ABSTRACT The split ratio of an axial‐flux permanent‐magnet (AFPM) machine, defined as the inner‐to‐outer stator diameter ratio, is optimised to maximise electromagnetic torque under thermal constraints considering both copper loss and iron loss. An analytical relationship between torque and split ratio is derived, and the predictions are validated by finite‐element analysis (FEA). The results show that, when stator iron loss is taken into account, the achievable torque is reduced and the optimal split ratio shifts compared with the copper‐loss‐only case. The influences of air‐gap length, flux‐density ratio and operating speed on the torque–split‐ratio relationship are further quantified, and the effect of slot shape is also examined. Three‐dimensional FEA and experimental results confirm the predicted trends and optimal points, demonstrating that the proposed method can serve as a fast preliminary sizing tool for thermally constrained YASA‐type AFPM machines.
Zhu et al. (Thu,) studied this question.