Active traction motor harmonic masking using random switching frequency process

1. A system comprising:

a traction motor;

an inverter configured to drive the traction motor with electrical energy from a traction battery; and

a controller programmed to select a base switching frequency for a control signal for the inverter such that a switching noise sideband frequency of the inverter is the same as a harmonic frequency of the traction motor, modify the selected base switching frequency by a random switching frequency to obtain a modified switching frequency, and control the inverter with the control signal having the modified switching frequency for the inverter to drive the traction motor, wherein the controller is further configured to select the base switching frequency by equating an expression representing the switching noise sideband frequency with an expression representing the harmonic frequency.

2. The system of claim 1 wherein:

the expression representing the switching noise sideband frequency is f c , where f c is the base switching frequency, and the expression representing the harmonic frequency is (k h ±3*k pp )*f m , where k h is an order of the harmonic frequency of the traction motor, k pp is a number of pole-pairs of the traction motor, and f m is a fundamental mechanical rotation frequency of the traction motor.

3. The system of claim 1 wherein:

the expression representing the switching noise sideband frequency is f c , where f c is the base switching frequency, and the expression representing the harmonic frequency is k h /2*f m , where k h is an order of the harmonic frequency of the traction motor, and f m is a fundamental mechanical rotation frequency of the traction motor.

4. The system of claim 1 wherein:

the control signal is a pulse-width-modulated (PWM) control signal.

5. The system of claim 4 wherein:

the inverter includes a plurality of power switches which switch on-and-off according to the modified switching frequency of the PWM control signal for the inverter to be controlled with the control signal.

6. The system of claim 1 wherein:

the random switching frequency varies over time whereby the modified switching frequency of the control signal varies correspondingly.

7. The system of claim 1 wherein:

the random switching frequency falls within a predetermined random switching frequency range which depends on a value of the harmonic frequency.

8. The system of claim 7 wherein:

the predetermined random switching frequency range is a range of ±the value of the harmonic frequency.

9. The system of claim 8 wherein:

the predetermined random switching frequency range is a proper fraction of the range of ±the value of the harmonic frequency.

10. A method comprising:

selecting a base switching frequency for a control signal of a power electronics module such that a switching noise sideband frequency of the power electronics module is the same as a harmonic frequency of a motor, wherein selecting the base switching frequency includes equating an expression representing the switching noise sideband frequency with an expression representing the harmonic frequency;

modifying the selected base switching frequency by a random switching frequency to obtain a modified switching frequency; and

controlling the power electronics module with the control signal having the modified switching frequency for the power electronics module to drive the motor.

11. The method of claim 10 wherein:

the control signal is a pulse-width-modulated (PWM) control signal.

12. The method of claim 10 wherein:

the random switching frequency varies over time whereby the modified switching frequency of the control signal varies correspondingly.

13. The method of claim 10 wherein:

the power electronics module is an inverter.

14. The method of claim 10 wherein:

the motor is a traction motor.

15. An automotive control system for use with an inverter configured to drive a traction motor with electrical energy from a traction battery, the automotive control system comprising:

a controller programmed to select a base switching frequency for a control signal for the inverter such that a switching noise sideband frequency of the inverter is the same as a harmonic frequency of the traction motor, modify the selected base switching frequency by a random switching frequency to obtain a modified switching frequency, and control the inverter with the control signal having the modified switching frequency for the inverter to drive the traction motor, wherein the controller is further configured to select the base switching frequency by equating an expression representing the switching noise sideband frequency with an expression representing the harmonic frequency.

16. The automotive control system of claim 15 wherein:

the control signal is a pulse-width-modulated (PWM) control signal.

17. The automotive control system of claim 16 wherein:

the inverter includes a plurality of power switches which switch on-and-off according to the modified switching frequency of the PWM control signal for the inverter to be controlled with the control signal.

18. The automotive control system of claim 15 wherein:

the expression representing the switching noise sideband frequency is f c , where f c is the base switching frequency, and the expression representing the harmonic frequency is (k h ±3*k pp )*f m , where k h is an order of the harmonic frequency of the traction motor, k pp is a number of pole-pairs of the traction motor, and f m is a fundamental mechanical rotation frequency of the traction motor.

19. The automotive control system of claim 15 wherein:

the expression representing the switching noise sideband frequency is f c , where f c is the base switching frequency, and the expression representing the harmonic frequency is k h /2*f m , where k h is an order of the harmonic frequency of the traction motor, and f m is a fundamental mechanical rotation frequency of the traction motor.