Potentials and limits of high speed PM motors

This paper illustrates the potentials and limits of high-speed permanent-magnet (PM) motors. The effect of the material choice, including PM, stator core and retaining sleeve is highlighted. Slotted and slotless configurations are taken into account and compared, computing magnetic, electrical, mechanical and thermal quantities by means of both an analytical and a finite element approach. In particular, the thermal and the PM demagnetization limits and the rotor losses are evaluated. A criteria of optimisation of the motor structure is described, with the diameter ratio and the iron flux density as main design variables.