Asymmetric PM Eddy Current Loss and Temperature Distributions of SPMSMs

This paper investigates the mechanism of asymmetric permanent magnet (PM) eddy current loss and temperature distributions of surface-mounted PM synchronous machines (SPMSMs) with different slot/pole number combinations for the first time. A finite element analysis (FEA) based harmonic restoration method is utilized to evaluate and quantify contributions of individual armature reaction spatial harmonics to PM eddy current loss and temperature distributions for 12-slot SPMSMs with different pole numbers. It shows that there is one dominant armature reaction spatial harmonic contributing to the majority of PM loss for each SPMSM with different slot/pole number combinations. The average PM loss distribution is symmetrical to the center line in circumferential direction with armature reaction or PM magnetic field only, while the interaction between the armature reaction and PM field causes the asymmetric PM loss distribution. Besides, the maximum loss density in one PM pole tends to move from the circumferential center to the edge when the rotor pole number increases. Consequently, the resultant PM local hotspot temperature has been calculated through 3-D thermal finite element method, which shows the same trend as loss density distribution. Finally, two prototypes are manufactured, and the corresponding electromagnetic and thermal tests are carried out to verify the validity of the FEA simulation.