Multilevel inverter and multilevel inverter device

Abstract

A multilevel inverter (24) inputs a multilevel voltage formed on the basis of voltages output from a plurality of batteries (26a to 26f) connected in series, and switches an output voltage to any one of the multilevel voltages. The multilevel inverter (24) is provided with: a plurality of high-voltage-side switches (Su1, Su2, Sv1, Sv2, Sw1, Sw2, S1, S3, S5, S7) connected in series, which receive a total voltage obtained by summing the voltages of the plurality of batteries, and switch between the output and cut-off of the total voltage; and a plurality of changeover switches (41 to 46) that switch a voltage input to the plurality of high-voltage-side switches to any one voltage, among voltages output from end points and connection points (CP, CP1 to CP3) of the plurality of batteries, which is lower than the total voltage and higher than 0.

Description

Multilevel inverter and multilevel inverter device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-155299, filed on September 9, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a multilevel inverter.

[0003] For example, there is an inverter device that includes a neutral-point clamped three-level inverter that has multiple switching elements and multiple diodes as elements for each phase and drives a three-phase motor, and a control device that controls the three-level inverter so that three-level voltages are applied to each phase of the three-phase motor (see Patent Document 1).When a short-circuit fault occurs in any of the elements for each phase, the control device described in Patent Document 1 controls the three-level inverter so that two-level voltages are applied to each phase of the three-phase motor using elements that are not short-circuited.

[0004] Japanese Patent Application Laid-Open No. 2020-115700

[0005] Each phase of the three-level inverter described in Patent Document 1 has first to fourth switches connected in series from the positive line to the negative line on the DC side in that order. The U-phase, V-phase, and W-phase of the motor are connected to the connection points of the second and third switches of each phase, respectively.

[0006] When the first and second switches are turned off and the third and fourth switches are turned on, the DC voltage is blocked by the first and second switches. Therefore, the withstand voltage required for the first and second switches is half the DC voltage. However, if the first switch experiences a short-circuit failure, the DC voltage must be blocked by only the second switch. In this case, the withstand voltage required for the second switch is the entire DC voltage. Therefore, in order to block the DC voltage even if either the first or second switch experiences a short-circuit failure, the withstand voltage of the first and second switches must be high, which may increase the cost of the first and second switches.

[0007] This situation is not limited to three-level inverters, but is generally common to multilevel inverters with four or more levels.

[0008] The present disclosure has been made to solve the above-mentioned problems, and a main object of the present disclosure is to provide a multilevel inverter that can reduce the withstand voltage of the switches.

[0009] A first means for solving the above problem is a multilevel inverter that receives an input of a multilevel voltage formed based on the voltages output from a plurality of batteries connected in series and switches the output voltage to one of the multilevel voltages, and includes: a plurality of high-side switches connected in series that receive an input of a total voltage obtained by adding up the voltages of the plurality of batteries and switch between outputting and cutting off the total voltage; and a plurality of change-over switches that switch the voltage input to the plurality of high-side switches to one of the voltages output from the end points and connection points of the plurality of batteries that is lower than the total voltage and higher than 0.

[0010] According to the above configuration, the multilevel inverter receives as input multilevel voltages formed based on voltages output from a plurality of series-connected batteries. The multilevel voltages may be formed by dividing the total voltage of the plurality of batteries by a plurality of series-connected capacitors, or may be formed by voltages output from terminals and connection points of the plurality of batteries. The multilevel inverter switches its output voltage to one of the multilevel voltages.

[0011] Here, the multiple high-side switches are connected in series, receive the total voltage, and switch between outputting and blocking the total voltage. Therefore, the withstand voltage required for each of the multiple high-side switches to block the total voltage is the total voltage divided by the number of high-side switches. However, if, for example, one high-side switch fails due to a short circuit, the total voltage must be blocked by only the normal high-side switches. Therefore, in order to block the total voltage even if one of the multiple high-side switches fails due to a short circuit, the withstand voltage of the high-side switches must be high, which may increase the cost of the high-side switches.

[0012] In this regard, the multilevel inverter includes a plurality of changeover switches that change the voltage input to the plurality of high-side switches to one of the voltages output from the terminals and connection points of the plurality of batteries, the voltage being lower than the total voltage and higher than zero. Therefore, for example, if one high-side switch fails due to a short circuit, the voltage input to the plurality of high-side switches can be changed to a voltage lower than the total voltage by the plurality of changeover switches. Therefore, it is not necessary to keep the withstand voltages of the plurality of high-side switches high, and the withstand voltages of the plurality of high-side switches can be lowered. Furthermore, even if, for example, one high-side switch fails due to a short circuit, a voltage lower than the total voltage and higher than zero can be input to the plurality of high-side switches, allowing the multilevel inverter to continue outputting voltage.

[0013] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a circuit diagram of a multilevel inverter device, a battery, and a motor according to a first embodiment, Fig. 2 is a circuit diagram showing switching of the changeover switch when a short-circuit fault occurs in the switch Su1, Fig. 3 is a flowchart showing a procedure for switching between normal running control and evacuation running control, Fig. 4 is a circuit diagram showing a modified example of a plurality of batteries, Fig. 5 is a circuit diagram showing a modified example of the multilevel inverter according to the first embodiment, Fig. 6 is a circuit diagram of a multilevel inverter device, a battery, and a motor according to a second embodiment, Fig. 7 is a circuit diagram showing switching of the changeover switch when a short-circuit fault occurs in the switch Su1, Fig. 8 is a circuit diagram of a multilevel inverter device, a battery, and a motor according to a third embodiment, and Fig. 9 is a flowchart showing the procedure for switching of the changeover switch when a short-circuit fault occurs in the switch Su1. 14 is a circuit diagram of a multilevel inverter and a battery according to a sixth embodiment; FIG. 15 is a circuit diagram showing a first example of switching of the changeover switch when a short-circuit failure occurs in the switch S1; FIG. 16 is a circuit diagram showing a second example of switching of the changeover switch when a short-circuit failure occurs in the switch S1; and FIG. 17 is a circuit diagram showing a modified example of the multilevel inverter according to the sixth embodiment.

[0014] First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings, which is embodied in a multilevel inverter device that is mounted on an electric vehicle or a hybrid vehicle and drives a motor.

[0015] As shown in Fig. 1, for example, an electric vehicle includes a driving motor 22, an inverter device 20, and a battery 26 (cells 26a and 26b). The battery 26 is configured as, for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery. The inverter device 20 (corresponding to a multilevel inverter device) includes an inverter 24 and an electronic control unit (ECU) 30. The battery 26 is connected to the inverter 24 via a power line 28. The ECU 30 (corresponding to a control device) controls the inverter 24 (corresponding to a multilevel inverter).

[0016] The battery 26 is composed of cells 26a and 26b (i.e., multiple cells) connected in series. The cells 26a and 26b are composed of one or more cells (single cells). The rated voltage of the cells 26a and 26b is both VH / 2, and the rated voltage of the battery 26 is VH.

[0017] The motor 22 is configured as, for example, a three-phase synchronous generator motor, and has a rotor in which a permanent magnet is embedded in a rotor core, and a stator in which a three-phase coil is wound around a stator core.

[0018] The inverter 24 is configured as a three-level neutral-point clamp inverter and includes U-phase, V-phase, and W-phase switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4, diodes Du1 to Du4, Dv1 to Dv4, and Dw1 to Dw4, clamp diodes Dc1 to Dc6, and capacitors C1 and C2. The switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 are, for example, IGBTs.

[0019] The U-phase switching elements Su1 to Su4 are connected in series to the positive line 28p and negative line 28n of the power line 28, in this order. U-phase diodes Du1 to Du4 are connected in parallel to the U-phase switching elements Su1 to Su4, respectively (with the forward direction being from the negative line 28n side to the positive line 28p side of the power line 28). The U-phase of the motor 22 is connected to the connection point of the U-phase switching elements Su2 and Su3. The cathode of the clamp diode Dc1 is connected to the connection point of the U-phase switching elements Su1 and Su2 (corresponding to multiple high-voltage side switches). The cathode of the clamp diode Dc2 is connected to the anode of the clamp diode Dc1. The connection point of the U-phase switching elements Su3 and Su4 (corresponding to multiple low-voltage side switches) is connected to the anode of the clamp diode Dc2.

[0020] The V-phase switching elements Sv1 to Sv4 are connected in series to the positive line 28p and negative line 28n of the power line 28, in this order. V-phase diodes Dv1 to Dv4 are connected in parallel to the V-phase switching elements Sv1 to Sv4, respectively (with the forward direction being from the negative line 28n side to the positive line 28p side of the power line 28). The V-phase of the motor 22 is connected to the connection point of the V-phase switching elements Sv2 and Sv3. The cathode of a clamp diode Dc3 is connected to the connection point of the V-phase switching elements Sv1 and Sv2 (corresponding to multiple high-voltage side switches). The cathode of a clamp diode Dc4 is connected to the anode of the clamp diode Dc3. The connection point of the V-phase switching elements Sv3 and Sv4 (corresponding to multiple low-voltage side switches) is connected to the anode of the clamp diode Dc4.

[0021] The W-phase switching elements Sw1 to Sw4 are connected in series to the positive line 28p and negative line 28n of the power line 28, in this order. W-phase diodes Dw1 to Dw4 are connected in parallel to the W-phase switching elements Sw1 to Sw4, respectively (with the forward direction being from the negative line 28n side to the positive line 28p side of the power line 28). The W-phase of the motor 22 is connected to the connection point of the W-phase switching elements Sw2 and Sw3. The cathode of a clamp diode Dc5 is connected to the connection point of the W-phase switching elements Sw1 and Sw2 (corresponding to multiple high-voltage side switches). The cathode of a clamp diode Dc6 is connected to the anode of the clamp diode Dc5. The connection point of the W-phase switching elements Sw3 and Sw4 (corresponding to multiple low-voltage side switches) is connected to the anode of the clamp diode Dc6.

[0022] The capacitors C1 and C2 have the same rated capacity and are connected in series, in this order, to the positive line 28p and negative line 28n of the power line 28. The connection point (neutral point NP) of the capacitors C1 and C2 is connected to the connection point of the clamp diodes Dc1 and Dc2, the connection point of the clamp diodes Dc3 and Dc4, and the connection point of the clamp diodes Dc5 and Dc6.

[0023] Although not shown, the ECU 30 is configured as a microprocessor centered around a CPU. In addition to the CPU, the ECU 30 also includes a ROM for storing processing programs, a RAM for temporarily storing data, and input / output ports. Signals from various sensors are input to the ECU 30 via the input ports. Examples of signals input to the ECU 30 include a rotational position θm from a rotational position sensor 22a that detects the rotational position of the rotor of the motor 22, and currents Iu and Iv from current sensors 14u and 14v that detect the currents of the respective phases of the motor 22. Other signals input to the ECU 30 include temperatures from temperature sensors (not shown) attached to the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4, the diodes Du1 to Du4, Dv1 to Dv4, and Dw1 to Dw4, and the clamp diodes Dc1 to Dc6 of the respective phases of the inverter 24.

[0024] Various control signals are output from the ECU 30 via an output port. For example, the signals output from the ECU 30 include control signals to the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase of the inverter 24. The ECU 30 calculates the electrical angle θe and rotational speed Nm of the motor 22 based on the rotational position θm of the rotor of the motor 22 from the rotational position sensor 22a.

[0025] In the inverter device 20, the ECU 30 performs switching control of the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of the inverter 24 by pulse width modulation control (PWM control) so that the motor 22 is driven by the torque command Tm*, for example.

[0026] In controlling the inverter 24, first, assuming that the sum of the currents flowing through each phase of the motor 22 is zero, the U-phase and V-phase currents Iu and Iv are converted to d-axis and q-axis currents Id and Iq (three-phase to two-phase conversion) using the electrical angle θe of the motor 22. Next, d-axis and q-axis current commands Id* and Iq* are set based on the torque command Tm* of the motor 22, and d-axis and q-axis voltage commands Vd* and Vq* are set so that the differences between the d-axis and q-axis currents Id and Iq and the current commands Id* and Iq* are canceled out. Then, the d-axis and q-axis voltage commands Vd* and Vq* are converted to U-phase, Vv*, and W-phase voltage commands Vw* (two-phase to three-phase conversion) using the electrical angle θe of the motor 22. Then, PWM signals for the U-phase, V-phase, and W-phase switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 are generated based on the U-phase, V-phase, and W-phase voltage commands Vu*, Vv*, and Vw*, and the generated PWM signals for the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 are used to perform switching control of the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4.

[0027] The inverter 24 includes a first changeover switch 41 , a high-pressure side bypass 51 , and a second changeover switch 42 .

[0028] The first changeover switch 41 and the second changeover switch 42 are configured, for example, by relays. The high-voltage side bypass 51 connects the connection point CP of the batteries 26a and 26b to the connection point HP of the battery 26a and the capacitor C1 on the positive electrode line 28p. The first changeover switch 41 is connected between the battery 26a and the connection point CP. When the first changeover switch 41 is turned on, it connects the battery 26a to the connection point CP, and when turned off, it disconnects the battery 26a from the connection point CP. In other words, the first changeover switch 41 connects and disconnects the connection point CP (predetermined connection point) of the batteries 26a and 26b (multiple batteries) to the high-voltage side battery 26a closest to the connection point CP.

[0029] A second changeover switch 42 is provided between the connection point CP and the connection point HP in the high-pressure side bypass 51. When the second changeover switch 42 is turned on, it connects the connection point CP to the connection point HP, and when turned off, it disconnects the connection point CP from the connection point HP. That is, the second changeover switch 42 connects and disconnects the connection point CP from the highest-pressure side switching element Su1, Sv1, or Sw1 among the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 (multiple high-pressure side switches). The first changeover switch 41 and the second changeover switch 42 are controlled by the ECU 30.

[0030] Next, the operation of the inverter device 20 configured in this manner will be described, in particular the control mode when PWM signals for the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase are generated based on the voltage commands Vu*, Vv*, and Vw* of each phase, and the switching control of these elements is performed.

[0031] When none of the elements of each phase of the inverter 24 (switching elements Su1 to Su4, Sv1 to Sv4, Sw1 to Sw4, diodes Du1 to Du4, Dv1 to Dv4, Dw1 to Dw4, and clamp diodes Dc1 to Dc6) are short-circuited, the ECU 30 executes the normal mode. The normal mode is a mode executed during normal driving control of the electric vehicle. In the normal mode, PWM signals for the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase are generated based on voltage commands Vu*, Vv*, and Vw* for each phase, and switching control of these elements is performed so that three voltage levels, high level (H level), middle level (M level), and low level (L level), are applied to each phase of the motor 22. The H level is voltage VH, the M level is voltage VH / 2, and the L level is voltage 0. That is, the inverter 24 inputs H-level, M-level, and L-level (corresponding to multi-level) voltages formed based on the voltages output from the series-connected batteries 26a, 26b (corresponding to multiple batteries), and switches the output voltage to one of the H-level, M-level, and L-level voltages.

[0032] When the ECU 30 executes the normal mode, it connects the connection point CP to the battery 26a on the high-voltage side closest to the connection point CP using the first changeover switch 41, and disconnects the connection point CP from the switching elements Su1, Sv1, and Sw1 (high-voltage side switches) on the highest-voltage side using the second changeover switch 42. This state corresponds to a first state in which a voltage VH (corresponding to a total voltage) obtained by summing the voltages VH / 2 of the batteries 26a and 26b (corresponding to multiple batteries) is input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 (corresponding to multiple high-voltage side switches).

[0033] Here, the relationship between the on / off states of U-phase switching elements Su1 to Su4 and the U-phase voltage Vu of motor 22 will be described. When switching elements Su1 and Su2 are turned on and switching elements Su3 and Su4 are turned off, current flows from positive line 28p of power line 28 to U-phase of motor 22 via switching elements Su1 and Su2. At this time, the voltage at the U-phase input terminal of motor 22 becomes substantially equal to the voltage of positive line 28p of power line 28, and U-phase voltage Vu of motor 22 becomes H level. In other words, switching elements Su1 and Su2 are switched so as to input H-level voltage VH (corresponding to the total voltage) obtained by summing voltages VH / 2 of batteries 26a and 26b, and output H-level voltage VH.

[0034] When switching elements Su3 and Su4 are turned on and switching elements Su1 and Su2 are turned off, current flows from the U-phase input terminal of motor 22 to negative line 28n of power line 28 via switching elements Su3 and Su4. At this time, the voltage at the U-phase input terminal of motor 22 becomes approximately equal to the voltage at negative line 28n of power line 28, and U-phase voltage Vu of motor 22 becomes low. At this time, switching elements Su1 and Su2 are switched so as to input high-level voltage VH and cut off high-level voltage VH. In this state, high-level voltage VH is cut off by switching elements Su1 and Su2 connected in series. Therefore, the withstand voltage required for switching elements Su1 and Su2 is voltage VH / 2.

[0035] When switching elements Su2 and Su3 are turned on and switching elements Su1 and Su4 are turned off, current flows from the junction (neutral point NP) of capacitors C1 and C2 via clamp diode Dc1 and switching element Su2 to the input terminal of motor 22, or current flows from the input terminal of motor 22 via switching element Su3 and clamp diode Dc2 to the junction of capacitors C1 and C2. At this time, the voltage of the U-phase input terminal of motor 22 becomes approximately equal to the voltage of the junction of capacitors C1 and C2, and U-phase voltage Vu of motor 22 becomes the M level.

[0036] The same applies to the relationship between the on / off of the V-phase switching elements Sv1 to Sv4 and the V-phase voltage Vv of the motor 22, and the relationship between the on / off of the W-phase switching elements Sw1 to Sw4 and the W-phase voltage Vw of the motor 22.

[0037] The ECU 30 executes the HL mode when it detects a short-circuit fault in any of the switching elements Su1, Sv1, Sw1 and diodes Du1, Dv1, Dw1. In the HL mode, the ECU 30 generates PWM signals for the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase based on the voltage commands Vu*, Vv*, and Vw* for each phase, and controls the switching of these elements so that two voltage levels, H level and L level, are applied to each phase of the motor 22.

[0038] When a short circuit fault is detected in any of the switching elements Su2, Sv2, and Sw2 and the diodes Du2, Dv2, and Dw2, the ECU 30 executes the HM mode. In the HM mode, the ECU 30 generates PWM signals for the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase of the motor 22, and controls the switching of these elements so that two voltage levels, H level and M level, are applied to each phase of the motor 22.

[0039] The ECU 30 executes the ML mode when it detects a short-circuit fault in any of the switching elements Su3, Sv3, Sw3 and diodes Du3, Dv3, Dw3. In the ML mode, the ECU 30 generates PWM signals for the switching elements Su1 to Su4, Sv1 to Sv4, Sw1 to Sw4 of each phase based on the voltage commands Vu*, Vv*, Vw* of each phase, and controls the switching of these elements so that two voltage levels, M level and L level, are applied to each phase of the motor 22.

[0040] The ECU 30 executes the HL mode when it detects a short-circuit fault in any of the switching elements Su4, Sv4, Sw4 and diodes Du4, Dv4, Dw4. In the HL mode, the ECU 30 generates PWM signals for the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase based on the voltage commands Vu*, Vv*, and Vw* for each phase, and controls the switching of these elements so that two voltage levels, H level and L level, are applied to each phase of the motor 22.

[0041] By implementing these modes, the motor 22 can be driven with a certain degree of accuracy even when any of the switching elements Su1 to Su4, Sv1 to Sv4, Sw1 to Sw4 of each phase and the diodes Du1 to Du4, Dv1 to Dv4, Dw1 to Dw4 suffers a short circuit failure.

[0042] However, for example, if the switching element Su1 or the diode Du1 has a short-circuit failure, the H-level voltage VH must be cut off only by the switching element Su2 in order to execute the HL mode. Therefore, in order to cut off the H-level voltage VH even if the switching element Su1 or the diode Du1 has a short-circuit failure, the withstand voltage of the switching element Su2 must be maintained at voltage VH. In other words, a withstand voltage twice as high as the withstand voltage required for the switching element Su2 when no short-circuit failure occurs is required, which may increase the cost of the switching element Su2. Furthermore, if the switching element Su2 or the diode Du2 has a short-circuit failure, the H-level voltage VH must be cut off only by the switching element Su1 in order to execute the HM mode. Therefore, a withstand voltage twice as high as the withstand voltage required for the switching element Su1 when no short-circuit failure occurs is required, which may increase the cost of the switching element Su1. This also applies to short-circuit failures not only in the U phase but also in the V phase and W phase.

[0043] Therefore, in this embodiment, when the ECU 30 detects a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, Sw2 (plurality of high-voltage side switches) and diodes Du1, Du2, Dv1, Dv2, Dw1, Dw2, the first changeover switch 41 disconnects the connection point CP from the high-voltage side battery 26a closest to the connection point CP, and the second changeover switch 42 connects the connection point CP to the highest-voltage side switching element Su1, Sv1, Sw1 (high-voltage side switch). That is, when ECU 30 detects a short-circuit failure in any of the plurality of high-side switches, it controls first changeover switch 41 and second changeover switch 42 (corresponding to the plurality of changeover switches) to switch the voltage input to the plurality of high-side switches to voltage VH / 2, which is lower than voltage VH (corresponding to the total voltage) and higher than 0, out of voltages VH, VH / 2, and 0 output from the end points of batteries 26a and 26b (the plurality of batteries) and connection point CP, respectively. Note that this state corresponds to a second state in which voltage VH / 2 (i.e., a voltage lower than the total voltage and higher than 0) at connection point CP is input to switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 (corresponding to the plurality of high-side switches).

[0044] For example, when the ECU 30 is in the HM mode, the ECU 30 controls the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase so that an M-level voltage is applied to the U-phase of the motor 22, and if the ECU 30 determines that a short-circuit current (a current different from that in normal operation) is flowing based on the currents Iu and Iv of each phase detected by the current sensors 14u and 14v, the ECU 30 detects that the switching element Su1 or the diode Du1 is short-circuited. Note that when the ECU 30 is in the HM mode, the ECU 30 controls the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase so that an H-level voltage is applied to the U-phase of the motor 22, and if the ECU 30 determines that a short-circuit current is not flowing based on the currents Iu and Iv of each phase detected by the current sensors 14u and 14v.

[0045] Furthermore, when the ECU 30 controls the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase so that an L-level voltage is applied to the U-phase of the motor 22 during execution of the ML mode, and determines based on the currents Iu and Iv of each phase detected by the current sensors 14u and 14v that a short-circuit current (a current different from that in normal operation) is flowing, the ECU 30 detects that the switching element Su2 or the diode Du2 has a short-circuit fault. Note that when the ECU 30 controls the switching elements Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 of each phase so that an M-level voltage is applied to the U-phase of the motor 22 during execution of the ML mode, the ECU 30 determines based on the currents Iu and Iv of each phase detected by the current sensors 14u and 14v that a short-circuit current is not flowing.

[0046] Furthermore, when the temperature from a temperature sensor (not shown) attached to each element of each phase of the inverter 24 is higher than a threshold value, it can be detected that each element has experienced a short circuit. This is because thermal destruction due to overheating is considered to be a cause of short circuit failure in each element of each phase of the inverter 24. It can also be determined that a short circuit current has flowed based on the result of detecting the current flowing through the neutral point NP.

[0047] 2, when the ECU 30 detects a short-circuit fault in the switching element Su1 or the diode Du1, the ECU 30 turns off the first changeover switch 41 and turns on the second changeover switch 42 to execute the HL mode, thereby executing evacuation travel control for causing the electric vehicle to perform evacuation travel.

[0048] 1, when the ECU 30 has not detected a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, Dw2, the ECU 30 turns on the first changeover switch 41 and turns off the second changeover switch 42 to execute the normal mode, thereby executing normal driving control for driving the electric vehicle normally.

[0049] 3 is a flowchart showing a procedure for switching between normal driving control and evacuation driving control. This series of processes is executed by the ECU 30 while the electric vehicle is driving.

[0050] First, normal driving control is executed (S11).

[0051] Next, it is determined whether an element short-circuit fault has been detected (S12). Specifically, it is determined whether a short-circuit fault has been detected in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, and Dw2. If it is determined that a short-circuit fault has not been detected in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, and Dw2 (S12: NO), the first changeover switch 41 is turned on and the second changeover switch 42 is turned off (S13). Then, the process is repeated from S11.

[0052] On the other hand, if it is determined in the judgment of S12 that a short-circuit fault has been detected in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, Dw2 (S12: YES), the first changeover switch 41 is turned off and the second changeover switch 42 is turned on (S14).

[0053] Next, the electric vehicle is controlled to run in an evacuation mode (S15). Specifically, if a short-circuit fault is detected in any of the switching elements Su1, Sv1, and Sw1 and the diodes Du1, Dv1, and Dw1 in the process of S12, the HL mode is executed to cause the electric vehicle to run in an evacuation mode. Furthermore, if a short-circuit fault is detected in any of the switching elements Su2, Sv2, and Sw2 and the diodes Du2, Dv2, and Dw2 in the process of S12, the HM mode is executed to cause the electric vehicle to run in an evacuation mode.

[0054] The present embodiment described above in detail has the following advantages.

[0055] The inverter 24 includes a first changeover switch 41 and a second changeover switch 42 that change the voltage input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 (corresponding to a plurality of high-side switches) to a voltage VH / 2 that is lower than the H-level voltage VH and higher than 0 among the voltages VH, VH / 2, and 0 output from the terminal points of the batteries 26a and 26b and the connection point CP, respectively. Therefore, for example, if one high-side switch experiences a short-circuit failure, the voltage input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 can be changed to the voltage VH / 2 that is lower than the H-level voltage VH by the first changeover switch 41 and the second changeover switch 42. Therefore, it is not necessary to increase the withstand voltage of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, and the withstand voltage of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, and the withstand voltage of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 can be lowered. Furthermore, even if, for example, one high-voltage side switch suffers a short-circuit failure, a voltage VH / 2 that is lower than the H-level voltage VH and higher than 0 can be input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, so that the inverter 24 can continue to output voltage (HL mode or HM mode).

[0056] By connecting the connection point CP of the batteries 26a, 26b to the battery 26a on the high-voltage side closest to the connection point CP with the first changeover switch 41 and disconnecting the connection point CP from the switching elements Su1, Sv1, and Sw1 on the highest-voltage side with the second changeover switch 42, it is possible to input an H-level voltage VH, which is the sum of the voltages of all batteries (one battery 26a in this embodiment) on the high-voltage side of the connection point CP, to the high-voltage side switch. On the other hand, by disconnecting the connection point CP from the battery 26a on the high-voltage side closest to the connection point CP with the first changeover switch 41 and connecting the connection point CP to the switching elements Su1, Sv1, and Sw1 on the highest-voltage side with the second changeover switch 42, it is possible to input the voltage at the connection point CP to the high-voltage side switch. Therefore, the two changeover switches 41 and 42 can be used to switch between a first state in which an H-level voltage VH is input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, and a second state in which a voltage VH / 2 (i.e., a voltage lower than the H-level voltage VH and higher than 0) at the connection point CP is input.

[0057] The ECU 30 controls the inverter 24 to output multi-level voltages VH, VH / 2, and 0. When the ECU 30 detects a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, and Dw2, the ECU 30 controls the first changeover switch 41 and the second changeover switch 42 to switch the voltage input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 to a voltage VH / 2 that is lower than the H-level voltage VH. This eliminates the need to increase the withstand voltage of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, and allows the withstand voltage of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 to be lowered.

[0058] When a short-circuit fault is not detected in switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, the high-level voltage VH obtained by adding the voltage VH / 2 at node CP to the voltages of all batteries (one battery 26a in this embodiment) on the higher voltage side of node CP can be input to the high-side switch. Furthermore, when a short-circuit fault is detected in switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, the voltage VH / 2 at node CP (i.e., a voltage lower than the high-level voltage VH and higher than 0) can be input to the high-side switch.

[0059] The first embodiment can be modified as follows: The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0060] 4, the electric vehicle may include batteries 26c and 26d (multiple batteries) each outputting a voltage VH / 4 instead of battery 26a, and may include batteries 26e and 26f (multiple batteries) each outputting a voltage VH / 4 instead of battery 26b. In this case, the first changeover switch 41 connects and disconnects a connection point CP (predetermined connection point) between batteries 26c and 26d and batteries 26e and 26f, and battery 26d on the high-voltage side closest to connection point CP.

[0061] When the ECU 30 does not detect a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, Sw2 (multiple high-voltage side switches) and the diodes Du1, Du2, Dv1, Dv2, Dw1, Dw2, the first changeover switch 41 connects the connection point CP to the high-voltage side battery 26d closest to the connection point CP, and the second changeover switch 42 disconnects the connection point CP from the highest-voltage side switching elements Su1, Sv1, Sw1. In addition, when the ECU 30 detects a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, Dw2, the first changeover switch 41 disconnects the connection point CP from the high-voltage battery 26d closest to the connection point CP, and the second changeover switch 42 connects the connection point CP to the highest-voltage switching element Su1, Sv1, Sw1.

[0062] According to the above configuration, when a short-circuit fault of switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 is not detected, an H-level voltage VH obtained by adding the voltage VH / 2 at node CP to the voltages VH / 4 of all batteries 26c and 26d on the higher voltage side of node CP can be input to the high-side switch. Furthermore, when a short-circuit fault of switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 is detected, the voltage VH / 2 at node CP (the voltage VH / 2 obtained by adding the voltages VH / 4 of all batteries 26e and 26f on the lower voltage side of node CP) can be input to the high-side switch.

[0063] As shown in Fig. 5, a backflow prevention diode 49 may be provided in the high-voltage side bypass 51. The anode of the backflow prevention diode 49 is connected to the connection point CP, and the cathode of the backflow prevention diode 49 is connected to the second changeover switch 42. Alternatively, the anode of the backflow prevention diode 49 may be connected to the second changeover switch 42, and the cathode of the backflow prevention diode 49 may be connected to the connection point HP. The backflow prevention diode 49 prevents current from flowing back into the battery 26b when the first changeover switch 41 is turned off and the second changeover switch 42 is turned on. In other words, the backflow prevention diode 49 prevents current from flowing back into the battery 26b when the ECU 30 detects a short-circuit fault in the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, controls the first changeover switch 41 and the second changeover switch 42, and switches the voltage input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 to a voltage VH / 2 that is lower than the H-level voltage VH and higher than 0, out of the voltages VH, VH / 2, and 0 output from the terminal points and connection point CP of the batteries 26a and 26b.

[0064] According to the above configuration, when the ECU 30 detects a short-circuit fault in the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 and a voltage VH / 2 lower than the H-level voltage VH and higher than 0 is input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, the backflow prevention diode 49 can prevent current from flowing back into the battery 26b. This prevents excessive voltage from being applied to the battery 26b (corresponding to a portion of the battery) of the batteries 26a and 26b, or excessive charging of the battery 26b, during regenerative power generation by the motor 22, etc. This ultimately prevents imbalances in the remaining capacities of the batteries 26a and 26b.

[0065] Second Embodiment The second embodiment will be described below, focusing on the differences from the first embodiment. Note that the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0066] Instead of the first changeover switch 41, the high-pressure side bypass 51, and the second changeover switch 42 in FIG. 1, the inverter 24 of this embodiment includes a third changeover switch 43, a low-pressure side bypass 52, and a fourth changeover switch 44 as shown in FIG. 6.

[0067] The third changeover switch 43 and the fourth changeover switch 44 are configured, for example, by relays. The low-voltage side bypass 52 connects the connection point CP of the batteries 26a, 26b to the connection point LP of the battery 26b and the capacitor C2 on the negative electrode line 28n. The third changeover switch 43 is connected between the battery 26b and the connection point CP. When the third changeover switch 43 is turned on, it connects the battery 26b to the connection point CP, and when turned off, it disconnects the battery 26b from the connection point CP. In other words, the third changeover switch 43 connects and disconnects the connection point CP (predetermined connection point) of the batteries 26a, 26b (multiple batteries) to the low-voltage side battery 26b closest to the connection point CP.

[0068] A fourth changeover switch 44 is provided between the connection point CP and the connection point LP in the low-pressure side bypass 52. The fourth changeover switch 44 connects the connection point CP and the connection point LP when turned on, and disconnects the connection point CP and the connection point LP when turned off. In other words, the fourth changeover switch 44 connects and disconnects the connection point CP from voltage 0 (ground). The third changeover switch 43 and the fourth changeover switch 44 are controlled by the ECU 30.

[0069] As shown in Fig. 6, when the ECU 30 does not detect a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 (corresponding to multiple high-voltage side switches) and the diodes Du1, Du2, Dv1, Dv2, Dw1, and Dw2, the ECU 30 connects the connection point CP to the low-voltage battery 26b closest to the connection point CP using the third changeover switch 43 and disconnects the connection point CP from ground using the fourth changeover switch 44. On the other hand, as shown in Fig. 7, when the ECU 30 detects a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, and Dw2, the ECU 30 disconnects the connection point CP from the low-voltage battery 26b closest to the connection point CP using the third changeover switch 43 and connects the connection point CP to ground using the fourth changeover switch 44.

[0070] The second embodiment has the following advantages. Here, only advantages different from the first embodiment will be described.

[0071] By connecting the connection point CP of the batteries 26a, 26b to the low-voltage battery 26b closest to the connection point CP with the third switch 43 and disconnecting the connection point CP from ground with the fourth switch 44, it is possible to input an H-level voltage VH, which is the sum of the voltage VH / 2 of the connection point CP and the voltage VH / 2 of all batteries (one battery 26a in this embodiment) on the higher voltage side of the connection point CP, to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2 (high-voltage side switches).On the other hand, by disconnecting the connection point CP from the low-voltage battery 26b closest to the connection point CP with the third switch 43 and connecting the connection point CP to ground with the fourth switch 44, it is possible to input a voltage VH / 2, which is the H-level voltage VH minus the voltages of all batteries (one battery 26b in this embodiment) on the lower voltage side of the connection point CP, to the high-voltage side switches. Therefore, the two changeover switches 43 and 44 can be used to switch between a first state in which an H-level voltage VH is input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, and a third state in which a voltage VH / 2 (i.e., a voltage lower than the H-level voltage VH and higher than 0) obtained by subtracting the voltages of all batteries on the lower voltage side of the connection point CP from the H-level voltage VH is input.

[0072] When a short-circuit fault is not detected in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, the high-level voltage VH obtained by adding the voltage of all batteries (one battery 26a in this embodiment) on the higher voltage side of the connection point CP to the voltage of the connection point CP can be input to the high-side switch. Also, when a short-circuit fault is detected in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, the high-level voltage VH / 2 obtained by subtracting the voltages of all batteries (one battery 26b in this embodiment) on the lower voltage side of the connection point CP from the high-level voltage VH can be input to the high-side switch.

[0073] Third Embodiment Hereinafter, the third embodiment will be described, focusing on the differences from the first and second embodiments. Note that the same parts as those in the first and second embodiments are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0074] As shown in FIG. 8, the inverter 24 of this embodiment includes a first changeover switch 41, a second changeover switch 42, a third changeover switch 43, a fourth changeover switch 44, and bypasses 53 to 55.

[0075] The first changeover switch 41 and the second changeover switch 42 are configured, for example, by relays. The bypasses 53 and 55 connect the connection point CP of the batteries 26a and 26b to the connection point HP of the battery 26a and the capacitor C1 on the positive electrode line 28p. The first changeover switch 41 is connected between the battery 26a and the connection point CP. When the first changeover switch 41 is turned on, it connects the battery 26a to the connection point CP, and when turned off, it disconnects the battery 26a from the connection point CP. In other words, the first changeover switch 41 connects and disconnects the connection point CP (predetermined connection point) of the batteries 26a and 26b (multiple batteries) to the high-voltage battery 26a closest to the connection point CP.

[0076] A second changeover switch 42 is provided in the bypass 53 between the connection point CP and the connection point HP. When the second changeover switch 42 is turned on, it connects the connection point CP to the connection point HP, and when it is turned off, it disconnects the connection point CP from the connection point HP. That is, the second changeover switch 42 connects and disconnects the connection point CP from the highest-voltage side switching element Su1 of the switching elements Su1 and Su2 (plurality of high-voltage side switches). The first changeover switch 41 and the second changeover switch 42 are controlled by the ECU 30.

[0077] The third and fourth switches 43 and 44 are configured, for example, by relays. Bypasses 54 and 55 connect the connection point CP between the batteries 26a and 26b to the connection point LP between the battery 26b and the capacitor C2 on the negative line 28n. The third switch 43 is connected between the battery 26b and the connection point CP. When the third switch 43 is turned on, it connects the battery 26b to the connection point CP, and when turned off, it disconnects the battery 26b from the connection point CP. In other words, the third switch 43 connects and disconnects the connection point CP (predetermined connection point) between the batteries 26a and 26b (multiple batteries) and the low-voltage battery 26b closest to the connection point CP.

[0078] A fourth changeover switch 44 is provided in the bypass 54 between the connection point CP and the connection point LP. The fourth changeover switch 44 connects the connection point CP and the connection point LP when turned on, and disconnects the connection point CP and the connection point LP when turned off. In other words, the fourth changeover switch 44 connects and disconnects the connection point CP and the voltage 0 (ground). The third changeover switch 43 and the fourth changeover switch 44 are controlled by the ECU 30.

[0079] The bypass 55 connects the connection point MP of the second changeover switch 42 and the fourth changeover switch 44 to the connection point CP.

[0080] As shown in FIG. 8, when the ECU 30 does not detect a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, Sw2 (corresponding to multiple high-voltage side switches) and diodes Du1, Du2, Dv1, Dv2, Dw1, Dw2, the first changeover switch 41 connects the connection point CP to the high-voltage side battery 26a closest to the connection point CP, the second changeover switch 42 disconnects the connection point CP from the switching elements Su1, Sv1, Sw1 (corresponding to the high-voltage side switches on the highest voltage side), the third changeover switch 43 connects the connection point CP to the low-voltage side battery 26b closest to the connection point CP, and the fourth changeover switch 44 disconnects the connection point CP from ground. Furthermore, as shown in FIG. 9, when the ECU 30 detects a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, Dw2, the first changeover switch 41 disconnects the connection point CP from the high-voltage battery 26a closest to the connection point CP, the second changeover switch 42 connects the connection point CP to the switching elements Su1, Sv1, Sw1, the third changeover switch 43 connects the connection point CP to the low-voltage battery 26b closest to the connection point CP, and the fourth changeover switch 44 disconnects the connection point CP from ground. Alternatively, as shown in FIG. 10, when the ECU 30 detects a short-circuit fault in any of the switching elements Su1, Su2, Sv1, Sv2, Sw1, Sw2 and the diodes Du1, Du2, Dv1, Dv2, Dw1, Dw2, the first changeover switch 41 connects the connection point CP to the high-voltage battery 26a closest to the connection point CP, the second changeover switch 42 disconnects the connection point CP from the switching elements Su1, Sv1, Sw1, the third changeover switch 43 disconnects the connection point CP from the low-voltage battery 26b closest to the connection point CP, and the fourth changeover switch 44 connects the connection point CP to ground.

[0081] The third embodiment has the following advantages. Here, only advantages different from the first and second embodiments will be described.

[0082] By connecting the connection point CP of the batteries 26a, 26b to the battery 26a on the high-voltage side closest to the connection point CP using the first changeover switch 41, disconnecting the connection point CP from the switching elements Su1, Sv1, and Sw1 using the second changeover switch 42, connecting the connection point CP to the battery 26b on the low-voltage side closest to the connection point CP using the third changeover switch 43, and disconnecting the connection point CP from ground using the fourth changeover switch 44, it is possible to input an H-level voltage VH, which is the sum of the voltage VH / 2 of the connection point CP and the voltage VH / 2 of all batteries (one battery 26a in this embodiment) on the high-voltage side of the connection point CP, to the high-voltage side switch (switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2).

[0083] By using the first changeover switch 41 to disconnect the connection point CP from the high-voltage side battery 26a closest to the connection point CP, and by using the second changeover switch 42 to connect the connection point CP to the switching elements Su1, Sv1, and Sw1, and by using the third changeover switch 43 to connect the connection point CP to the low-voltage side battery 26b closest to the connection point CP, and by using the fourth changeover switch 44 to disconnect the connection point CP from ground, it is possible to input the voltage VH / 2 at the connection point CP (the sum of the voltages of all the batteries on the low-voltage side of the connection point CP) to the high-voltage side switch.

[0084] By connecting the connection point CP to the high-voltage battery 26a closest to the connection point CP using the first changeover switch 41, disconnecting the connection point CP from the switching elements Su1, Sv1, and Sw1 using the second changeover switch 42, disconnecting the connection point CP from the low-voltage battery 26b closest to the connection point CP using the third changeover switch 43, and connecting the connection point CP to ground using the fourth changeover switch 44, it is possible to input a voltage VH / 2, which is the H-level voltage VH minus the voltages of all batteries on the low-voltage side of the connection point CP, to the high-voltage side switch.

[0085] The four changeover switches 41 to 44 can be used to switch between three states: a first state (FIG. 8) in which an H-level voltage VH is input to the switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2; a second state (FIG. 9) in which a voltage VH / 2 obtained by adding the voltages of all batteries on the lower-voltage side of the connection point CP is input; and a third state (FIG. 10) in which a voltage VH / 2 obtained by subtracting the voltages of all batteries on the lower-voltage side of the connection point CP from the H-level voltage VH is input.

[0086] When a short-circuit fault is not detected in switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, the high-level voltage VH obtained by adding the voltage VH / 2 at node CP and the voltages of all batteries on the higher voltage side of node CP can be input to the high-side switch. Furthermore, when a short-circuit fault is detected in any of switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, the high-side switch can be input with the voltage VH / 2 obtained by adding the voltages of all batteries on the lower voltage side of node CP, or the voltage VH / 2 obtained by subtracting the voltages of all batteries on the lower voltage side of node CP from the high-level voltage VH. Therefore, when a voltage VH / 2 lower than the high-level voltage VH and higher than zero is input to switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2, the second or third state can be selected, thereby preventing imbalances in the remaining capacities of batteries 26a and 26b.

[0087] Fourth Embodiment The fourth embodiment will be described below, focusing on the differences from the first embodiment. Note that the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0088] As shown in Fig. 11, the inverter 24 of this embodiment does not include the capacitors C1 and C2 shown in Fig. 1. The junction CP of the batteries 26a and 26b is connected to the junction CP of the clamp diodes Dc1 and Dc2, the junction CP of the clamp diodes Dc3 and Dc4, and the junction CP of the clamp diodes Dc5 and Dc6. The batteries 26a and 26b have rated capacities that are sufficiently larger than those of the capacitors C1 and C2 and are configured identically to each other.

[0089] According to the above configuration, the inverter 24 receives a multi-level voltage formed based on the voltages output from the series-connected batteries 26a, 26b (corresponding to multiple batteries). The multi-level voltage is formed by the voltages VH, VH / 2, and 0 output from the terminal points of the batteries 26a, 26b and the connection point CP. The inverter 24 switches the output voltage to one of the multi-level voltages. Even with this configuration, it is possible to achieve the same effects as in the first embodiment.

[0090] Fifth Embodiment Hereinafter, a fifth embodiment will be described, focusing on differences from the first embodiment. Note that the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0091] Each phase of the inverter 24 in Fig. 1 can also be changed to the circuit shown in Fig. 12. Each phase of the inverter 24 includes switching elements S1 to S4 and diodes D1 to D4. The inverter 24 includes a first changeover switch 41 and a second changeover switch 42 that are common to each phase. That is, the switching elements S1 to S4 and diodes D1 to D4 of each phase are connected in parallel to connection points HP, CP, and LP.

[0092] The inverter 24 receives three voltage levels (VH, VH / 2, 0) and switches the output voltage Vo to each phase of the motor 22 to one of the three voltage levels. Specifically, the ECU 30 (not shown) turns on the switching elements S1 and S3 and turns off the switching elements S2 and S4, thereby outputting the H-level voltage VH. The ECU 30 turns on the switching elements S2 and S3 and turns off the switching elements S1 and S4, thereby outputting the M-level voltage VH / 2. The ECU 30 turns off the switching element S3 and turns on the switching element S4, thereby outputting the 0-level voltage.

[0093] As shown in Fig. 12, when the ECU 30 has not detected a short-circuit fault in any of the switching elements S1, S3 (corresponding to multiple high-voltage side switches) of each phase or the diodes D1, D3 of each phase, the ECU 30 connects the connection point CP to the battery 26a on the high-voltage side closest to the connection point CP using the first changeover switch 41, and disconnects the connection point CP from the switching element S1 on the highest-voltage side of each phase using the second changeover switch 42. On the other hand, as shown in Fig. 13, when the ECU 30 detects a short-circuit fault in any of the switching elements S1, S3 or diodes D1, D3 of each phase, the ECU 30 disconnects the connection point CP from the battery 26a on the high-voltage side closest to the connection point CP using the first changeover switch 41, and connects the connection point CP to the switching element S1 on the highest-voltage side of each phase using the second changeover switch 42. That is, when ECU 30 detects a short-circuit failure in any of the plurality of high-side switches of each phase, it controls first changeover switch 41 and second changeover switch 42 (corresponding to a plurality of changeover switches) to switch the voltage input to the plurality of high-side switches of each phase to voltage VH / 2, which is lower than voltage VH (corresponding to the total voltage) and higher than voltage 0, out of voltages VH, VH / 2, and 0 output from the end points and connection point CP of batteries 26a, 26b (a plurality of batteries). Even with this configuration, it is possible to achieve the same effects as in the first embodiment.

[0094] Sixth Embodiment Hereinafter, a sixth embodiment will be described, focusing on differences from the fifth embodiment. Note that the same parts as those in the fifth embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0095] The three-level inverter 24 of Fig. 12 can also be changed to a five-level inverter 24 as shown in Fig. 14. In this embodiment, each phase of the inverter 24 includes switching elements S1 to S8 and diodes D1 to D8. The inverter 24 includes first changeover switches 41 and 45 and second changeover switches 42 and 46 that are common to each phase. That is, the switching elements S1 to S8 and diodes D1 to D8 of each phase are connected in parallel to connection points HP, CP1 to CP3, and LP.

[0096] The inverter 24 receives five voltage levels (VH, 3VH / 4, 2VH / 4, VH / 4, 0) and switches the output voltage Vo to each phase of the motor 22 to one of the five voltage levels. For example, the ECU 30 (not shown) turns on switching elements S1, S3, S5, and S7 and turns off switching elements S2, S4, S6, and S8, thereby outputting a high-level voltage VH. The ECU 30 turns on switching elements S4, S5, and S7 and turns off switching elements S1 to S3, S6, and S8, thereby outputting a voltage VH / 2. The ECU 30 turns off switching element S7 and turns on switching element S8, thereby outputting a voltage of 0.

[0097] As shown in FIG. 14, when the ECU 30 detects no short-circuit fault in any of the switching elements S1, S3, S5, S7 (corresponding to multiple high-voltage side switches) of each phase and the diodes D1, D3, D5, D7 of each phase, the ECU 30 connects the connection point CP1 (predetermined connection point) to the high-voltage side battery 26c closest to the connection point CP1 using the first changeover switch 41, connects the connection point CP2 (predetermined connection point) to the high-voltage side battery 26d closest to the connection point CP2 using the first changeover switch 45, disconnects the connection point CP1 from the highest-voltage side switching element S1 of each phase using the second changeover switch 42, and disconnects the connection point CP2 from the highest-voltage side switching element S1 of each phase using the second changeover switch 46.

[0098] On the other hand, as shown in FIG. 15, when the ECU 30 detects a short-circuit failure in any of the switching elements S1, S3, S5, S7 of each phase and the diodes D1, D3, D5, D7 of each phase, it uses the first changeover switch 41 to disconnect the connection point CP1 from the battery 26c on the high-voltage side closest to the connection point CP1, uses the second changeover switch 42 to connect the connection point CP1 to the switching element S1 on the highest-voltage side of each phase, uses the first changeover switch 45 to connect the connection point CP2 to the battery 26d on the high-voltage side closest to the connection point CP2, and uses the second changeover switch 46 to disconnect the connection point CP2 from the switching element S1 on the highest-voltage side of each phase. That is, when ECU 30 detects a short-circuit failure in any of the multiple high-voltage side switches, it controls the first changeover switches 41, 45 and the second changeover switches 42, 46 (corresponding to multiple changeover switches) to switch the voltage input to the multiple high-voltage side switches to voltage 3VH / 4, which is lower than voltage VH (corresponding to the total voltage) and higher than voltage 0, out of voltages VH, 3VH / 4, 2VH / 4, VH / 4, and 0 output from the end points and connection points CP1 to CP3 of batteries 26c to 26f (multiple batteries), respectively.

[0099] Alternatively, as shown in FIG. 16, when the ECU 30 detects a short-circuit failure in any of the switching elements S1, S3, S5, S7 of each phase and the diodes D1, D3, D5, D7 of each phase, it uses the first changeover switch 41 to connect the connection point CP1 to the battery 26c on the high-voltage side closest to the connection point CP1, uses the second changeover switch 42 to disconnect the connection point CP1 from the switching element S1 on the highest-voltage side of each phase, uses the first changeover switch 45 to disconnect the connection point CP2 from the battery 26d on the high-voltage side closest to the connection point CP2, and uses the second changeover switch 46 to connect the connection point CP2 to the switching element S1 on the highest-voltage side of each phase. That is, when ECU 30 detects a short-circuit failure in any of the plurality of high-side switches, it controls first changeover switches 41, 45 and second changeover switches 42, 46 (corresponding to a plurality of changeover switches) to switch the voltage input to the plurality of high-side switches to voltage 2VH / 4, which is lower than voltage VH (corresponding to the total voltage) and higher than voltage 0, out of voltages VH, 3VH / 4, 2VH / 4, VH / 4, and 0 output from the end points and connection points CP1 to CP3 of batteries 26c to 26f (a plurality of batteries). With the above configuration, it is possible to achieve the same effects as in the fifth embodiment.

[0100] 17, a reverse current prevention diode 49 may be provided in the bypass 56 connecting the connection point CP1 of the batteries 26c, 26d to the connection point HP. The anode of the reverse current prevention diode 49 is connected to the connection point CP1, and the cathode of the reverse current prevention diode 49 is connected to the second changeover switch 42. Alternatively, the anode of the reverse current prevention diode 49 may be connected to the second changeover switch 42, and the cathode of the reverse current prevention diode 49 may be connected to the connection point HP. The backflow prevention diode 49 prevents current from flowing back into the batteries 26d to 26f when the ECU 30 detects a short-circuit fault in any of the switching elements S1, S3, S5, and S7, controls the changeover switches 41, 42, 45, and 46, and switches the voltage input to the switching elements S1, S3, S5, and S7 to a voltage 3VH / 4 that is lower than the H-level voltage VH and higher than 0, out of the voltages VH, 3VH / 4, 2VH / 4, VH / 4, and 0 output from the terminal points and connection points CP1 to CP3 of the batteries 26c to 26f.

[0101] A reverse current prevention diode 49 may also be provided in the bypass 57 connecting the connection point CP2 of the batteries 26d, 26e to the connection point HP. The anode of the reverse current prevention diode 49 is connected to the connection point CP2, and the cathode of the reverse current prevention diode 49 is connected to the second changeover switch 46. Alternatively, the anode of the reverse current prevention diode 49 may be connected to the second changeover switch 46, and the cathode of the reverse current prevention diode 49 may be connected to the connection point HP. The backflow prevention diode 49 prevents current from flowing back into the batteries 26e, 26f when the ECU 30 detects a short-circuit failure in any of the switching elements S1, S3, S5, S7 and controls the changeover switches 41, 42, 45, 46, causing the voltage input to the switching elements S1, S3, S5, S7 to be switched to a voltage 2VH / 4 that is lower than the H-level voltage VH and higher than 0, out of the voltages VH, 3VH / 4, 2VH / 4, VH / 4, 0 output from the terminal points and connection points CP1 to CP3 of the batteries 26c to 26f.

[0102] The above-described embodiments and modifications may be combined within the scope of possible combinations.

[0103] Characteristic configurations extracted from the above-described embodiments and modifications are described below. [Configuration 1] A multilevel inverter (24) receives a multilevel voltage formed based on voltages output from a plurality of series-connected batteries (26a-26f) and switches an output voltage to one of the multilevel voltages, the multilevel inverter comprising: a plurality of series-connected high-side switches (Su1, Su2, Sv1, Sv2, Sw1, Sw2, S1, S3, S5, S7) that receive a total voltage obtained by adding up the voltages of the plurality of batteries and switch between outputting and cutting off the total voltage, and a plurality of changeover switches (41-46) that change the voltage input to the plurality of high-side switches to one voltage that is lower than the total voltage and higher than zero, among voltages output from terminal points and connection points (CP, CP1-CP3) of the plurality of batteries. [Configuration 2] The multilevel inverter according to Configuration 1, wherein the plurality of changeover switches include a first changeover switch (41, 45) that connects and disconnects predetermined connection points (CP, CP1, CP2) of the plurality of batteries to a high-voltage side battery (26a, 26c, 26d) closest to the predetermined connection points, and a second changeover switch (42, 46) that connects and disconnects the predetermined connection points to the high-voltage side switch (Su1, Sv1, Sw1, S1) that is the highest-voltage side. [Configuration 3] The multilevel inverter according to Configuration 1, wherein the plurality of changeover switches include a third changeover switch (43) that connects and disconnects predetermined connection points of the plurality of batteries to a low-voltage side battery (26b) closest to the predetermined connection point (CP), and a fourth changeover switch (44) that connects and disconnects the predetermined connection points to ground. [Configuration 4] The multilevel inverter according to Configuration 1, wherein the plurality of changeover switches include a first changeover switch (41) that connects and disconnects predetermined connection points (CP) of the plurality of batteries to a high-voltage side battery (26 a) closest to the predetermined connection points, a second changeover switch (42) that connects and disconnects the predetermined connection points to the high-voltage side switches (Su1, Sv1, Sw1) that are on the highest voltage side, a third changeover switch (43) that connects and disconnects the predetermined connection points to a low-voltage side battery (26 b) closest to the predetermined connection points, and a fourth changeover switch (44) that connects and disconnects the predetermined connection points to ground.[Configuration 5] A multilevel inverter device (20) comprising: the multilevel inverter according to any one of configurations 1 to 4; and a control device (30) that controls the multilevel inverter, wherein when the control device detects a short-circuit fault in any of the plurality of high-voltage side switches, the control device controls the plurality of changeover switches to switch the voltage input to the plurality of high-voltage side switches to any one voltage output from the end points and connection points of the plurality of batteries that is lower than the total voltage and higher than 0. [Configuration 6] A multilevel inverter device (20) comprising the multilevel inverter according to configuration 2; and a control device (30) for controlling the multilevel inverter, wherein the control device, when a short-circuit failure of the plurality of high-voltage side switches is not detected, connects the predetermined connection point to a battery on the high-voltage side closest to the predetermined connection point using the first changeover switch, and disconnects the predetermined connection point from the high-voltage side switch on the highest voltage side using the second changeover switch; and, when a short-circuit failure of any of the plurality of high-voltage side switches is detected, disconnects the predetermined connection point from the battery on the high-voltage side closest to the predetermined connection point using the first changeover switch, and connects the predetermined connection point to the high-voltage side switch on the highest voltage side using the second changeover switch. [Configuration 7] A multilevel inverter device (20) comprising the multilevel inverter according to Configuration 3; and a control device (30) for controlling the multilevel inverter, wherein the control device, when no short-circuit fault is detected in any of the plurality of high-side switches, connects the predetermined connection point to a battery on the low-voltage side closest to the predetermined connection point using the third changeover switch and disconnects the predetermined connection point from ground using the fourth changeover switch; and, when a short-circuit fault is detected in any of the plurality of high-side switches, disconnects the predetermined connection point from the battery on the low-voltage side closest to the predetermined connection point using the third changeover switch and connects the predetermined connection point to ground using the fourth changeover switch.[Configuration 8] A multilevel inverter device (20) comprising the multilevel inverter according to configuration 4, and a control device (30) for controlling the multilevel inverter, wherein the control device, when no short-circuit faults of the plurality of high-voltage side switches are detected, connects the predetermined connection point to a battery on a high-voltage side closest to the predetermined connection point using the first changeover switch, disconnects the predetermined connection point from the high-voltage side switch on the highest voltage side using the second changeover switch, connects the predetermined connection point to a battery on a low-voltage side closest to the predetermined connection point using the third changeover switch, and disconnects the predetermined connection point from the ground using the fourth changeover switch, a first selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a first selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a second selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a second selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a second selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a second selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a third selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; [Configuration 9] The multilevel inverter device according to any one of configurations 5 to 8, further comprising a backflow prevention diode (49) that prevents current from flowing back into the plurality of batteries when the control device detects a short-circuit failure in any of the plurality of high-voltage side switches and controls the plurality of changeover switches, and the voltage input to the plurality of high-voltage side switches is switched to one voltage output from the end points and connection points of the plurality of batteries that is lower than the total voltage and higher than 0.

[0104] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A multilevel inverter (24) that receives a multilevel voltage formed based on the voltages output from a plurality of series-connected batteries (26a-26f) and switches the output voltage to one of the multilevel voltages, comprising: a plurality of series-connected high-side switches (Su1, Su2, Sv1, Sv2, Sw1, Sw2, S1, S3, S5, S7) that receive a total voltage obtained by adding up the voltages of the plurality of batteries and switch between outputting and cutting off the total voltage; and a plurality of changeover switches (41-46) that change the voltage input to the plurality of high-side switches to one voltage that is lower than the total voltage and higher than 0, among voltages output from terminal points and connection points (CP, CP1-CP3) of the plurality of batteries.

2. The multilevel inverter of claim 1, wherein the plurality of changeover switches include first changeover switches (41, 45) that connect and disconnect predetermined connection points (CP, CP1, CP2) of the plurality of batteries to the high-voltage side battery (26a, 26c, 26d) closest to the predetermined connection points, and second changeover switches (42, 46) that connect and disconnect the predetermined connection points to the high-voltage side switch (Su1, Sv1, Sw1, S1) on the highest voltage side.

3. The multilevel inverter of claim 1, wherein the plurality of changeover switches include a third changeover switch (43) that connects and disconnects a predetermined connection point of the plurality of batteries to a low-voltage battery (26b) that is closest to the predetermined connection point (CP), and a fourth changeover switch (44) that connects and disconnects the predetermined connection point to ground.

4. The multilevel inverter of claim 1, wherein the plurality of changeover switches include a first changeover switch (41) that connects and disconnects a predetermined connection point (CP) of the plurality of batteries to a high-voltage side battery (26a) closest to the predetermined connection point, a second changeover switch (42) that connects and disconnects the predetermined connection point to the high-voltage side switch (Su1, Sv1, Sw1) that is the highest-voltage side, a third changeover switch (43) that connects and disconnects the predetermined connection point to a low-voltage side battery (26b) closest to the predetermined connection point, and a fourth changeover switch (44) that connects and disconnects the predetermined connection point to ground.

5. A multilevel inverter device (20) comprising the multilevel inverter according to any one of claims 1 to 4, and a control device (30) that controls the multilevel inverter, wherein when the control device detects a short-circuit fault in any of the plurality of high-voltage side switches, the control device controls the plurality of changeover switches to switch the voltage input to the plurality of high-voltage side switches to one voltage output from the end points and connection points of the plurality of batteries that is lower than the total voltage and higher than 0.

6. A multilevel inverter device (20) comprising the multilevel inverter according to claim 2, and a control device (30) for controlling the multilevel inverter, wherein the control device, when no short-circuit fault is detected in any of the plurality of high-voltage side switches, connects the predetermined connection point to the battery on the high-voltage side closest to the predetermined connection point using the first changeover switch, and disconnects the predetermined connection point from the high-voltage side switch on the highest voltage side using the second changeover switch, and, when a short-circuit fault is detected in any of the plurality of high-voltage side switches, disconnects the predetermined connection point from the battery on the high-voltage side closest to the predetermined connection point using the first changeover switch, and connects the predetermined connection point to the high-voltage side switch on the highest voltage side using the second changeover switch.

7. A multilevel inverter device (20) comprising the multilevel inverter according to claim 3 and a control device (30) for controlling said multilevel inverter, wherein said control device, when no short-circuit fault is detected in said plurality of high-voltage side switches, connects said predetermined connection point to a battery on the low-voltage side nearest to said predetermined connection point with said third changeover switch and disconnects said predetermined connection point from ground with said fourth changeover switch, and when a short-circuit fault is detected in any of said plurality of high-voltage side switches, disconnects said predetermined connection point from a battery on the low-voltage side nearest to said predetermined connection point with said third changeover switch and connects said predetermined connection point to ground with said fourth changeover switch.

8. A multilevel inverter device (20) comprising the multilevel inverter according to claim 4, and a control device (30) for controlling the multilevel inverter, wherein the control device, when no short-circuit faults of the plurality of high-voltage side switches are detected, connects the predetermined connection point to the high-voltage side battery closest to the predetermined connection point using the first changeover switch, disconnects the predetermined connection point from the high-voltage side switch with the second changeover switch, connects the predetermined connection point to the low-voltage side battery closest to the predetermined connection point using the third changeover switch, and disconnects the predetermined connection point from the ground using the fourth changeover switch; a first selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a first selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a second selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a second selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a second selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a second selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; a third selector switch that selects whether or not a short circuit fault has occurred in any of the plurality of high-voltage side switches; 9. A multilevel inverter device as described in claim 5, further comprising a backflow prevention diode (49) that prevents current from flowing back into the plurality of batteries when the control device detects a short-circuit failure in any of the plurality of high-side switches and controls the plurality of changeover switches, and the voltage input to the plurality of high-side switches is switched to any one of the voltages output from the terminal points and connection points of the plurality of batteries that is lower than the total voltage and higher than 0.

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