Investigation of a high speed and high power density bearingless motor with neodymium bonded magnet

Bearingless motors (BelMs), which can realize magnetic levitation rotation with no mechanical contact, have been proposed and developed. In general, in high speed and high output BelMs, distributed winding structure is adopted in order to suppress iron loss, and neodymium sintered permanent magnet (Nd sintered PM) is employed to achieve a high power density. However, output power fall is caused due to long coil end of the distributed winding structure because a shaft length is limited by primary bending mode under high speed rotation. Furthermore, eddy current loss easily occurs in the Nd sintered PM because of its high conductivity. It is difficult to achieve continuous high-speed and high-output operation due to the temperature raising in a rotor. Therefore, in this paper, a high speed and high power density BelM using concentrated winding stator and neodymium bonded permanent magnet (Nd bonded PM) is proposed in order to suppress output power reduction caused by the coil end and eddy current loss generated in PM. In addition, this paper indicates analysis results of various BelM models using distributed winding structure, concentrated winding structure, Nd sintered PM, and Nd bonded PM, respectively. Comparison of these results is discussed in detail and effectiveness of the proposed structure is clarified.