Cogging Torque Reduction in Permanent Magnet Machines

This paper examines two methods of reducing cogging torque in permanent magnet machines: magnet shifting and optimizing the magnet pole-arc. The methods were applied to existing machine designs and the performance calculated using finite element analysis (FEA). Prototypes of the machine designs were constructed and experimental results obtained. It is shown that the FEA predicted the cogging torque to be nearly eliminated by this method but in the prototype there was some residual cogging due to manufacturing difficulties. In both cases, the back EMF was improved by reducing harmonics while preserving the magnitude