Study of Magnet Shifting for Reduction of Cogging Torque in Permanent Magnet Motors

It is found that if the slot number per pole is not an integer, new lower harmonics of cogging torque may be introduced when permanent magnet (PM) shifting is adopted. To reduce cogging torque, both the original and newly introduced lower harmonics of cogging torque should be reduced. In this paper, the effect of PM shifting on B_nz(B _nz is the Fourier coefficient of the square of magnetic flux density B² in the center of airgap without the effect of slot and tooth) is studied. The finite element method (FEM) and evolution strategies are combined to find the best shifting angles to reduce the original and new lower harmonics of cogging torque. It is verified cogging torque can be greatly reduced by the shifting angles calculated in this paper