Step skewing method for thrust ripple reduction of PMLSM
CAI Jiong-jiong1,2, LU Qin-fen1, LIU Xiao1, YE Yun-yue1
1.College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China; 2. Department of Electrical and
Electronic Engineering, Zhejiang Institute of Mechanical and Electrical Engineering, Hangzhou 310053, China
The characteristics of thrust ripples of permanent magnet linear synchronous motor (PMLSM) were analyzed to effectively reduce thrust ripples, optimize positioning accuracy, thrust accuracy and speed accuracy. The results show that after fractional slot design and armature length optimization, the 2nd, 4th and 6th harmonics, not the 12th harmonic of cogging force, become the main components of the thrust ripples. After the study of the advantage of step skewing, the skewing coefficients of harmonics and the weakening coefficients of electromagnetic thrusts were investigated. Then the best skewing angle was discussed. It is concluded that the skewing angle selection principles are different for rotary and linear motors because of different ripple origins and performances. At last the analysis method for asymmetric skewing model with a two-dimensional finite element method（FEM）was introduced, with which the skewing coefficients with different step numbers and skewing angles were computed. The resulting curves validate the theories for step selection and skewing angle optimization. It shows that PMLSM with 2-step magnets of 30 degree skew angle can reduce the thrust ripple to 61.3% while keeping the output thrust at 96.8%.
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