Analysis of Thrust Ripple of Permanent Magnet Linear Synchronous Motor with Skewed PMs

The thrust ripple of Permanent Magnet Linear Synchronous Motor (PMLSM) at load can reach 10% average thrust, which deteriorates thrust performance. To reduce the thrust ripple, two methods of optimizing the primary length and skewing are widely adopted during PMLSM design. In this paper, the effect of skewing technology is investigated. Based on 2D finite element method (FEM), the characteristics of thrust ripple at open circuit and on load are analysed respectively. It is found that the main components of thrust ripple are 2nd, 4th and 6th harmonics and that the effectiveness of skewing on load is reduced compared with that of at open circuit due to magnetic saturation and electromagnetic thrust ripple. Moreover, By comparing the effectiveness of skewing accounting for step skewing numbers and slot/pole number combinations, the optimal skewing angles are obtained, which is benefit for PMLSM design, and the thrust ripple can be decreased less than 4.4% with skewing 60 electrical degree. In the end, a coefficient is given to value the reducing of average thrust after skewing.