Motor control device and electric vehicle system using the same

1. A motor control device comprising:

a power converter that is controlled by a pulse width modulation signal;

a motor that is driven by the power converter; and

a controller that generates the pulse width modulation signal, based on a carrier signal, wherein

when switching between a first carrier frequency of the carrier signal and a second carrier frequency of the carrier signal, the controller varies proportions of the first carrier frequency and the second carrier frequency in accordance with a number of rotations of the motor, the second carrier frequency being higher than the first carrier frequency,

wherein neither the first carrier frequency nor the second carrier frequency coincides with a mechanical natural frequency of the motor, and

when a frequency of a sideband of the carrier signal coincides with the natural frequency, the proportions of the first carrier frequency and the second carrier frequency are varied in accordance with the number of rotations of the motor.

2. The motor control device according to claim 1 , wherein the controller dynamically varies the proportions of the first carrier frequency and the second carrier frequency.

3. The motor control device according to claim 1 , wherein the controller varies the proportions of the first carrier frequency and the second carrier frequency in a stepwise manner.

4. The motor control device according to claim 3 , wherein a pair (r1, r2) of the proportion r1 [%] of the first carrier frequency and the proportion r2[%] of the second carrier frequency is set in five stages to (0, 100), (25, 75), (50, 50), (75, 25), and (100, 0).

5. The motor control device according to claim 4 , wherein the controller sets in the five stages in accordance with the number of rotations of the motor.

6. The motor control device according to claim 1 , wherein the controller decreases the proportion of the first carrier frequency and increases the proportion of the second carrier frequency as the number of rotations of the motor increases.

7. The motor control device according to claim 6 , wherein

when the number of rotations of the motor is smaller than or equal to a predetermined first number of rotations, the proportion of the first carrier frequency is set to 100%, and the proportion of the second frequency is set to 0%,

when the number of rotations of the motor is equal to or larger than a predetermined second number of rotations that is higher than the first number of rotations of the motor, the proportion of the first carrier frequency is set to 0%, and the proportion of the second carrier frequency is set to 100%, and

when the number of rotations of the motor is equal to or larger than the first number of rotations and is smaller than or equal to the second number of rotations, the proportion of the first carrier frequency is decreased from 100% and the proportion of the second carrier frequency is increased by 0% as the number of rotations of the motor increases.

8. The motor control device according to claim 1 , wherein the controller linearly varies the proportions of the first carrier frequency and the second carrier frequency in accordance with the number of rotations of the motor.

9. The motor control device according to claim 1 , wherein the second carrier frequency is equal to an integral multiple ≥2 of the first carrier frequency.

10. The motor control device according to claim 1 , wherein the controller alternately selects the first carrier frequency and the second carrier frequency in durations proportional to the respective proportions.

11. The motor control device according to claim 7 , wherein

when neither the first carrier frequency nor the second carrier frequency coincides with a mechanical natural frequency of the motor, the second carrier frequency is closer to the natural frequency than the first carrier frequency, and

the frequency of the sideband of the carrier signal whose fundamental frequency is the second carrier frequency coincides with the natural frequency, the proportions of the first carrier frequency and the second carrier frequency are varied in accordance with the number of rotations of the motor.

12. The motor control device according to claim 1 , wherein when switching from the first carrier frequency to the second carrier frequency or when switching from the second carrier frequency to the first carrier frequency, hysteresis is provided for a variation in each of the proportions.

13. The motor control device according to claim 1 , wherein both of the first carrier frequency and the second carrier frequency are subjected to spectrum spreading.

14. The motor control device according to claim 1 , wherein the timing of detecting a current flowing through the motor is changed in accordance with both of the first carrier frequency and the second carrier frequency.

15. The motor control device according to claim 1 , wherein the motor is a three-phase synchronous motor.

16. An electric vehicle system comprising:

a vehicle body;

a wheel provided on the vehicle body;

a drive power source that drives the wheel, the drive power source including a motor;

a power converter that is controlled by a pulse width modulation signal and drives the motor; and

a controller that generates the pulse width modulation signal, based on a carrier signal, wherein

when switching between a first carrier frequency of the carrier signal and a second carrier frequency of the carrier signal, the controller varies proportions of the first carrier frequency and the second carrier frequency in accordance with a number of rotations of the motor, the second carrier frequency being higher than the first carrier frequency,

wherein neither the first carrier frequency nor the second carrier frequency coincides with a mechanical natural frequency of the motor, and

when a frequency of a sideband of the carrier signal coincides with the natural frequency, the proportions of the first carrier and the second carrier frequency are varied in accordance with the number of rotations of the motor.