Calculation of Eddy-current loss in the magnets of an Axial-Flux PM machine with a fractional-slot concentrated winding

On the rotors of an axial-flux PM machine, NdFeB permanent-magnets 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. In this paper, the eddy-current losses are calculated for an axial-flux PM machine, which requires a full 3D-model for accurate prediction of the magnet losses. To save calculation time and effort, two 3D finite element models are coupled by transfer of the magnetic vector potential. By doing this, calculation time is decreased without affecting the accuracy. Afterwards, the introduced coupled 3D finite element model is used to study the effect of segmentation on the eddy-current losses in the permanent-magnets of an axial-flux PM machine simulating different segmentation grades