Motor drive apparatus and vehicle with the same mounted thereon

1. A motor drive apparatus for driving an AC motor using electric power provided from a DC power supply,

said AC motor being configured to rotate a rotor provided with a permanent magnet using a current magnetic field generated by passing a drive current through a coil of a stator,

said motor drive apparatus comprising:

a power conversion device configured to convert DC electric power provided from said DC power supply into AC electric power for driving said AC motor; and

a control device for controlling said power conversion device such that an offset current is superimposed on at least one phase of said coil and a temperature of said permanent magnet is raised.

2. The motor drive apparatus according to claim 1 , wherein

said control device changes magnitude of said offset current in accordance with a rotation speed of said AC motor.

3. The motor drive apparatus according to claim 2 , wherein

said control device controls said power conversion device such that said offset current increases as said rotation speed becomes higher.

4. The motor drive apparatus according to claim 3 , wherein

said control device sets the magnitude of said offset current in proportional to said rotation speed.

5. The motor drive apparatus according to claim 3 , wherein

said control device increases said offset current in a stepwise manner as said rotation speed increases.

6. The motor drive apparatus according to claim 3 , wherein

said control device sets the magnitude of said offset current using a map predetermined based on said rotation speed.

7. The motor drive apparatus according to claim 2 , wherein

said control device stops superimposition of said offset current when said rotation speed is lower than a reference rotation speed.

8. The motor drive apparatus according to claim 7 , wherein

said control device executes superimposition of said offset current when a temperature related to said permanent magnet is lower than a reference value at the start of driving of said AC motor, and does not execute superimposition of said offset current when the temperature related to said permanent magnet is higher than said reference value.

9. The motor drive apparatus according to claim 1 , wherein

said control device has a map defining a temporal change in temperature rise of said permanent magnet based on a driving state of said AC motor, estimates the temperature of said permanent magnet by calculating a value of the temperature rise of said permanent magnet using said map based on a torque command value and a rotation speed of said AC motor, and summing the calculated values of the temperature rise in a time axis direction since the start of driving of said AC motor, and stops superimposition of said offset current when the estimated temperature of said permanent magnet reaches a threshold value.

10. The motor drive apparatus according to claim 1 , wherein

said power conversion device includes an inverter configured to include a switching element and making power conversion by controlling said switching element in accordance with pulse width modulation control, and

said control device sets a frequency of a carrier wave used in said pulse width modulation control to be relatively lower when the temperature of said permanent magnet is lower than a reference temperature than when the temperature of said permanent magnet is higher than said reference temperature.

11. A vehicle, comprising:

a DC power supply;

an AC motor configured to rotate a rotor provided with a permanent magnet using a current magnetic field generated by passing a drive current through a coil of a stator and to generate driving force for causing said vehicle to run;

a power conversion device configured to convert electric power provided from said DC power supply into AC electric power for driving said AC motor; and

a control device for controlling said power conversion device such that an offset current is superimposed on at least one phase of said coil and a temperature of said permanent magnet is raised.