The Measurements And Analysis Of Core Losses for a 4kW Bearingless Permanent Magnet Slice Motor

As bearingless motors have all advantages of magnetic bearings, they play an important role in solving difficult problems of electric drives. The simplest and most versatile form of bearingless motor is the bearingless slice motor. When the rotor, which carries an impeller and is levitated within the hermetically closed pump housing, turns with a high rotational speed, liquid is pumped from the inlet to the outlet. This type of magnetically levitated centrifugal pump system has a wide range of applications like in life science, chemical processing industry, semiconductor manufacturing industry, foodstuff processing industry and so on. The technology of small power bearingless slice motors is already mature and bearingless pump systems have been applied in industries. However no bearingless slice motors over 1.2kW have been produced. In this paper, a system of bearingless permanent magnet slice motors is introduced; a 3-phase permanent magnet slice motor with the power around 4kW is set up; theoretical formulas of core losses in bearingless motors are introduced and the core losses are investigated. Based on experiments and analysis, it has been found that choosing an appropriate permanent magnetic rotor, a back iron, and appropriate isolation between iron cores and a back iron can reduce core losses of the motor. And core losses account for only about 3~4% of total power, when the bearingless permanent magnet slice motor works at rating speed 7 700rpm.