Identifying cogging torque harmonics affected by misalignment in axial flux fractional pitch PMSM

Cogging torque in fractional pitch PMSM is minimized when manufacturing induced errors are also minimized. This paper investigates additional cogging torque harmonics resulting from misalignment of the rotor and stator caused by assembly and manufacturing tolerances in an axial flux, fractional pitch PMSM. A simulation method utilizing superposition of a single magnet / single slot interaction has been used previously to decouple manufacturing errors such as magnet placement and stator non-uniformity. This work extends on that previously published by inducing varying degrees of assembly misalignment of the stator and rotor to determine the effect on cogging torque waveforms. Experimental data is presented indicating that increasing degrees of offset misalignment leads to increasing sideband magnitudes in the frequency spectrum. There is good agreement between the simulation method and measured data.

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