Impact of the Rotor Yoke Geometry on Rotor Losses in Permanent-Magnet Machines

This paper presents a study on the rotor losses of surface-mounted permanent-magnet (PM) machine with fractional-slot windings. Two rotor losses sources are considered: the losses due to the slot opening (without currents in the stator) and due to the magneto motive force harmonics (mounting a rotor with demagnetized PMs). The rotor losses are measured at no load and under load. It is shown that the rotor losses under load are lower than considering the sum of the two contributions. This phenomenon is investigated using both analytical models and finite-element-based simulations. Then, the impact of the rotor geometry on the rotor losses is considered, and some design advices are reported.