Position detection for a brushless DC motor without Hall effect

Details Position detection for a brushless DC motor without Hall effect Position detection for a brushless DC motor without Hall effect

1990-06-29

1993-10-19

Smith, Jr., David

Electricity: motive power systems

Switched reluctance motor commutation control

318138, H02K 2900

Patent

active

052549143

ABSTRACT:
The present method and apparatus detects the rotor position of a brushless DC motor with an accuracy of .pi./m electrical radians (where m = the number of motor phases) within one electrical period, and provides enough information to enable starting the motor in the correct direction with certainty. After starting the motor in an open loop mode of one or two steps, a closed loop mode may be switched on, using a dynamic indirect position detection as is already well known in the technology. More specifically, the position at start is determined by the injection of short current pulses in different motor phases, each phase or pair of phases being energized first by a pulse of one polarity and of the opposite polarity. The sign of the time difference between the decay times of the induced voltages in the un-energized phase is detected. By performing a succession of these tests on different phases or pairs of phases of the standing motor, a table of results is established which clearly defines the position of the rotor relative to the motor phases. The same table then defines what polarity currents should be applied to each phase to reliably and certainly start the motor in the proper direction.

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P. P. Acarnley et al., "Detection of Rotor Position in Stepping and Switched Motors by Monitoring of Current Waveforms", IEEE Transactions on Industrial Electronics, vol. IE-32, No. 3, Aug. 1985.

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