A Novel Architecture of Urban Rail Transit Based on Hybrid Energy Storage Systems Using Droop Control

Urban rail transit plays an important role in modern life and consumes a massive amount of energy every day. It is essential to guarantee the high power quality and reliability of the system and maximize energy utilization. Traditional power supply architecture has problems of large fluctuation of power and grid voltage, a waste of braking energy and low utilization of uninterrupted power supply (UPS) in the station. In this paper, a novel architecture of urban rail transit based on hybrid energy storage system (H-ESS) is proposed. Supercapacitor (SC) and UPS are used to smooth the pulse power of the metro train. The H-ESS integrated by high efficiency, three-port isolated bidirectional DC-DC converter (IBDC) module are parallel connected to the DC traction network. Droop control is used to properly allocate the power between the modules and guarantee the reliability of the system. Low-pass-filter (LPF) of adaptive coefficient control schemes and voltage-shifting method for battery state-of-charge (SOC) recovery are proposed to enhance performance of the H-ESS. The effectiveness and advantages of the proposed architecture, control methods and energy management strategies are validated by analysis and simulation.