Torque Enhancement of Electrically Excited Synchronous Machines by Cross Coupling Braking Torque Mitigation

This paper aims at torque enhancement of electrically excited synchronous machines (EESMs) with focus on cross coupling braking torque mitigation. Firstly, cross coupling and torque components of a baseline EESM are analyzed, which is designed referring to a commercial interior permanent magnet (IPM) machine in electrical vehicles (EVs). By analyzing the flux paths of different current components, a cross coupling mitigation method is proposed for torque enhancement using general shaping on the pole shoe of EESMs. Then, the EESMs with symmetrical (A) and asymmetric (B) pole shoe general shaping are optimized and compared to the baseline EESM and the IPM. The results show that both A and B exhibit around 4% higher torque, higher efficiency, and higher drive cycle efficiency than the baseline EESM, while A has lower torque ripple and higher output power than the baseline and B. The performance difference between EESM and IPM for EV application is narrowed by the proposed cross coupling mitigation and torque enhancement method.