New cogging-torque reduction method for brushless permanent-magnet motors

We present a new design method for reducing cogging torque in brushless permanent-magnet (PM) motors. In our method, the auxiliary slots are put on the pole face of the magnetizing yoke, which results in a not fully magnetized zone (NFMZ) at the PM. Through Fourier expansion of the field and armature functions, the position and shape of the NFMZ that eliminate the cogging torque are found. In an example, we discuss the effectiveness and applicability of the new method.