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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 i

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.

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What is claimed is: 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 sw

What is claimed is: 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.