Control techniques for an interior permanent magnet synchronous motor of an electrified vehicle

1. An electrified vehicle, comprising:

an interior permanent magnet synchronous motor (IPMSM) configured to generate drive torque in response to a three-phase AC voltage;

a power source configured to generate a direct current (DC) voltage;

a three-phase inverter configured to convert the DC voltage to the three-phase AC voltage for the IPMSM; and

a controller comprising a memory configured to store a set of instructions and one or more processors configured to execute the set of instructions, which causes the controller to perform operations comprising:

control the three-phase inverter based on an initial switching frequency to generate the three-phase AC voltage;

determine transformed voltages in a rotating reference frame based on the three-phase AC voltage in a stationary reference frame;

determine voltage ripples in the rotating reference frame based on the transformed voltages;

determine current ripples in the rotating reference frame based on the voltage ripples;

determine phase current ripples in the stationary reference frame based on the current ripples in the rotating reference frame;

determine a modified switching frequency for the three-phase inverter based on the initial switching frequency and the phase current ripples; and

perform variable switching frequency pulse-width modulation (VSFPWM) control of the three-phase inverter based on the modified switching frequency.

2. The electrified vehicle of claim 1 , wherein the controller is configured to obtain the transformed voltages by applying a Park transformation to convert the three-phase AC voltage from the stationary reference frame to the rotating reference, and wherein the controller is configured to obtain the phase current ripples by applying an inverse Park transformation to convert the current ripples from the rotating reference frame to the stationary reference frame.

3. The electrified vehicle of claim 1 , wherein the controller is further configured to:

determine a maximum phase current ripple for VSFPWM control of the three-phase inverter; and

determine the modified switching frequency based on the maximum phase current ripple and the initial switching frequency.

4. The electrified vehicle of claim 3 , wherein the maximum phase current ripple for VSFPWM is a same maximum phase current ripple as for constant switching frequency pulse-width modulation (CSFPWM) control of the three-phase inverter.

5. The electrified vehicle of claim 3 , wherein the controller is configured to determine the modified switching frequency based on the maximum phase current ripple and the initial switching frequency by:

comparing each phase current ripple to the maximum phase current ripple; and

determining the modified switching frequency based on the initial switching frequency and the comparing.

6. The electrified vehicle of claim 5 , wherein the controller is configured to determine the modified switching frequency based on the initial switching frequency and the comparing by:

increasing the initial switching frequency when one of the phase current ripples is greater than or within a first predetermined threshold and the maximum phase current ripple; and

decreasing the initial switching frequency when one of the phase current ripples is less than the first predetermined threshold or a second predetermined threshold that is less than the first predetermined threshold.

7. The electrified vehicle of claim 1 , wherein the controller is configured to constrain the modified switching frequency within a predetermined range of switching frequencies.

8. The electrified vehicle of claim 7 , wherein a fundamental frequency of the IPMSM is substantially less than the predetermined range of switching frequencies.

9. The electrified powertrain of claim 7 , wherein the predetermined range of switching frequencies is approximately 8.6 kilohertz (kHz) to 10 kHz.

10. The electrified vehicle of claim 1 , wherein the power source is a battery system, and wherein the electrified vehicle is one of a battery electric vehicle (BEV) and a hybrid electric vehicle (HEV).

11. A method, comprising:

controlling, by a controller of an electrified vehicle, a three-phase inverter of the electrified vehicle based on an initial switching frequency to generate a three-phase alternating current (AC) voltage for an interior permanent magnet synchronous motor (IPMSM) of the electrified vehicle;

determining, at the controller, transformed voltages in a rotating reference frame based on the three-phase AC voltage in a stationary reference frame;

determining, at the controller, voltage ripples in the rotating reference frame based on the transformed voltages;

determining, at the controller, current ripples in the rotating reference frame based on the voltage ripples;

determining, at the controller, phase current ripples in the stationary reference frame based on the current ripples in the rotating reference frame;

determining, at the controller, a modified switching frequency for the three-phase inverter based on the initial switching frequency and the phase current ripples; and

performing, by the controller, variable switching frequency pulse-width modulation (VSFPWM) control of the three-phase inverter based on the modified switching frequency.

12. The method of claim 11 , wherein the transformed voltages are obtained by applying a Park transformation to convert the three-phase AC voltage from the stationary reference frame to the rotating reference frame, and wherein the phase current ripples are obtained by applying an inverse Park transformation to convert the current ripples from the rotating reference frame to the stationary reference frame.

13. The method of claim 11 , further comprising:

determining, at the controller, a maximum phase current ripple for VSFPWM control of the three-phase inverter; and

determining, at the controller, the modified switching frequency based on the maximum phase current ripple and the initial switching frequency.

14. The method of claim 13 , wherein the maximum phase current ripple for VSFPWM is a same maximum phase current ripple as for constant switching frequency pulse-width modulation (CSFPWM) control of the three-phase inverter.

15. The method of claim 13 , wherein determining the modified switching frequency based on the maximum phase current ripple and the initial switching frequency includes:

comparing, at the controller, each phase current ripple to the maximum phase current ripple; and

determining, at the controller, the modified switching frequency based on the initial switching frequency and the comparing.

16. The method of claim 15 , wherein determining the modified switching frequency based on the initial switching frequency and the comparing includes:

increasing, by the controller, the initial switching frequency when one of the phase current ripples is greater than or within a first predetermined threshold and the maximum phase current ripple; and

decreasing, by the controller, the initial switching frequency when one of the phase current ripples is less than the first predetermined threshold or a second predetermined threshold that is less than the first predetermined threshold.

17. The method of claim 11 , further comprising constraining, by the controller, the modified switching frequency within a predetermined range of switching frequencies.

18. The method of claim 17 , wherein a fundamental frequency of the IPMSM is substantially less than the predetermined range of switching frequencies.

19. The method of claim 17 , wherein the predetermined range of switching frequencies is approximately 8.6 kilohertz (kHz) to 10 kHz.