Pulse-width modulation scheme for managing thermal loading of an inverter during stall

1. A system including a controller for a direct-current (DC) to alternating current (AC) inverter, the controller comprising:

a memory configured to store instructions; and

at least one processor configured to execute the stored instructions to perform operations including:

generating a first pulse for a first phase of a Pulse-Width Modulated (PWM) signal to alternately activate a first phase switch of a first switch group of the inverter for a first duration and a first phase switch of a second switch group of the inverter for a second duration within a period of the PWM signal to generate a first phase of AC power; and

generating a second pulse for a second phase of the PWM signal to alternately activate a second phase switch of the first switch group of the inverter for a third duration and a second phase switch of the second switch group of the inverter for a fourth duration within the period of the PWM signal to generate a second phase of the AC power,

wherein the second pulse is center-aligned with the first pulse, and

wherein the second duration is different from the third duration during a stall condition.

2. The system of claim 1 , the operations further including:

generating a third pulse for a third phase of the PWM signal to alternately activate a third phase switch of the first switch group of the inverter for a fifth duration and a third phase switch of the second switch group of the inverter for a sixth duration within the period of the PWM signal to generate a third phase of the AC power,

wherein the third pulse is center-aligned with the first pulse and the second pulse.

3. The system of claim 1 , wherein the generating the first pulse and the second pulse is based on a non-constant duty cycle bias relative to phase angle.

4. The system of claim 3 , wherein the non-constant duty cycle bias is a sinusoidal signal varying from a 25% duty cycle bias to a 75% duty cycle bias relative to the phase angle.

5. The system of claim 3 , wherein an amplitude of the non-constant duty cycle bias increases as a rotational speed of a motor driven by the inverter decreases below a threshold speed for the stall condition.

6. The system of claim 1 , wherein the second duration being different from the third duration reduces a maximum heat flux during the stall condition in any switch among the first switch group of the inverter and the second switch group of the inverter, relative to a condition where the second duration equals the third duration in a PWM scheme with 50% null vector modulation.

7. The system of claim 1 , wherein

the second duration is different from the third duration during the stall condition, and

the second duration is equal to the third duration outside the stall condition.

8. The system of claim 7 , wherein

the first pulse and the second pulse define an active vector and a null vector for the PWM signal,

a duration of the active vector remains constant regardless of the stall condition, and

a duration of the null vector changes during the stall condition.

9. The system of claim 1 , further comprising:

the inverter;

a set of input terminals configured to receive DC power;

the first switch group including the first phase switch and the second phase switch configured to receive the first phase of the PWM signal to generate the first phase of the AC power;

the second switch group including the first phase switch and the second phase switch configured to receive the second phase of the PWM signal to generate the second phase of the AC power; and

a set of output terminals configured to output the generated first phase of the AC power and the second phase of the AC power,

wherein the controller is configured to generate the PWM signal to operate the first switch group and the second switch group.

10. The system of claim 9 ,

wherein the inverter is configured to receive the DC power and generate the AC power; and

the system further comprises:

a motor configured to receive the generated AC power from the inverter, and to rotate based on the received AC power.

11. A method for controlling a direct-current (DC) to alternating current (AC) inverter, the method comprising performing, by at least one processor, operations including:

generating a first pulse for a first phase of a Pulse-Width Modulated (PWM) signal to alternately activate a first phase switch of a first switch group of the inverter for a first duration and a first phase switch of a second switch group of the inverter for a second duration within a period of the PWM signal to generate a first phase of AC power; and

generating a second pulse for a second phase of the PWM signal to alternately activate a second phase switch of the first switch group of the inverter for a third duration and a second phase switch of the second switch group of the inverter for a fourth duration within the period of the PWM signal to generate a second phase of the AC power,

wherein the second pulse is center-aligned with the first pulse, and

wherein the second duration is different from the third duration during a stall condition.

12. The method of claim 11 , further comprising:

generating a third pulse for a third phase of the PWM signal to alternately activate a third phase switch of the first switch group of the inverter for a fifth duration and a third phase switch of the second switch group of the inverter for a sixth duration within the period of the PWM signal to generate a third phase of the AC power,

wherein the third pulse is center-aligned with the first pulse and the second pulse.

13. The method of claim 11 , wherein the generating the first pulse and the second pulse is based on a non-constant duty cycle bias relative to phase angle.

14. The method of claim 13 , wherein the non-constant duty cycle bias is a sinusoidal signal varying from a 25% duty cycle bias to a 75% duty cycle bias relative to the phase angle.

15. The method of claim 13 , wherein an amplitude of the non-constant duty cycle bias increases as a rotational speed of a motor driven by the inverter decreases below a threshold speed for the stall condition.

16. The method of claim 11 , wherein the second duration being different from the third duration reduces a maximum heat flux during the stall condition in any switch among the first switch group of the inverter and the second switch group of the inverter, relative to a condition where the second duration equals the third duration in a PWM scheme with 50% null vector modulation.

17. The method of claim 11 , wherein

the second duration is different from the third duration during the stall condition, and

the second duration is equal to the third duration outside the stall condition.

18. The method of claim 17 , wherein

the first pulse and the second pulse define an active vector and a null vector for the PWM signal,

a duration of the active vector remains constant regardless of the stall condition, and

a duration of the null vector changes during the stall condition.

19. The method of claim 11 , further comprising:

outputting the generated first phase of the AC power and the second phase of the AC power from the inverter.

20. A non-transitory computer readable medium storing instructions that, when executed by at least one processor, perform operations including:

generating a first pulse for a first phase of a Pulse-Width Modulated (PWM) signal to alternately activate a first phase switch of a first switch group of an inverter for a first duration and a first phase switch of a second switch group of the inverter for a second duration within a period of the PWM signal to generate a first phase of AC power; and

generating a second pulse for a second phase of the PWM signal to alternately activate a second phase switch of the first switch group of the inverter for a third duration and a second phase switch of the second switch group of the inverter for a fourth duration within the period of the PWM signal to generate a second phase of the AC power,

wherein the second pulse is center-aligned with the first pulse, and

wherein the second duration is different from the third duration during a stall condition.