Extended MTPA and Flux-Weakening Control with Total Copper Loss Minimisation and Transient Torque Compensation for Wound-Rotor Synchronous Machines

Wound Rotor Synchronous Machine (WRSM), namely Electrically Excited Synchronous Machine (EESM) and Hybrid Excited Synchronous Machine (HESM), can represent effective solutions to address the concerns raised by the use of Rare Earth Elements (REE) in Permanent Magnet Synchronous Machines (PMSMs), which involve geopolitical implications, environmental impact and cost. The possibility to vary the rotor excitation brings opportunities (especially in Flux-Weakening operation, FW), but also some additional challenges, namely in the selection of the optimal operating point in terms of stator and rotor currents. This paper analyses the operation of EESM and HESM and proposes a strategy for the minimisation of overall Joule losses. A comprehensive control scheme will be developed, which achieves smooth and efficient operation across the whole speed range. An "Extended MTPA" strategy is proposed in the low-speed range, while a closed-loop FW algorithm is proposed for the high-speed. Furthermore, the torque actuation lag issue (related to the slow dynamics of the rotor current) is addressed by providing a novel compensation strategy.