Optimal winding arrangement of a surface-mounted permanent magnet motor for torque ripple reduction

We are aiming to develop a high precision micro-milling machine with a high speed spindle which is driven by a permanent magnet motor and supported by active magnetic bearings. The torque ripple, however, has influence on the positioning accuracy. As a first step of this study, we investigate torque ripple reduction of a permanent magnet motor. This paper considers optimal winding arrangement of a 2-pole/12-slot surface permanent magnet motor with double-layer distributed winding to minimize magnet torque ripple. The magnet torque with double-layer winding is theoretically derived by considering the spatial harmonics of the MMF distribution. The torque ripple with 6wt variation is theoretically zero when the ratio of the secondary winding with respect to the primary winding is approximately 0.37. In addition, the step skew of the permanent magnet is investigated to reduce the cogging torque, based on three-dimensional finite element method analysis. The experimental results demonstrate that the optimal double-layer winding configuration with the winding ratio of 0.37 is effective to reduce the magnet torque ripple.