Position detection for a brushless DC motor

Electricity: motive power systems – Switched reluctance motor commutation control

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318138, H02K 2900

Patent

active

050014056

ABSTRACT:
The present method and apparatus detects the position with an accuracy of .pi./m electrical radians (where m=the number of motor phases) within one electrical period, and provides enough information to be able to start in the correct direction with certainty. After starting the motor in an open loop mode of one or two steps, starting the rotor in the correct direction, the 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 difference between the induced voltages 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 when polarity currents should be applied to each phase to reliably and certainly start the motor in the proper direction.

REFERENCES:
patent: 4673849 (1987-06-01), Sears et al.
patent: 4678973 (1987-07-01), Elliott et al.
patent: 4752724 (1988-06-01), Radziwill et al.
patent: 4876491 (1989-10-01), Squires
patent: 4879498 (1989-11-01), Shinohara et al.
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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