Voltage Equalization Scheme for Onboard Supercapacitor Based on Sliding Mode Observer

In recent years, with the growing population of people swarmed into urban city, supercapacitor tram has been a promising candidate for the current urban rail transportation. However, the series-connection of cells will typically lead to the cell imbalance and dispersion because of the different individual cell properties such as capacitance, internal resistance, self-discharge rate, and environmental conditions. In this paper, a voltage equalization scheme based on an advanced isolated converter topology that utilizes a multi-winding transformer is proposed for onboard supercapacitors of catenary-free trams. Voltage equalization is essential for series-connected supercapacitors in the energy storage system because of the system sustainability and maximizes the available storage energy. An equalizer algorithm based on sliding mode observer is designed. The balancing approach provides both excellent performance and good reliability. Analysis and experiment results are provided to illustrate the effectiveness of the design.