Cogging torque reduction in axial-flux permanent magnet wind generators with yokeless and segmented armature by radially segmented and peripherally shifted magnet pieces

The inherent cogging torque component of the PM generators can cause problems at the start-up of wind turbines. To improve the operation of wind turbines, especially at low starting speeds, the wind generator cogging torque should be minimized. In this paper, an effective and practical approach is proposed for cogging torque reduction in the AFPM generators with yokeless and segmented armature (YASA). The proposed approach is based on the dividing magnets radially and shifting the magnet pieces peripherally with an appropriate shifting angle. Using a series of 3-D FEA simulations, the proposed approach is compared with the two conventional approaches, i.e. the magnet skewing approach and the selecting an appropriate magnet pole arc to pole pitch ratio, according to the cogging torque reduction and the negative impacts on the generator loadability. It is shown that using the proposed approach, the generator cogging torque can be greatly reduced (about 87%). Also, it is shown that compared with the other studied cogging torque reduction techniques, the proposed approach has less negative impact on the generator loadability. Some of the simulation results are verified using the experimental tests.