Design of a Low Cogging Torque Axial Flux Multilayer Permanent Magnet Synchronous Machine for Wind Turbines Applications

For wind turbine generating systems, Axial Flux Permanent Magnet Synchronous Generators (AFPMSG) are becoming increasingly popular due to the many advantages they offer. Nevertheless, these machines suffer from the so-called cogging torque that affects the self-start ability and causes noise and mechanical vibration. Therefore, minimizing its effect is a major design concern for a reliable and smooth operation of small wind turbines. This paper presents a new method for reducing cogging torque based on stacking and shifting rotor magnets in the normal direction. First, the exact magnetic field distribution is computed using Maxwell's equations in magnetostatics. This analytical model takes into account the armature slotting effect and the multilayer permanent magnets configuration. Then, the cogging torque is computed by means of Maxwell's stress tensor. The accuracy of the proposed model is validated by FEA. Simulation results show that a substantial peak reduction can be achieved.