Design techniques for reduction of reluctance torque in brushless permanent magnet motors

Reluctance torque is often a principal source of vibration and control difficulty in motors, especially at low speeds and loads. This paper examines two motor design techniques, stator tooth notching and rotor pole skewing with magnetic pole shaping, for reduction of reluctance torque, and the effect of each method on the output torque. Prediction of results was performed by finite element analysis of the airgap flux, Maxwell stress method and Fourier decomposition to calculate the periodic reluctance torque. The analyses show that the reluctance torque can be nearly eliminated by the suggested designs, with minimal sacrifice of output torque