Method of reducing cogging torque in permanent magnet motor

Two methods of reducing cogging torque, namely, the stator tooth notching and the two rotor pole stacks shifting are presented. The calculation formula of the cogging torque are derived by the Fourier decomposition and the virtual displacement method. Based on the analysis of the harmonics, the mechanism of the present methods and the effect of the methods on the waveforms of the cogging torque are clarified and analyzed. Some important conclusions are pointed out: the number of the notches should be chosen to make the 6q equal to an odd; the dimension of the notches and cutting off pole corners can affect the waveforms of the cogging torque; and the basic component of the cogging torque can be reduced by shifting the pole into two stacks.