Design Optimization of Radial Flux-Focusing Coaxial Magnetic Gears and Comparison with Conventional Surface Permanent Magnet and Halbach Topologies

Magnetic gears offer the benefits of mechanical gears with the potential for added advantages stemming from contactless power transfer. This work compares optimized coaxial radial flux-focusing magnetic gears (FF-MGs) with similarly optimized surface permanent magnetic gears (SPM-MGs) and Halbach magnetic gears (HB-MGs). All the topologies are independently optimized for volumetric torque density (VTD), gravimetric torque density (GTD), and the permanent magnet gravimetric torque density (PM GTD) across a range of gear ratios using a genetic algorithm (GA). Pareto optimization of all three objectives was performed for the three topologies. The results show that FF-MGs offer a significant improvement in VTD and GTD when compared to SPM-MGs. However, when compared to HB-MGs, FF-MGs have comparable VTDs, but lower GTDs. The PM-GTDs of all three topologies are quite similar. 3D FEA suggests that the FF-MG designs experience higher drops in torque due to end effects than the SPM-MG and HB-MG designs. Harmonic analysis and transient simulations show that the FF-MG can experience higher amplitude undesirable harmonics and higher losses when compared to the SPM-MGs and HB-MGs.