Commutation control method for a switched reluctance machine

Abstract

An improved commutation control method precisely controls commutation in a switched reluctance machine with a relatively low resolution position encoder and a low cost micro-processor based controller. The control method involves the formation of a motor position signal having logic level transitions, or edges, that define base commutation signals for commutating the motor phase windings in sequence with no phase advance. When no phase advance is desired, the controller turns the phase windings on and off in time with the respective base commutation signals. When phase advance is desired, the controller turns each of the windings on and off relative to the base commutation signal for the preceding phase winding. More specifically, the turn-on and turn-off points for phase advance control are timed to occur a delay time after the edges of the base commutation signal for the preceding phase. The delay time is determined by measuring the time between two successive edges of the motor position signal, and reducing such measure by a constant value corresponding to a selected linear profile of phase advance vs. motor speed. The control method may be utilized in the context of a motor control strategy in which the motor is operated with no phase advance at low speeds, at a fixed maximum phase advance at very high speeds, and at a speed dependent variable phase advance at intermediate motor speeds.