Improvement of accuracy in cogging torque computation in fractional-slot flux modulating permanent magnet machines

It is well-known that cogging torque is difficult to be precisely computed in fractional-slot permanent magnet (PM) machines even using finite-element method (FEM). In this paper an improved and simple method of cogging torque computation with normal-size mesh elements in FEM is presented. The main merit is that the accuracy is guaranteed, complicated mesh refinement work is avoided and computing time is reduced. As an example, the cogging torque of a fractional-slot flux modulating PM machine is computed and the simulation results serve to validate the effectiveness of this proposed method.