A rapid cell voltage balancing scheme for supercapacitor based energy storage systems for urban rail vehicles

Supercapacitors are widely used in energy storage systems (ESS) due to the merits including high power density, relatively long life cycle, and fast charging/discharging capability. Recently, it is becoming possible to use supercapacitor based ESS as the single energy source to power an urban rail vehicle. Cell voltage balancing control is necessary for the ESSs where supercapacitor cells are connected in series in order to have safe and reliable operations. A typical charging cycle of onboard supercapacitor stack is around 30 s. A high voltage balancing current is demanded in order to realize cell voltage balancing within the charging courses. In this paper, a new voltage balancing circuit, which is derived from an improved push-pull converter and with high current capability, is proposed for supercapacitor based ESS applications. A voltage balancing algorithm based on predicted cell behaviors is proposed to shorten the cell balancing time and improve the cell balancing efficiency. Simulation and experimental results are provided to verify the effectiveness and advantages of the proposed cell voltage balancing system.