Comparison of Reluctance and Surface Permanent Magnet Coaxial Magnetic Gears

The noncontact operation of magnetic gears offers significant potential advantages over mechanical gears. Reluctance magnetic gears (RMGs) have been proposed as an alternative to surface permanent magnet gears (SPMGs) at high speeds. This paper explains the operating principles of RMGs and provides a thorough parametric comparison between RMGs and SPMGs using 2-D and 3-D finite element analysis (FEA). SPMGs are found to outperform RMGs in torque density, as expected. However, contrary to the results of nonoptimized comparisons in previous papers, optimal SPMGs also can achieve better magnet utilizations and efficiencies than optimal RMGs. Additionally, the RMGs with the highest torque densities suffer from significantly more torque ripple than the SPMGs with the highest torque densities. Also, the simulations demonstrate that the optimal SPMGs and optimal RMGs with the same stack lengths tend to suffer comparable reductions in torque from end effects.