Permanent Magnet Eddy Current Loss Reduction in Dual-Stator Axial Flux Permanent Magnet Machines with Sandwich Rotor

The performance of dual-stator axial flux permanent magnet machines (AFPMMs) is constrained by significant eddy current loss in the permanent magnets (PMs). In this paper, a method is proposed to reduce PM eddy current loss by employing sandwich rotor to divert the armature field harmonics. Based on the minimum reluctance principle, the feasibility of sandwich rotor preventing armature field harmonics from penetrating in PM is first investigated. Then, a general quasi-three-dimensional (3D) magnetic field analytical model based on the subdomain method is established, the effectiveness of soft magnetic material in diverting high-order armature field harmonics is quantitatively analyzed. Moreover, a PM eddy current loss evaluation model using equivalent resistance network is developed. The overall performance, including no-load back EMF, output torque, and PM eddy current loss with different thicknesses of soft magnetic material is analyzed, and guidelines are provided for the design of sandwich-rotor AFPMMs. Finally, a prototype is manufactured, the feasibility and effectiveness of the proposed method is confirmed through finite element method (FEM) and prototype experiments.