Power management in co-phase traction power supply system with super capacitor energy storage for electrified railways

Increasing railway traffic and energy utilization issues prompt electrified railway systems to be more economical, efficient and sustainable. As regenerative braking energy in railway systems has huge potential for optimized utilization, a lot of research has been focusing on how to use the energy efficiently and gain sustainable benefits. The energy storage system is an alternative because it not only deals with regenerative braking energy but also smooths drastic fluctuation of load power profile and optimizes energy management. In this work, we propose a co-phase traction power supply system with super capacitor (CSS_SC) for the purpose of realizing the function of energy management and power quality management in electrified railways. Besides, the coordinated control strategy is presented to match four working modes, including traction, regenerative braking, peak shaving and valley filling. A corresponding simulation model is built in MATLAB/Simulink to verify the feasibility of the proposed system under dynamic working conditions. The results demonstrate that CSS_SC is flexible to deal with four different working conditions and can realize energy saving within the allowable voltage unbalance of 0.008% in simulation in contrast to 1.3% of the standard limit. With such a control strategy, the performance of super capacitor is controlled to comply with efficiency and safety constraints. Finally, a case study demonstrates the improvement in power fluctuation with the valley-to-peak ratio reduced by 20.3% and the daily load factor increased by 17.9%.