Analytical Calculation of Slotless Axial Flux Permanent Magnet Motor With Sinusoidal Magnets for Torque Ripple Reduction

As the applications and production demands for high-speed axial flux permanent magnet (AFPM) motors continue to expand, conventional motor designs are increasingly challenged to achieve high-quality torque while adhering to shorter design cycles. To address this issue, this article proposes an analytical method for slotless AFPM motors with specific magnets to make back electromotive force (EMF) sinusoidal for low torque ripple. Initially, the design principle of the sinusoidal magnet is introduced, and the air gap magnetic field of the AFPM motor is modeled based on the sinusoidal magnet shape, with a comparison of the ring magnet. Subsequently, the back EMF of the AFPM motor with toroidal and bunched winding is deduced and compared by winding function. The torque performance is further calculated to verify the effectiveness of the low torque ripple design. Finally, the prototype with sinusoidal magnets and bunched winding is manufactured, and the analytical results are consistent with experimental tests.