Thrust Ripple Influence of Fractional-Slot Permanent Magnet Linear Motors

For permanent magnet linear motor (PMLM), the thrust ripple is bigger compared with the conventional rotary motor, which deteriorates the thrust performance. Based on FEM, the influences of thrust ripple are investigated including slot/pole combination, magnetic load, electric load and end tooth. First, the PMLM topologies with four feasible slot/pole number combinations are introduced and corresponding winding factors are calculated. Then, the thrust ripple is comparatively analysed under different magnetic load and electric load. Finally, the end tooth of motor structure is optimized by the global optimization method to minimize the thrust ripple. It is shown the thrust ripple can be much reduced by adopting asymmetry end tooth structure, and the optimal slot/pole combination is that the difference between pole and slot is two.