before the pre-charge operation, it is assumed that relays RLa, RLb, RL1s~RL4s, RLd, RLe, RL1m~RL3m are in the open state.

[0043] The vehicle control unit 2 controls the closing of relays RL1s, RL3s, and RL4s. The relay controller 11 controls the closing of relay RL3m. For this reason, the smoothing capacitor 22 and the battery Ed are connected in parallel. As a result, the smoothing capacitor 22 is precharged from the battery Ed along the path Kb, so that the voltage VL becomes substantially equal to the voltage between the two electrodes of the battery Ed. The voltage drop due to the resistor r is compensated for by the charging of the smoothing capacitor 22 from the battery Ed when relay RL4s is opened and relay RL2s is closed after precharging. After the smoothing capacitors 21 and 22 are precharged, the vehicle control unit 2 instructs the control unit 1 to control the operation of various inverters 6 and 7 according to the vehicle state.

[0044] (Relay diagnostic process) Figure 3 illustrates the diagnostic process for relay RL3m. In Figure 3, components common to Figure 1 are indicated by the same reference numerals. Furthermore, explanations of components common to Figure 1 in Figure 3 are omitted here.

[0045] The diagnostic controller 12 performs a diagnosis of relay RL3m, for example, after the operation of inverters 6 and 7 has finished. Before the diagnosis, relays RLa, RLd, RLe, RL4s, RL1m to RL3m are in the open state, and relays RLb, RL1s to RL3s are in the closed state.

[0046] Therefore, inverter 6 is connected to both terminals of battery Eu, and inverter 7 is connected to both terminals of battery Ed. Smoothing capacitor 21 is connected in parallel to battery Eu, and smoothing capacitor 22 is connected in parallel to battery Ed.

[0047] During diagnosis, the relay controller 11 controls the opening of the relay RL3m to be diagnosed. After controlling the opening of relay RL3m, the PWM controller 10 controls inverters 6 and 7 to charge smoothing capacitor 22 from smoothing capacitor 21 via windings Lu~Lw. If relay RL3m is properly opened, the voltage VL between the two terminals of smoothing capacitor 22 increases from the pre-charge value, i.e., the battery voltage Vs, due to charging from the other smoothing capacitor 21.

[0048] On the other hand, if relay RL3m is closed due to a malfunction such as sticking, the smoothing capacitor 22 is connected in parallel with battery Ed via the high-potential wiring H2v and the low-potential wiring Hs, and becomes energized. As a result, the voltage Vs of battery Ed is applied between both terminals of the smoothing capacitor 22. Therefore, the voltage VL between both terminals of the smoothing capacitor 22 is maintained at the voltage Vs and does not increase.

[0049] Figure 4(A) illustrates the time variation of the voltage VL of the smoothing capacitor 22 when relay RL3m is in the open state. In the graph of Figure 4(A), the horizontal axis represents the time since the start of the diagnostic process, and the vertical axis represents the voltage VL of the smoothing capacitor 22. The charging operation by inverters 6 and 7 is performed during the period from time Ta to Tb (hereinafter referred to as the charging period).

[0050] When relay RL3m is open, the voltage VL increases during the charging period from the battery voltage Vs to the target voltage Vtg set by the diagnostic controller 12. The diagnostic controller 12 obtains the detected voltage V1 of the voltage sensor 24 when relay RL3m is closed before time Ta, and the detected voltage V2 of the voltage sensor 24 after time Tb.

[0051] The diagnostic controller 12 detects that the voltage VL across the smoothing capacitor 22 has increased because the detected voltage V2 after time Tb is greater than the detected voltage V1 before time Ta. Based on this, the diagnostic controller 12 can determine that the relay RL3m is functioning correctly.

[0052] Figure 4(B) illustrates the time variation of the voltage VL across the smoothing capacitor 22 when relay RL3m is in the closed state. Here, explanations of content common to both Figure 4(A) and Figure 4(B) are omitted.

[0053] When relay RL3m is closed, the voltage VL is maintained at substantially the battery voltage Vs during the charging period and does not increase to the target voltage value Vtg. The diagnostic controller 12 detects that the voltage VL of the smoothing capacitor 22 has not increased because the detected voltage V1 before time Ta and the detected voltage V2 after time Tb are substantially equal. Based on this, the diagnostic controller 12 can determine that relay RL3m is abnormal (e.g., stuck).

[0054] The detected voltages V1 and V2 may contain errors due to various factors. Therefore, the diagnostic controller 12 may compare, for example, the value obtained by subtracting the detected voltage V1 before time Ta from the detected voltage V2 after time Tb (V2-V1) with a predetermined threshold TH (>0). For example, the diagnostic controller 12 determines that relay RL3m is normal if the value obtained by subtracting the detected voltage V1 from the detected voltage V2 (V2-V1) is greater than or equal to the predetermined threshold TH. Also, the diagnostic controller 12 determines that relay RL3m is abnormal if the value obtained by subtracting the detected voltage V1 from the detected voltage V2 is less than the predetermined threshold TH. The threshold TH is set, for example, based on the results of prior simulations or experiments. Furthermore, the detected voltages V1 and V2 are examples of first and second detected values, respectively.

[0055] (Capacitor charging control) Figure 5 is a diagram illustrating the functions of the PWM controller 10. The PWM controller 10 includes arithmetic units 100, 102u~102w, converters 104u~104w, generator 105, adders 103u~103w, and dividers 101u~101w. The arithmetic units 100, 102u~102w, converters 104u~104w, generator 105, adders 103u~103w, and dividers 101u~101w are implemented by at least one of hardware and software.

[0056] Itg = {(1 / 2) × C × (Vtg 2 -V1 2 ) / V1 ···(1)

[0057] The diagnostic controller 12 calculates the target current value Itg of the three-phase AC current from the target voltage value Vtg of the smoothing capacitor 22's voltage VL using the above equation (1). In equation (1), C is the capacitance of the smoothing capacitor 22. The diagnostic controller 12 calculates the target current value Itg and outputs it to the arithmetic unit 100. The arithmetic unit 100 calculates Itg / 3 and outputs it to the dividers 101u to 101w respectively.

[0058] Current sensors 9u to 9w output the detected current values ​​Iu to Iw to dividers 101u to 101w, respectively. Dividers 101u to 101w calculate the difference between the detected current values ​​Iu to Iw and Itg / 3 and output it to arithmetic units 102u to 102w, respectively. Arithmetic units 102u to 102w multiply the difference in current values ​​by a predetermined gain and output it to adders 103u to 103w, respectively.

[0059] Furthermore, voltage sensors 23 and 24 output detected voltages (voltages VH and VL) to the arithmetic unit 106. The arithmetic unit 106 calculates the sum of the duty cycles of the PWM control and outputs it to adders 103u to 103w, so that VL / VH is fed forward to the PWM signal to inverter 6 and VH / VL is fed forward to the PWM signal to inverter 7.

[0060] The adders 103u to 103w calculate the duty cycle by adding the sum to the difference in current values ​​and output it to the converters 104u to 104w. The converters 104u to 104w convert the duty cycle into a pulse wave and output it to the generator 105. The generator 105 generates a PWM signal from each pulse wave and outputs it to the switching elements 61 to 66 and 71 to 76.

[0061] In this way, the PWM controller 10 generates a PWM signal from the target voltage value Vtg. As shown in Figures 2(A) and 2(C), when the smoothing capacitors 21 and 22 are precharged, the switching elements 61 to 63 of the inverter 6 are kept in the ON state, the switching elements 64 to 66 are kept in the OFF state, and the switching elements 71 to 76 of the inverter 7 perform switching operations. Therefore, the voltage VH across the smoothing capacitor 21 is boosted by the inverters 6 and 7.

[0062] Furthermore, the PWM controller 10 controls inverters 6 and 7 based on the detected current values ​​Iu to Iw so that the voltage VL across both terminals of the smoothing capacitor 22 becomes the target voltage value Vtg. Therefore, since the PWM controller 10 can control the voltage VL of the smoothing capacitor 22 with high precision, it is also possible to diagnose the relay RL3m with high precision.

[0063] (Power supply operation) Figure 6 is a flowchart illustrating the operation of power supply unit S. This operation includes the pre-charge operation and diagnostic processing described above. It is assumed that relays RLa, RLb, RL1s~RL4s, RLd, RLe, RL1m~RL3m are in the open state before the start of operation.

[0064] First, the vehicle control unit 2 closes relays RL1s, RL3s, and RL4s, and the relay controller 11 closes relay RL3m (St1). This forms the charging path Kb shown in Figure 2(B).

[0065] Next, the vehicle control unit 2 precharges the smoothing capacitor 22 from the power supply Ed (St2). Then, the vehicle control unit 2 opens relay RL4s, and the relay controller 11 opens relay RL3m (St3). This completes the precharge operation. At this time, the vehicle control unit 2 controls the timing of stopping the charge based, for example, on the voltage detected by the voltage sensor 24. After precharging, the voltage VL of the smoothing capacitor 22 becomes substantially equal to the voltage of the power supply Ed.

[0066] Next, the vehicle control unit 2 closes relays RLb and RL4s (St4). This forms the charging path Ka shown in Figure 2(A).

[0067] Next, the vehicle control unit 2 precharges the smoothing capacitor 21 from the power supply Eu (St5). Then, the vehicle control unit 2 controls the closing of relay RL2s and the opening of relay RL4s (St6). This completes the precharge operation. At this time, the vehicle control unit 2 controls the timing of stopping the charge based, for example, on the voltage detected by the voltage sensor 23. After precharging, the voltage VH of the smoothing capacitor 21 becomes substantially equal to the voltage of the power supply Eu. Also, by closing relay RL2s, the power supply PWR and the power converter U are energized via the power lines VDDa, VDDb and the ground line SG.

[0068] Next, the relay controller 11 performs closing control on the relay RL3m to be diagnosed (St7). Thereby, the inverter 7 is energized with the battery Ed.

[0069] Next, the PWM controller 10 controls the inverters 6 and 7 in accordance with instructions from the vehicle control unit 2 (St8). The vehicle control unit 2 instructs the operations of the inverters 6 and 7 according to the vehicle state. Such operations include, for example, charging the batteries Eu and Ed from the DC charger 9, supplying power from the batteries Eu and Ed to the DC charger 9, and adjusting the SOC (State of Charge) between the batteries Eu and Ed. Subsequent Steps St9 to St15 are an operation example of the diagnosis process for the relay RL3m. The start of the diagnosis process is instructed by the vehicle control unit 2. Note that the diagnosis process may be executed prior to St8.

[0070] Next, the diagnosis controller 12 acquires the detection voltage V1 from the voltage sensor 24 (St9). The detection voltage V1 is the voltage VL of the precharged smoothing capacitor 22.

[0071] Next, the relay controller 11 performs opening control on the relay RL3m to be diagnosed (St10). Next, the PWM controller 10 controls the inverters 6 and 7 such that the smoothing capacitor 22 is charged from the smoothing capacitor 21 via the inverters 6 and 7 (St11).

[0072] Next, the diagnosis controller 12 acquires the detection voltage V2 from the voltage sensor 24 (St12). The detection voltage V2 is the voltage VL of the smoothing capacitor 22 after the opening control of the relay RL3m.

[0073] Next, the diagnosis controller 12 compares a value obtained by subtracting the detection voltage V1 from the detection voltage V2 (V2-V1) with a threshold TH (St13). When V2-V1≧TH is satisfied (Yes in St13), the diagnosis controller 12 determines that the relay RL3m is normal (St14). Further, when V2-V1<TH is satisfied (No in St13), the diagnosis controller 12 determines that the relay RL3m is abnormal due to sticking or other causes (St15).

[0074] In this way, the diagnostic controller 12 can detect an abnormality in relay RL3m. The diagnostic controller 12 may also notify the vehicle occupants of the abnormality in relay RL3m by means of a screen display or audio output.

[0075] The embodiments described above are preferred examples of the present invention. However, the invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0076] M Motor, Lu~Lw Winding, S Power supply, PWR Power supply, 1 Control unit (control section), 6,7 Inverter (1st and 2nd inverter), 9u~9w Current sensor (current detection section), 21,22 Smoothing capacitor (1st and 2nd capacitor), 24 Voltage sensor (voltage detection section), RL3m Relay,

Claims

1. In a power conversion device that converts DC power from a first battery and a second battery supplied to a motor into AC power, A first inverter is connected to both poles of the first battery and to one end of each phase winding of the motor, A second inverter is connected to both poles of the second battery and to the other end of each phase winding of the motor, A first capacitor connected in parallel with the first battery between the first inverter and the first battery, A second capacitor connected in parallel to the second battery between the second inverter and the second battery, A voltage detection unit for detecting the voltage between both terminals of the second capacitor, A relay is interposed in the wiring connecting one end of the second capacitor and one terminal of the second battery, The system comprises a first inverter, a second inverter, and a control unit that controls the relay, The control unit, When the relay is in the closed state, the first detected value of the voltage detection unit is acquired. After obtaining the first detected value, the relay is opened and closed. After the relay is opened, the first inverter and the second inverter are controlled to charge the second capacitor from the first capacitor through the windings of each phase. After controlling the first inverter and the second inverter, the second detection value of the voltage detection unit is acquired. If the second detection value is substantially equal to the first detection value, an abnormality in the relay is detected. Power converter.

2. The control unit, If the value obtained by subtracting the first detection value from the second detection value is greater than or equal to a predetermined value greater than 0, the abnormality of the relay is not detected. If the value obtained by subtracting the first detection value from the second detection value is less than the predetermined value, an abnormality of the relay is detected. The power conversion device according to claim 1.

3. It has a current detection unit that detects the current value flowing through the windings of each of the phases, The control unit controls the first inverter and the second inverter based on the current value detected by the current detection unit so that the voltage between both terminals of the second capacitor reaches a predetermined target value. The power conversion device according to claim 1 or 2.

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