Analysis of hunting in Synchronous Hysteresis Motor

Abstract

The Synchronous Hysteresis Motor has an inherent instability when it is used to drive a gyroscope wheel. The motor ideally should spin at a constant angular velocity, but it instead sporadically oscillates about synchronous speed. This phenomenon is known as 'hunting'. This problem produces current ripples at the motor's electrical terminals and induces noise on the sensors that monitor gyro activity. This thesis examines the cause of hunting by deriving the motor's torque characteristics from first principles. It also derives a scheme for suppressing hunting by monitoring the motor's current as an indicator of drag angle and using it to modulate the motor's drive frequency. Explanation of the circuit that successfully implements this scheme is included and lab results are shown to verify the working theory.