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 PM machine with fractional-slot windings. Two rotor losses sources are considered: the losses measured due to the slot opening (without currents in the stator) and due to the MMF harmonics (mounting a rotor with de-magnetized PMs). The rotor losses are measured at no-load and under load. In this condition, the two losses sources give rise to the rated rotor losses. It is shown that these rotor losses are lower than considering the sum of the first two measurements. This is investigated using both analytical models and FE simulations. Then the impact of the rotor geometry on the rotor losses is considered and some design considerations are reported.