Modeling and state of charge-based energy management strategy of ultracapacitor energy storage system of urban rail transit

Applying ultracapacitor to store regenerative braking energy in urban rail transit can achieve good effects on energy efficiency and voltage regulation. But when multiple devices distributed in one rail line, it cannot be coordinated by current energy management strategy, which leads to higher power dissipation and voltage stress. The paper firstly establishes models of train, traction power grid and energy storage system combined with characteristics of ultracapacitor. Then operating features are analyzed under constant voltage-based energy management strategy, in view of the analysis a state of charge-based energy management strategy is proposed, which can be sufficiently utilize the configuration capacity of all ultracapacitors, lower the power dissipation and the voltage stress and help to extend the service life of the ultracapacitors. Finally, simulation and experiment results show the correctness of the model and the effectiveness of the proposed energy management strategy.