Analysis and Optimization of Cogging Torque for Axial Flux Machine with Halbach Permanent Magnet Array

Axial flux permanent magnet synchronous machine (AFPMSM) has the advantages of high power density and excellent efficiency, which is widely used in electric vehicles, renewable energy and so on. The AFPMSM with yokeless and segment armature (YASA) has cogging structure that lead to cogging torque, which will deteriorate torque performance and operating conditions. Halbach permanent magnet array that has the characteristics of unilateral magnetic aggregation, which can improve the sine degree of air gap flux density. In this paper, the analytical model of YASA is derived by the conformal transformation and complex air gap flux conductance. Based on the analytical model, the air gap flux density distribution and cogging torque of YASA are calculated. The results obtained by analytical model are greet agreement with those obtained by finite element analysis(FEA). On this basis, the influence of 90 degrees Halbach permanent magnet array on the YASA's torque performance is analyzed. The analysis results show that the cogging torque and torque ripple of YASA can be greatly reduced, and the average torque can be improved by adopting a reasonable proportion of main and auxiliary poles.