HIGH PERFORMANCE VARIABLE RELUCTANCE DRIVE: A NEW BRUSHLESS SERVO.

Synchronously commutated variable reluctance machines have a history stretching back 150 years to the first 'Electromagnetic Engines'. In this decade, because of their inherent robustness and simple unipolar drive requirements, they have again been applied, this time as brushless industrial drives in the kw range. The system described is distinguished from other 'stepper' motors by its power and speed range, and from other high power reluctance drives by its quiet operation and low torque ripple. This article describes the special adaptations and control strategies that make possible high-performance servo application. A magnetic design is employed to control torque sensitivity as a function of angle. Current is shaped to vary with angle in a complementary manner. Torque contributions from two phases sum to a constant. The system does not require costly resolvers or delicate encoders.