Study on radial suspension forces of bearingless permanent magnet slice motor based on accurate inductance model

Abstract

An accurate mathematical model of radial suspension forces for a bearingless permanent magnet slice motor (BPMSM) is of great significance to levitate the rotor stably and to improve the control accuracy of radial suspension force. In this paper, after a brief introduction on the suspension principle of the BPMSM, the accurate inductance model of two sets of stator windings (torque windings and bearing windings) is deduced. Based on the accurate inductance model and taking rotor eccentricity into account, a complete and precise mathematical model of radial suspension forces of the BPMSM is obtained. In order to confirm the validity and feasibility of this mathematical model, the experiments are carried out on a 4kW prototype of the BPMSM. The experimental results show that the control system designed by using this method has high control accuracy of radial suspension force, strong capability of resisting disturbance, and good static and dynamic performance. Index Terms-bearingless permanent magnet slice motor (BPMSM), radial suspension force, inductance, mathematical model I. INTRODUCTION BPMSM (bearingless permanent magnet slice motor) is a new type of bearingless motors, whose axial length of rotor is small compared with the diameter, in this case, the stabilization of slice rotor for the axial and two tilt deflections (left-right tilt and forth-back tilt) can be achieved by passive suspension forces and the active stabilization degrees are reduced to the two radial deflections only [1-2]. The BPMSM not only has all the advantages of magnetic bearing such as mechanical contact-free, no mechanical noise, no wear, no lubrication, long operating life, high speed and precision, but also has the superiority of small structure, high power density and high stability. The absolute stabilization of slice rotor makes high sealing available, therefore, the BPMSM has a wide range of applications in the fields of special electric drives such as high-speed-precision mechanical processing, aeronautics and astronautics, life science, canned pumps, semiconductor and biotechnology industries [1]-[5]. It's indispensable for a bearingless motor's high-precision operation to establish an accurate model of radial suspension forces. Over the past decades, some typical models of radial suspension forces have been put forward. In literature [6], the model of radial suspension forces for the single-windings BPMSM is proposed on the basis of equivalent circuit method, however, the coupling is serious because the magnetic field of torque windings and