Current determination in a permanent magnet electric machine

• US 7,042,227 B2
• Filed: 01/23/2002
• Issued: 05/09/2006
• Est. Priority Date: 09/16/1999
• Status: Expired due to Term

• Current Assignee: Pacific Century Motors, Inc. (Aviation Industry Corporation of China, Ltd.), GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Mir, Sayeed A., McCann, Roy Alan, Colosky, Mark Philip, Skellenger, Dennis B.
• Primary Examiner(s): TERESINSKI, JOHN
• Assistant Examiner(s): TERESINSKI, JOHN
• Application Number:
  US10/056,634
• Publication Number:
  US 20020105335A1
• Time in Patent Office: 1,567 Days
• Field of Search: 324/503, 324/207.17, 324/207.25, 324/772, 324/803, 318/432, 318/434, 318/716, 318/650, 318/825, 318/599, 318/798, 318/811, 318/802, 388/806, 701/41
• US Class Current: 324/503
• CPC Class Codes: B62D 5/046 Controlling the motor
• CPC Class Codes: B62D 5/0487 detecting motor faults B62D5/0496 takes precedence
• CPC Class Codes: G01D 3/08 with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
• CPC Class Codes: H02P 2209/07 Trapezoidal waveform
• CPC Class Codes: H02P 6/28 Arrangements for controlling current H02P6/10 takes precedence
• CPC Class Codes: Y10S 388/903 Protective, e.g. voltage or current limit

Abstract

A method and system for determining a torque current in an electric machine coupled to a polyphase bus. The method comprises: detecting a rotational position of the electric machine with a position encoder; controlling an inverter comprising a plurality of switching devices, the inverter having an input coupled to a direct current bus, and an output coupled to the polyphase bus. Where the inverter is responsive to commands from a controller coupled to the inverter and to the position encoder. The method also includes measuring a current from the direct current bus; and capturing the current at a predefined interval of time.

Claims

1. A method of determining a current in an electric machine coupled to a polyphase bus, the method comprising:

detecting a rotational position of said electric machine with a position encoder coupled to said electric machine;

controlling an inverter comprising a plurality of switching devices, said inverter having an input coupled to a direct current bus, and an output coupled to said polyphase bus, said inverter responsive to commands from a controller coupled to said inverter and to said position encoder;

measuring a current from said direct current bus; and

capturing said current at a predefined interval of time.

2. The method of claim 1 further comprising:

determining a set of values representative of a magnitude of currents on each phase of said polyphase bus.

3. The method of claim 2 wherein said predefined interval of time is established when:

said electric machine is within a predefined rotational angle;

a predefined combination of said switching devices are active; and

an angle between a phase voltage and a corresponding phase current on each phase of said polyphase bus being within a range of about minus thirty to about thirty degrees.

4. The method of claim 1 further comprising:

determining a value representative of a torque current from said current.

5. The method of claim 4 wherein said predefined interval of time is established when:

a particular back EMF voltage waveform for a given phase of said electric machine attains its peak value;

said electric machine is within a predefined rotational angle;

a predefined combination of said switching devices are active; and

an angle between a phase voltage and a corresponding back EMF on each phase of said polyphase bus being within a range of about minus thirty to about thirty degrees.

6. The method of claim 1 wherein said electric machine comprises a permanent magnetic motor and said position encoder includes a rotor position sensor.

7. The method of claim 1 wherein said electric machine is a permanent magnet DC brushless motor characterized by a sinusoidal magnetic field excitation.

8. The method of claim 1 wherein said capturing is characterized by sampling a signal value representative of said current and said sampling is controlled by said controller to be operative only at said predefined interval of time.

9. A system for determining a current in an electric machine coupled to a polyphase bus, the system comprising:

a position encoder coupled to said electric machine to detect rotational position;

an inverter having an input coupled to a direct current bus, and an output coupled to said polyphase bus, responsive to commands from a controller;

said controller coupled to said inverter and to said position encoder;

a sensor to detect a current from said direct current bus; and

wherein said sensor captures said current at a predefined interval of time.

10. The system of claim 9 wherein said controller determines a set of values representative of a magnitude of currents on each phase of said polyphase bus.

11. The system of claim 10 wherein said predefined interval of time is established when:

said electric machine is within a predefined rotational angle;

a predefined combination of said switching devices are active; and

an angle between a phase voltage and a corresponding phase current on each phase of said polyphase bus being within a range of about minus thirty to about thirty degrees.

12. The system of claim 9 wherein said controller determines a value representative of a torque current from said current.

13. The system of claim 12 wherein said predefined interval of time is established when:

a particular back EMF voltage waveform for a given phase of said electric machine attains its peak value;

said electric machine is within a predefined rotational angle;

a predefined combination of said switching devices are active; and

an angle between a phase voltage and a corresponding back EMF on each phase of said polyphase bus being within a range of about minus thirty to about thirty degrees.

14. The system of claim 9 wherein said electric machine comprises a permanent magnetic motor and said position encoder includes a rotor position sensor.

15. The system of claim 9 wherein said electric machine is a permanent magnet DC brushless motor characterized by a sinusoidal magnetic field excitation.

16. The system of claim 9 wherein said inverter is comprised of switching devices coupled to and responsive to commands from said controller.

17. The system of claim 9 wherein said capturing is characterized by sampling a signal value representative of said current and said sampling is controlled by said controller to be operative only at said predefined interval of time.

18. A storage medium encoded with a machine-readable computer program code for determining a current in an electric machine coupled to a polyphase bus, said storage medium including instructions for causing controller to implement a method comprising:

detecting a rotational position of said electric machine with a position encoder coupled to said electric machine;

controlling an inverter comprising a plurality of switching devices, said inverter having an input coupled to a direct current bus, and an output coupled to said polyphase bus, said inverter responsive to commands from a controller coupled to said inverter and to said position encoder;

measuring a current from said direct current bus; and

capturing said current at a predefined interval of time.

19. The storage medium of claim 18 further including instructions for causing said controller to perform said method further comprising:

determining a set of values representative of a magnitude of currents on each phase of said polyphase bus.

20. The storage medium of claim 19 wherein said predefined interval of time is established when:

said electric machine is within a predefined rotational angle;

a predefined combination of said switching devices are active; and

an angle between a phase voltage and a corresponding phase current on each phase of said polyphase bus being within a range of about minus thirty to about thirty degrees.

21. The storage medium of claim 18 further including instructions for causing said controller to perform said method further comprising:

determining a value representative of a torque current from said current.

22. The storage medium of claim 21 wherein said predefined interval of time is established when:

a particular back EMF voltage waveform for a given phase of said electric machine attains its peak value;

said electric machine is within a predefined rotational angle;

a predefined combination of said switching devices are active; and

an angle between a phase voltage and a corresponding back EMF on each phase of said polyphase bus being within a range of about minus thirty to about thirty degrees.

23. The storage medium of claim 18 wherein said electric machine comprises a permanent magnetic motor and said position encoder includes a rotor position sensor.

24. The storage medium of claim 18 wherein said electric machine is a permanent magnet DC brushless motor characterized by a sinusoidal magnetic field excitation.

25. The storage medium of claim 18 wherein said capturing is characterized by sampling a signal value representative of said current and said sampling is controlled by said controller to be operative only at said predefined interval of time.

26. A computer data signal embodied in a carrier wave for determining a current in an electric machine coupled to a polyphase bus, said data signal comprising code configured to cause a controller to implement a method comprising:

detecting a rotational position of said electric machine with a position encoder coupled to said electric machine;

controlling an inverter comprising a plurality of switching devices, said inverter having an input coupled to a direct current bus, and an output coupled to said polyphase bus, said inverter responsive to commands from a controller coupled to said inverter and to said position encoder;

measuring a current from said direct current bus; and

capturing said current at a predefined interval of time.

27. The computer data signal of claim 26 further comprising code configured to cause a controller to implement said method further comprising:

determining a set of values representative of a magnitude of currents on each phase of said polyphase bus.

28. The computer data signal of claim 27 wherein said predefined interval of time is established when:

said electric machine is within a predefined rotational angle;

a predefined combination of said switching devices are active; and

an angle between a phase voltage and a corresponding phase current on each phase of said polyphase bus being within a range of about minus thirty to about thirty degrees.

29. The computer data signal of claim 26 further comprising code configured to cause a controller to implement said method further comprising:

determining a value representative of a torque current from said current.

30. The computer data signal of claim 29 wherein said predefined interval of time is established when:

a particular back EMF voltage waveform for a given phase of said electric machine attains its peak value;

said electric machine is within a predefined rotational angle;

a predefined combination of said switching devices are active; and

an angle between a phase voltage and a corresponding back EMF on each phase of said polyphase bus being within a range of about minus thirty to about thirty degrees.

31. The computer data signal of claim 26 wherein said electric machine comprises a permanent magnetic motor and said position encoder includes a rotor position sensor.

32. The computer data signal of claim 26 wherein said electric machine is a permanent magnet DC brushless motor characterized by a sinusoidal magnetic field excitation.

33. The computer data signal of claim 26 wherein said capturing is characterized by sampling a signal value representative of said current and said sampling is controlled by said controller to be operative only at said predefined interval of time.