An analysis and characteristics of a permanent magnet type bearingless motor

Abstract

Super high speed and high power electric machines are required for turbomolecular pumps and spindle drives. High rotational speed and high power drives can be achieved with bearingless motors. In this paper, a bearingless motor with principles of permanent magnet type synchronous motors is proposed. High power factor and high efficiency can be expected in permanent magnet type bearingless motors. The proposed bearingless motor is a 4-pole permanent magnet synchronous motor, in which additional 2-pole windings are wound together with 4-pole motor windings in stator slots. With currents of 2-pole windings, radial magnetic forces are produced to support a rotor shaft. Principles of radial force production of surface-mounted permanent magnet bearingless motors are analyzed mathematically. The relationships between radial forces and the permanent magnet thickness were derived. From these relationships, the optimal permanent magnet thickness to produce radial forces efficiently is found. A test machine was built to confirm relationships of radial forces, currents and voltages. © 1995, The Institute of Electrical Engineers of Japan. All rights reserved.