Magnet eddy current loss reduction in a 3-slot 2-pole permanent magnet machine

Magnet eddy current loss is very important for any types of permanent magnet machines, especially for high-speed permanent magnet machine since it increases significantly with rotating speed and has a great effect on the temperature of magnet material, and hence the electromagnetic performance, as well as irreversible demagnetization of the magnets. In this paper, a new method is proposed to reduce the rotor permanent magnet eddy current loss. The auxiliary slots with optimized size and position are proposed. By this mean, the asynchronous spatial harmonics caused by the armature reaction and the conventional slots can be partially cancelled by the harmonics produced by the introduced auxiliary slots. It is proved that the rated on-load magnet eddy current loss can be reduced as much as 85% by this method while the rated on-load torque is only decreased by 4.8%.