Control device for multi-phase AC motor

1. A control device for controlling energization of a multi-phase AC motor, which generates a steering assist torque in an electric power steering device of a vehicle, the control device comprising:

a first inverter in a first system that outputs a first alternating current voltage to a first multi-phase winding wire set;

a second inverter in a second system that outputs a second alternating current voltage to a second multi-phase winding wire set; and

a control unit that controls a phase difference between the first alternating current voltage applied to the first multi-phase winding wire set and the second alternating current voltage applied to the second multi-phase winding wire set,

wherein the first inverter and the second inverter are electrically independent from each other,

wherein the first multi-phase winding wire set and the second multi-phase winding wire set provide a stator of the multi-phase AC motor, and generate a rotating magnetic field in a rotor,

wherein the control unit sets a control range including a reference phase difference, which reduces a torque ripple due to a specified-order harmonic component as an A-th order torque ripple, and another phase difference which reduces another torque ripple due to another specified-order harmonic component as a B-th order torque ripple, and

wherein the control unit changes the phase difference within the control range according to a steering speed of a driver as a characteristic required of the multi-phase AC motor.

2. The control device according to claim 1 ,

wherein the control unit changes the phase difference based on a speed of a steering wheel operated by a driver of the vehicle.

3. The control device according to claim 1 ,

wherein the control unit changes the phase difference based on a current supplied to the multi-phase AC motor.

4. The control device according to claim 1 ,

wherein the control unit changes the phase difference with a lapse of time to cause the fluctuation in the energization of the multi-phase AC motor.

5. The control device according to claim 4 ,

wherein the control unit periodically changes the phase difference within the control range from a predetermined minimum value to a predetermined maximum value, and

wherein the predetermined minimum value and the predetermined maximum value are set in such a manner that the reference phase difference is disposed between the predetermined minimum value and the predetermined maximum value.

6. The control device according to claim 1 ,

wherein the multi-phase AC motor is a three-phase AC motor, and

wherein the reference phase difference reduces a fifth-order harmonic component and a seventh-order harmonic component.

7. The control device according to claim 1 , wherein:

the control unit changes the phase difference based on a steering speed of the vehicle.

8. The control device according to claim 1 , wherein:

the control unit changes the phase difference based on a motor current.

9. The control device according to claim 1 , wherein:

the control unit changes the phase difference based on a steering speed of the vehicle and a motor current.

10. The control device according to claim 1 , wherein:

the A-th order torque ripple is a fifth order torque ripple or a seventh order torque ripple; and

the B-th order torque ripple is an eleventh order torque ripple or a thirteenth order torque ripple.

11. The control device according to claim 1 , wherein:

the phase difference is set to 30° as the reference phase difference when the steering speed is 0;

the phase different is reduced to 0° as the steering speed increases so that a range from 0° to 30° corresponds to the control range.