Optimal Stator/Rotor Copper Loss Ratio for Maximum Torque of Electrically Excited Machines

This paper focuses on torque maximization of electrically excited (EE) machines considering variable stator/rotor copper loss ratio (SRCLR) in design optimization. Firstly, two EE machines are optimized with SRCLR fixed to 1 (EE1) and variable SRCLR (EE2) based on a baseline interior permanent magnet (IPM) machine, which proves that an optimal SRCLR exists in EE machines. Then, the influence of SRCLR and geometrical parameters on the torque of EE2 machine is studied. EE and IPM machines are compared by finite element analyses (FEA). The results show that EE2 exhibits higher torque, output power, efficiency, and better temperature distribution than EE1 with the same power factor due to optimal SRCLR. It is also prospective to replace IPM machines with EE machines for electric/hybrid electric vehicles and aircraft starter-generators considering power factor, constant power operation, and cost advantages despite of lower efficiency. A scaled EE machine with optimized SRCLR is prototyped and tested to verify the improved torque capability and temperature distribution of the EE machine with optimized SRCLR.