Composite PM Rotor Design and Alternating Flux Density Harmonic Component Analysis of a 200 kW High-Speed PMSM Used in FESS

The flywheel energy storage system (FESS) is a short-time high-power energy storage technology widely used in various fields. To improve speed and reduce air friction loss, the rotor of the high-speed permanent magnet synchronous machine (HSPMSM) used in FESS operates at a magnetic suspension state in vacuum. It is very difficult for the rotor to dissipate heat, which may even lead to PM demagnetization. In this paper, a 200 kW 20000 r/min HSPMSM is designed for FESS of an uninterruptible power supply (UPS), and a composite PM rotor with multilayer sleeves is proposed. Distinct from the previously proposed retaining sleeve design of the HSPMSM rotor, a silicon steel sleeve is added in the composite PM rotor, which can provide a bypass for alternating flux density harmonic components in the rotor and prevent them from entering the alloy sleeve and PM. Moreover, a post-processing method of finite-element analysis (FEA) results is proposed to obtain the alternating harmonic components in the rotor and further analyze the suppression effect of the silicon steel sleeve on them. As the silicon steel sleeve is introduced, the amplitudes of alternating harmonic components are effectively suppressed, which can mitigate the eddy current loss and heat generation of the HSPMSM rotor from the source.