Five-axis rotor magnetic suspension with bearingless PM motor levitation systems

In this work, two bearingless permanent magnet (PM) synchronous motor prototypes with different mechanical and electrical ratings are presented from the design and performance point of view. The first prototype Conical-BM was designed for a rotational speed of nN = 18 000 rpm and a mechanical power of PN = 1 000 W. It is a novel type of bearingless PM synchronous motor, which consists of two conical air gap bearingless PM half-motors, mounted on a single shaft. Through this developed magnetically levitated drive arrangement not only the radial magnetic bearings, but also the axial active magnetic bearing is replaced by the bearingless system, without any additional motor windings. This designed drive is therefore able to actively stabilize and control all six degrees of freedom of the rigid rotor, without using any active magnetic bearings. The second prototype Cylindrical-BM has an increased mechanical output power of PN = 40 kW at a rated speed of nN = 40 000 rpm, being a suitable drive for compressors and for high-speed tooling machines. It has a hybrid five-axis levitation system, consisting of a cylindrical air gap bearingless PM motor and a combined axial-radial magnetic bearing from the company Levitec (Lahnau, Germany). This prototype was designed and built at the Institute of Electrical Energy Conversion during the research work of Mr. Dipl.-Ing. Tobias Schneider. Mainly due to technical control problems of the bearingless levitation system, only low rotational speeds have been reached during Mr. Schneider's work. The prototype was optimized by the author regarding the control of the bearingless magnetic levitation system, and measurements were performed over the entire speed and power range. Based on the measurement results of both prototypes, the analytical calculation models are verified. Additionally, it is proven that the bearingless PM motors have a very good motoring behaviour and that the magnetic levitation performance parameters are comparable with the ones of the active magnetic bearings.