Torque controller in an electric motor

• US 7,898,198 B2
• Filed: 05/31/2006
• Issued: 03/01/2011
• Est. Priority Date: 06/29/2005
• Status: Active Grant

• Current Assignee: DRS Network & Imaging Systems, LLC (Leonardo S.p.A.)
• Original Assignee: DRS Test & Energy Management, Inc. (Leonardo S.p.A.)
• Inventors: Murphree, Jerry Eony
• Primary Examiner(s): Ro; Bentsu
• Assistant Examiner(s): Luo; David S
• Application Number:
  US11/443,822
• Publication Number:
  US 20070001636A1
• Time in Patent Office: 1,735 Days
• Field of Search: 318/432, 318/434
• US Class Current: 318/432
• CPC Class Codes: H02P 23/03 specially adapted for very low speeds

Abstract

The torque of a motor operated by an inverter circuit is controlled to allow maximum torque in the motor when the motor is stalled or at low rotation speeds. Control is accomplished by providing a switching frequency to the motor at a first switching frequency, detecting a rotation speed of the motor, and switching the current to the motor to a second switching frequency when the rotation speed of the motor drops to a predetermined slow rotation speed. The second switching frequency is less than the first switching frequency.

Claims

1. A method of controlling the efficiency of power electronics driving a motor, comprising:

switching a voltage within said power electronics at a first fundamental frequency;

providing a high frequency pulse width modulated component within said first fundamental frequency, said high frequency component have a frequency greater than said fundamental frequency;

detecting a rotation speed of said motor; and

responsive to said rotation speed, altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency to control efficiency in said power electronics, said altering including determining said second frequency by the equation;

2. The method of claim 1, wherein said rotation speed is a stall condition.

3. The method of claim 1, wherein said first switching frequency comprises 20 kHz and said altering said frequency of said high frequency pulse width modulated component comprises reducing said first switching frequency to a second switching frequency of 5 kHz.

4. The method of claim 1, wherein said switching a voltage in said power electronics produces maximum torque in said motor.

5. The method of claim 1, wherein said altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency further comprises altering said frequency of said high frequency pulse width modulated component to a third switching frequency when said rotation speed of said motor increases to a high rotation speed, and wherein said third switching frequency is higher than said second switching frequency.

6. The method of claim 5, further comprising suppressing a change to said third switching frequency when said high rotation speed is greater than a predetermined speed and said high rotation speed decreases by a relatively small amount.

7. The method of claim 1, wherein altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency is dependant upon a torque requirement of said motor.

8. The method of claim 7, wherein said altering is determined by the equation:

9. The method of claim 7, further comprising reducing said fundamental frequency of said voltage switching when said torque requirement at said motor is less than a maximum rated torque of said motor.

10. A controller for an electric motor, comprising:

means for switching a voltage within power electronics at a first fundamental frequency to drive said motor

means for providing a high frequency pulse width modulated component within said first fundamental frequency, said high frequency component having a frequency greater than said fundamental frequency;

means for detecting a rotation speed of said motor; and

,

means responsive to said detecting means for altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency to control efficiency in said power electronics, said altering means further comprising means for switching said high frequency component means to a third switching frequency when said rotation speed of said motor increases to a high rotation speed, wherein said third switching frequency is higher than said second switching frequency.

11. The controller of claim 10, wherein said means for detecting comprises:

a sensor configured to locate a point on the rotor of said motor; and

a timer configured to measure the time between a first time said sensor locates said point and a second time said sensor locates said point.

12. The controller of claim 11, wherein said sensor is a Hall effect sensor.

13. The controller of claim 10, further comprising a power supply configured to supply said voltage to said switching means, said power supply configured to supply said voltage at an amplitude to produce maximum torque in said motor.

14. The controller of claim 10, wherein said altering means further comprises means for linearly varying said first switching frequency to said second switching frequency.

15. The controller of claim 10, wherein said detecting means further comprises means for determining the required torque of said motor.

16. The controller of claim 15, wherein said altering means further comprises means for linearly varying said first switching frequency to said second switching frequency responsive to the required torque of said motor.

17. The controller of claim 15, further comprising a power supply configured to supply said voltage to said switching means and further configured to limit said voltage when said required torque of said motor is less than a maximum rated torque of said motor.

18. The controller of claim 10, wherein said altering means is further configured to suppress a change to said third switching frequency when said high rotation speed is greater than a predetermined speed and said high rotation speed decreases by a relatively small amount.

19. A method of generating a smooth, rated torque at a slow rotation speed of a motor, said motor including a rotor, comprising:

passing a first switched pulse width modulated voltage to power electronics driving said motor at a first switching frequency when said rotor is rotating at a rotation speed above said slow rotation speed;

passing a second switched pulse width modulated voltage to said power electronics at a second switching frequency when said rotor is rotating at a rotation speed at or below said slow rotation speed, said second switching frequency being less than said first switching frequency;

wherein a single specified torque of said motor is produced at both said first switching frequency and said second switching frequency; and

further comprising determining said second switching frequency as a linear relationship to said first switching frequency given by the equation,

20. The method of claim 19, wherein said slow rotation speed is a stall condition.

21. The method of claim 19, wherein said first switching frequency is a switching frequency of 20 kHz and said second switching frequency is 5 kHz.

22. The method of claim 19, wherein said first switched voltage produces a maximum rated torque of the motor.

23. The method of claim 19, further comprising switching said current at a third switching frequency when said rotation speed of said rotor increases to a high rotation speed, wherein said third switching frequency is higher than said second switching frequency.

24. The method of claim 23, wherein said high rotation speed is greater than said slow rotation speed such that a small change in rotation speed does not change the switching frequency.

25. The method of claim 19, further comprising determining said second switching frequency based on a torque requirement of said motor.

26. The method of claim 25, wherein said determining is defined by:

27. The method of claim 25, wherein said voltage is derated when the torque requirement at said motor is less than the maximum rated torque of said motor.

28. A controller for an electric motor, comprising:

a switching converter configured to alter a drive signal to power electronics from a first pulse width modulated switching frequency to a second pulse width modulated switching frequency; and

a position sensor configured to detect a rotation speed of said motor,

wherein said switching converter switches said frequencies when said position sensor detects a rotation speed of said motor equivalent to a predetermined rotation speed, said switching converter being configured to alter said drive signal at a third switching frequency when said rotation speed of said motor increases to a predetermined fast rotation speed, said third switching frequency being higher than said second switching frequency.

29. The controller of claim 28, wherein said predetermined speed is at a stall condition.

30. The controller of claim 28, wherein said switching converter is configured to vary said switching frequencies according to a linear relationship between said second switching frequency and said first switching frequency.

31. The controller of claim 28, wherein said predetermined high rotation speed is greater than said predetermined speed such that a small drop in rotation speed at said predetermined high rotation speed does not change the switching frequency.

32. The controller of claim 28, wherein said position sensor is further configured to determine said second switching frequency based on a torque requirement of said motor.

33. The controller of claim 32, wherein current is derated when said torque requirement at said motor is less than a maximum rated torque of said motor.

34. The controller of claim 28, wherein said position sensor comprises a Hall effect sensor.

35. The controller of claim 28, wherein said position sensor determines the rotation speed by back-emf.

36. A method of controlling the efficiency of power electronics driving a motor, comprising:

switching a voltage within said power electronics at a first fundamental frequency;

providing a high frequency pulse width modulated component within said first fundamental frequency, said high frequency component have a frequency greater than said fundamental frequency;

detecting a rotation speed of said motor; and

responsive to said rotation speed, altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency to control efficiency in said power electronics, said altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency further comprises altering said frequency of said high frequency pulse width modulated component to a third switching frequency when said rotation speed of said motor increases to a high rotation speed, and wherein said third switching frequency is higher than said second switching frequency.

37. The method of claim 36, wherein said altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency comprises determining said second frequency by the equation:

38. The method of claim 36, further comprising suppressing a change to said third switching frequency when said high rotation speed is greater than a predetermined speed and said high rotation speed decreases by a relatively small amount.

39. The method of claim 36, wherein altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency is dependant upon a torque requirement of said motor.

40. The method of claim 39, wherein said altering is determined by the equation:

41. The method of claim 39, further comprising reducing said fundamental frequency of said voltage switching when said torque requirement at said motor is less than said maximum rated torque of said motor.

42. A method of controlling the efficiency of power electronics driving a motor, comprising:

switching a voltage within said power electronics at a first fundamental frequency;

providing a high frequency pulse width modulated component within said first fundamental frequency, said high frequency component have a frequency greater than said fundamental frequency;

detecting a rotation speed of said motor; and

responsive to said rotation speed, altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency to control efficiency in said power electronics, said altering said frequency of said high frequency pulse width modulated component from a first switching frequency to a second switching frequency being dependant upon a torque requirement of said motor.

43. The method of claim 42, wherein said altering is determined by the equation:

44. The method of claim 42, further comprising reducing said fundamental frequency of said voltage switching when said torque requirement at said motor is less than said maximum rated torque of said motor.

45. A method of generating a smooth, rated torque at a slow rotation speed of a motor, said motor including a rotor, comprising:

passing a first switched pulse width modulated voltage to power electronics driving said motor at a first switching frequency when said rotor is rotating at a rotation speed above said slow rotation speed;

passing a second switched pulse width modulated voltage to said power electronics at a second switching frequency when said rotor is rotating at a rotation speed at or below said slow rotation speed, said second switching frequency being less than said first switching frequency, a single specified torque of said motor being produced at both said first switching frequency and said second switching frequency; and

switching said current at a third switching frequency when said rotation speed of said rotor increases to a high rotation speed, wherein said third switching frequency is higher than said second switching frequency.

46. The method according to claim 45, further comprising determining said second switching frequency as a linear relationship to said first switching frequency given by the equation,

47. The method according to claim 45, wherein said high rotation speed is greater than said slow rotation speed such that a small change in rotation speed does not change the switching frequency.

48. The method according to claim 45, further comprising determining said second switching frequency based on the torque requirement of said motor, said determining being defined by:

49. The method according to claim 48, wherein said voltage being derated when the torque requirement at said motor is less than a maximum rated torque of said motor.

50. A controller for an electric motor, comprising:

a switching converter configured to alter a drive signal to power electronics from a first pulse width modulated switching frequency to a second pulse width modulated switching frequency; and

a position sensor configured to detect a rotation speed of said motor, said switching converter switches said frequencies when said position sensor detects a rotation speed of said motor equivalent to a predetermined rotation speed, said position sensor further being configured to determine said second switching frequency based on a torque requirement of said motor, said current is derated when said torque requirement at said motor is less than a maximum rated torque of said motor.