Design of a Compact Axial Flux Permanent Magnet Machine for Hybrid Electric Vehicle

Aiming to an integrated starter generator (ISG) application with a compact dimension requirement, this article proposes an axial flux machine with the internal rotor (AFIR). Compared with the traditional AFIR, the proposed machine shows a 21% increase in torque density due to its excellent thermal performance, which is implemented by suppressing the rotor losses and enhancing the cooling capability of the stator. The rotor design adopts the segmented permanent magnets and the separated rotor covers to prevent overheating. The loss analysis is carried out through the three-dimensional finite-element method (FEM). The results indicate that the optimized rotor loss is 24% less than the original design. After that, an innovative cooling system with the cooling rings and modified assembly process are proposed. Based on the lumped parameter thermal network and FEM, the improvement of thermal performance is investigated in detail. Compared with the conventional cooling system, the proposed one reduces the temperature of the machine by more than 20 C-White circle. Finally, this article provides experimental verification based on a 100-kW prototype. The experimental results are in agreement with the analysis and indicate that the proposed AFIR is a promising candidate for the ISG.