Reduction of eddy-current losses by circumferential and radial PM segmentation in axial flux permanent magnet machines with fractional-slot concentrated winding

Eddy current loss is a typical problem in permanent magnet machines especially in machines equipped with fractional-slot concentrated windings. PM segmentation which cut the circulating path of eddy current in radial flux PM machines have been widely studied in literature to reduce this loss. Both circumferential and axial magnet segmentations were evaluated by an analytical method concerning the skin effect in [1], and it was pointed that PM segmentation may increase rather than reduce the eddy current losses when skin depth is smaller than pole-arc width and magnet thickness. The influence due to the rotor shape in the loss-reduction effect is studied by the 3D finite-element analysis considering PWM carrier harmonics in [2]. Analytical calculation of eddy current loss due to space harmonics has been given in [3-5] to investigate the effect of circumferential or axial PM segmentation for loss reduction. The reported analytical methods to calculate eddy current losses were validated by 2-D time-stepping finite element (FE) analysis [3, 4] and by 3-D magneto-static FE analysis[5], for cases when skin depth at the frequency of interest is greater than both pole-arc and radial dimensions of magnets.