Analytical Solution for Electromagnetic Torque of Ultrahigh Speed AFPM Motor With Slotless Stator Core and Toroidal Coils

The ultrahigh-speed axial-flux permanent magnet (AFPM) motor usually adopts the slotless stator core to eliminate the cogging torque. However, the torque ripple still arises because of two factors, namely, the stator winding construction and the permanent magnet (PM) topology structure. In order to determine the influence of the above two factors on the torque ripple of ultrahigh-speed AFPM motor, the article presents an analytical solution to the electromagnetic torque. In addition, in order to increase the spatial utilization ratio of PM and to obtain a sinusoidal back electromotive force (back EMF), a new topology structure of PM is designed. Results show that the ratio of the net torque to total torque can achieve 99.2% when N
_q
(number of coil-pairs per phase) equals 6, and back EMF of the proposed rotor is 7.69% greater than that of the previous rotor. The analytical model is verified by 3-D finite-element method (FEM) and experiment data.