Mitigation of PM Eddy Current Losses Using Offset Windings in Coreless AFPM Machines

Permanent magnet eddy current losses can become substantial in coreless stator axial flux permanent magnet (AFPM) machines operating at high speeds and under high electric loading, potentially leading to elevated temperatures and an increased risk of demagnetization. This paper investigates the origins of these losses through a detailed harmonic analysis of the winding factor and introduces a mitigation strategy. The proposed method utilizes two-layer offset windings, effectively minimizing undesirable armature flux harmonics through harmonic interaction between the offset layers. Two cases are studied: one in which each stator layer is connected to a separate inverter and another in which both layers are connected in parallel and driven by a single inverter. Three-dimensional finite element analysis (FEA) results demonstrate a significant reduction in PM eddy current losses achieved using this approach. Further PM eddy current loss mitigation is explored through the combined use of winding offset and segmented magnets, demonstrating that these losses are reduced by 95% compared to the original design.