Motor driving circuit, motor device, and electric vehicle

1. A motor driving circuit, comprising:

a supply line connected to a direct-current power source;

an inverter of which an input side is connected to the supply line and of which an output side is connected to a motor, the inverter converting direct-current electric power fed from the supply line into alternating-current electric power and feeding the alternating-current electric power to the motor;

a power switch inserted in the supply line for switching the supply line between a conducting state and a cut-off state;

a voltage detector for detecting a voltage between the direct-current power source and the power switch; and

an insulation resistance detector for

first performing a first detection operation to detect, based on a result of detection by the voltage detector with the power switch in the cut-off state, an insulation resistance on a preceding-stage side of the power switch and

subsequently performing a second detection operation to detect, based on a result of detection by the voltage detector with the power switch in the conducting state, an insulation resistance on a succeeding-stage side of the power switch.

2. The motor driving circuit according to claim 1 ,

wherein the power switch is provided between the direct-current power source and the inverter.

3. The motor driving circuit according to claim 2 ,

wherein

the inverter has an arm for a single phase, or arms for a plurality of phases,

the arm, or each of the arms, includes an upper device and a lower device as switching devices connected in series between a positive electrode and a negative electrode of the direct-current power source,

the motor is connected between the upper and lower devices, and

the insulation resistance detector

performs, as the second detection operation, an operation to detect, based on a result of detection by the voltage detector with every upper device in an off state, an insulation resistance on a preceding-stage side of the upper device, and

performs, subsequently to the second detection operation, as a third detection operation, an operation to detect, based on a result of detection by the voltage detector with at least one upper device in an on state, an insulation resistance on a succeeding-stage side of the upper device.

4. The motor driving circuit according to claim 3 ,

wherein

the inverter has, as the arms, three-phase arms, and has, as the motor, a three-phase motor connected between the upper and lower devices of each of the arms, and

the insulation resistance detector

performs, as the second detection operation, an operation to detect, based on a result of detection by the voltage detector with every upper device in an off state, an insulation resistance of the inverter, and

performs, as the third detection operation, an operation to detect, based on a result of detection by the voltage detector with at least one upper device in an on state, an insulation resistance of three-phase lines of the motor.

5. The motor driving circuit according to claim 3 ,

wherein

the inverter comprises inverters provided in parallel to belong to a plurality of groups respectively,

the power switch comprises a plurality of power switches provided to belong to the plurality of groups respectively,

the voltage detector detects, for each of the power switches, the voltage between the direct-current power source and the power switch, and

the insulation resistance detector

first performs, as the first detection operation, an operation to detect, based on a result of detection by the voltage detector with all the power switches in a cut-off state, an insulation resistance on a preceding-stage side of all the power switches, and

subsequently performs the second and third detection operations for each of the plurality of groups.

6. The motor driving circuit according to claim 5 ,

wherein the insulation resistance detector performs the second detection operation for each of the plurality of groups, and subsequently performs the third detection operation for each of the plurality of groups.

7. The motor driving circuit according to claim 3 ,

wherein, when an abnormal insulation resistance is detected in any of the first to third detection operations, an output that is set to differ among the first to third detection operations is delivered.

8. The motor driving circuit according to claim 3 ,

wherein, when an abnormal insulation resistance is detected in any of the first to third detection operations, execution of any detection operation thereafter is omitted.

9. A motor device, comprising:

a motor driving circuit according to claim 1 ; and

a motor connected to the output side of the inverter.

10. An electric vehicle, comprising:

the motor device according to claim 9 ; and

a driving wheel rotated by the motor.

11. An electric vehicle, comprising:

a motor driving circuit according to claim 1 , wherein the inverter comprises inverters provided to belong to two groups respectively,

a left driving wheel and a right driving wheel;

a left motor connected to an output side of one of the inverters, for rotating the left driving wheel;

a right motor connected to an output side of the other of the inverters, for rotating the right driving wheel.