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Traction power fluctuations have economic and environmental effects on high-speed railway system (HSRS). The combination of energy storage system (ESS) and HSRS shows a promising potential for utilization of regenerative braking energy and peak shaving and valley filling. This paper studies a hybrid energy storage system (HESS) for traction substation (TS) which integrates super-capacitor (SC) and vanadium redox battery (VRB). According to the characteristics of the traction load under actual operating conditions, an energy management strategy with fixed-period control (FPC) is proposed, which fully leverages the periodicity and regularity of HSRS operation. To achieve the optimal size, economic feasibility is selected as the optimization objective, which is fully assessed in terms of Net Present Value (NPV). The optimization constraints are formulated in which the Discrete Fourier Transform (DFT) is performed for power allocation between SC and VRB. Besides, an improved mutation-based particle swarm optimization (IMBPSO) is proposed to efficiently solve the optimization and enhance convergence performance. Finally, combined with the measured traction load data, the effectiveness of the FPC energy management strategy is verified and the optimal scale of the HESS is provided.

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%.

The rational use of regenerative braking energy for urban rail transit trains directly affects the voltage safety of the traction power supply system and the electric braking function of the train. It is also of great significance for the implementation of train traction energy saving. This paper proposes a scheme of train regenerative braking ground absorbing device based on super-capacitor energy storage. It adopts multiple modular Buck/Boost DC conversion topology to realize bidirectional control of electric energy and stabilize the secondary utilization of traction network voltage and regenerative electric energy. According to the scheme of this paper, the energy storage device was developed and verified in the engineering of the Guangzhou Line 6 main line traction substation. The test indicators have met the design expectations.