Investigation of Sinusoidal Shaped Rotor to Reduce Torque Ripple in Axial Flux Permanent Magnet Machine

Abstract

Cogging torque is one of the main reasons for torque pulsation in AFPM machines that arises due to the force of attraction between stator slots and rotor poles thus adversely affecting the smoothness of output torque. In this paper a rotor shape for the axial flux internal rotor (AFIR) PM machine is proposed for cogging torque reduction and smoothing the output torque. In this research, the reduction in cogging torque is accomplished in two stages. In the first stage, a sinusoidal magnet shape is proposed having less cogging torque as compared to conventional and arced shaped magnet. In the second stage, the magnet overhang technique is used in the optimization process of the machine to further improve the performance characteristics. The optimization process comprises of a selection of variables, Latin hypercube sampling (LHS), model approximation by kriging method, and Genetic Algorithm (GA) to get optimum values of variables. Output results of proposed and optimized models are also compared to demonstrate that the optimized model has reduced torque ripples and improved average output torque. Models are simulated using 3D finite element analysis (FEA) for comparative analysis.