Influence of pole pair combinations on high-speed bearingless permanent magnet motor performance

Extending the speed range of bearingless motors into the high-speed domain requires certain restrictions of the general bearingless motor design rules. An inadequate choice of the number of poles for the drive and the levitation system leads to large parasitic lateral forces generated by field harmonics and excessive rotor eddy-current losses caused by the asynchronously rotating levitation field. Special design guidelines for high-speed bearingless motors are obtained from analytical equations and finite element (FE) calculations and are applied to a 40 kW, 40 000 rpm bearingless prototype motor.