Analysis of PM Eddy Current Loss in Rotor-PM and Stator-PM Flux-switching Machines by Air-gap Field Modulation Theory

This paper investigates and compares the eddy current loss induced in permanent magnet (PM) in both rotor-PM flux-switching (RPM-FS) machines and stator-PM flux-switching (SPM-FS) machines. Based on the field modulation principle, the harmonic components of both the PM field and armature reaction field are deduced, as well as the corresponding frequencies. Then, the PM loss production mechanisms due to eddy current are revealed for the RPM-FS and SPM-FS machines, respectively. Consequently, the similarities and differences between two FS machines are investigated from the perspectives of both electromagnetic torque and PM eddy current loss production mechanisms. The results indicate that the PM eddy current loss in SPM-FS machines influences efficiency dramatically. However, for the RPM-FS machine, the armature reaction field affects the PM loss more sensitively. In addition, a large PM eddy current loss is associated with high-power rating and large current density FS machines for electric vehicle application, and can be reduced by utilizing PM segmentation method.