Effect of End-Winding on Electromagnetic Performance of Fractional Slot and Vernier PM Machines with Different Slot/Pole Number Combinations and Winding Configurations

In this paper, the effects of end-winding on electromagnetic performance of surface mounted permanent magnet machines (SPMMs) (including vernier machines) with different slot/pole number combinations and winding configurations are analyzed and compared. By using genetic algorithm based on finite element analysis, SPMMs with different coil pitches are optimized for maximum average torque under fixed copper loss or fixed copper and iron losses, with/without considering the influence of end-winding. The effects of coil pitch and stack length on torque and torque density are investigated, and the optimal coil pitch for each slot/pole number combination is obtained. The efficiencies, inductances, and power factors of optimized SPMMs are also compared. The torques of optimized SPMMs considering iron loss decrease, especially at high speed and larger rotor pole number. It is found that the end-winding has significant effect on torque, torque density, winding inductance, and power factor etc. Compared with the fractional slot concentrated winding SPMMs with the same lamination stack length but slot number higher than pole number, the integer-slot distributed winding SPMMs with pole number higher than slot number have higher torques due to field modulation effect, but lower torque densities due to longer axial end-winding lengths. In addition, all the above analyzed SPMMs are also compared with the consequent pole rotor counterparts. It demonstrates that the consequent pole SPMMs can achieve higher PM utilization but sacrifice PM torques. However, the consequent pole SPMMs with higher pole numbers can achieve competitive torque output capacity due to the enhanced field modulation effect.