Modeling and analysis of effects of skew on torque ripple and stator tooth forces in permanent magnet AC machines

In this paper, simplified FE-based modeling and analysis of torque ripples in permanent magnet ac machines is presented. The electromagnetic torque is calculated based on the virtual work principle, where field quantities are evaluated using a minimal number of nonlinear magnetostatic finite element solutions. A simple and fast method of incorporating the effects of the stator and/or rotor skew in the torque calculation is introduced. The proposed method requires a minimum number of 2-D finite element evaluations to estimate the electromagnetic torque profile of the skewed machine at a given load condition. This is especially beneficial for rapid evaluation of the effects of stator and/or rotor skew in large-scale design optimization studies. A fast method of evaluating stator tooth forces using a Maxwell stress tensor approach applied to the field quantities calculated using minimum number of 2-D magnetostatic finite element solutions is introduced. Finally, effects of the skew on the developed tooth forces are evaluated.