Cogging Torque Reduction by Slot-Opening Shift for Permanent Magnet Machines

In this paper, an effective cogging torque reduction method based on shifting the slot-openings is presented. Stator teeth are divided into groups and proper slot-opening shift is applied for each group. The cogging torque can then be greatly reduced while the back-EMF waveforms remain symmetrical. No additional back-EMF harmonic components will be introduced by this method. Analytical analysis revealing the working principle of this method is given, which gives a clear guide about how this method may be applied to different permanent magnet machines.