New design of radial displacement sensor for control of a switched reluctance motor without bearings

Accurate and fast detection of the radial displacement of rotor position is one of the key factors for successful bearingless control. In this paper, a new design of displacement sensor is proposed, which has a simple structure and inherent low-cost. The basic principle of the proposed sensor is that the airgap difference between two opposite sides can be reflected by an EMF difference of two opposite coils, detected by injecting high frequency PWM. The detection is designed to make the sign of output reflect the direction of displacement and two methods for displacement signal output are presented. Simulation is done by using Pspice software and an experimental sensor and detection circuit is built The results from simulation and experiment confirm the design. In addition, the sensor is also tested to balance the radial force in a real motor successfully.