Apparatus and method for detection and control of circulating currents in a variable speed DC motor

• US 5,552,685 A
• Filed: 03/28/1994
• Issued: 09/03/1996
• Est. Priority Date: 08/18/1993
• Status: Expired due to Fees

• Current Assignee: Regal Beloit Electric Motors Inc (Regal Rexnord Corp.)
• Original Assignee: General Electric Company
• Inventors: Schneider, Eric D., Young, Glen C., Bonner, Guy Jr.
• Primary Examiner(s): Ip, Paul
• Application Number:
  US08/219,022
• Time in Patent Office: 890 Days
• Field of Search: 318/138, 318/254, 318/700-832, 388/800-810, 62/228.4, 62/215
• US Class Current: 318/400.32
• CPC Class Codes: H02H 7/0838 with H-bridge circuit
• CPC Class Codes: H02P 6/08 Arrangements for controlling the speed or torque of a single motor H02P6/10, H02P6/28 take precedence
• CPC Class Codes: H02P 6/15 Controlling commutation time
• CPC Class Codes: H02P 6/182 using back-emf in windings

Abstract

A current regulation circuit for a motor. The motor includes a stationary assembly having windings adapted for energization in at least one preselected sequence and a rotatable assembly in magnetic coupling relation to the stationary assembly. A power supply link connects the windings to a power supply and includes power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly. The power switching devices each have a conducting state and a nonconducting state. The current regulation circuit includes a timing circuit, a current sensing circuit and a control circuit. The timing circuit defines preset periods during which each of the power switching devices may be nonconducting. The current sensing circuit senses current in the power supply link. The control circuit controls the power switching devices so that each of the power switching devices is nonconducting when the sensed current exceeds a peak current reference level during the preset periods. In this manner, the current regulation circuit controls current which circulates during periods when only one power switching device is conducting.

Claims

1. A motor comprising:

a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted to be energized in at least one preselected sequence;

a power supply link for connecting the windings to a power supply, said power supply link including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply; and

a current regulation circuit including;

a timing circuit for defining periods during which each of the power switching devices may be nonconducting;

a current sensing circuit for sensing current in only one of the rails of the power supply link; and

a control circuit for controlling the power switching devices so that each of the power switching devices is nonconducting only during portions of the defined periods during which the sensed current exceeds a peak current reference level.

2. The motor of claim 1 wherein the current sensing circuit comprises a shunt resistor for sensing current in only one of the rails of the power supply link.

3. The motor of claim 1 wherein the current sensing circuit comprises a bi-directional current comparator for comparing the sensed current in the power supply link to a positive peak current reference level when the sensed current is positive and for comparing the sensed current in the power supply link to a negative peak current reference level when the sensed current is negative.

4. The motor of claim 3 further comprising a network for scaling the sensed current input to the current comparator.

5. The motor of claim 3 further comprising a circuit for generating the peak current reference level and including an adjustable resistor network having an adjustable resistance for varying the peak current reference level.

6. The motor of claim 1 wherein each of the power switching devices is nonconducting for an interval of time when the sensed current exceeds the peak current reference level during the defined periods whereby current which circulates during periods when only one power switching device is conducting is reduced.

12. The motor of claim 1 wherein the control circuit controls the power switching devices so that each of the power switching devices is nonconducting when the sensed current exceeds a negative peak current reference level during the defined periods and further comprising a pulse width modulation circuit for pulse width modulating the power being provided to at least one of the windings at a duty cycle having alternating on and off periods, said timing circuit defining the defined periods to be a predetermined number of off periods after the sensed current exceeds a positive peak current reference level.

13. The motor of claim 12 wherein the timing circuit comprises a counter for counting the predetermined number of off periods.

14. The motor of claim 12 wherein the predetermined number is a positive integer greater than 1.

7. A motor comprising:

a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted to be energized in at least one preselected sequence;

a power supply link for connecting the windings to a power supply, said power supply link including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state; and

a current regulation circuit comprising;

a current sensing circuit for sensing current in the power supply link and for generating an overcurrent signal in response to the sensed current exceeding a peak current reference level;

a timing circuit for defining periods during which each of the power switching devices may be nonconducting, said timing circuit comprising a current blanking circuit for inhibiting the overcurrent signal during a blanking interval triggered by the energization of the windings; and

a control circuit for controlling the power switching devices so that each of the power switching devices is nonconducting in response to the overcurrent signal whereby the power switching devices are nonconducting during the defined periods except during the blanking interval.

8. The motor of claim 7 wherein the power switching devices comprise an inverter bridge having a positive rail and a negative rail supplied by the power supply and including a free-wheeling diodes each corresponding to and connected across one of the power switching devices, and wherein the rails of the power supply link normally carry a diode recovery current at energization, the blanking interval exceeding an interval of time corresponding to a time period during which the diode recovery current decays below a level.

9. The motor of claim 7 wherein the current blanking circuit comprises a blanking interval counter triggered by the energization of the windings for timing the blanking interval, said blanking interval counter generating a blanking signal for inhibiting the control circuit during the blanking interval.

10. The motor of claim 9 wherein the control circuit comprises an RS flip flop responsive during the defined periods to the overcurrent signal for generating a control signal for controlling the power switching devices so that each of the power switching devices is nonconducting, the blanking interval counter providing the blanking signal and a window signal that defines the defined periods to the RS flip flop whereby during the defined periods the RS flip flop generates the control signal in response to the overcurrent signal except during the blanking interval.

11. The motor of claim 7 wherein the defined periods during which each of the power switching devices may be nonconducting includes a first period of approximately 20 microseconds beginning with the energization of the windings and wherein the blanking interval is approximately one half of the first period.

15. A motor comprising:

a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted to be energized in at least one preselected sequence;

a power supply link for connecting the windings to a power supply, said power supply link including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state; and

a current sensing circuit for sensing current in the power supply link;

a current blanking circuit for inhibiting the sensed current for a blanking interval triggered by the energization of the windings; and

a control circuit for defining a first period during which each of the power switching devices may be nonconducting and for controlling the power switching devices so that each of the power switching devices is nonconducting when the sensed current exceeds a peak current reference level during the first period except during the predetermined blanking interval whereby current which circulates during periods when only one power switching device is conducting is reduced.

16. The motor of claim 15 wherein the power switching devices comprise an inverter bridge including a positive rail and a negative rail supplied by the power supply and wherein the current sensing circuit comprises a shunt resistor for detecting current in the one of the rails of the power supply link.

17. The motor of claim 16 wherein the inverter bridge includes free-wheeling diodes, each corresponding to one of the power switching devices, and wherein the shunt resistor normally carries a diode recovery current at energization, the blanking interval exceeding an interval of time corresponding to a time period during which the diode recovery current decays below a level threshold.

18. The motor of claim 15 wherein the current blanking circuit comprises a blanking interval counter triggered by the energization of the windings for timing the blanking interval, said blanking interval counter generating a blanking signal for inhibiting the control circuit during the blanking interval.

19. The motor of claim 18 wherein the current sensing circuit generates an overcurrent signal in response to the sensed current exceeding the peak current reference level and wherein the control circuit includes an RS flip flop responsive during the first period to the overcurrent signal for generating a control signal for controlling the power switching devices so that each of the power switching devices is nonconducting, the blanking interval counter providing the blanking signal and a window signal that defines the first period to the RS flip flop whereby during the first period the RS flip flop generates the control signal in response to the overcurrent signal except during the blanking interval.

20. The motor of claim 15 wherein the first period is approximately 20 microseconds beginning with the energization of the windings and wherein the blanking interval is approximately one half of the first preset period.

21. The motor of claim 15 wherein each of the power switching devices is nonconducting for an interval of time when the sensed current exceeds the peak current reference level during the first period.

22. The motor of claim 15 wherein the control circuit defines a second period during which each of the power switching devices may be nonconducting and controls the power switching devices so that each of the power switching devices is nonconducting when the sensed current exceeds a negative peak current reference level during the second preset period and further comprising a pulse width modulation circuit for pulse width modulating the power being provided to at least one of the windings at a duty cycle having alternating on and off periods, said control circuit defining the second preset period to be a predetermined number of off periods after the sensed current exceeds a positive peak current reference level.

23. The motor of claim 22 further comprising a counter for counting the predetermined number of off periods.

24. The motor of claim 22 wherein the predetermined number is a positive integer greater than 1.

25. The motor of claim 22 wherein the current sensing circuit comprises a bi-directional current comparator for comparing the sensed current in the power supply link to the positive and negative peak current reference levels.

26. The motor of claim 25 further comprising a network for scaling the sensed current input to the current comparator.

27. The motor of claim 25 further comprising a circuit for generating the positive and negative peak current reference levels and including an adjustable resistor network having an adjustable resistance for varying the positive and negative peak current reference levels.

28. A motor comprising:

a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted to be energized in at least one preselected sequence;

a power supply link for connecting the windings to a power supply, said power supply link including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply;

a pulse width modulation circuit for pulse width modulating the power being provided to at least one of the windings at a duty cycle having alternating on and off periods;

a counter circuit for counting a predetermined number of off periods;

a current sensing circuit for sensing current in one of the rails of the power supply link; and

a current regulation circuit for controlling the power switching devices so that each of the power switching devices is nonconducting in response to the sensed current exceeding a first peak current reference level only after the predetermined number of off periods is counted whereby current which circulates during periods when only one power switching device is conducting is periodically reduced.

29. The motor of claim 28 further comprising a counter for counting the predetermined number of off periods.

30. The motor of claim 28 wherein the predetermined number is a positive integer greater than 1.

31. The motor of claim 28 wherein the current sensing circuit comprises a shunt resistor for sensing current in only one of the rails of the power supply link.

32. The motor of claim 28 further comprising a timing circuit for defining a first period during which each of the power switching devices may be nonconducting, said timing circuit defining the first period to be the predetermined number of off periods after when the sensed current exceeds the first peak current reference level, said current regulation circuit controlling the power switching devices so that each of the power switching devices is nonconducting when the sensed current exceeds a second peak current reference level during the first period.

33. The motor of claim 32 wherein the current sensing circuit comprises a bi-directional current comparator for comparing the sensed current in the power supply link to the first and second peak current reference levels.

34. The motor of claim 33 further comprising a network for scaling the sensed current input to the current comparator.

35. The motor of claim 33 further comprising a circuit for generating the first and second peak current reference levels and including an adjustable resistor network having an adjustable resistance for varying the first and second peak current reference levels.

36. A motor comprising:

a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted to be energized in at least one preselected sequence;

a power supply link for connecting the windings to a power supply, said power supply link including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state;

a pulse width modulation circuit for pulse width modulating the power being provided to at least one of the windings at a duty cycle having alternating on and off periods;

a current sensing circuit for sensing current in the power supply link and for generating an overcurrent signal in response to the sensed current exceeding a peak current reference level;

a control circuit for defining a period during which each of the power switching devices may be nonconducting;

a current sensing circuit for sensing current in the power supply link and for generating an overcurrent signal in response to the sensed current exceeding a peak current reference level, said control circuit including a current blanking circuit for inhibiting the overcurrent signal during a blanking interval triggered by the energization of the windings; and

a current regulation circuit for controlling the power switching devices so that each of the power switching devices is nonconducting in response to the overcurrent signal during the defined period except during the blanking interval and after a predetermined number of off periods whereby current which circulates during periods when only one power switching device is conducting is periodically reduced.

37. The motor of claim 36 wherein the power switching devices comprise an inverter bridge having a positive rail and a negative rail supplied by the power supply and including free-wheeling diodes, each corresponding to one of the power switching devices, and wherein the rails of the power supply link normally carry a diode recovery current at energization, the blanking interval exceeding an interval of time corresponding to a time period during which the diode recovery current decays below a threshold level.

38. The motor of claim 36 wherein the current blanking circuit comprises a blanking interval counter triggered by the energization of the windings for timing the blanking interval, said blanking interval counter generating a blanking signal for inhibiting the control circuit during the blanking interval.

39. The motor of claim 38 wherein the control circuit comprises an RS flip flop responsive to the overcurrent signal for generating a control signal for controlling the power switching devices so that each of the power switching devices is nonconducting, the blanking interval counter providing the blanking signal and a window signal that defines the defined period to the RS flip flop whereby during the defined period the RS flip flop generates the control signal in response to the overcurrent signal except during the blanking interval.

40. The motor of claim 36 wherein the defined period is approximately 20 microseconds beginning with the energization of the windings and wherein the blanking interval is approximately one half of the defined period.

41. The motor of claim 36 wherein each of the power switching devices is nonconducting for a interval of time when the sensed current exceeds the first peak current reference level during the preset period.

42. A method of operating a system for driving a rotatable component, said system comprising a motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said rotatable assembly in driving relation to the rotatable component, said motor also having a power supply link for connecting the windings to a power supply, said power supply link including power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply, said method comprising the steps of:

selectively energizing the windings in the preselected sequence by connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly; and

regulating current by defining periods during which each of the power switching devices may be nonconducting, sensing current in only one of the rails of the power supply link and controlling the power switching devices so that each of the power switching devices is nonconducting only during portions of the defined periods during which the sensed current exceeds a peak current reference level.

44. The method of claim 42 further comprising the steps of pulse width modulating the power being provided to at least one of the windings at a duty cycle having alternating on and off periods and controlling the power switching devices so that each of the power switching devices is nonconducting when the sensed current exceeds a negative peak current reference level during the defined periods, said regulating current step defining the defined periods to be a predetermined number of off periods after the sensed current exceeds a positive peak current reference level.

43. A method of operating a system for driving a rotatable component, said system comprising a motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said rotatable assembly in driving relation to the rotatable component, said motor also having a power supply link for connecting the windings to a power supply, said power supply link including power switching devices each having a conducting state and a nonconducting state, said method comprising the steps of:

selectively energizing the windings in the preselected sequence by connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly;

sensing current in the power supply link;

generating an overcurrent signal in response to the sensed current exceeding a peak current reference level;

inhibiting the overcurrent signal during a blanking interval triggered by the energization of the windings;

regulating current by defining periods during which each of the power switching devices may be nonconducting; and

controlling the power switching devices so that each of the power switching devices is nonconducting in response to the overcurrent signal whereby the power switching device are nonconducting during the defined periods except during the blanking interval.

45. A system comprising:

a rotatable component;

a motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted to be energized in at least one preselected sequence, said rotatable assembly being in driving relation to the rotatable component;

a power supply link for connecting the windings to a power supply, said power supply link including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply; and

a current regulation circuit including a timing circuit for defining periods during which each of the power switching devices may be nonconducting, a current sensing circuit for sensing current in only one of the rails of the power supply link and a control circuit for controlling the power switching devices so that each of the power switching devices is nonconducting only during portions of the defined periods during which the sensed current exceeds a peak current reference level.

46. An application specific integrated circuit (ASIC) for use with a motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said motor further having a power supply link for connecting the windings to a power supply, said power supply link including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply, said ASIC comprising:

a timing circuit for defining periods during which each of the power switching devices may be nonconducting;

a circuit for sensing current in only one of the rails of the power supply link; and

a control circuit for controlling the power switching devices so that each of the power switching devices is nonconducting only during portions of the defined periods during which the sensed current exceeds a peak current reference level.

47. A current regulation circuit for controlling excessive circulating currents in a power supply link of a motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said power supply link connecting the windings to a power supply and including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply, said current regulation circuit comprising:

a timing circuit for defining periods during which each of the power switching devices may be nonconducting;

a circuit for sensing current in only one of the rails of the power supply link; and

a control circuit for controlling the power switching devices so that each of the power switching devices is nonconducting only during portions of the defined periods during which the sensed current exceeds a peak current reference level whereby current which circulates during periods when only one power switching device is conducting is reduced.

48. A method of operating a motor, said motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said motor also having a power supply link for connecting the windings to a power supply, said power supply link including power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply, said method comprising the steps of:

selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly;

regulating current by defining periods during which each of the power switching devices may be nonconducting;

sensing current in only one of the rails of the power supply link; and

controlling the power switching devices so that each of the power switching devices is nonconducting only during portions of the defined periods during which the sensed current exceeds a peak current reference level.

49. A method of operating a motor, said motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said motor also having a power supply link for connecting the windings to a power supply, said power supply link including power switching devices each having a conducting state and a nonconducting state, said method comprising the steps of:

selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly;

sensing current in the power supply link;

inhibiting the sensed current for a blanking interval triggered by the energization of the windings;

defining a period during which each of the power switching devices may be nonconducting; and

controlling the power switching devices so that each of the power switching devices is nonconducting when the sensed current exceeds a peak current reference level during the defined period except during the blanking interval whereby current which circulates during periods when only one power switching device is conducting is reduced.

50. A method of operating a motor, said motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said motor also having a power supply link for connecting the windings to a power supply, said power supply link including power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply, said method comprising the steps of:

selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly;

pulse width modulating the power being provided to at least one of the windings at a duty cycle having alternating on and off periods;

counting a predetermined number of off periods;

sensing current in one of the rails of the power supply link; and

controlling the power switching devices so that each of the power switching devices is nonconducting in response to the sensed current exceeding a peak current reference level only after the predetermined number of off periods is counted whereby current which circulates during periods when only one power switching device is conducting is periodically reduced.

51. A method of operating a motor, said motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said motor also having a power supply link for connecting the windings to a power supply, said power supply link including power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply, said method comprising the steps of:

selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly;

defining by an application specific integrated circuit periods during which each of the power switching devices may be nonconducting;

sensing current in only one of the rails of the power supply link; and

controlling the power switching devices so that each of the power switching devices is nonconducting only during portions of the defined periods during which the sensed current exceeds a peak current reference level.

52. A method of regulating current for controlling excessive circulating currents in a power supply link of a motor, said motor having a stationary assembly and a rotatable assembly in magnetic coupling relation thereto, said stationary assembly including windings adapted for energization in at least one preselected sequence, said power supply link connecting the windings to a power supply and including power switching devices for selectively energizing the windings in the preselected sequence by selectively connecting the power supply link to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switching devices each having a conducting state and a nonconducting state and comprising an inverter bridge, said inverter bridge having a positive rail and a negative rail supplied by the power supply, said method comprising the steps of:

defining periods during which each of the power switching devices may be nonconducting;

sensing current in only one of the rails of the power supply link; and

controlling the power switching devices so that each of the power switching devices is nonconducting only during portions of the defined periods during which the sensed current exceeds a peak current reference level whereby current which circulates during periods when only one power switching device is conducting is reduced.