The Impact of Production Tolerances on the PMSM Cogging Torque

A detailed analysis of the cogging torque components reveals that besides the well-known native cogging torque components these are also some other cogging torque components which are provoked by assembly tolerances in mass-production of permanent magnet synchronous motors (PMSM). Slightly inappropriate dimensions and misplacements of the permanent magnets (PM) introduce asymmetries in the magnetic field distribution which give rise to additional harmonic components. The finite element method and the Fast Fourier transform were used to calculate the cogging torque harmonic components for several combinations of the PM assembly imperfections. It is also shown that in some particular combinations the impact of an individual PM imprecision can compensate for those which are due to different phase shifts which may eventually decrease the cogging torque. Hypothetically, it is possible that the level of cogging torque of PMSMs with certain faults in the PM dimensions, position and magnetization can be even negligible. Considering the presented results, the harmonic components comprising the cogging torque of the mass-produced PMSMs, caused by PM imperfections can be foreseen. This enables the designers to predetermine the required manufacturing tolerances within which the level of the cogging torque will be kept within the admissible level.