A Multilayer 2-D–2-D Coupled Model for Eddy Current Calculation in the Rotor of an Axial-Flux PM Machine

On the rotors of an axial-flux PM machine, NdFeB permanent magnets (PM) are very often placed because of their high energy density. As the NdFeB-magnets are good electric conductive, electric currents are induced in the magnets when they are exposed to a varying magnetic field. This varying magnetic field has two causes: variation of the airgap reluctance due to the effect of stator slots and armature reaction due to the stator currents. As axial-flux PM machines have an inherent 3-D-geometry, full 3-D-finite-element modeling seems necessary to calculate the eddy currents in the PM and to evaluate their corresponding losses. In this paper, however, the 1-D airgap magnetic fields of multiple multilayer 2-D finite-element simulations are combined to a 2-D airgap magnetic field using static simulations. In a subsequent step, this 2-D airgap magnetic field is imposed to a 2-D finite-element model of the PM to calculate the eddy currents and eddy current losses. The main benefit of this multilayer 2-D-2-D coupled model compared to 3-D finite-element modeling is the reduction in calculation time. Accuracy of the suggested multilayer 2-D-2-D coupled model is verified by simulations using a 3-D finite-element model.