Commutation position detection system and method

• US 5,821,713 A
• Filed: 02/03/1997
• Issued: 10/13/1998
• Est. Priority Date: 09/11/1995
• Status: Expired due to Term

• Current Assignee: Rocky Mountain Technologies Inc.
• Original Assignee: Advanced Motion Controls Inc.
• Inventors: Holling, George, Schmitt, Michael, Yeck, Mark
• Primary Examiner(s): IP, SHIK LUEN PAUL
• Application Number:
  US08/794,608
• Time in Patent Office: 617 Days
• Field of Search: 318/138, 318/139, 318/245, 318/254, 318/439, 318/260-296, 318/560-696, 318/699-832, 388/800-824, 360/70-88
• US Class Current: 318/400.32
• CPC Class Codes: H02P 6/18 without separate position detecting elements
• CPC Class Codes: H02P 6/185 using inductance sensing, e.g. pulse excitation
• CPC Class Codes: H02P 6/20 Arrangements for starting H02P6/08 takes precedence
• CPC Class Codes: H02P 6/34 Modelling or simulation for control purposes

Abstract

An improved commutation position detection system for accurately determining commutation position within polyphase brushless motors without employing proximity sensors or transducers. The present invention determines commutation position. by differentiating the current flowing within the stator coils and comparing the differentiated current waveforms to one another (absolute commutation position detection) or a predetermined threshold (incremental commutation position detection) to obtain a real-time assessment of commutation position.

Claims

1. A method of starting a polyphase brushless motor, said brushless motor having a plurality of field coils disposed about a rotor, comprising the steps of:

(a) simultaneously energizing each of said plurality of field coils with a driving signal while said rotor is maintained in a fixed position within said motor;

(b) continuously monitoring the current waveform for each of said plurality of field coils during said step of simultaneously energizing;

(c) continuously differentiating said current waveform for each of said plurality of field coils to define a current rate of change waveform for each of said plurality of field coils;

.(d) comparing said current rate of change waveform for each of said plurality of field coils to a predetermined voltage threshold to determine commutation position; and

(e) applying a driving signal to an active field coil based on said commutation position to initiate said rotor into motion within said motor.

2. The method as set forth in claim 1 and further wherein said step (b) comprises the steps of:

(i) providing current sensing means associated with each of said plurality of field coils; and

(ii) sensing the current waveform of each of said plurality of field coils during step (a).

3. The method as set forth in claim 2 and further wherein said step (c) comprises the steps of:

(i) providing differentiation means associated with said current sensing means;

(ii) differentiating said current waveform of each of said plurality of field coils to define a current rate of change waveform for each of said plurality of field coils.

4. The method as set forth in claim 3 and further, wherein said step (d) comprises the steps of:

(i) providing means for adjustably setting said predetermined voltage threshold associated with said differentiation means;

(ii) setting said means for adjustably setting such that said predetermined voltage threshold provides a reference upon which to compare said current rate of change waveform for each of said plurality of field coils; and

(iii) comparing said current rate of change waveform for each of said plurality of field coils to determine said active field coil.

5. The method as set forth in claim 3 and further, wherein said step (e) comprises the further steps of:

(i) providing commutation means for generating said driving signal; and

(ii) applying said driving signal to said active field coil to initiate said rotor into motion within said motor.

6. The method as set forth in claim 1 and further, wherein step (b) includes the further step of continuously normalizing the current waveform within said stator coil.

7. The method as set forth in claim 6 and further, comprising the further steps of:

(i) providing normalization means associated with said differentiation means; and

(ii) employing said normalization means to remove unwanted noise artifacts from one of said current waveform and said current rate of change waveform of said stator coil.

8. The method as set forth in claim 1 and further, wherein step (e) includes the further step of providing sample and hold means for selectively sampling and holding the commutation position signal generated in step (d) to eliminate switching transients.

9. A method of starting a brushless polyphase motor having a rotor and a plurality of field coils, comprising the steps of:

(a) applying a driving signal to each of said plurality of field coils while said rotor is stationary;

(b) continuously differentiating the current waveform within each of said plurality of field coils during step (a);

(c) continuously comparing the differentiated current waveforms from step (b) to a predetermined voltage threshold; and

(d) selectively energizing at least one of said plurality of field coils based on the comparisons from step (c) to force said rotor into proper rotational motion.

10. The method set forth in claim 9 and further wherein step (b) comprises the steps of:

(i) providing current sensing means for sensing the current waveform within each of said plurality of field coils;

(ii) providing differentiation means associated with said current sensing means; and

(iii) differentating said current waveform within each of said plurality of field coils via said differentiation means.

11. The method set forth in claim 10 and further, wherein step (c) comprises the substeps of:

(i) providing means for adjustably setting said predetermined voltage threshold;

(ii) providing comparing means for comparing each of said differentiated current waveforms to said predetermined voltage threshold; and

(iii) comparing said differentiated current waveforms from step (b) to said predetermined threshold to determine the relative position of each of said plurality of field coils to said rotor.

12. The method set forth in claim 11 and further wherein step (d) comprises the steps of:

(i) determining which of said plurality of field coils is in the closest positional alignment with said rotor to define an active field coil; and

(ii) applying said driving signal to said active field coil.

13. A method for detecting the position of a rotor with respect to a plurality of field coils in a polyphase brushless motor, comprising the steps of:

(a) continuously injecting at least a predetermined nominal exciting current into each of said plurality of field coils;

(b) continuously monitoring the current waveform for each of said plurality of field coils during said step of continuously injecting;

(c) continuously differentiating said current waveform for each of said plurality of field coils to define a current rate of change waveform for each of said plurality of field coils; and

(d) comparing the magnitude of at least two of said current rate of change waveforms to one another to produce an absolute reference indicative of the position of said rotor within said motor.

14. The method as set forth in claim 13 and further wherein said step (b) comprises the steps of:

(i) providing current sensing means associated with each of said plurality of field coils; and

(ii) sensing said current waveform of each of said plurality of field coils during step (a).

15. The method as set forth in claim 13 and further wherein said step (c) comprises the steps of:

(i) providing differentiation means associated with each of said current sensing means;

(ii) differentiating said current waveform of each of said plurality of field coils to define a current rate of change waveform for each of said plurality of field coils.

16. The method as set forth in claim 13 and further, wherein said step (d) comprises the further steps of:

(i) providing comparator means associated with at least two of said plurality of differentiation means;

(ii) comparing together the magnitude of said current rate of change waveform of each of said at least two of said plurality of differentiation means.

17. The method as set forth in claim 16 and further, wherein said step (d)(i) comprises the step of providing a plurality of comparators associated with at least two of said plurality of differentiation means.

18. The method as set forth in claim 16 and further, wherein said step (d)(i) comprises the steps of:

(a) providing at least two multiplexers having inputs coupled to each of said plurality of differentiation means and an output coupled to a comparator; and

(b) controlling said at least two multiplexers to selectively submit two of said plurality of current rate of rate waveforms to said comparator.

19. A method for determining commutation position within a brushless motor having a plurality of stator coils disposed about a rotor, comprising the steps of:

(a) applying at least a predetermined nominal electric current to each of said plurality of stator coils;

(b) continuously differentiating the electric current flowing within each of said plurality of stator coils during step (a) to produce a current rate of change waveform for each of said plurality of stator coils; and

(c) continuously comparing together at least two of said current rate of change waveforms to determine an absolute reference indicative of the position of said rotor within said motor.

20. The method set forth in claim 19 and further wherein step (b) comprises the steps of:

(i) providing current sensing means for sensing said electric current within each of said plurality of field coils;

(ii) providing differentiation means associated with said current sensing means; and

(iii) differentating said electric current within each of said plurality of field coils via said differentiation means.

21. The method set forth in claim 19 and further, wherein step (c) comprises the substeps of:

(i) providing comparator means associated with said differentiation means;

(ii) comparing at least two of said current rate of change waveforms.

22. The method as set forth in claim 21 and further, wherein said step (c)(i) comprises the step of providing a plurality of comparators associated with said differentiation means.

23. The method as set forth in claim 21 and further, wherein said step (c)(i) comprises the step of providing a comparator, a first multiplexer for selectively submitting at least one of said plurality of current rate of change waveforms to said comparator, and a second multiplexer for selectively submitting at least one of said plurality of current rate of change waveforms to said comparator, and step (c)(ii) comprises the step of controlling said first and second multiplexers to selectively submit at least two of said plurality of current rate of change waveforms to said comparator.

24. An apparatus for controlling the operation of a polyphase brushless motor having rotor and a plurality of stator coils, comprising:

(a) commutation position detection means for determining the position of said rotor relative to said plurality of stator coils, said commutation position detection means including;

(i) current sensing means for sensing the amount of electric current flowing within each of said plurality of stator coils;

(ii) differentiation means for differentiating said amount of electric current flowing within each of said plurality of stator coils; and

(iii)comparator means for comparing together said differentiated electric current of at least two of said plurality of stator coils to determine an absolute reference indicative of a position of said rotor within said motor; and

(b) commutation means for selectively applying at least a predetermined nominal electric current to each of said plurality of stator coils and selectively applying a driving signal to one or more of said plurality of stator coils depending upon said absolute reference.

25. The apparatus as set forth in claim 24 and further, wherein said comparator means comprises at least two comparators coupled between said differentiation means and said commutation means.

26. The apparatus as set forth in claim 24 and further, said comparator means comprising multiplexing means and a comparator, said multiplexing means for selectively passing said differentiated electric current for at least two of said plurality of stator coils to said comparator.

27. The apparatus as set forth in claim 24 and further, said commutation position detection means including sample and hold means disposed between said comparator means and said commutation means, said sample and hold means for selectively sampling and holding the commutation position signal generated by said comparator so as deliberating block out the transient-laden portions of said commutation position signal.

28. An apparatus for determining commutation position within a brushless motor having a rotor and plurality of stator coils, comprising:

(a) current sensing means for sensing the amount of electric current flowing within each of said plurality of stator coils;

(b) differentiation means for differentiating said amount of electric current flowing within each of said plurality of stator coils; and

(c) comparator means for comparing together said differentiated electric current of at least two of said plurality of stator coils to determine an absolute reference indicative of a position of said rotor within said motor.

29. The apparatus as set forth in claim 28 and further, wherein said comparator means comprises at least two comparators coupled between said differentiation means and said commutation means.

30. The apparatus as set forth in claim 28 and further, said comparator means comprising multiplexing means and a comparator, said multiplexing means for selectively passing said differentiated electric current for at least two of said plurality of stator coils to said comparator.