Cogging Torque Minimization in Low-Speed Transverse Flux Permanent Magnet Generator Using Improved Skewing Techniques

The transverse flux permanent magnet machine is known for its high torque density, simple winding, and high pole number. These unique features enable its utilization in a variety of low-speed applications. However, in direct-drive applications and small-scale wind turbines, high-cogging torque is one of the main concerns. In this paper, a transverse flux permanent magnet generator with rotary structure and magnetic shunts is designed and prototyped to validate the FEM results. To study the effects of the cogging torque, the 3D magnetic equivalent circuit of the designed generator is obtained. Then, numerical analysis based on the displacement of the torque waveform is proposed to eliminate the major harmonics of the cogging torque. This displacement can be employed by skewing the stator U-shaped cores. A geometric scheme is proposed to calculate the optimum skew angle to minimize the cogging torque. FEM results indicate that the proposed method for the optimum skewed angle calculation is an effective solution to reduce the cogging torque. According to the results, by applying the skewed angle in U-shaped cores, the cogging torque decreases by 55.85%.