Regenerating energy storage system based on ultra-capacitor for urban railway vehicles

This paper presents an energy storage system based on ultra-capacitor to absorbing the regenerating energy of urban railway vehicles and releasing the energy when the train starts, which can cut down the energy waste. A modular power conversion scheme is proposed to accommodate the application of different electric supply system, where several modules are connected in series to endure high supply voltage. Multi-phase power conversion topology is adopted to share the high current, and a dual-loop control system is proposed to realize the bidirectional energy flow and achieve input voltage balance in series modules. A voltage balance scheme is also introduced to guarantee that the ultra-capacitor works reliably and efficiently, which consists of cells equalization in groups and voltage balancing between the groups. At last, a small scale prototype is build and the experimental results validate the feasibility of power conversion strategy.