Computationally Efficient Method for Identifying Manufacturing Induced Rotor and Stator Misalignment in Permanent Magnet Brushless Machines

A computationally efficient method is presented to investigate 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. The hybrid analytical / FEA method utilizes superposition of a pole transition over a single stator slot and is used to predict the effect on cogging torque of eccentricity misalignment in combination with pole and slot placement inaccuracies. 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 supporting the analytical data indicating that static and dynamic eccentricity produce first and second order sidebands about the rotor and stator affected harmonics respectively. There is good agreement between the hybrid analytical method, FEA and measured experimental data.