Reduction of cogging torque in AFPM machines via sinusoidal shaped magnet

Cogging torque reduction is an essential concern in the permanent magnet electrical machine design, especially at low-speed applications. Minimizing cogging torque is required for better performance of the machine at starting with a low amount of torque ripple and noise problem. Numerous approaches have been reported in the literature for reducing cogging torque in radial flux permanent magnet (RFPM). However, few of these methods can be applied because the geometrical configuration, magnetic field distribution, and flux path orientation are dissimilar in both of them. Also, these approaches may increase either manufacturing cost or the complexity of the machine structure. This study investigates the cogging torque effect on AFPM with surface-mounted sinusoidally shaped magnets. The result of applied magnet shapes is compared with other cogging torque reduction techniques such as PM skewing. 3D Finite-Element Method (FEM) is utilized for comparison. FEM results show a remarkable decrease in the amount of cogging torque by the sinusoidally formed magnet. Additionally, the resultant distribution of flux density in the air-gap region becomes almost sinusoidal. Hence, the proposed method effectively reduced the cogging torque.