Torque Density Optimization of Spoke Array Vernier Permanent-Magnet Machines

This paper works on an outer-rotor spoke-array Vernier permanent-magnet machine. It can provide high torque in low-speed direct-drive conditions. In this paper, the working principle of Vernier permanent-magnet machines is presented. A magnetic finite element model, a thermal finite element model and a thermal analytical model are built. Using these models, the torque density without considering the end parts of the Vernier permanent-magnet machine with fixed outer radius is optimized. From the optimized dimensions result, a new Vernier machine structure with disconnected flux modulation poles is proposed. Based on 2D modeling, with temperature limits of 120 °C and 100 °C for the coils and PMs respectively, and fixed outer radius of 71 mm, its torque density can overcome 70 Nm/L, which is higher than conventional Vernier PM machines.