Minimization of motor torque ripple due to unbalanced conditions

Claims

What is claimed is:

1. A method of minimizing the torque ripple produced by unbalanced phase currents in a sinusoidally excited motor, the method comprising:

measuring the position of the motor;

sampling the phase currents of the motor generating thereby at least one phase current;

synchronizing the at least one phase current of the motor with the position of the motor;

determining the imbalance in the magnitudes of the at least one phase current of the motor;

generating a set of modulation index terms for reducing the imbalance in the magnitudes of the at least one phase current to ensure acceptable torque ripple characteristics over the operating velocity of the motor; and

responsive to the set of modulation index terms, generating a set of minimized line-to-ground voltage commands.

2. The method as set forth in claim 1 further comprising:

converting the set of minimized line-to-ground voltage commands into a set of modulation commands; and

converting the set of modulation commands into a set of phase currents.

3. The method as set forth in claim 2 further comprising determining the imbalance in the phases of the at least one phase current of the motor; and

generating a set of phase angle offset variables for reducing the imbalance in the phases of the phase currents to ensure acceptable torque ripple characteristics over the operating velocity of the motor.

4. The method as set forth in claim 2 wherein generating a set of minimized line-to-ground voltage command includes:

adding the measured position of the motor to a set of phase shift terms;

calculating a trigonometric function of the summation of the measured position of the motor and the set of phase shift terms;

multiplying the trigonometric function of the summation of the measured position of the motor and the set of phase shift terms by the set of modulation index terms, generating thereby a set of line-to-ground voltage commands;

comparing the instantaneous values of the set of line-to-ground voltage commands;

selecting the minimum value of the get of line-to-ground voltage commands;

subtracting the minimum value of the set of line-to-ground voltage commands from the set of line-to-ground voltage commands providing thereby a set of minimized line-to-voltage commands.

5. The method as set forth in claim 4 wherein calculating a trigonometric function includes calculating the trigonometric sine.

6. The method as set forth in claim 3 wherein generating a set of minimized line-to-ground voltage commands includes:

adding the measured position of the motor to the set of phase angle offset variables;

adding the summation of the measured position of the motor and the set of phase angle offset variables to a set of phase shift terms;

calculating a trigonometric function of the summation of the measured position of the motor and the set of phase angle offset variables and the set of phase shift terms;

multiplying the trigonometric function of the summation of the measured position of the motor and the set of phase angle offset variables and the set of phase shift terms by the set of modulation index terms, generating thereby a set of line-to-ground voltage commands;

comparing the instantaneous values of the set of line-to-ground voltage commands;

selecting the minimum value of the set of line-to-ground voltage commands; and

subtracting the minimum value of the set of line-to-ground voltage commands from the set of line-to-ground voltage commands generating thereby a set of minimized line-to-voltage commands.

7. The method as set forth in claim 6 wherein calculating a trigonometric function includes calculating the trigonometric sine.

8. A method of generating a set of minimized line-to-ground voltage commands for minimizing the torque ripple produced by unbalanced phase currents in a sinusoidally excited motor in an automotive steering system, the method comprising:

measuring the position of the motor;

generating a set of modulation index terms;

adding the measured position of the motor to a set of phase shift terms;

calculating a trigonometric function of the summation of the measured position of the motor and the set of phase shift terms;

multiplying the trigonometric function of the summation of the measured position of the motor and the set of phase shift terms by the set of modulation index terms, generating thereby a set of line-to-ground voltage commands;

comparing the instantaneous values of the set of line-to-ground voltage commands;

selecting the minimum value of the set of line-to-ground voltage commands;

subtracting the minimum value of the set of line-to-ground voltage commands from the set of line-to-ground voltage commands providing thereby a set of minimized line-to-voltage commands.

9. The method as set forth in claim 8 wherein calculating a trigonometric function includes calculating a trigonometric sine function.

10. The method as set forth in claim 8 further comprising generating a set of phase angle offset variables.

11. The method as set forth in claim 10 further comprising:

adding the measured position of the motor to the set of phase angle offset variables;

adding the summation of the measured position of the motor and the set of phase angle offset variables to the set of phase shift terms;

calculating a trigonometric function of the summation of the measured position of the motor and the set of phase angle offset variables and the set of phase shift terms;

multiplying the trigonometric function of the summation of the measured position of the motor and the set of phase angle offset variables and the set of phase shift terms by the set of modulation index terms, generating thereby a set of line-to-ground voltage commands;

comparing the instantaneous values of the set of line-to-ground voltage commands;

selecting the minimum value of the set of line-to-ground voltage commands; and

subtracting the minimum value of the set of line-to-ground voltage commands from the set of line-to-ground voltage commands generating thereby a set of minimized line-to-voltage commands.

12. The method as set forth in claim 11 wherein calculating a trigonometric function includes calculating a trigonometric sine.

13. A storage medium encoded with machine-readable computer program code for minimizing the torque ripple produced by unbalanced phase currents in a sinusoidally excited motor in an automotive steering system, the computer code being executable whereby the computer code when run by a computer system will minimize the torque ripple produced by unbalanced phase currents in a sinusoidally excited motor in an automotive steering system, the program code including instructions for causing the computer system to implement a method comprising:

measuring the position of the motor;

sampling the phase currents of the motor generating thereby at least one phase current;

synchronizing the at least one phase current of the motor with the position of the motor;

determining the imbalance in the magnitudes of the at least one phase current of the motor;

generating a set of modulation index terms for reducing the imbalance in the magnitudes of the at least one phase current to ensure acceptable torque ripple characteristics over the operating velocity of the motor; and

responsive to the set of modulation index terms, generating a set of minimized line-to-ground voltage commands.

14. The method as set forth in claim 13 further comprising:

converting the set of minimized line-to-ground voltage commands into a set of modulation commands; and

converting the set of modulation commands into a set of phase currents.

15. The method as set forth in claim 14 further comprising:

determining the imbalance in the phases of the at least one measured phase current of the motor; and

generating a set of phase angle offset variables for reducing the imbalance in the phases of the measured phase currents to ensure acceptable torque ripple characteristics over the operating velocity of the motor.

16. The method as set forth in claim 14 wherein generating a set of minimized line-to-ground voltage command includes;

adding the measured position of the motor to a set of phase shift terms;

calculating a trigonometric function of the summation of the measured position of the motor and the set of phase shift terms;

multiplying the trigonometric function of the summation of the measured position of the motor and the set of phase shift terms by the set of modulation index terms, generating thereby a set of line-to-ground voltage commands;

comparing the instantaneous values of the set of line-to-ground voltage commands;

selecting the minimum value of the set of line-to-ground voltage commands;

subtracting the minimum value of the set of line-to-ground voltage commands from the set of line-to-ground voltage commands providing thereby a set of minimized line-to-voltage commands.

17. The method as set forth in claim 16 wherein calculating a trigonometric function includes calculating the trigonometric sine.

18. The method as set forth in claim 15 wherein generating a set of minimized line-to-ground voltage commands includes:

adding the measured position of the motor to the set of phase angle offset variables;

adding the summation of the measured position of the motor and the set of phase angle offset variables to a set of phase shift terms;

calculating a trigonometric function of the summation of the measured position of the motor and the set of phase angle offset variables and the set of phase shift terms;

multiplying the trigonometric function of the summation of the measured position of the motor and the set of phase angle offset variables and the set of phase shift terms by the set of modulation index terms, generating thereby a set of line-to-ground voltage commands;

comparing the instantaneous values of the set of line-to-ground voltage commands;

selecting the minimum value of the set of line-to-ground voltage commands; and

subtracting the minimum value of the set of line-to-ground voltage commands from the set of line-to-ground voltage commands generating thereby a set of minimized line-to-voltage commands.

19. The method as set forth in claim 18 wherein calculating a trigonometric function includes calculating the trigonometric sine.

20. A storage medium encoded with machine-readable computer program code for generating a set of minimized line-to-ground voltage commands for minimizing the torque ripple produced by unbalanced phase currents in a sinusoidally excited motor in an automotive steering system, the computer code being executable whereby the computer code when run by a computer system will minimize line-to-ground voltage commands for minimizing the torque ripple produced by unbalanced phase currents in a sinusoidally excited motor in an automotive steering system, the program code including instructions for causing the computer system to implement a method comprising:

measuring the position of the motor;

generating a set of modulation index terms;

adding the measured position of the motor to a set of phase shift terms;

calculating a trigonometric function of the summation of the measured position of the motor and the set of phase shift terms;

multiplying the trigonometric function of the summation of the measured position of the motor and the set of phase shift terms by the set of modulation index terms, generating thereby a set of line-to-ground voltage commands;

comparing the instantaneous values of the set of line-to-ground voltage commands;

selecting the minimum value of the set of line-to-ground voltage commands;

subtracting the minimum value of the set of line-to-ground voltage commands from the set of line-to-ground voltage commands providing thereby a set of minimized line-to-voltage commands.

21. The method as set forth in claim 20 wherein calculating a trigonometric function includes calculating a trigonometric sine function.

22. The method as set forth in claim 20 further comprising generating a set of phase angle offset variables.

23. The method as set forth in claim 22 further comprising:

adding the measured position of the motor to the set of phase angle offset variables;

adding the summation of the measured position of the motor and the set of phase angle offset variables to the set of phase shift terms;

calculating a trigonometric function of the summation of the measured position of the motor and the set of phase angle offset variables and the set of phase shift terms;

multiplying the trigonometric function of the summation of the measured position of the motor and the set of phase angle offset variables and the set of phase shift terms by the set of modulation index terms, generating thereby a set of line-to-ground voltage commands;

comparing the instantaneous values of the set of line-to-ground voltage commands;

selecting the minimum value of the set of line-to-ground voltage commands; and

subtracting the minimum value of the set of line-to-ground voltage commands from the set of line-to-ground voltage commands generating thereby a set of minimized line-to-voltage commands.

24. The method as set forth in claim 23 wherein calculating a trigonometric function includes calculating a trigonometric sine.

25. The method as set forth in claim 1 wherein determining the imbalance in the magnitudes of the at least one phase current of the motor includes:

normalizing the at least one phase current;

assigning a phase to the at least one phase current; and

filtering the at least one phase current.

26. The method as set forth in claim 25 wherein normalizing the at least one phase current includes normalizing the at least one phase current to an average value thereof.

27. The method as set forth in claim 3 wherein the imbalance in the phases of the at least one phase current of the motor includes:

normalizing the at least one phase current;

assigning a phase to the at least one phase current; and

filtering the at least one phase current.

28. The method as set forth in claim 27 wherein normalizing the at least one phase current includes normalizing the at least one phase current to an average value thereof.

29. The method as set forth in claim 13 wherein determining the imbalance in the magnitudes of the at least one phase current of the motor includes:

normalizing the at least one phase current;

assigning a phase to the at least one phase current; and

filtering the at least one phase current.

30. The method as set forth in claim 29 wherein normalizing the at least one phase current includes normalizing the at least one phase current to an average value thereof.

31. The method as set forth in claim 15 wherein the imbalance in the phases of the at least one phase current of the motor includes:

normalizing the at least one phase current;

assigning a phase to the at least one phase current; and

filtering the at least one phase current.

32. The method as set forth in claim 31 wherein normalizing the at least one phase current includes normalizing the at least one phase current to an average value thereof.

33. The method as set forth in claim 25 further comprising:

selecting a phase as a reference phase; and

adjusting the remaining phases with respect to the reference phase.

34. The method as set forth in claim 33 further comprising:

setting the modulation index term corresponding to the reference phase equal to a nominal value; and

setting the modulation index terms corresponding to the remaining phases equal to a correction factor times the modulation index term corresponding to the reference phase.

35. The method as set forth in claim 25 wherein assigning a phase to the at least one phase current includes assigning a phase thereto according to the table: Motor Direction Motor Position i.sub.q Phase Assignment Positive -15 degrees to 7.5 degrees I_A_NORM Positive 45 degrees to 67.5 degrees I_B_NORM Positive 105 degrees to 127.5 degrees I_C_NORM Positive 165 degrees to 187.5 degrees I_A_NORM Positive 225 degrees to 247.5 degrees I_B_NORM Positive 285 degrees to 307.5 degrees I_C_NORM Negative -7.5 degrees to 15 degrees I_A_NORM Negative 52.5 degrees to 75 degrees I_B_NORM Negative 112.5 degrees to 135 degrees I_C_NORM Negative 172.5 degrees to 195 degrees I_A_NORM Negative 232.5 degrees to 255 degrees I_B_NORM Negative 292.5 degrees to 315 degrees I_C_NORM

wherein a positive motor direction refers to increasing motor position angles such that the motor generated voltage characteristic transitions through an a-b-c sequence and motor position is referenced to a sinusoidal function associated with the motor phase reference-to-neutral generated voltage characteristic.

36. The method as set forth in claim 27 further comprising:

selecting a phase as a reference phase; and

adjusting the remaining phases with respect to the reference phase.

37. The method as set forth in claim 36 further comprising:

setting the modulation index term corresponding to the reference phase equal to a nominal value; and

setting the modulation index terms corresponding to the remaining phases equal to a correction factor times the modulation index term corresponding to the reference phase.

38. The method as set forth in claim 27 wherein assigning a phase to the at least one phase current includes assigning a phase thereto according to the table: Motor Direction Motor Position i.sub.q Phase Assignment Positive -15 degrees to 7.5 degrees I_A_NORM Positive 45 degrees to 67.5 degrees I_B_NORM Positive 105 degrees to 127.5 degrees I_C_NORM Positive 165 degrees to 187.5 degrees I_A_NORM Positive 225 degrees to 247.5 degrees I_B_NORM Positive 285 degrees to 307.5 degrees I_C_NORM Negative -7.5 degrees to 15 degrees I_A_NORM Negative 52.5 degrees to 75 degrees I_B_NORM Negative 112.5 degrees to 135 degrees I_C_NORM Negative 172.5 degrees to 195 degrees I_A_NORM Negative 232.5 degrees to 255 degrees I_B_NORM Negative 292.5 degrees to 315 degrees I_C_NORM

wherein a positive motor direction refers to increasing motor position angles such that the motor generated voltage characteristic transitions through an a-b-c sequence and motor position is referenced to a sinusoidal function associated with the motor phase reference-to-neutral generated voltage characteristic.

39. The method as set forth in claim 31 further comprising:

selecting a phase as a reference phase; and

adjusting the remaining phases with respect to the reference phase.

40. The method as set forth in claim 39 further comprising:

setting the modulation index term corresponding to the reference phase equal to a nominal value; and

setting the modulation index terms corresponding to the remaining phases equal to a correction factor times the modulation index term corresponding to the reference phase.

41. The method as set forth in claim 31 wherein assigning a phase to the at least one phase current includes assigning a phase thereto according to the table: Motor Direction Motor Position i.sub.q Phase Assignment Positive -15 degrees to 7.5 degrees I_A_NORM Positive 45 degrees to 67.5 degrees I_B_NORM Positive 105 degrees to 127.5 degrees I_C_NORM Positive 165 degrees to 187.5 degrees I_A_NORM Positive 225 degrees to 247.5 degrees I_B_NORM Positive 285 degrees to 307.5 degrees I_C_NORM Negative -7.5 degrees to 15 degrees I_A_NORM Negative 52.5 degrees to 75 degrees I_B_NORM Negative 112.5 degrees to 135 degrees I_C_NORM Negative 172.5 degrees to 195 degrees I_A_NORM Negative 232.5 degrees to 255 degrees I_B_NORM Negative 292.5 degrees to 315 degrees I_C_NORM

wherein a positive motor direction refers to increasing motor position angles such that the motor generated voltage characteristic transitions through an a-b-c sequence and motor position is referenced to a sinusoidal function associated with the motor phase reference-to-neutral generated voltage characteristic.