Effect of radial asymmetry of magnets in surface-mounted permanent magnet motors on cogging torque

During the mass production of surface-mounted permanent magnet motors the rotor and stator geometrical dimensions usually deviate from their nominal values due to manufacturing tolerances which impact machine performance. One such common tolerance can be noticed in the placement of the permanent magnets on the rotor surface which creates new orders of cogging torque. Finite element models can be used to analyze the cogging generated due to the asymmetry in the magnet placement. However, it is time consuming to study the effect of imbalance of each magnet numerically since periodicity and symmetry conditions cannot be used to reduce the model. Therefore, in this paper an analytical model is presented to study the effect of such imbalance on the cogging torque. The model is validated against a finite element model and also with experimental results.