Analysis and Optimization of Cogging Torque in Yokeless and Segmented Armature Axial-Flux Permanent-Magnet Machine With Soft Magnetic Composite Core

Yokeless and segmented armature (YASA) axial-flux permanent-magnet machine has high power density and efficiency, which is suitable for electric traction drive, especially for in-wheel or near-wheel direct-drive electric vehicles. This paper investigates and optimizes the cogging torque of the YASA machine with soft magnetic composite (SMC) core. First, the structure of YASA with SMC core is introduced. Then, the influence of magnet pole-arc ratio, magnet skewing, stator shoe width ratio, and stator shoe shifting on cogging torque is analyzed, based on which the cogging torque is optimized by establishing the response surface model and using the genetic algorithm. Finally, the optimization results are verified by the 3-D finite-element method. The results confirm that based on a certain magnet pole-arc ratio, there exists an optimum combination of magnet skew angle, stator shoe width ratio, and stator shoe shift angle for the cogging torque minimization, while the main performances of the machine remain nearly invariable.