Split Ratio Optimization of High-Speed Permanent Magnet Synchronous Machines Based on Thermal Resistance Network

The split ratio is a significant parameter which affects the torque output and efficiency of permanent magnet machines. It has been optimized for obtaining the maximum torque output with a fixed maximum allowable copper loss or current density as the thermal constraints in the current findings. However, these indirect thermal constraints could be influenced by the split ratio due to the changing machine dimensions and may fail to limit the winding temperature rise. To solve this matter, an analytical split ratio optimization method is proposed in this paper based on the thermal resistance network (TRN). It takes the winding temperature rise limitation as the thermal constraint directly. Both the influence of the core loss and air-friction loss on the optimal split ratio is considered in the analytical optimization method. The proposed analytical method is validated by the electromagnetic and thermal finite element analysis (FEA).