POWER CONVERSION DEVICE AND DRIVE DEVICE

This power conversion device comprises: a power conversion circuit in which at least three-phases of upper/lower arm circuits having switching elements connected in series are connected in parallel and which outputs AC current to a motor via an output line, said AC current being generated by the switching elements of each phase; a breaker that is provided on the output line of each phase and allows the AC current to flow or interrupts the AC current; a first failure location determination unit that determines a failure location of the switching elements; a breaker control unit that sets, as a failure phase, a phase corresponding to the switching element determined as the failure location by the first failure location determination unit and controls the breaker of the failure phase so that the AC current of the failure phase is allowed to flow at a predetermined specific electric angle in one electric angle cycle and the AC current of the failure phase is interrupted at another electric angle except the specific electric angle; and a failure-time current control unit that controls the drive of other switching elements different from the switching element determined as the failure location.

TECHNICAL FIELD

The present invention relates to a power conversion device and a drive device.

BACKGROUND ART

When a short-circuit failure is generated in the switching elements configuring an inverter, current of the failure phase cannot be controlled, and there is a possibility that motor output torque becomes excessive or winding burnout of a motor is caused. For this reason, a technique in which the current of the failure phase at the time of the short-circuit failure is cut off using a circuit breaker or the like is known.

PTL 1 describes an invention of an electric power steering device that turns off the circuit breaker of the failure phase and drives normal switching elements of two phases to continue motor driving when the switching element or the motor fails.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the electric power steering device described in PTL 1, because the output torque decreases to 0 [Nm] at two electrical angles during one cycle of an electrical angle, the average output torque decreases as compared with a normal time. In order to increase the average output torque, it is necessary to increase the normal two-phase torque, but when this is performed, there is a problem that the torque fluctuation increases.

Solution to Problem

A power conversion device according to the present invention includes: a power conversion circuit in which upper and lower arm circuits in which switching elements are connected in series are connected in parallel for three phases, the power conversion circuit outputting an AC current generated by the switching elements of each phase to a motor through an output line; a circuit breaker provided on the output line of each phase to conduct or cut off the AC current; a first failure portion determination unit that determines a failure portion of the switching element; a circuit breaker controller that controls the circuit breaker of a failure phase such that the AC current of the failure phase is conducted at a predetermined specific electrical angle in one cycle of an electrical angle and such that the AC current of the failure phase is cut off at other electrical angles except for the specific electrical angle, with a phase corresponding to the switching element determined as the failure portion by the first failure portion determination unit as the failure phase; and a failure-time current controller that controls drive of another switching element different from the switching element determined to be the failure portion.

A drive device according to the present invention includes: a power conversion device that outputs a three-phase AC current; and a motor that is driven by the three-phase AC current, in which the power conversion device includes: a power conversion circuit in which upper and lower arm circuits in which switching elements are connected in series are connected in parallel for at least three phases, the power conversion circuit outputting an AC current generated by the switching elements of each phase to a motor through an output line; a circuit breaker provided on the output line of each phase to conduct or cut off the AC current; a first failure portion determination unit that determines a failure portion of the switching element; a circuit breaker controller that controls the circuit breaker of a failure phase such that the AC current of the failure phase is conducted at a predetermined specific electrical angle in one cycle of an electrical angle and such that the AC current of the failure phase is cut off at other electrical angles except for the specific electrical angle, with a phase corresponding to the switching element determined as the failure portion by the first failure portion determination unit as the failure phase; and a failure-time current controller that controls drive of another switching element different from the switching element determined to be the failure portion.

Advantageous Effects of Invention

Even after the switching element failure, motor drive can be continued while torque fluctuation is prevented.

DESCRIPTION OF EMBODIMENTS

FIG.1is a view illustrating an example of a vehicle on which a drive device of the present invention is mounted. A vehicle1illustrated inFIG.1is equipped with a drive device200while including driving wheels2and non-driving wheels3. The drive device200is connected to an axle4in which driving wheels2are attached to both ends of the axle4, and includes a power conversion device100and a motor190(seeFIG.2) in the drive device200. In accordance with operation of an accelerator pedal by a driver, the power conversion device100and the motor190are controlled to generate driving force, and the driving force is transmitted to the axle4. Thus, the driving wheels2are driven to cause the vehicle1to travel. In addition, a speed reducer may be disposed in the drive device, and the driving force of the motor190may be transmitted to the axle4through the speed reducer.

InFIG.1, a front wheel of the vehicle1is the driving wheel2, a rear wheel is the non-driving wheel3, and the drive device200is connected to the axle4on the front wheel side. However, the drive device200may be connected to the axle on the rear wheel side with the rear wheel as the driving wheel. In addition, the drive device200may be connected to each axle using all the front and rear wheels as driving wheels, or independent drive devices200may be installed and connected to the left and right driving wheels instead of the axle.

Subsequently, each embodiment of the power conversion device100and the drive device200will be described below.

First Embodiment

FIG.2is a view illustrating a configuration example of the power conversion device100and the drive device200according to a first embodiment of the present invention. The first embodiment illustrates an example of the power conversion device and the drive device that improve average output torque while maintaining a torque fluctuation and facilitate starting of the vehicle when a power semiconductor fails.

The drive device200includes the power conversion device100and the motor190. The motor190is a three-phase AC motor having three windings inside, and for example, corresponds to a synchronous motor using a permanent magnet or an induction motor not using a permanent magnet. An angle sensor (not illustrated) that measures an electric angle of the motor is mounted on the motor190, and the angle sensor outputs the measured electric angle to the power conversion device100as an angle sensor value θ.

An electronic control device230, a DC power supply210, and a failure notification device220are provided around the drive device200. The electronic control device230transmits information such as target torque T* to the drive device200. The DC power supply210is a power supply that drives the motor190, and for example, corresponds to a battery. The failure notification device220receives a failure notification signal from the drive device200and notifies a passenger of the generation of the failure. Examples of a failure notification method include a method for turning on a lamp, a method for generating a warning sound, and a method for notifying the passenger by voice.

The power conversion device100converts DC power obtained from the DC power supply210into AC power to drive the motor190. The power conversion device100also has a function of converting power of the motor190into the DC power to charge the DC power supply210. The power conversion device100internally includes a control circuit10, a driver circuit20, a power conversion circuit30, a voltage sensor40, an AC current sensor50, a circuit breaker drive circuit60, and a circuit breaker70. The power conversion circuit30receives a driving signal20afrom the driver circuit20, drives the internal power semiconductor, and controls the current that flows through the motor190. The circuit breaker drive circuit60drives the circuit breaker70to cut off the connection between the power conversion circuit30and the motor190. The internal configuration of the power conversion circuit30will be described first with reference toFIG.3, and the internal configuration and other configurations of the control circuit10will be described later.

FIG.3is a view illustrating a configuration example of the power conversion circuit30and the motor190. The power conversion circuit30internally includes a smoothing capacitor31and six power semiconductor elements32.

The smoothing capacitor31is a capacitor that smoothes the current generated by turning on and off the power semiconductor element32and prevents a ripple of the DC current supplied from the DC power supply210to the power conversion circuit30. For example, an electrolytic capacitor or a film capacitor is used as the smoothing capacitor31.

The power semiconductor element32is a switching element that switches on and off according to the driving signal20ainput from the driver circuit20, and converts the DC power and the AC power. For example, the power semiconductor element32corresponds to a power metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT). In addition, the power semiconductor element32includes a sense terminal33. From the sense terminal33, a current of a certain ratio, for example, 1/100 or 1/1000 of the current flowing between the collector and the emitter (between a drain and a source) of the power semiconductor element32is output as a sense current. The sense current is output from the power conversion circuit30to the driver circuit20. In the following embodiment, an example in which the IGBT is used as the power semiconductor element32will be described.

The six power semiconductor elements32are divided into upper and lower two for each phase, and the output is connected to the winding of each phase of the motor190. Hereinafter, the upper three power semiconductor elements32are collectively referred to as an upper arm, and the lower three power semiconductor elements32are collectively referred to as a lower arm. That is, upper and lower arm circuits in which the two power semiconductor elements32of the upper and lower arms are connected in series for each phase (U-phase, V-phase, W-phase) of the motor190are provided in the power conversion circuit30. The power conversion circuit30includes wirings connected to a positive electrode side and a negative electrode side of the DC power supply210, and upper and lower arm circuits of each phase are connected in parallel between the wirings.

In the first embodiment, a motor neutral point191is in a floating state, but may be connected to the ground (not illustrated). Methods for connecting the motor neutral point191to the ground include a direct grounding method, a resistance grounding method, a compensation reactor grounding method, an arc-extinguishing reactor grounding method, and the like.

Returning toFIG.2, the configuration of the first embodiment will be described. The voltage sensor40is a sensor that measures the output voltage of the DC power supply210, and outputs the measured voltage value to the control circuit10as a voltage sensor value40a.

The AC current sensor50is a sensor that measures an AC current flowing through each phase (U-phase, V-phase, W-phase) of the motor190, and outputs a measured AC current of each phase to the control circuit10as an AC current sensor value50a. In the first embodiment, a total of three AC current sensors50are provided for each phase, but the AC current sensors may be provided for only two phases. In this case, because a relationship of U-phase current+V-phase current+W-phase current=0 holds, the control circuit10calculates the AC current sensor value for the remaining one phase. In the first embodiment, the current flowing from the power conversion circuit30to the motor190is treated as a positive current, and the current flowing from the motor190to the power conversion circuit30is treated as a negative current.

The driver circuit20receives a pulse width modulation (PWM) signal16aoutput from a PWM signal generator16to be described later, and outputs the driving signal20athat switches on and off of the power semiconductor element32. In addition, the driver circuit20detects the generation of a short-circuit failure in the power semiconductor element32using a sense current33aoutput from the power semiconductor element32, and outputs a short-circuit failure detection signal20bto the control circuit10.

Normally, the PWM signal16ais generated such that the upper and lower power semiconductor elements32are not simultaneously turned on. However, in the case where the short-circuit failure is generated in the power semiconductor element32, the upper and lower power semiconductor elements32can be simultaneously turned on. When the upper and lower power semiconductor elements32are simultaneously turned on, a large through current flows through the power semiconductor element32. The driver circuit20monitors whether the sense current33aof each power semiconductor element32is equal to or larger than a certain threshold, and determines that the short-circuit failure is generated in the power semiconductor element32in the corresponding phase in the case where the sense current33ais equal to or larger than the certain value. The driver circuit20outputs the short-circuit failure detection signal20bdivided for each phase.

In the first embodiment, the short-circuit failure of the power semiconductor element32is determined using the sense current33aof the power semiconductor element32. However, the short-circuit failure of the power semiconductor element32may be detected by another method. For example, there is a method in which a shunt resistor for current measurement is disposed on the collector side or the emitter side of the power semiconductor element32and a current value flowing through the shunt resistor is measured to detect the short-circuit failure of the power semiconductor element32. In addition, because a collector-emitter voltage of the power semiconductor element32increases according to the flowing current, there is also a method for measuring the collector-emitter voltage to detect the short-circuit failure of the power semiconductor element32.

The circuit breaker drive circuit60receives a circuit breaker control signal17aoutput from a circuit breaker controller17to be described later, and outputs a circuit breaker driving signal60athat switches a conduction or cutoff state of the circuit breaker70.

The circuit breaker70is provided on an output line of each phase that connects the power conversion circuit30and the winding of the motor190, and switches the conduction or cutoff state according to the circuit breaker driving signal60ato conduct or cut off the AC current that flows from the power conversion circuit30to the winding of the motor190through the output line of each phase. When the circuit breaker70is in the conduction state, the AC current flows between the power conversion circuit30and the winding of the motor190. When the circuit breaker70is in the cutoff state, the current does not flow. In the first embodiment, the circuit breaker70is installed for each phase of the motor190.

Although the circuit breaker70is disposed in the power conversion device100in the first embodiment, the circuit breaker70may be disposed in the motor190, or disposed independently of the power conversion device100and the motor190. However, when the circuit breaker70is installed in the motor190, it is necessary to disassemble the motor190at the time of replacing the circuit breaker70. Consequently, installing the circuit breaker70in the power conversion device100facilitates replacement work of the circuit breaker70.

For example, a mechanical switch such as a relay or a semiconductor switch such as the IGBT or the MOSFET can be used as the circuit breaker70. The semiconductor switch has a feature that switching of the conduction or cutoff state is faster than that of the mechanical switch. On the other hand, even when the semiconductor switch is turned off, the current may flow through an internal freewheeling diode. For this reason, in the case where the semiconductor switch is used for the circuit breaker70, it is necessary to adopt a configuration that reliably cuts off the current when the semiconductor switch is switched off.

FIG.4is a view illustrating a configuration example of the circuit breaker70using the semiconductor switch. For example, as illustrated inFIG.4, the circuit breaker70capable of cutting off the current flowing in both directions can be implemented by connecting the two semiconductor switches71in series in opposite directions to each other.

On the other hand, although the switching time of the mechanical switch is longer than that of the semiconductor switch, the bidirectional current can be reliably cut off by one switch. For this reason, the mechanical switch is superior to the semiconductor switch in terms of cost.

The configuration of the circuit breaker70is not limited to the semiconductor switch or the mechanical switch having the circuit configuration inFIG.4. When the AC current that is output from the power conversion circuit30and flows through the winding of the motor190can be reliably conducted or cut off, the circuit breaker70can be implemented by an arbitrary circuit configuration.

The control circuit10communicates with the external electronic control device230and receives the target torque T* of the motor190from the electronic control device230. In the case where the power conversion device100is normal, the control circuit10outputs the PWM signal16aso as to control the current of each phase output from the power conversion device100to a predetermined value based on the target torque T*, and drives the power conversion circuit30through the driver circuit20. In the case where determining that the failure is generated in the power conversion device100, the control circuit10outputs the failure notification signal to the external failure notification device220.

The control circuit10internally includes a CPU, a RAM, a ROM, and a communication circuit (not illustrated). The ROM may be an electrically erasable programmable ROM (EEPROM) or a flash ROM that is electrically rewritable. In addition, the control circuit10may include a logic circuit configured using hardware such as a field programmable gate array (FPGA).

In addition, the control circuit10includes functional blocks of a motor speed calculation unit11, a target current calculation unit12, a normal-time current controller13, a failure-time current controller15, the PWM signal generator16, the circuit breaker controller17, a power semiconductor failure portion determination unit18, and a state determination unit19. For example, these functional blocks may be implemented by the CPU executing a predetermined program in the control circuit10, or a part or all of them may be implemented by hardware such as the FPGA.

The motor speed calculation unit11calculates a motor rotation speed (rotation speed) from the change in the angle sensor value θ of the motor190, and outputs a calculated motor speed value11ato the target current calculation unit12.

The target current calculation unit12output a target current value12ato the normal-time current controller13using the target torque T*, the voltage sensor value40a, and the motor speed value11athat is output from the motor speed calculation unit11. The target current value12ais calculated as a current value that should be supplied to the motor190in order that the motor190outputs the same torque as the target torque T*. For example, the target current value12ais expressed in the form of a d-axis target current value and a q-axis target current value.

The normal-time current controller13calculates a duty value13aof each phase using the target current value12aand the motor angle sensor value θ that are output by the target current calculation unit12, the AC current sensor value50aof each phase, and the voltage sensor value40a, and outputs the duty value13ato the PWM signal generator16. Details of a method for calculating the duty value13aby the normal-time current controller13will be described later.

The failure-time current controller15calculates the duty value15aof each phase and the circuit breaker switching signal15bthat controls the state of the circuit breaker70at the time of failure using the target current value12aoutput from the target current calculation unit12, the motor angle sensor value θ, the AC current sensor value50aof each phase, the voltage sensor value40a, and the power semiconductor failure information18aoutput from the power semiconductor failure portion determination unit18. Then, the calculated duty value15aand the circuit breaker switching signal15bare output to the PWM signal generator16and the circuit breaker controller17, respectively. Details of a method for calculating the duty value15aand the circuit breaker switching signal15bby the failure-time current controller15will be described later.

The PWM signal generator16switches the signal that is output to the driver circuit20according to an internal state19aoutput from the state determination unit19. The PWM signal generator16internally includes a timer. In the case where the internal state19ais a “normal state”, the PWM signal generator16generates the PWM signal16ausing the timer value and the duty value13aof each phase output from the normal-time current controller13, and outputs the PWM signal16ato the driver circuit20. In the case where the internal state19ais a “one-phase failure state” to be described later, the PWM signal generator16generates the PWM signal16ausing the timer value and the duty value15aof each phase that is output by the failure-time current controller15, and outputs the PWM signal16ato the driver circuit20. In the case where the internal state19ais “at least two-phase failure state” to be described later, the PWM signal generator16outputs the PWM signal16athat does not drive the motor190to the driver circuit20. For example, the state in which the motor190is not driven includes a state in which all the six power semiconductor elements32in the power conversion circuit30are turned off (referred to as a free wheel state in the first embodiment).

The circuit breaker controller17generates and outputs the circuit breaker control signal17athat switches the conduction or cutoff of the circuit breaker70of each phase using the internal state19aoutput from the state determination unit19, the power semiconductor failure information18aoutput from the power semiconductor failure portion determination unit18, and the circuit breaker switching signal15boutput from the failure-time current controller15. Details of a method for calculating the circuit breaker control signal17aby the circuit breaker controller17will be described later.

The power semiconductor failure portion determination unit18determines a failure portion and a failure mode of the power semiconductor element32based on the PWM signal16a, the short-circuit failure detection signal20boutput from the driver circuit20, and the AC current sensor value50aof each phase. The failure mode of the power semiconductor element32is roughly divided into two types of the short-circuit failure and an open failure. In the case of the short-circuit failure, the power semiconductor element32is always in an on-state. In the case of the open failure, the power semiconductor element32is always in an off-failure. In the case where the short-circuit failure detection signal20bis output from the driver circuit20, the power semiconductor failure portion determination unit18determines that the short-circuit failure is generated. In the case where the AC current sensor value50aof each phase does not change within a predetermined value, the power semiconductor failure portion determination unit18determines that the open failure is generated.

Because the short-circuit failure detection signal20boutput from the driver circuit20at the time of the generation of the short-circuit failure is divided for each phase, the power semiconductor failure portion determination unit18can specify which phase the failure is generated from the short-circuit failure detection signal20b, but cannot specify which of the upper and lower arms fails. For this reason, for example, the power semiconductor failure portion determination unit18compares the timing at which the short-circuit failure detection signal20bis output with the state of the PWM signal16a, and determines that the short-circuit failure is generated in the arm in which the short-circuit failure detection signal20bis in an off-state among the PWM signals16aof the upper and lower arms in the phase in which the failure is generated. This is because the upper and lower power semiconductor elements32are not normally simultaneously turned on, and thus, the detection of the short-circuit failure of the power semiconductor element32is considered that the upper and lower power semiconductor elements32are simultaneously turned on because the short-circuit failure is generated in the power semiconductor element32originally supposed to be in the off-state. In the case where determining that the short-circuit failure of the power semiconductor element32is generated, the power semiconductor failure portion determination unit18outputs the power semiconductor failure information18aindicating the failure portion and the failure mode to the failure-time current controller15, the circuit breaker controller17, the state determination unit19, and the external failure notification device220.

In addition, when the open failure is generated, the power semiconductor failure portion determination unit18can specify which phase the failure is generated from the AC current sensor value50aof each phase output by the AC current sensor50, but cannot specify which of the upper and lower arms fails. For this reason, for example, the power semiconductor failure portion determination unit18divides the AC current sensor value50aof each phase into a positive current value and a negative current value, smooths each value, and compares each value with a predetermined threshold, thereby determining which one of the upper and lower arms has the open failure. When determining that the open failure of the power semiconductor element32is generated, the power semiconductor failure portion determination unit18outputs the power semiconductor failure information18aindicating the failure portion and the failure mode to the failure-time current controller15, the circuit breaker controller17, the state determination unit19, and the external failure notification device220.

The state determination unit19determines whether the state of the power conversion device100is any one of the “normal state”, the “one-phase failure state”, and the “at least two-phase failure state” based on the power semiconductor failure information18aoutput from the power semiconductor failure portion determination unit18. Then, the internal state19arepresenting the current state of the power conversion device100is output to the PWM signal generator16and the circuit breaker controller17.

FIG.5is a view illustrating an example of internal state determination of the state determination unit19according to the first embodiment of the present invention. The state determination unit19determines a next state from a current state and a generation matter at regular time intervals, and updates the next state to the current state. An initial state is the “normal state”. In a case where the current state is the “normal state”, the state determination unit19changes the next state to the “one-phase failure state” when receiving the power semiconductor failure information18aindicating that the power semiconductor element32of any phase fails from the power semiconductor failure portion determination unit18. Otherwise, the next state remains in the “normal state”. In addition, the state determination unit19changes the next state to the “at least two-phase failure state” when receiving the power semiconductor failure information18aindicating that the power semiconductor element32of the phase different from the previous failure phase fails from the power semiconductor failure portion determination unit18while the current state is the “one-phase failure state”. For example, when the new notification of the power semiconductor failure information18afor the power semiconductor element32of the V-phase or W-phase is performed while the current state is the “one-phase failure state” due to the failure of the power semiconductor element32of the U-phase, the next state is changed to the “at least two-phase failure state”. Otherwise, the next state remains the “one-phase failure state”. In the case where the current state is the “at least two-phase failure state”, the state determination unit19keeps the next state as the “at least two-phase failure state”.

Current control during the normal operation and current control at the time of the one-phase failure performed by the normal-time current controller13and the failure-time current controller15, respectively, will be described below. In the first embodiment, an example in which a coefficient of the absolute transform is used at the time of axis transform is illustrated. However, a coefficient of relative transform may be used.

In the current control in the normal state, first, the target current calculation unit12inFIG.2determines the d-axis target current value and the q-axis target current value according to the target torque T*. Subsequently, the normal-time current controller13calculates the duty value13aof each phase that achieves the d-axis target current value and the q-axis target current value that are determined by the target current calculation unit12. Then, the PWM signal generator16generates the PWM signal16aof each phase according to the duty value13aof each phase calculated by the normal-time current controller13. At this time, the circuit breaker controller17controls all the three-phase circuit breakers70to be in the conduction state.

The normal-time current controller13converts the three-phase AC current sensor values50aoutput from the AC current sensor50into d-axis and q-axis current values using [Mathematical Formula 1]. Iu, Iv, and Iw in [Mathematical Formula 1] are AC current sensor values of the U-phase, the V-phase, and the W-phase, respectively, and θ is the angle sensor value. In addition, Id represents a d-axis current value after conversion, and Iq represents a q-axis current value after conversion.

Subsequently, the normal-time current controller13obtains a difference between the d-axis current and the d-axis target current value and a difference between the q-axis current and the q-axis target current value. Then, the normal-time current controller13performs feedback control on the d-axis current difference and the q-axis current difference to determine a d-axis target voltage value and a q-axis target voltage value. The normal-time current controller13converts the d-axis target voltage value and the q-axis target voltage value into the form of an α-axis target voltage value and a β-axis target voltage value using [Mathematical Formula 2] such that the d-axis target voltage value and the q-axis target voltage value become the values of an α-axis and a β-axis. In [Mathematical Formula 2], Vd is the d-axis target voltage value, Vq is the q-axis target voltage value, θ is the angle sensor value, Vα is the α-axis target voltage value, and Vβ is the β-axis target voltage value.

Then, the normal-time current controller13converts the α-axis target voltage value and the β-axis target voltage value into target voltage values of the U-phase, the V-phase, and the W-phase using [Mathematical Formula 3]. In [Mathematical Formula 3], Va is the α-axis target voltage value, Vβ is the β-axis target voltage value, Vu is a U-phase target voltage value, Vv is a V-phase target voltage value, and Vw is a W-phase target voltage value.

Finally, the normal-time current controller13calculates the duty value13aof each phase from the target voltage value of each phase and the voltage sensor value40a.

In the current control at the time of the one-phase failure, first, the target current calculation unit12determines the d-axis target current value and the q-axis target current value according to the target torque T* similarly to the normal state. Subsequently, in the failure-time current controller15, the duty value13aof the failure phase is calculated such that one of the power semiconductor elements32of the upper and lower arms of the failure phase is always turned on and the other is always turned off. Specifically, in the case of the short-circuit failure, the failure-time current controller15calculates the duty value13aof the power semiconductor element32as zero such that the power semiconductor element32in phase with the failure portion indicated by the power semiconductor failure information18aand on the upper and lower opposite arm sides is always in the off-state. In addition, in the case of the open failure, the failure-time current controller15calculates the duty value13aof the power semiconductor element32to1such that the power semiconductor element32in phase with the failure portion indicated by the power semiconductor failure information18aand on the opposite side of the upper and lower arms is always in the on-state.

In addition, the failure-time current controller15corrects the target voltage in a conversion portion from the α-axis target voltage value (Vα) and the β-axis target voltage value (Vβ) to the U-phase target voltage value (Vu), the V-phase target voltage value (Vv), and the W-phase target voltage value (Vw) while the motor angle sensor value θ is within a certain range of electrical angles (hereinafter, referred to as “specific electrical angle”). The specific electrical angle corresponds to a range of the electrical angle that brings the circuit breaker70of the failure phase into the conduction state in one cycle of the electrical angle, and differs for each failure phase as described later.

For example, in the case where the short-circuit failure is generated in the power semiconductor element32of the U-phase upper arm and the power semiconductor element32of the U-phase lower arm is controlled to the off-state, or in the case where the open failure is generated in the power semiconductor element32of the U-phase lower arm and the power semiconductor element32of the U-phase upper arm is controlled to the on-state, if the voltage of the DC power supply210is Vdc, the voltage output from the U-phase upper and lower arm circuits is fixed at ½·Vdc. In addition, for example, in the case where the short-circuit failure is generated in the power semiconductor element32of the U-phase lower arm and the power semiconductor element32of the U-phase upper arm is controlled to the off-state, or in the case where the open failure is generated in the power semiconductor element32of the U-phase upper arm and the power semiconductor element32of the U-phase lower arm is controlled to the on-state, the voltage output from the U-phase upper and lower arm circuits is fixed at −½·Vdc. For this reason, even when the U-phase, V-phase, and W-phase target voltages are converted as usual, the power conversion circuit30cannot output the voltage according to the target voltage. For this reason, the target voltages of the remaining two phases is required to be calculated in consideration of the difference between the output voltages of the failure phases such that voltages corresponding to the α-axis target voltage value (Vα) and the β-axis target voltage value (Vβ) that are the same as those before the generation of the failure can be output even after the generation of the failure.

In the case where the short-circuit failure is generated in the U-phase power semiconductor element32, the target voltage values of the V-phase and the W-phase are calculated by [Mathematical Formula 4]. At this point, when the voltage of the DC power supply210is Vdc, in the case where the short-circuit failure is generated in the power semiconductor element32of the U-phase upper arm and the power semiconductor element32of the U-phase lower arm is controlled to the off-state, or in the case where the open failure is generated in the power semiconductor element32of the U-phase lower arm and the power semiconductor element32of the U-phase upper arm is controlled to the on-state, the value of the U-phase target voltage value (Vu) is set to ½·Vdc. In addition, in the case where the short-circuit failure is generated in the power semiconductor element32of the U-phase lower arm and the power semiconductor element32of the U-phase upper arm is controlled to the off-state, or in the case where the open failure is generated in the power semiconductor element32of the U-phase upper arm and the power semiconductor element32of the U-phase lower arm is controlled to the on-state, the value of the U-phase target voltage value (Vu) is set to −½·Vdc.

In the case where the short-circuit failure is generated in the V-phase power semiconductor element32, the target voltage values of the U-phase and the W-phase are calculated by [Mathematical Formula 5]. At this point, when the voltage of the DC power supply210is Vdc, in the case where the short-circuit failure is generated in the power semiconductor element32of the V-phase upper arm and the power semiconductor element32of the V-phase lower arm is controlled to the off-state, or in the case where the open failure is generated in the power semiconductor element32of the V-phase lower arm and the power semiconductor element32of the V-phase upper arm is controlled to the on-state, the value of the V-phase target voltage value (Vv) is set to ½·Vdc similarly to the time of the U-phase failure. In addition, in the case where the short-circuit failure is generated in the power semiconductor element32of the V-phase lower arm and the power semiconductor element32of the V-phase upper arm is controlled to the off-state, or in the case where the open failure is generated in the power semiconductor element32of the V-phase upper arm and the power semiconductor element32of the V-phase lower arm is controlled to the on-state, the value of the V-phase target voltage value (Vv) is set to −½·Vdc.

In the case where the short-circuit failure is generated in the W-phase power semiconductor element32, the target voltage values of the U phase and the V phase are calculated by [Mathematical Formula 6]. At this point, when the voltage of the DC power supply210is Vdc, in the case where the short-circuit failure is generated in the power semiconductor element32of the W-phase upper arm and the power semiconductor element32of the W-phase lower arm is controlled to the off-state, or in the case where the open failure is generated in the power semiconductor element32of the W-phase lower arm and the power semiconductor element32of the W-phase upper arm is controlled to the on-state, the value of the W-phase target voltage value (Vw) is set to ½·Vdc similarly to the time of the U-phase failure or the V-phase failure. In addition, in the case where the short-circuit failure is generated in the power semiconductor element32of the W-phase lower arm and the power semiconductor element32of the W-phase upper arm is controlled to the off-state, or in the case where the open failure is generated in the power semiconductor element32of the W-phase upper arm and the power semiconductor element32of the W-phase lower arm is controlled to the on-state, the value of the W-phase target voltage value (Vw) is set to −½·Vdc.

As described above, after setting the corrected target voltage value of each phase at the specific electrical angle, the failure-time current controller15calculates the duty value15aof each phase from the set target voltage value of each phase and the voltage sensor value40asimilarly to the normal-time current controller13.

Furthermore, the failure-time current controller15generates the circuit breaker switching signal15bbased on the angle sensor value θ separately from the calculation of the duty value15a, and outputs the generated circuit breaker switching signal15bto the circuit breaker controller17. At this time, the failure-time current controller15generates the circuit breaker switching signal15bthat brings the circuit breaker70of the failure phase into the conduction state only during the specific electrical angle and brings the circuit breakers70of the two phases other than the failure phase into the conduction state at all times.

The circuit breaker controller17generates the circuit breaker control signal17abased on the circuit breaker switching signal15boutput from the failure-time current controller15. At this time, the circuit breaker control signal17ais changed such that the circuit breaker70of the failure phase is in the conduction state only during the specific electrical angle and is in the cutoff state at other electrical angles and such that the circuit breaker70of the two phases other than the failure phase is always in the conduction state.

In the first embodiment, the failure-time current controller15generates the circuit breaker switching signal15bbased on the angle sensor value θ, and the circuit breaker controller17performs switching control of the circuit breaker70by changing the circuit breaker control signal17abased on the circuit breaker switching signal15b. However, the circuit breaker controller17may determine whether the current electrical angle is the specific electrical angle based on the angle sensor value θ, and control the conduction or cutoff state of the circuit breaker70of the failure phase according to the determination result.

FIG.6is a view illustrating an example of the specific electrical angle at which the circuit breaker70of the failure phase is brought into the conduction state. In the current control at the time of the one-phase failure, the failure-time current controller15corrects the target voltage, and the specific electrical angle that brings the circuit breaker70of the failure phase into the conduction state is determined according to the failure phase, for example, as illustrated inFIG.6. In each failure situation illustrated inFIG.6, the d-axis target voltage value and the q-axis target voltage value that are the same as those in the normal state can be output from the power conversion circuit30by performing the current control at the time of the one-phase failure as described above in the range of each specific electrical angle. α inFIG.6is a variable, and changes depending on the values of the d-axis target voltage and the q-axis target voltage.

In the first embodiment, the specific electrical angle at which the current control at the time of the one-phase failure is performed is set to be in the range of 120° in terms of the electrical angle for each failure phase as illustrated inFIG.6. However, for example, the current control at the time of the one-phase failure may be performed in the range of the electrical angle narrower than the specific electrical angle, or conversely, the current control at the time of the one-phase failure may be performed in the range of the electrical angle wider than the specific electrical angle. However, the narrower the range of the electrical angle to which the current control at the time of the one-phase failure is applied, the smaller the effect of improving the output torque. On the other hand, as the range of the electrical angle to which the current control at the time of the one-phase failure is applied becomes wider, stability at the time of control is impaired. For this reason, it is preferable to determine the range of the potential angle that performs the current control at the time of the one-phase failure in consideration of the balance.

FIG.7illustrates an example of a control flowchart according to the first embodiment of the present invention. In the first embodiment, the control circuit10inFIG.2periodically performs the control illustrated in the flowchart ofFIG.7at regular intervals.

First, in the processing of step S100, the control circuit10determines whether the internal state19aoutput from the state determination unit19is the “normal state”. The processing proceeds to step S101in the case where the internal state19ais the “normal state”, and the processing proceeds to step S104in the case where the internal state is other than the “normal state”.

In the processing of step S101, the control circuit10performs the current control in the normal state according to a torque command value. More specifically, as described above, the target current calculation unit12generates the target current value12aaccording to the target torque T*, and the normal-time current controller13generates the duty value13aof each phase according to the target current value12a. Then, the PWM signal generator16generates the PWM signal16abased on the duty value13aof each phase, and outputs the PWM signal16ato the driver circuit20. At this time, the circuit breaker controller17outputs the circuit breaker control signal17asuch that the circuit breakers70of the three phases are always in the conduction state.

Subsequently, in the processing of step S102, the power semiconductor failure portion determination unit18determines whether the generation of the open failure or the short-circuit failure is detected in any one of the power semiconductor elements32based on the AC current sensor value50aof each phase output from the AC current sensor50and the short-circuit failure detection signal20boutput from the driver circuit20. In the case where the open failure or the short-circuit failure is detected, the failure portion is determined as described above using the AC current sensor value50aand the PWM signal16a, the power semiconductor failure information18ais output based on the determination result, and then the processing proceeds to step S103.

In the processing of step S103, the state determination unit19determines that the current state of the power conversion device100is the “one-phase failure state” and updates the internal state19a. After executing the processing of step S103, the control circuit10ends the control flowchart ofFIG.7.

On the other hand, in the case where no failure is detected for any of the power semiconductor elements32in step S102, the control circuit10does not execute the processing of step S103and ends the control flowchart ofFIG.7. In this case, the power semiconductor failure portion determination unit18does not output the power semiconductor failure information18a, and the state determination unit19maintains the internal state19ain the “normal state”.

In the case where it is determined in step S100that the internal state19aoutput from the state determination unit19is not the “normal state”, the control circuit10determines whether the internal state19ais the “one-phase failure state” in the processing of step S104. The processing proceeds to step105in the case where the internal state19ais the “one-phase failure state”, and the processing proceeds to step108in the case where the internal state19ais other than the “one-phase failure state”.

In the processing of step S105, the control circuit10performs the current control at the time of the one-phase failure according to the torque command value. More specifically, as described above, the target current calculation unit12generates the target current value12aaccording to the target torque T*, and the failure-time current controller15generates the duty value15aof each phase according to the target current value12a. Then, the PWM signal generator16generates the PWM signal16abased on the duty value15aof each phase, and outputs the PWM signal16ato the driver circuit20. Thus, driving of another power semiconductor element32different from the power semiconductor element32determined to be the failure portion by the power semiconductor failure portion determination unit18is controlled.

In addition, the failure-time current controller15generates the circuit breaker switching signal15bsuch that the circuit breaker70other than the failure phase is always brought into the conduction state and such that the circuit breaker70of the failure phase is brought into the conduction state only during the specific electrical angle, and outputs the circuit breaker switching signal15bto the circuit breaker controller17. The circuit breaker controller17outputs the circuit breaker control signal17abased on the circuit breaker switching signal15boutput from the failure-time current controller15. Thus, the circuit breaker70of the phase corresponding to the power semiconductor element32determined to be the failure portion by the power semiconductor failure portion determination unit18is controlled such that the AC current generated by the power semiconductor element32of the failure phase is conducted in a predetermined conduction period corresponding to the specific electrical angle in one cycle of the electrical angle of the motor190and such that the AC current is cut off in other periods.

Subsequently, in the processing of step S106, the power semiconductor failure portion determination unit18determines whether the generation of the open failure or the short-circuit failure is detected for any of the power semiconductor elements32in the phase different from the phase in which the failure is already detected. In the case where the generation of the open failure or the short-circuit failure is detected, the power semiconductor failure information18ais updated and output, and the processing proceeds to step S107.

In the processing of step S107, the state determination unit19determines that the current state of the power conversion device100is the “failure state of at least two phases” and updates the internal state19a. After executing the processing of step S107, the control circuit10ends the control flowchart ofFIG.7.

On the other hand, in the case where no failure is detected in the power semiconductor element32of the phase different from the failure phase in step S106, the control circuit10does not execute the processing of step S107and ends the control flowchart ofFIG.7. In this case, the state determination unit19maintains the internal state19ain the “one-phase failure state”.

In the case where it is determined in step S104that the internal state19aoutput from the state determination unit19is not the “one-phase failure state”, namely, in the case where the internal state19ais the “at least two-phase failure state”, the control circuit10performs control to stop the drive of the motor190in the processing of step S108. For example, the PWM signal generator16outputs the PWM signal16ato the driver circuit20such that the power conversion circuit30is in the free wheel state, or the circuit breaker controller17outputs the circuit breaker control signal17ato the circuit breaker drive circuit60such that all the circuit breakers70are in the cutoff state. Alternatively, both are performed. Thus, the driving of the motor190is stopped.

FIG.8is a view illustrating an example of output torque at the time of the one-phase failure according to the first embodiment of the present invention. In this example, it is assumed that the target torque T* is set to 100 [Nm] and the short-circuit failure is generated in the power semiconductor element32of the U-phase upper arm. InFIG.8, the graph on the left side illustrates waveform examples of each phase current and torque in the case where the U-phase circuit breaker70of the failure phase is cut off to continue the motor drive only in two normal phases (V-phase, W-phase) based on the same target voltage as that in the normal time (conventional control). In addition, the graph on the right side illustrates waveform examples of each phase current and torque in the case where the current control at the time of the one-phase failure described in the first embodiment is applied.

In the conventional control illustrated in the left graph, because the circuit breaker70of the U-phase is in the cutoff state, no current flows in the U-phase, and the torque is controlled using only the normal V-phase and W-phase currents. In this state, the output torque changes sinusoidally between the target torque and 0 [Nm], and the average torque becomes about 50% of the target torque. In order to improve the average torque in this state, the target torque is required to be made larger than that at the normal time, and the amount of torque fluctuation further increases at that time.

On the other hand, in the first embodiment, when the current control at the time of the one-phase failure is applied, the circuit breaker70of the U-phase is conducted between the specific electrical angles as described above, and the current also flows in the U-phase. Thus, as illustrated in the graph on the right side, because the output torque close to the target torque can be obtained during the specific electrical angle, the average torque can be improved. Because the output torque during the application of this control fluctuates between the target torque and 0 [Nm], a torque fluctuation amount can be maintained at a value similar to that of the conventional control.

As described above, according to the power conversion device100of the first embodiment, when the current control at the time of the one-phase failure is applied, the average torque can be improved while the torque fluctuation amount equivalent to the conventional torque fluctuation amount is maintained. For this reason, deterioration of ride comfort can be prevented while acceleration capability of the vehicle1is maintained to some extent even after the failure.

The current control at the time of the one-phase failure according to the first embodiment can obtain the effect of improving the average torque not only in the conventional control in which the control is performed at the same target voltage as that at the time of the normal state even at the time of the failure but also in comparison with the control method described in PTL 1 described above. That is, in the control of PTL 1, the output torque decreases to 0 [Nm] at two electrical angles in one cycle of the electrical angle, but when the current control at the time of one-phase failure according to the first embodiment is applied, the output torque at one electrical angle can be improved to the same level as the target torque as illustrated in the graph on the right side ofFIG.8. For this reason, the average torque can be improved as compared with the control of PTL 1.

According to the first embodiment of the present invention described above, the following operational effects are achieved.

(1) The power conversion device100includes the power conversion circuit30, the circuit breaker70, and the control circuit10that functions as the power semiconductor failure portion determination unit18, the circuit breaker controller17, and the failure-time current controller15. In the power conversion circuit30, the upper and lower arm circuits in which the power semiconductor elements32as the switching elements are connected in series are connected in parallel for at least three phases, and the AC current generated by the power semiconductor elements32of each phase is output to the motor190through the output line. The circuit breaker70is provided on the output line of each phase to conduct or cut off the AC current. The power semiconductor failure portion determination unit18determines the failure portion of the power semiconductor element32. The circuit breaker controller17controls the circuit breaker70of the failure phase such that the AC current of the failure phase is conducted at a predetermined specific electrical angle in one cycle of the electrical angle and such that the AC current of the failure phase is cut off at other electrical angles except for the specific electrical angle, with the phase corresponding to the power semiconductor element32determined as the failure portion by the power semiconductor failure portion determination unit18as the failure phase. The failure-time current controller15controls the driving of another power semiconductor element32different from the power semiconductor element32determined to be the failure portion. With this configuration, even after the failure of the power semiconductor element32, the driving of the motor190can be continued while the torque fluctuation is prevented.

(2) The specific electrical angle has the range of 1200 in the electrical angle. With this configuration, even when any of the power semiconductor elements32fails, the driving of the motor190that is the three-phase AC motor can be reliably continued.

(3) The circuit breaker controller17changes the specific electrical angle for each failure phase. With this configuration, even when the power semiconductor element32fails in any phase, the driving of the motor190can be reliably continued.

Second Embodiment

An example of a power conversion device and a drive device that improve the average output torque while maintaining the torque fluctuation even after the failure of the power semiconductor and make it easy to start the vehicle in the case where the switching of the circuit breaker is delayed will be described in a second embodiment.

The power conversion device100and the drive device200in the second embodiment have the same configurations as those inFIG.2described in the first embodiment. For this reason, the power conversion device100and the drive device200of the second embodiment will be described below with reference to the configuration ofFIG.2.

FIG.9is an explanatory diagram illustrating switching timing of the circuit breaker70according to the second embodiment of the present invention. InFIG.9, (a) illustrates an example of a timing chart in the case where there is no switching delay of the circuit breaker70, and (b) illustrates an example of a timing chart in the case where there is the switching delay of the circuit breaker70. In both ofFIGS.9(a) and9(b), it is assumed that the short-circuit failure is generated in the power semiconductor element32of the U-phase upper arm. In addition, it is assumed that the variable a of the specific electrical angle inFIG.6described above is zero.FIG.9(a)corresponds to the switching timing of the circuit breaker70by the current control at the time of the one-phase failure described in the first embodiment, andFIG.9(b)corresponds to the switching timing of the circuit breaker70by the current control at the time of the one-phase failure in the second embodiment.

InFIG.9(a), an ideal state in which there is no switching delay of the circuit breaker70is assumed. For this reason, at the start timing of the specific electrical angle (180 to 300 [deg]), the circuit breaker controller17switches the circuit breaker70of the U-phase from the cutoff state to the conduction state according to the change in the circuit breaker switching signal15boutput from the failure-time current controller15. In addition, at the end timing of the specific electrical angle, the circuit breaker70of the U-phase is switched from the conduction state to the cutoff state according to the change in the circuit breaker switching signal15boutput from the failure-time current controller15.

However, because the normal circuit breaker70has a switching delay time, it is actually necessary to control the switching of the circuit breaker70in consideration of this delay time. In the second embodiment, as illustrated inFIG.9(b), the switching timing of the circuit breaker70is set in consideration of the delay time. Specifically, the timing at which the circuit breaker controller17switches the circuit breaker70from the cutoff state to the conduction state is the same as in the case ofFIG.9(a)in which the switching is not delayed, but the timing at which the circuit breaker70is switched from the conduction state to the cutoff state is advanced from the end timing of the specific electrical angle by the switching delay time of the circuit breaker70. The switching timing of the circuit breaker70may be advanced by changing the timing of the circuit breaker switching signal15bin the failure-time current controller15, or may be advanced by changing the timing of the circuit breaker switching signal15bin the circuit breaker controller17without changing the timing of the circuit breaker switching signal15b.

When the circuit breaker70is brought into the conduction state, the output voltage of the failure phase becomes ½·Vdc or −½·Vdc as described above. In the current control at the time of the one-phase failure described in the first embodiment, the d-axis target voltage value and the q-axis target voltage value that are the same as those in the normal state can be output from the power conversion circuit30by correcting the normal two-phase output voltages within the range of the specific electrical angle. However, in other ranges, the corrected normal two-phase voltage becomes too large to be corrected. Because the current control becomes unstable in this state, it is desirable not to bring the circuit breaker70of the failure phase into the conduction state in the range other than the specific electrical angle. Accordingly, in the second embodiment, the timing at which the circuit breaker controller17instructs the circuit breaker70to switch from the conduction state to the cutoff state is advanced by the switching delay time of the circuit breaker70, thereby preventing the circuit breaker70of the failure phase from becoming the conduction state in the range other than the specific electrical angle. Thus, even when there is the switching delay of the circuit breaker70, the current control can be stabilized.

According to the second embodiment of the present invention described above, the circuit breaker controller17instructs the circuit breaker70of the failure phase to switch from the conduction state to the cutoff state before the end timing of the specific electrical angle. With this configuration, the circuit breaker70of the failure phase can be prevented from being brought into the conduction state in the range other than the specific electrical angle to stabilize the current control at the time of the one-phase failure.

Third Embodiment

An example of a power conversion device and a drive device that reduce a processing load of a control circuit, improve the average output torque while maintaining the torque fluctuation even after the failure of the power semiconductor, and make it easy to start the vehicle in the case where the switching of the circuit breaker is delayed will be described in a third embodiment.

FIG.10is a view illustrating a configuration example of the power conversion device100and the drive device200according to the third embodiment of the present invention. The power conversion device100in the third embodiment has the same configuration as that ofFIG.2described in the first embodiment, and is different in that the motor speed value11acalculated by the motor speed calculation unit11is further output to the failure-time current controller15and the circuit breaker controller17in addition to the target current calculation unit12. Hereinafter, the description of portions common to the first and second embodiments will be omitted.

FIG.11is an explanatory diagram illustrating the switching timing of the circuit breaker70according to the third embodiment of the present invention. In the second embodiment described above, the switching control in a case where the switching of the circuit breaker70is delayed has been described. However, as illustrated inFIG.11, when the delay time of the circuit breaker70becomes equal to or longer than the electrical angle corresponding to 60 [deg], in this control method, the time for the circuit breaker70of the failure phase to be in the conduction state is eliminated, and the effect of the current control at the time of the one-phase failure cannot be obtained. That is, because a ratio of the electrical angle occupied by the delay time of the circuit breaker70in one cycle of the electrical angle increases as the motor rotation speed increases, the effect of the current control at the time of the one-phase failure cannot be obtained in a situation where the motor rotation speed is fast.

Accordingly, in the third embodiment, at the motor rotational speed at which the delay time of the circuit breaker70is equal to or longer than the electrical angle corresponding to 60 [deg], the control circuit10does not perform the current control at the time of the one-phase failure but controls the circuit breaker70to be always in the cutoff state. Thus, unnecessary switching of the circuit breaker70is eliminated, and the processing load of the control circuit10in the power conversion device100is reduced.

FIG.12illustrates an example of the control flowchart according to the third embodiment of the present invention. In the third embodiment, the control circuit10inFIG.10periodically performs the control illustrated in the flowchart ofFIG.12at regular intervals. InFIG.12, portions performing the same pieces of processing as those in the control flowchart ofFIG.7described in the first embodiment are denoted by the same symbols as those inFIG.7, and description of those pieces of processing is omitted.

In the third embodiment, in the processing of step S104, the processing proceeds to step S109in the case where the internal state19ais the “one-phase failure state”, and the processing proceeds to step S108in the case where the internal state19ais other than the “one-phase failure state”.

In the processing of step S109, the control circuit10determines whether the motor rotational speed (rotation speed) is less than a predetermined threshold based on the motor speed value11acalculated by the motor speed calculation unit11. The processing proceeds to step S105in the case where the motor rotational speed is less than the threshold, and the processing proceeds to step S110in the case where the motor rotational speed is equal to or greater than the threshold.

In the processing of step S110, the control circuit10performs conventional failure-time control. Specifically, the circuit breaker70of the failure phase is controlled so as to be in the cutoff state at all times, and the normal two-phase power semiconductor elements32other than the failure phase are controlled in the same manner as in the normal state. Thereafter, the processing proceeds to step S106.

As described above, according to the power conversion device100of the third embodiment, the current control at the time of the one-phase failure is applied in the case where the motor rotational speed is less than the predetermined threshold. However, the current control at the time of the one-phase failure is not applied in the case where the motor rotational speed is equal to or greater than the threshold, but the current control similar to the conventional current control in which the failure phase is not energized is performed. Thus, unnecessary switching control of the circuit breaker70can be eliminated, and the processing load of the control circuit10can be reduced.

According to the third embodiment of the present invention described above, when the rotation speed of the motor190is equal to or greater than the predetermined threshold (No in step S109), the circuit breaker controller17controls the circuit breaker70of the failure phase such that the AC current is cut off in the entire period of one cycle of the electrical angle (step S110). On the other hand, in the case where the rotation speed of the motor190is less than the threshold (Yes step S109), the circuit breaker70of the failure phase is controlled such that the AC current of the failure phase is conducted at the specific electrical angle and the AC current of the failure phase is cut off at other electrical angles except the specific electrical angle (step S105). With this configuration, the current control at the time of the one-phase failure can be performed while the processing load of the control circuit10is reduced.

Fourth Embodiment

An example of a power conversion device and a drive device that improve the average output torque while maintaining the torque fluctuation even after the failure of the power semiconductor by a method different from the second and third embodiments and make it easy to start the vehicle in the case where the switching of the circuit breaker is delayed will be described in a fourth embodiment.

The power conversion device100and the drive device200in the second embodiment have the same configurations as those inFIG.2described in the first embodiment. For this reason, the power conversion device100and the drive device200of the second embodiment will be described below with reference to the configuration ofFIG.2.

FIG.13is an explanatory diagram illustrating the switching timing of the circuit breaker70according to the fourth embodiment of the present invention. InFIG.13, (a) illustrates an example of a timing chart in the case where the circuit breaker switching and the current control described in the second embodiment are performed, and (b) illustrates an example of a timing chart in the case where the circuit breaker switching and the current control according to the fourth embodiment are performed. In both ofFIGS.13(a)and13(b), it is assumed that the open failure is generated in the power semiconductor element32of the U-phase upper arm.

In the first and second embodiments, even when the power semiconductor element32has the open failure or the short-circuit failure, in the current control at the time of the one-phase failure, one of the upper and lower arms of the failure phase is controlled such that the power semiconductor element32is always turned on and the other is always turned off, and the circuit breaker70of the failure phase is controlled so as to be in the conduction state only during the specific electrical angle. For this reason, for example, in the second embodiment, in the case where the open failure is generated in the power semiconductor element32of the U-phase lower arm, as illustrated inFIG.13(a), the power semiconductor element32of the U-phase upper arm is always turned on, and the circuit breaker70of the U-phase is controlled to be in the conduction state in the period shorter than the specific electrical angle by the switching delay time of the circuit breaker70.

However, in the case where the open failure is generated in any one of the power semiconductor elements32of the upper and lower arms, the output voltage control similar to the current control at the time of the one-phase failure described in the first and second embodiments can be implemented in the power conversion device100not by controlling the cutoff or conduction of the circuit breaker70but by controlling the on- or off-states of the power semiconductor elements32on the upper and lower opposite sides in phase with the failure portion. Accordingly, in the fourth embodiment, in the case where the open failure of the power semiconductor element32is generated, as the current control at the time of the one-phase failure, the circuit breaker70of the failure phase is controlled to be always in the conduction state, and the power semiconductor element32on the upper and lower opposite sides in phase with the failure portion is controlled to be in the on-state only for the specific electrical angle.

Specifically, for example, as in the timing chart ofFIG.13(b), the circuit breaker70of the failure phase (U-phase) is always brought into the conduction state, and the power semiconductor element32on the upper and lower opposite sides (U-phase upper arm) in the same phase as the failure portion is controlled to be in the on-state only during the specific electrical angle described in the first embodiment. Thus, the current control at the time of the one-phase failure similar to that in the first and second embodiments can be implemented.

For example, as in the case where the mechanical switch is used for the circuit breaker70, in the case where the conduction or cutoff switching delay time of the circuit breaker70is long and the on or off switching delay time of the power semiconductor element32is short compared to this, the influence of the switching delay time of the circuit breaker70can be reduced by performing the control of the fourth embodiment. Consequently, even in the situation where the motor rotation speed is high, the same control as the current control at the time of the one-phase failure can be applied in the power conversion device100. For this reason, even when the vehicle1is traveling at a high speed, the average output torque can be improved while the torque fluctuation similar to the conventional control is maintained.

FIG.14illustrates an example of a control flowchart according to the fourth embodiment of the present invention. In the fourth embodiment, the control circuit10inFIG.2periodically performs the control illustrated in the flowchart ofFIG.14at regular intervals. InFIG.14, portions performing the same pieces of processing as those in the control flowchart ofFIG.7described in the first embodiment are denoted by the same symbols as those inFIG.7, and description of those pieces of processing is omitted.

In the fourth embodiment, in the processing of step S104, the processing proceeds to step S111in the case where the internal state19ais the “one-phase failure state”, and the processing proceeds to step S108in the case where the internal state is other than the “one-phase failure state”.

In the processing of step S111, the control circuit10determines whether the failure state of the power semiconductor element32in which the failure is detected is the open failure. The processing proceeds to step S112when the open failure is detected, and the processing proceeds to step S105in the case where the short-circuit failure is detected instead of the open failure.

In the processing of step S112, the control circuit10controls the circuit breaker70of the failure phase to be always in the conduction state, and controls the power semiconductor elements32on the upper and lower opposite sides in phase with the failure portion to be in the on-state only during the specific electrical angle. Thus, the current control at the time of the one-phase failure is performed. Thereafter, the processing proceeds to step S106.

As described above, according to the power conversion device100of the fourth embodiment, in the case where the open failure of the power semiconductor element32is generated, the circuit breaker70of the failure phase is controlled so as to be always in the conduction state, and the power semiconductor element32on the upper and lower opposite sides in phase with the failure portion is controlled so as to be in the on-state only for the specific electrical angle. Thus, the influence of the switching delay time of the circuit breaker70can be eliminated and the current control at the time of the one-phase failure can be performed.

According to the fourth embodiment of the present invention described above, in the case where the open failure is generated in the power semiconductor element32(Yes in step S111), the circuit breaker controller17brings the circuit breaker70of the failure phase into the conduction state, and the failure-time current controller15controls the drive of the power semiconductor element32of the phase different from the failure phase and the power semiconductor element32that is not the power semiconductor element32determined to be the failure portion in the upper and lower arm circuits in the failure phase (step S112). With this configuration, the influence of the switching delay time of the conduction or cutoff of the circuit breaker70can be reduced, and the same control as the current control at the time of the one-phase failure can be implemented even in the situation where the motor rotation speed is high.

Fifth Embodiment

An example of a power conversion device and a drive device capable of coping with the failure of the circuit breaker, improving the average output torque, and maintaining the torque fluctuation even after the failure of the power semiconductor will be described in a fifth embodiment.

FIG.15is a view illustrating a configuration example of the power conversion device100and the drive device200according to the fifth embodiment of the present invention. In the power conversion device100of the fifth embodiment, the control circuit10further includes a circuit breaker failure portion determination unit14in addition to the configuration similar to that ofFIG.2described in the first embodiment. Hereinafter, description of portions common to the first to fourth embodiments will be omitted.

When diagnosing the circuit breaker70, the circuit breaker failure portion determination unit14generates a predetermined duty value14afor each phase and outputs the duty value14ato the PWM signal generator16. During the diagnosis of the circuit breaker70, a predetermined circuit breaker switching signal14bis generated for each phase and output to the circuit breaker controller17. The circuit breaker failure portion determination unit14can determine whether the circuit breaker70of each phase fails using the AC current sensor value50aof each phase output from the AC current sensor50when these signals are output. When the diagnosis of the circuit breaker70is completed, the circuit breaker failure portion determination unit14outputs circuit breaker diagnostic information14cindicating that the diagnosis of the circuit breaker70is completed to the state determination unit19, and the failure portion when there is the failure.

FIG.16is a view illustrating an example of internal state determination of the state determination unit19according to the fifth embodiment of the present invention. In the fifth embodiment, the initial state of the state determination unit19is a “circuit breaker diagnostic state”. When the state determination unit19receives the circuit breaker diagnostic information14cfrom the circuit breaker failure portion determination unit14while the current state is the “circuit breaker diagnostic state”, the next state is changed to the “normal state”.

When receiving the power semiconductor failure information18aindicating that the power semiconductor element32of any phase fails from the power semiconductor failure portion determination unit18while the current state is the “normal state”, the state determination unit19changes the current state according to contents of the circuit breaker diagnostic information14creceived from the circuit breaker failure portion determination unit14so far. Specifically, in the case where the circuit breaker diagnostic information14cindicating that the circuit breaker70having the same phase as the failed power semiconductor element32fails is received, the next state is changed to a “at least two-phase failure state”. On the other hand, in the case where the circuit breaker diagnostic information14cindicating that the circuit breaker70of the phase different from that of the failed power semiconductor element32fails or the circuit breaker diagnostic information14cindicating that the circuit breaker70does not fail is received, the next state is changed to the “one-phase failure state”. When the current state is the “normal state”, the next state remains in the “normal state” in the case other than the above.

The case where the current state is the “one-phase failure state” or the “at least two-phase failure” is similar to that of the first embodiment.

A method for diagnosing the circuit breaker70according to the fifth embodiment will be described below. In the case where the internal state output from the state determination unit19is the “circuit breaker diagnostic state”, the PWM signal generator16generates the PWM signal16aof each phase according to the duty value14aof each phase output from the circuit breaker failure portion determination unit14. In the case where the internal state output from the state determination unit19is the “circuit breaker diagnostic state”, the circuit breaker controller17controls the conduction or cutoff states of the circuit breakers70of each phase according to the circuit breaker switching signal14boutput from the circuit breaker failure portion determination unit14. The circuit breaker failure portion determination unit14can determine whether the circuit breaker70of each phase fails based on the AC current sensor value50aof each phase output from the AC current sensor50when these signals are output.

The failure of the circuit breaker70roughly includes two types of failure states of a cutoff fixing failure in which the circuit breaker70does not change from the cutoff state and a conduction fixing failure in which the circuit breaker70does not change from the conduction state. In the case where the circuit breaker70has the conduction fixing failure, when the short-circuit failure is generated in the power semiconductor element32having the same phase as the failed circuit breaker70, the power conversion device100cannot cut off the AC current flowing through the failure phase regardless of whether the circuit breaker70or the power semiconductor element32is used. Consequently, in this case, the current control at the time of the one-phase failure cannot be continued. Accordingly, in the fifth embodiment, in order to determine such a situation, the circuit breaker failure portion determination unit14diagnoses the presence or absence of the conduction fixing failure for the circuit breaker70of each phase.

When determining the presence or absence of the conduction fixing failure of the circuit breaker70using a certain phase as a diagnostic object phase, the circuit breaker failure portion determination unit14selects one phase (hereinafter, referred to as “selection phase”) different from the diagnostic object phase, and generates and outputs the circuit breaker switching signal14bto the circuit breaker controller17so as to bring the circuit breaker70of the selection phase into the conduction state and to bring the circuit breakers70of the other two phases into the cutoff state. In addition, the circuit breaker failure portion determination unit14generates the duty value14asuch that the power semiconductor element32of the upper arm of the diagnostic object phase and the power semiconductor element32of the lower arm of the selection phase are turned on only for a predetermined short time, and outputs the duty value14ato the PWM signal generator16. The upper arm and the lower arm may be replaced with each other in a combination of the power semiconductor elements32to be turned on at this time. That is, the power semiconductor element32of the lower arm of the diagnostic object phase and the power semiconductor element32of the upper arm of the selection phase may be turned on only for the predetermined short time.

When the circuit breaker switching signal14band the duty value14aas described above are output, no current flows through the diagnostic object phase in the case where the circuit breaker70of the diagnostic object phase is normally cut off. However, in the case where the circuit breaker70of the diagnostic object phase has the conduction fixing failure, a current path passing through the power semiconductor element32of the diagnostic object phase, the circuit breaker70and the motor winding, the motor winding of the selection phase, the circuit breaker70, and the power semiconductor element32is formed, and the current flows through the current path. For this reason, when performing the circuit breaker diagnosis operation, the circuit breaker failure portion determination unit14determines whether the current of at least a certain value flows through the diagnostic object phase based on the AC current sensor value50a. As a result, in the case where it is determined that the current flows, it is determined that the circuit breaker70of the diagnostic object phase is in the conduction fixing failure state.

FIG.17illustrates an example of a flowchart of the circuit breaker diagnosis according to the fifth embodiment of the present invention. In the fifth embodiment, the circuit breaker failure portion determination unit14performs the control illustrated in the flowchart ofFIG.17before the operation of the driver circuit20and the power conversion circuit30.

In the processing of step S200, the circuit breaker failure portion determination unit14performs the diagnostic operation of the conduction fixing failure of the circuit breaker70of the U-phase. Specifically, as described above, with the U-phase as the diagnostic object phase and either the V-phase or the W-phase as the selection phase, the circuit breaker switching signal14bthat brings the circuit breaker70of the selection phase into the conduction state and brings the circuit breaker70of the U-phase and the circuit breaker70of the phase that is not the selection phase into the cutoff state is output to the circuit breaker controller17. The duty value14a, with which the power semiconductor element32of the upper arm (or lower arm) of the U-phase and the power semiconductor element32of the lower arm (or upper arm) of the selection phase are turned on only for the short time, is output to the PWM signal generator16.

When the duty value14aand the circuit breaker switching signal14bare output from the circuit breaker failure portion determination unit14, the PWM signal generator16generates the PWM signal16abased on the duty value14aand outputs the PWM signal to the driver circuit20. In addition, the circuit breaker controller17controls the conduction or cutoff state of the circuit breaker70of each phase based on the circuit breaker switching signal14b.

In the processing of step S201, the circuit breaker failure portion determination unit14determines whether the current at least a certain value flows in the U-phase based on the U-phase AC current sensor value50aoutput from the AC current sensor50. In the case where the current of at least the certain value flows through the U-phase, the circuit breaker failure portion determination unit14next performs the processing of step S202, and otherwise, the circuit breaker failure portion determination unit14next performs the processing of step S203.

In the processing of step S202, the circuit breaker failure portion determination unit14determines that the circuit breaker70of the U-phase has the conduction fixing failure. In the processing of step S203, the circuit breaker failure portion determination unit14determines that the circuit breaker70of the U-phase is normal. After the processing of step S202or S203is performed, the processing proceeds to step S204.

In the processing of step S204, the circuit breaker failure portion determination unit14performs the diagnostic operation of the conduction fixing failure of the V-phase circuit breaker70. Specifically, as described above, with the V-phase as the diagnostic object phase and either the U-phase or the W-phase as the selection phase, the circuit breaker switching signal14bthat brings the circuit breaker70of the selection phase into the conduction state and brings the circuit breaker70of the V-phase and the circuit breaker70of the phase that is not the selection phase into the cutoff state is output to the circuit breaker controller17. In addition, the duty value14awith which the power semiconductor element32of the upper arm (or lower arm) of the V-phase and the power semiconductor element32of the lower arm (or upper arm) of the selection phase are turned on only for the short time is output to the PWM signal generator16.

When the duty value14aand the circuit breaker switching signal14bare output from the circuit breaker failure portion determination unit14, the PWM signal generator16generates the PWM signal16abased on the duty value14aand outputs the PWM signal to the driver circuit20. In addition, the circuit breaker controller17controls the conduction or cutoff state of the circuit breaker70of each phase based on the circuit breaker switching signal14b.

In the processing of step S205, the circuit breaker failure portion determination unit14determines whether the current of at least a certain value flows in the V-phase based on the V-phase AC current sensor value50aoutput from the AC current sensor50. In the case where the current of at least certain value flows in the V-phase, the circuit breaker failure portion determination unit14next performs the processing of step S206, and otherwise, the circuit breaker failure portion determination unit14next performs the processing of step S207.

In the processing of step S206, the circuit breaker failure portion determination unit14determines that the circuit breaker70of the V-phase has the conduction fixing failure. In the processing of step S207, the circuit breaker failure portion determination unit14determines that the circuit breaker70of the V-phase is normal. After the processing of step S206or S207is performed, the processing proceeds to step S208.

In the processing of step S208, the circuit breaker failure portion determination unit14performs the diagnostic operation of the conduction fixing failure of the W-phase circuit breaker70. Specifically, as described above, with the W-phase as the diagnostic object phase and either the U-phase or the V-phase as the selection phase, the circuit breaker switching signal14bthat brings the circuit breaker70of the selection phase into the conduction state and brings the circuit breaker70of the W-phase and the circuit breaker70of the phase that is not the selection phase into the cutoff state is output to the circuit breaker controller17. In addition, the duty value14awith which the power semiconductor element32of the upper arm (or lower arm) of the W-phase and the power semiconductor element32of the lower arm (or upper arm) of the selection phase are turned on only for the short time is output to the PWM signal generator16.

When the duty value14aand the circuit breaker switching signal14bare output from the circuit breaker failure portion determination unit14, the PWM signal generator16generates the PWM signal16abased on the duty value14aand outputs the PWM signal to the driver circuit20. In addition, the circuit breaker controller17controls the conduction or cutoff state of the circuit breaker70of each phase based on the circuit breaker switching signal14b.

In the processing of step S209, the circuit breaker failure portion determination unit14determines whether the current of at least a certain value flows in the W-phase based on the W-phase AC current sensor value50aoutput from the AC current sensor50. In the case where the current of at least certain value flows in the W-phase, the circuit breaker failure portion determination unit14next performs the processing of step S210, and otherwise, the circuit breaker failure portion determination unit14next performs the processing of step S211.

In the processing of step S210, the circuit breaker failure portion determination unit14determines that the circuit breaker70of the W-phase has the conduction fixing failure. In the processing of step S211, the circuit breaker failure portion determination unit14determines that the circuit breaker70of the W-phase is normal. After the processing of step S210or S211is performed, the processing proceeds to step S212.

In the processing of step S212, the circuit breaker failure portion determination unit14generates the circuit breaker diagnostic information14cbased on the diagnostic results of the circuit breaker70of each phase obtained in steps S202and S203, S206and S207, and S210and S211, and outputs the circuit breaker diagnostic information14cto the state determination unit19.

When the circuit breaker diagnostic information14cis output from the circuit breaker failure portion determination unit14, the state determination unit19changes the internal state from the “circuit breaker diagnostic state” to the “normal state” and starts the operations of the driver circuit20and the power conversion circuit30.

After executing the process of step S212, the circuit breaker failure portion determination unit14ends the control flowchart ofFIG.17. Thus, the diagnostic operation of the circuit breaker70is completed.

FIG.18illustrates an example of a control flowchart according to the fifth embodiment of the present invention. In the fifth embodiment, the control circuit10inFIG.15periodically performs the control illustrated in the flowchart ofFIG.18at regular intervals. InFIG.18, portions performing the same pieces of processing as those in the control flowchart ofFIG.7described in the first embodiment are denoted by the same symbols as those inFIG.7, and description of those pieces of processing is omitted.

In the fifth embodiment, the processing proceeds to step S113in the case where the open failure or the short-circuit failure is detected in any one of the power semiconductor elements32in the processing of step S102.

In the processing of step S113, the state determination unit19determines whether the circuit breaker70in phase with the failed power semiconductor element32fails based on the circuit breaker diagnostic information14coutput from the circuit breaker failure portion determination unit14in step S212ofFIG.17and the power semiconductor failure information18aoutput from the power semiconductor failure portion determination unit18. As a result, the processing proceeds to step S114in the case where it is determined in step S102that the circuit breaker70in phase with the power semiconductor element32in which the open failure or the short-circuit failure is detected fails, and the processing proceeds to step S103in the case where it is determined that the circuit breaker70of the different phase fails.

In the processing of step S114, the state determination unit19determines that the current state of the power conversion device100is the “at least two-phase failure state” and updates the internal state19a. After executing the processing of step S114, the control circuit10ends the control flowchart ofFIG.18.

As described above, according to the power conversion device100of the fifth embodiment, the presence or absence of the conduction fixing failure of the circuit breaker70is determined before the operations of the driver circuit20and the power conversion circuit30are started. Then, when the failure of the power semiconductor element32is generated, in the case where the circuit breaker70in phase with the power semiconductor element32is in the conduction fixing failure state, the current of the failure phase cannot be cut off and the transition to the one-phase failure current control cannot be made, so that the drive of the motor190is stopped similarly to the case of the at least two-phase failure. For this reason, the operation corresponding to the failure of the circuit breaker70can be taken.

According to the fifth embodiment of the present invention described above, the power conversion device100includes the circuit breaker failure portion determination unit14that determines the failure portion of the circuit breaker70. In the case where the power semiconductor element32determined to be the failure portion by the power semiconductor failure portion determination unit18and the circuit breaker70determined to be the failure portion by the circuit breaker failure portion determination unit14have the same phase (Yes in step S113), it is determined that the current state of the power conversion device100is the “at least two-phase failure state” (step S114), and the drive of the motor190is stopped (step S108). With this configuration, the drive of the motor190can be safely stopped in the case where the circuit breaker70fails not to be able to perform the current control at the time of one-time failure.

The present invention is not limited to the above embodiments, and various modifications are included. For example, the above embodiments are described in detail for the purpose of easy understanding of the present invention, and do not necessarily include all the described configurations. A part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Furthermore, another configuration can be added to, deleted from, and replaced with other configurations for a part of the configuration of each embodiment. Some or all of the configurations, functions, processing units, processing measure, and the like may be designed with, for example, an integrated circuit, and implemented by hardware. Furthermore, the above-described respective configurations, functions, and the like may be implemented by software by the processor interpreting and executing a program implementing the respective functions. Information such as a program, a table, and a file, that implements each function can be stored in a memory, a recording device such as a hard disk and a solid state drive (SSD), or a recording medium such as an IC card, an SD card, and a DVD.

REFERENCE SIGNS LIST