Electric motor with adjustable timing

• US 7,486,041 B2
• Filed: 09/29/2006
• Issued: 02/03/2009
• Est. Priority Date: 09/30/2005
• Status: Active Grant

• Current Assignee: Mcmillan Electric Company
• Original Assignee: Mcmillan Electric Company
• Inventors: Cox, Karmen D., Wasson, Dewain L.
• Primary Examiner(s): Masih; Karen
• Application Number:
  US11/537,221
• Publication Number:
  US 20070159124A1
• Time in Patent Office: 858 Days
• Field of Search: 318/254, 318/138, 318/439, 318/432, 318/433, 318/434, 318/636, 318/400.1
• US Class Current: 318/434
• CPC Class Codes: G04C 3/143 Means to reduce power consumption by reducing pulse width or amplitude and related problems, e.g. detection of unwanted or missing step
• CPC Class Codes: H02P 6/14 Electronic commutators
• CPC Class Codes: H02P 6/15 Controlling commutation time
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position

Abstract

An electrically commutated motor includes a first module to measure a current in a coil of the motor, and a second module to adjust timing of commutation of the motor based on the current measurement.

Claims

1. A single coil, single phase, direct current permanent magnet brushless motor, comprising:

a rotor with a plurality of permanent magnets;

a single coil;

a stator with a plurality of salient poles, with each pole being formed by winding the single coil in a direction opposite to an adjacent pole to form a series of alternating poles wound in different directions;

a sensor to sense a position of the rotor relative to the stator;

a commutation module to commutate the motor;

a current sample module programmed to sample a current through the single coil of the motor at least two times during a single commutation cycle; and

a waveform shape module programmed to compare sampled currents to estimate a current waveform characteristic through the single coil;

wherein the commutation module is programmed to adjust timing of a commutation of the motor based upon the current waveform characteristic to adjust advance or delay the commutation.

2. The motor of claim 1, wherein the sensor is a single output Hall sensor.

3. The motor of claim 1, wherein the sensor is a dual output hall sensor.

4. The motor of claim 1, further comprising a second sensor to sense the position of the rotor relative to the stator.

5. The motor of claim 1, wherein the sensor is located mechanically near a leading edge of one of the salient poles.

6. The motor of claim 1, wherein the commutation module is programmed to adjust timing of the commutation to advanced or delay timing during a startup sequence.

7. The motor of claim 1, wherein the current sample module is programmed to sample the current at about ¼

of a commutation cycle.

8. The motor of claim 1, wherein the current sample module is programmed to sample the current at about ⅞

of a commutation cycle.

9. The motor of claim 1, wherein the waveform shape module is programmed to calculate an average of the sampled current prior to adjusting timing.

10. The motor of claim 1, wherein the waveform shape module is programmed to determine whether a first current sample is about equal to a second current sample, and wherein the commutation module is programmed to adjust the timing of the commutation of the motor if the first current sample is not about equal to the second current sample.

11. The motor of claim 1, wherein the waveform shape module is programmed to calculate a difference between a first current sample and a second current sample, and to determine whether the difference is outside of a predetermined range, and wherein the commutation module is programmed to adjust the timing of the commutation of the motor if the difference is outside of the predetermined range.

12. The motor of claim 1, wherein the waveform shape module is programmed to calculate a ratio between a first current sample and a second current sample, and to determine whether the ratio is outside of a predetermined range, and wherein the commutation module is programmed to adjust the timing of the commutation of the motor if the ratio is outside of the predetermined range.

13. The motor of claim 1, wherein the commutation module is programmed to adjust timing of the commutation such that a first current sample is about equal to a second current sample when a pulse width modulation is equal to and less than 75%, and such that the first current sample is greater than the second current sample when the pulse width modulation is about equal to 100%, and such that the first current sample is linearly scaled for the pulse width modulation between about 75% and 100%.

14. The motor of claim 1, wherein the current sample module is programmed to sample the current during each N commutation cycles, where N is an integer greater than 1.

15. The motor of claim 1, wherein the current sample module is programmed to take a first sample of the current during a first half of a commutation cycle and a second sample of the current during a second half of the commutation cycle.

16. A method of commutation of a single coil, single phase, direct current permanent magnet brushless motor, the method comprising:

commutating the motor;

sampling a current through the single coil of the motor at least two times during a single commutation cycle, wherein the current sample module is programmed to take a first sample of the current during a first half of a commutation cycle and a second sample of the current during a second half of the commutation cycle;

comparing sampled currents to estimate a current waveform characteristic through the single coil; and

adjusting timing of the commutation of the motor based upon the current waveform characteristic to advance or delay the commutation.

17. The method of claim 16, wherein measuring the current further comprises:

sampling the current at about ¼

of a commutation cycle; and

sampling the current at about ⅞

of the commutation cycle.

18. The method of claim 16, wherein comparing the sampled currents further comprises determining whether a first current sample is about equal to a second current sample, and wherein adjusting the timing further comprises adjusting the timing of the commutation of the motor if the first current sample is not about equal to the second current sample.

19. The method of claim 16, wherein comparing the sampled currents further comprises calculating a difference between a first current sample and a second current sample, and wherein adjusting the timing further comprises adjusting the timing of the commutation of the motor if the difference is outside of a predetermined range.

20. The method of claim 16, wherein comparing the sampled currents further comprises calculating a ratio between a first current sample and a second current sample, and wherein adjusting the timing further comprises adjusting the timing of the commutation of the motor if the ratio is outside of a predetermined range.

21. The method of claim 16, wherein adjusting the timing further comprises adjusting the timing of the commutation such that a first current sample is about equal to a second current sample when a pulse width modulation is equal to and less than 75%, and such that the first current sample is greater than the second current sample when the pulse width modulation is about equal to 100%, and such that the first current sample is linearly scaled for the pulse width modulation between about 75% and 100%.

22. The method of claim 16, further comprising:

powering the motor in a first phase for a first time period, and then a second opposite phase for a second time period;

monitoring the current through the single coil until a current peak is detected;

adjusting a virtual encoder to a next commutation angle;

continuing to monitor for additional current peaks and adjusting the virtual encoder until the current peaks stop occurring;

once the current peaks stop occurring, ceasing to monitor for the current peaks; and

commutating the motor using output of the virtual encoder.

23. A single coil, single phase, direct current permanent magnet brushless motor, comprising:

a rotor with a plurality of permanent magnets;

a single coil;

a stator with a plurality of salient poles, with each pole being formed by winding the single coil in a direction opposite to an adjacent pole to form a series of alternating poles wound in different directions;

at least one reluctance notch formed in at least one of the poles of the stator, the reluctance notch being configured to pre-locate the rotor relative to the stator when the motor is at rest;

a commutation module to commutate the motor;

a current sample module programmed to take a first sample of a current through the single coil during a first half of a commutation cycle and a second sample of the current during a second half of the commutation cycle; and

a waveform shape module programmed to compare sampled currents to estimate a current waveform characteristic through the single coil, wherein the current waveform characteristic swings through zero current at each commutation cycle to form alternating crests and troughs;

wherein the commutation module is programmed to adjust timing of a commutation of the motor based upon the current waveform characteristic to adjust advance or delay the commutation.

24. The motor of claim 23, further comprising a sensor to sense a position of the rotor relative to the stator.

25. The motor of claim 23, further comprising:

a virtual RPM sensor programmed to estimate an RPM of the motor; and

a virtual encoder programmed to estimate a position of a rotor of the motor;

wherein timing for commutation of the motor is based on output from one of the virtual RPM sensor and the virtual encoder.

26. The motor of claim 25, wherein the timing for commutation is based on the output from the virtual RPM sensor at startup of the motor.

27. The motor of claim 25, wherein current through the single coil is measured until a current peak is detected, and the virtual encoder is adjusted to a next commutation angle upon measuring the current peak.

28. The motor of claim 27, wherein the timing for the commutation is based on the output of the virtual encoder once current peaks through the single coil stop.