Simple and accurate analytical estimation of slotting effect on magnet loss in fractional-slot surface-mounted PM machines

This paper analytically predicts the slotting effect on the magnet losses due to open-circuit and armature reaction magnet fields in fractional-slot surface-mounted permanent magnet machines. An improved relative permeance model for predicting the open-circuit magnet loss is developed based on the 2-D magnetic field model, relative airgap permeance and Carter coefficient, while the conventional one uses a 1-D field model and neglects the Carter coefficient. Extensive comparison shows that the improved model has much higher accuracy. For the magnet loss due to armature reaction, the slot opening factor is used for evaluation of the slotting effect. The investigation shows that the slotting can reduce magnet loss due to armature reaction, but increases the open-circuit magnet loss. The finite element results confirm the analytical predictions.