A Unified Approach for the Design of Accurate Torque Controllers for Electrically Excited Synchronous Motors

Permanent magnet synchronous machines (PMSMs) with rare-earth magnets are widely recognized as the preferred choice for electric powertrains due to their high 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 auto motive applications. EESMs offer enhanced control flexibility over PMSMs, as their magnetic flux can be actively regulated through the rotor field current. The existing literature provides several torque control solutions for EESM, such as direct current control of the machine's currents and hybrid solutions that directly control the stator flux amplitude and torque. These torque control approaches (TCA) seem to lead to very different control structures, requiring a case-by-case design. However, this article proposes a unified approach specifically designed for traction EESMs that enables selecting the most common TCA reported in the literature while preserving accurate torque regulation and minimizing total copper loss. The effectiveness of the proposed solution is experimentally validated using a commercially available 100 kW EESM, which is employed in the Renault Zoe EV R135.