Control of super-capacitor SOC in a railway transit network

This paper proposes a control strategy for Energy Storage System (ESS) in railway transit network. The system includes a super-capacitor (SC) and a DC-DC convertor. The super-capacitor is used for energy storing and regulating the DC line voltage which is achieved by a bidirectional DC-DC convertor. First the structure of the metro network is introduced, then the model of ESS and its control strategy are explained. An important feature of this simple and effective control strategy is the use of appropriate reference current for charging and discharging of SC. Simulation in MATLAB/Simulink showed that DC bus voltage fluctuation is limited, which is acceptable, and the super-capacitor voltage changes are kept within the allowable range and total input energy of substations is reduced considerably.