Low-Frequency Stability Analysis of Co-Phase Traction Power Supply System Based on a Control-Oriented Model

Co-phase power supply is a promising technology for the future traction power supply thanks to its power quality compensation and no need for the phase breaker. However, the embedding of numerous power electronic devices, termed co-phase power supply units (CPSUs), complicates the stability of train-grid systems. This paper proposes a novel modeling approach oriented towards controller design. Compared to existing impedance-based models, the key innovation lies in decoupling the CPSU controller from the train-grid system. This provides a theoretical basis for the controller design. Subsequently, the stability of the co-phase traction power supply system (CTPSS) is quantitatively evaluated with the robust stability margin. On this basis, the impacts of CPSU controller parameters and the number of operational trains on system stability are revealed. The results demonstrate that conventional proportional-integral (PI) controller fails to ensure good system stability under multi-train operating conditions. The system can maintain stable operation for a maximum of 6 trains. To improve the robust stability of the CTPSS, an H-infinity controller is designed, which can ensure the stable operation of the system with 10 trains running. Finally, the effectiveness of the proposed model and control strategy is validated through time-domain simulations and hardware-in-the-loop experiments.