Influences of machine structure on high speed PM BLDC motor

High speed permanent magnet (PM) brushless dc (BLDC) motors have increasingly been used in a wide range of commercial and industrial applications, while low rotor loss and reliable rotor dynamic feature of the motor are essential requirements. Due to the high power densities, the high speed PM BLDC motors´ unit volume losses are high, and also it is difficult to disperse heat, thus, the rotor losses are no longer negligible compared to the conventional-speed machines and must be considered in the design process. Besides, the rotors of high speed PM BLDC motors are subject to the resonance vibration, limiting the maximum operation speed. This paper describes the design and analysis of a high speed PM BLDC motor with surface mounted magnets for a rated power of 10kW at 70,000 rpm. Influences of the stator and rotor structures as well as magnet materials on the motor´s electromagnetic performance and rotor dynamic property are analyzed. Both analytical and FEA methods are adopted to calculate the motor losses and rotor resonance modals with different motor configurations.