Comparison of Electrically Excited Synchronous Machines Using Copper and Aluminum Windings in Stator and Rotor

In this paper, electrically excited synchronous machines (EESMs) using copper (Cu) and aluminum (AI) windings are compared for the feasibility of replacing Cu windings with Al windings in electric vehicle (EV) applications since Al windings have lower mass density and cost per weight, but higher resistivity and lower thermal conductivity than Cu windings. The EESMs with four winding configurations are optimized with an electromagnetic-thermal co-optimization method. The optimized EESM with only Cu windings is considered as the baseline in this study. Results show that the EESM with stator-Cu/rotor-Al windings has the least torque reduction (12.1%) compared to the baseline among the three EESMs with Al windings and the highest torque mass density among all EESMs. Meanwhile, although the new European driving cycle efficiency of the stator-Cu/rotor-Al EESM is 1.8% lower than that of the baseline, the torque per cost is 71% higher, and the maximum rotor mechanical stress is 8% lower. Therefore, the EESMs with stator-Cu/rotor-Al windings are prospective substitutions of those with only Cu windings for EV applications considering the trade-off between performance and cost.