Electric motor control device

1. An electric motor control device that controls driving of an electric motor based on a magnetic pole position of a rotor, the electric motor control device comprising:

a control unit that controls operation of a drive circuit supplying an electric power to the electric motor; and

a current sensor that detects a current generated in the electric motor, wherein

the control unit detects, through the current sensor, a fundamental high frequency current generated in the electric motor when the electric motor is applied with a fundamental high frequency voltage for estimating the magnetic pole position through the drive circuit, and selects a first electric angle and a second electric angle corresponding to a d-axis direction of the magnetic pole position based on a detection value of the fundamental high frequency current,

the control unit detects, through the current sensor, a first specific high frequency current generated in the electric motor when a position of the first electric angle is applied with a specific high frequency voltage through the drive circuit and a second specific high frequency current generated in the electric motor when a position of the second electric angle is applied with the specific high frequency voltage through the drive circuit, and

the control unit compares a detection value of the first specific high frequency current with a detection value of the second specific high frequency current to estimate a positive d-axis direction of the magnetic pole position.

2. The electric motor control device according to claim 1 , wherein

the control unit detects, through the current sensor, the fundamental high frequency current, which is generated in the electric motor when the electric motor is applied with the fundamental high frequency voltage through the drive circuit, at every predetermined electric angle,

the control unit calculates a magnitude of the fundamental high frequency current at every predetermined electric angle based on the detection value of the fundamental high frequency current detected at every predetermined electric angle,

the control unit uses an electric angle at which the magnitude of the fundamental high frequency current is maximum as the first electric angle, and

the control unit uses an electric angle deviated from the first electric angle by 180° as the second electric angle.

3. The electric motor control device according to claim 1 , wherein

the control unit detects, through the current sensor, the fundamental high frequency current, which is generated in the electric motor when the electric motor is applied with the fundamental high frequency voltage through the drive circuit, at every predetermined electric angle and for a plurality of cycles,

the control unit calculates an average value of magnitudes of the fundamental high frequency currents at every predetermined electric angle based on the detection values of the fundamental high frequency currents detected at every predetermined electric angle and for the plurality of cycles,

the control unit uses an electric angle at which the average value of the magnitudes of the fundamental high frequency currents is maximum as the first electric angle, and

the control unit uses an electric angle deviated from the first electric angle by 180° as the second electric angle.

4. The electric motor control device according to claim 1 , wherein

the control unit further estimates a third electric angle and a fourth electric angle corresponding to the d-axis direction of the magnetic pole position based on the detection value of the fundamental high frequency current,

the control unit detects, through the current sensor, a third specific high frequency current generated in the electric motor when a position of the third electric angle is applied with the specific high frequency voltage through the drive circuit and a fourth specific high frequency current generated in the electric motor when a position of the fourth electric angle is applied with the specific high frequency voltage through the drive circuit, and

the control unit compares the detection value of the first specific high frequency current, the detection value of the second specific high frequency current, a detection value of the third specific high frequency current, and a detection value of the fourth specific high frequency current with each other to estimate a positive d-axis direction of the magnetic pole position.

5. The electric motor control device according to claim 4 , wherein

the control unit detects, through the current sensor, the fundamental high frequency current, which is generated in the electric motor when the electric motor is applied with the fundamental high frequency voltage through the drive circuit, at every predetermined electric angle,

the control unit calculates a magnitude of the fundamental high frequency current at every predetermined electric angle based on the detection value of the fundamental high frequency current detected at every predetermined electric angle,

the control unit uses two electric angles at which the magnitude of the fundamental high frequency current is maximum as the first electric angle and the third electric angle,

the control unit uses an electric angle deviated from the first electric angle by 180° as the second electric angle, and

the control unit uses an electric angle deviated from the third electric angle by 180° as the fourth electric angle.

6. The electric motor control device according to claim 4 , wherein

the control unit detects, through the current sensor, the fundamental high frequency current, which is generated in the electric motor when the electric motor is applied with the fundamental high frequency voltage through the drive circuit, at every predetermined electric angle and for a plurality of cycles,

the control unit calculates an average value of magnitudes of the fundamental high frequency currents at every predetermined electric angle based on the detection values of the fundamental high frequency currents detected at every predetermined electric angle and for the plurality of cycles,

the control unit uses two electric angles at which the average value of the magnitudes of the fundamental high frequency currents is maximum as the first electric angle and the third electric angle,

the control unit uses an electric angle deviated from the first electric angle by 180° as the second electric angle, and

the control unit uses an electric angle deviated from the third electric angle by 180° as the fourth electric angle.

7. The electric motor control device according to claim 1 , wherein

the fundamental high frequency voltage has a frequency higher than a frequency of a drive voltage used for driving the electric motor.

8. The electric motor control device according to claim 1 , wherein

the control unit estimates the d-axis direction of the magnetic pole position a plurality of times and estimates the d-axis direction of the magnetic pole position based on a plurality of estimation results.

9. The electric motor control device according to claim 1 , wherein

the control unit estimates a positive d-axis direction of the magnetic pole position a plurality of times and estimates the positive d-axis direction of the magnetic pole position based on a plurality of estimation results.

10. The electric motor control device according to claim 1 , wherein

the fundamental high frequency voltage changes sinusoidally with time.

11. The electric motor control device according to claim 1 , wherein

the specific high frequency voltage changes in a rectangular waveform with time.

12. The electric motor control device according to claim 1 , wherein

the electric motor is used as a power source of a vehicle electric compressor.