Most small wind turbines use permanent magnet (PM) generators. The generators are usually direct-drive (i.e., no gearbox is required). Direct-drive PM generators are characterized by low maintenance and high efficiency. Small wind turbines are usually self-starting and require very simple controls. Cogging torque is an inherent characteristic of PM generators and is caused by the geometry of the generator. Cogging torque affects self-start ability and produces noise and mechanical vibration. Thus, minimizing cogging torque is important in improving the operation of small wind turbines. In this paper, we investigate three design options to minimize cogging torque: uniformity of air gap, pole width, and skewing. Although the design improvement is intended for small wind turbines, it is also applicable to larger wind turbines.

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