Impact of manufacturing imperfections on cogging torque level in PMSM

A detailed analysis of cogging torque components reveals that besides well-know native cogging torque components exist also additional cogging torque components which are provoked by assembly tolerances in mass-production. Since these two groups of cogging torque components are within reference to common applied design techniques mostly in contradiction, a minimization of the total cogging torque becomes a challenging task for motor designers. A finite element method and Fast Fourier transformation were used to study and analyse a simple model of PMSM and a real design of PMSM from mass-production which enable simulation of manufacturing tolerances and assembly imperfections. Calculations and measurements confirmed that imprecision in mass-production cause the phenomena of additional cogging torque harmonic components, which are not present in the case of a perfectly assembled motor.