Optimisation method to maximise torque density of high-speed slotless permanent magnet synchronous machine in aerospace applications

This study presents an optimisation method for slotless permanent magnet synchronous machines to maximise torque density. The slotless structure with outer rotor and Halbach array has been selected to limit iron losses, torque ripple, cogging torque, and high-order harmonics. High-speed operation compounds both ac copper loss and mechanical stress. The former causes a temperature rise in the machine, while the latter is induced by strong centrifugal forces. A finite-element analysis-based optimisation method that utilises a parallel multistart, mesh adaptive direct search strategy is proposed to consider ac copper loss and mechanical stress as constraint variables. Finally, the torque densities of titanium and aermet shell designs were compared to show how material selection provides a trade-off in terms of torque production, mechanical stress, and weight.