Torque Comparison Between Slotless and Slotted Ultra-High-Speed AFPM Motors Using Analytical Method

It is well known that the slotted motor has higher power and torque ripple than the slotless motor. However, how much the power and torque ripple can increase is rarely reported. In this article, the analytical method is used to compare the torque of the slotless and slotted motor. First, the armature reaction field (ARF) and open-circuit permanent magnets (PMs) field are solved by the subdomain model. Then, the torque is calculated by the Maxwell stress tensor method. Moreover, we also obtain the back electromotive force (back EMF) and cogging torque. Finally, the average torque and the torque ripple of the slotless and slotted motor are compared and discussed. The above analytical model is verified by the 3-D finite element method (FEM) and experiment. Results show that the average torque and torque ripple of the slotted motor have increased 52.6% and 22.5 times compared with that of the slotless motor. This article will provide a useful reference for the design of both the slotted and slotless ultra-high-speed axial flux permanent magnet (AFPM) motors.