Optimal Current Command Determination Under Unity Power Factor Operation of Biaxial Excitation Synchronous Machines

Rare-earth free biaxial excited synchronous machines (BESMs) are well-suited for achieving unity power factor (UPF) at base speed, enabling high power density and costeffective solutions in traction motor drive systems. With dual excitation sources, the rotor field current can be effectively controlled to optimize machine performance across the entire operating range of the motor drive system. This paper proposes a novel algorithm for the generation of optimal stator and rotor current commands, aimed at minimizing copper losses while ensuring UPF operation. The algorithm also guarantees compliance with stator and rotor voltage constraints under all operating conditions. Developed using the machine's analytical model and numerical optimization techniques, the proposed method is validated through comprehensive simulations across a wide range of torque and speed scenarios. The results confirm the algorithm's effectiveness in maintaining UPF and reducing copper losses, providing valuable insights for enhancing BESM efficiency in traction applications.