Torque ripple alleviation of a radial magnetic gearbox using step skewing approach

Recently, magnetic gearboxes (MGBs) are serious contenders to their conventional mechanical counterparts in terms of reduced maintenance requirements, improved reliability, tolerance to mechanical inaccuracies, and inherent overload protection. MGBs are preferably employed in high speed applications and compact harsh environments. One of the challenging design aspects of MGBs is the proper selection of the combination of the number of pole-pairs of both inner and outer rotors, yielding specific gear ratios, to minimize cogging torque magnitude. For any general desired gear ratio, the torque ripple magnitude may be unacceptable. Since MGBs generally belongs to permanent magnet (PM) machines family, the same techniques for torque ripple mitigation can be employed. This paper introduces a new technique for torque ripple reduction in MGB based on step skew technique. In the proposed technique, the MGB is divided into two equal parts along its stack length and the optimum skew angle between the two parts is determined for minimum torque ripple. A conventional 14/4 MGB, which is normally results in a significant cogging torque magnitude, is designed and simulated using 3D finite-element analysis (FEA) for different skew angles. Based on the simulation results, the required optimum skew angle that optimizes torque transmission while minimizes the corresponding cogging torque is recognized.