Research On Analysis And Reduction Of Thrust Ripple In Permanent Magnet Linear Synchronous Machine

Due to the merits such as high force density,high speed operation,high efficiency and accurate positioning,permanent magnet linear synchronous machine(PMLSM)has been increasingly applied in high-grade CNC machine tool,semiconductor industry and high speed transportation system.This dissertation is focused on the analysis and suppresion of thrust ripple in PMLSM and the main contents are summarized below.A periodic model of PMLSM with a virtual slot is presented.Based on the Equivalent Magnetizing Current(EMC)method,subdomain method and Schwarz-Christoffel transformation,the analytical model for magnetic field and force calculation in PMLSM is built.Comparing with numerical results obtained by finite-element method,the accuracy of the analytical model is validated.Based on finite element analyses,the on-load thrust ripple of PLMSM is separated into three components:thrust ripple contributed by permanent magnets,reluctance thrust ripple,and on-load detent force.The influence of electric loading on each ripple component has been studied,which illustrates the increase of thrust ripple with current increase.By using frozen permeability(FP)method,a hybrid FE-analytical method is proposed for fast calculation of on-load detent force,which only needs to calculate the thrust force and flux linkage of two FE models.One is the nonlinear model with both PM and armature current excitations,and the other is the linear model with armature current only by using the FP method.The predicted result is compared with those of two existing approaches,which validates that the detent force can be calculated properly under different load conditions by the proposed method.Various methods to minimize thrust ripple in PMLSM have been studied comprehensively.By changing the primary length and step-skewed auxiliary irons,the 2nd and 4th harmonics of detenr end force in PMLSM are eliminated.With the smooth formed edge shape,all the harmonics of thrust ripple is weakened.Two PMLSMs with different windings arrangements are compared in terms of the cogging force.Based on the genetic algorithm(GA),the shape of the side teeth is optimized globally and the detent force of PMSLM with double-layer concentrated nonoverlapping windings is greatly reduced.The method of skewed PMs to reduce thrust ripple is investigated under different load conditions.The weakening effect of flux gap and shaping the end teeth on thrust ripple for four modular permanent magnet linear machines(PMLMs)with E-core and C-core primary segments and 12-slot/13-pole and 12-slot/14-pole slot/pole combinations is investigated.Moreover,the influences of flux gap width on the electromagnetic performances and power losses of the four modular PMLMs have been analysed.The 12s/13p E-core modular PMLM is proved to be the best type among these four modular machines.The thrust ripples of the novel segmented structure PMLSM and traditional PMLSM are studied comparatively.The analytical models of the two PMLSMs are established,and the air gap flux density,open-circuit flux linkage,back electromotive force,and average thrust force of the two machines are calculated.Finally,two PMLSM prototypes are manufactured and experiments are conducted.The results show that the novel segmented structure PMLSM has lower thrust ripple and the same average thrust force.