Electric motor control

• US 9,030,137 B2
• Filed: 02/15/2011
• Issued: 05/12/2015
• Est. Priority Date: 03/11/2010
• Status: Active Grant

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Williams, Connel Brett, Dixon, Christopher David, Huxford, Robert James
• Primary Examiner(s): Luo, David S
• Application Number:
  US13/583,770
• Publication Number:
  US 20130134914A1
• Time in Patent Office: 1,547 Days
• Field of Search: 318/400.13, 318/400.01, 318/700
• US Class Current: 318/400.13
• CPC Class Codes: H02P 27/08 with pulse width modulation
• CPC Class Codes: H02P 6/007 wherein the position is detected using the ripple of the current caused by the commutation
• CPC Class Codes: H02P 6/34 Modelling or simulation for control purposes

Abstract

A drive system, for a multi-phase brushless electric motor comprising a plurality of phases, comprises: a drive circuit including switch means arranged to vary the phase voltage applied to each of the phases so as to switch the motor between a plurality of active states; and control means. The control means is arranged to control the switch means so as to provide PWM control of the phase voltages to control the mechanical output of the motor. The control means is arranged to define a sequence for all of the active states and, for each PWM period, to allocate state times for the states required for that period to generate a desired net voltage, and to order the required states in the same order as they occur in the sequence.

Claims

1. A drive system for a multi-phase brushless electric motor comprising a plurality of phases, said drive system comprising:

a drive circuit including switch means arranged to vary a phase voltage applied to each of said phases so as to switch said motor between a plurality of active states, and

control means arranged to control said switch means so as to provide PWM control of said phase voltages to control a mechanical output of said motor,

wherein said control means is arranged to define a sequence for all of said active states in which states appear in an order and, said PWM control defining PWM periods, and for each of said PWM periods, to allocate state times for states required for said each period to generate a desired net voltage, and to order said required states in said order in which they occur in said sequence,

wherein said control means is arranged, for each said PWM period, to identify which of said states are required states and to allocate state times to said required states, and

wherein either (1) said required states include states required for motor position measurement, or (2) said control means is arranged to determine a set of state times having zero net voltage.

2. The drive system according to claim 1 wherein said control means is arranged to control said switch means so that all of said active states occur in each of said PWM periods.

3. The drive system according to claim 1 wherein said required states include states required to generate said desired net voltage.

4. The drive system according to claim 1 wherein said required states include states which are required for current measurement.

5. The drive system according to claim 1 wherein said required states include states required for motor position measurement.

6. The drive system according to claim 1 wherein said control means is arranged to determine a set of state times having zero net voltage.

7. The drive system according to claim 6 wherein said set of state times includes all of said active states not otherwise required.

8. The drive system according to claim 6 wherein said set of state times is selected so as to reduce differences in length between said state times.

9. The drive system according to claim 8 wherein said control means is arranged to define a measure of the differences in length between said state times, and to select said set of state times so as to reduce the measure of said differences.

10. The drive system according to claim 1 wherein said control means is arranged to use said defined sequence for all desired net voltages for all PWM periods when an operating parameter of said motor is within a predetermined range.

11. The drive system according to claim 1 wherein said control means is arranged to use said defined sequence for all desired net voltages within a predetermined range of magnitudes of said desired net voltage.

12. The drive system according to claim 11 wherein said range of magnitudes includes all net voltages having a modulation index below a predetermined maximum.

13. A drive system for a multi-phase brushless electric motor comprising a plurality of phases, said drive system comprising

a drive circuit including switch means arranged to vary a phase voltage applied to each of said phases so as to switch said motor between a plurality of active states, and

control means arranged to control said switch means so as to provide PWM control of said phase voltages to control a mechanical output of said motor,

wherein said control means is arranged to define a sequence for all of said active states in which states appear in an order and, said PWM control defining PWM periods, and for each of said PWM periods, to allocate state times for states required for said each period to generate a desired net voltage, and to order said required states in said order in which they occur in said sequence,

wherein said control means is arranged to use said defined sequence for all desired net voltages either (1) for all PWM periods when an operating parameter of said motor is within a predetermined range, or (2) within a predetermined range of magnitudes of said desired net voltage.

14. The drive system according to claim 13 wherein said control means is arranged to control said switch means so that all of said active states occur in each of said PWM periods.

15. The drive system according to claim 13 wherein said control means is arranged, for each said PWM period, to identify which of said states are required states and to allocate state times to said required states.

16. The drive system according to claim 15 wherein said required states include states required to generate said desired net voltage.

17. The drive system according to claim 15 wherein said required states include states which are required for current measurement.

18. The drive system according to claim 15 wherein said required states include states required for motor position measurement.

19. The drive system according to claim 15 wherein said control means is arranged to determine a set of state times having zero net voltage.

20. The drive system according to claim 19 wherein said set of state times includes all of said active states not otherwise required.

21. The drive system according to claim 19 wherein said set of state times is selected so as to reduce differences in length between said state times.

22. The drive system according to claim 21 wherein said control means is arranged to define a measure of the differences in length between said state times, and to select said set of state times so as to reduce the measure of said differences.

23. The drive system according to claim 13 wherein said control means is arranged to use said defined sequence for all desired net voltages for all PWM periods when an operating parameter of said motor is within a predetermined range.

24. The drive system according to claim 13 wherein said control means is arranged to use said defined sequence for all desired net voltages within a predetermined range of magnitudes of said desired net voltage.

25. The drive system according to claim 24 wherein said range of magnitudes includes all net voltages having a modulation index below a predetermined maximum.