High-speed IPM Motors with Rotor Sleeve: Structural Design and Performance Evaluation

This paper deals with the structural design of sleeves for high-speed interior permanent magnet (IPM) synchronous machines. Wrapped IPM (WIPM) motors are a new player in the field of high-speed e-machines for traction, where a retaining sleeve is used to hold the magnetic poles in place against centrifugal forces, replacing the role of conventional iron bridges. The wrapping technique, originating from surface-mounted permanent magnet rotors, is believed to push speed limitations to new heights, as demanded by the increasing requirements of the automotive industry. By developing an equivalent rotor geometry of the WIPM rotor, an analytical model is formulated to evaluate the stress in the rotor and to provide a quick and intuitive tool for the sleeve design. The results are successfully validated by structural finite element analysis. Also, the output figures of a WIPM machine are compared to those of an equivalent IPM machine with iron bridges.