Rotor Pole Design of Radial Flux Magnetic Gear for Reduction of Flux Density Harmonics and Cogging Torque

This article focuses on a novel design of rotor topology for an interior permanent magnet superconductive radial flux magnetic gear to achieve sinusoidal air-gap flux density and lower cogging torque. The method is based on optimization of buried magnet's pole shape in a radial flux structure, modified by using a pulsewidth modulation technique and variable air-gap length applying the supershape formula on the iron core of the inner rotor. The unsatisfied harmonic contents of the air-gap flux density can be reduced with this technique while the main harmonic component and average torque can be maintained or enhanced. The key idea is to set the distribution of the air-gap flux density by segmenting the pole shoe into several elementary blocks and predetermined grooves based on a special curve. Superconductor bulks are placed between pole pieces of modulator ring to improve the flux-modulation effect and decrease cogging torque percentage. The computation of the block sizes and effects of variation of supershape formula parameters are performed by solving a constrained optimization problem. Results show that the radial air-gap flux density harmonics are eliminated, leading to almost sinusoidal air-gap flux density and lower level of cogging torque.