Unified Torque Control of Electrically Excited Synchronous Machines for Traction Applications

Permanent Magnet Synchronous Machines (PMSMs) equipped with rare-earth magnets are widely recognized as the preferred choice for electric powertrains due to their exceptional torque density and efficiency. However, in an effort to reduce reliance on rare-earth materials, Electrically Excited Synchronous Machines (EESMs) have emerged as a promising alternative for automotive applications. EESMs offer enhanced control flexibility over PMSMs, as their magnetic flux can be actively regulated through the rotor field current. Despite this advantage, existing literature provides limited solutions for torque control in EESMs that guarantee optimal torque generation. This paper presents a Unified Torque Controller (UTC) specifically developed for traction EESMs, which is compatible with a variety of control strategies. Moreover, the proposed control framework integrates a copper loss minimization strategy, accounting for both stator and rotor copper losses, thus improving overall system efficiency. The efficacy of the proposed control scheme is experimentally validated using a commercially available 100 kW EESM, which is employed in the Renault Zoe EV R135.