Research On The Method Of Reducing Torque Ripple For Surface-inset Permanent Magnet Motor Based On Magnet Shifting

Permanent magnet motors have been widely applied in various occasions due to its high efficiency and high torque density.For some demanding applications,such as servo motor and electric vehicle,reduction of torque ripple has been one of key technologies to ensure stability of permanent magnet motor.Nowadays,many methods have been proposed to reduce torque ripple effectively.However,the average torque may decrease with the reduction of torque ripple.Moreover,most studies consider only reduction of cogging torque but ignore other torque ripple components.In this paper,with a surface-inset permanent magnet(SIPM)motor as the research object,cogging torque of individual repeating unit is separated accurately based on principles of cogging torque.Then,the magnet shifting method to reduce torque ripple is further researched.At the same time,both expression of torque with magnet shifting and shifting angle are deduced and improved.By reasonably choosing repeating units and shifting ways,optimal balance between torque ripple and average torque is realized.Also,electromagnetic structure with low torque ripple is designed for SIPM motor.Furthermore,a method of auxiliary migration design is introduced to enhance average torque,thus maintaining the torque density.In addition,the size parameters of SIPM motor is optimized with the aid of sensitivity analysis,and the final model is established.Comprehensive characteristic with both low torque ripple and high average torque is achieved,which provides a new thought for reduction of torque ripple.The main contents of study are as follows: 1.According to the duplication superposition of cogging torque,the generation mechanism of cogging torque is analyzed.The expression of cogging torque based on Fourier series is deduced.Also,principle of magnet shifting to reduce cogging torque is explained,and the shifting angle is studied and deduced.Considering the edge effect,the precise separation of cogging torque from individual repeating unit for SIPM motor is realized.Meanwhile,the theoretical analysis of magnet shifting is verified by Finite Element method.2.As for different sources of torque ripple,the torque expression with magnet shifting is analyzed and improved.The unity of reducing different sources of torque ripple by magnet shifting is studied,and then three schemes are proposed and compared.Finally,an optimal scheme is determined to realize ideal suppression with low torque ripple and low torque loss.3.Based on the mechanism of magnet shifting,a method of auxiliary migration design for SIPM motor is proposed.In this method,the reluctance torque-angle characteristic is shifted through reasonable design of auxiliary slots.As a result,the average torque of SIPM motor is maintained or even enhanced without other extra torque harmonics.4.After determining SIPM motor's structure,some parameters are chosen to be optimized by sensitivity analysis,targeting at both low torque ripple and high average torque.Finally,the finite element model of SIPM motor is established,and then the back-EMF and torque performance are analyzed.5.A five-phase SIPM prototype based on auxiliary migration design is manufactured.And,the related experimental platform is introduced and built.Back-EMF and torque performance is tested.Great agreements are achieved between finite element results and measurement results,which verify the correctness and effectiveness of auxiliary migration design.