Direct Flux and Torque Control of Electrically Excited Synchronous Traction Motors

Permanent Magnet Synchronous Machines (PMSMs) utilizing rare-earth magnets are currently the most prevalent solution for electric powertrains due to their high torque density and efficiency. However, Electrically Excited Synchronous Machines (EESMs) have emerged as a viable alternative for automotive powertrains to reduce the reliance on rare-earth materials. Indeed, the EESMs offer a higher degree of freedom compared to PMSMs, as the machine flux can be regulated through the rotor field current. However, the literature provides few torque control solutions for EESM with optimal torque production, primarily based on current vector control (CVC) algorithms. Therefore, this article presents a torque controller based on the Direct Flux Vector Control (DFVC) approach for highly saturated EESMs used in traction applications. The proposed torque controller is based on a total copper loss-minimizing approach. At the same time, it fastly regulates the torque with high performance regardless of the rotor excitation dynamics. Furthermore, the proposed torque controller can deal with variable stator and rotor current limits, allowing the potential implementation of the thermal strategies reported in the literature. Experimental results obtained on a commercial 100 kW EESM employed by the Renault Zoe EV R135 are reported, validating the proposed torque controller’s performance.