Cogging Torque Minimization and Torque Ripple Suppression in Surface-Mounted Permanent Magnet Synchronous Machines Using Different Magnet Widths

Permanent magnet synchronous machines are vulnerable to significant amounts of torque ripple if they are not carefully designed. Even though minimizing cogging torque can help reduce the torque ripple, but can not definitely give rise to a low level torque ripple. This paper presents a simple solution for minimizing the cogging torque and suppressing operation torque ripple simultaneously. The principle of that simple solution is illustrated, where a magnet with different width is used so that the flux density distribution in the machine is substantially changed. The magnet widths for minimizing cogging torque are obtained by using an analytical model. The influence of magnet widths on operation torque ripple and average operation torque is examined by using Finite Element Analysis (FEA) which gives more preciseness to calculations. It is found that the cogging torque and operation torque ripple can be greatly reduced, but with slight average output torque reduction. At last, the Unbalance Magnetic Pull (UMP) is examined, indicating that the presented method can substantially increase the UMP due to the asymmetric distribution of magnets.