Modified voltage equaliser based on Cockcroft-Walton voltage multipliers for series-connected supercapacitors

It is essential for electric vehicle to equalise the voltages of battery or supercapacitor (SC) cells in series connection. Comparing with other equalisation methods based on energy transfer, Cockcroft-Walton (CW) voltage multiplier brings great benefits to the simplification of equalisation structure. Voltage equaliser formed by voltage multiplier can realise voltage balance automatically without voltage detection and control unit. However, the traditional (CW) voltage multiplier structure has two demerits. One is incapable of realising the voltage balancing for all the cells in series; the other one is the large inrush current of parallel capacitors that reduces the lifetime of the equaliser. To solve these problems, a modified voltage equalisation circuit is proposed. The new equaliser is constituted by a half-bridge frontend and a multiplier backend. The half-bridge generates the alternating voltage, and the multiplier accomplishes the voltage balancing. The operation principles, circuit analysis and parameters calculation are examined in detail. The performance is evaluated by simulation and experimental with three SCs in series. The accordance between simulation and experiment further proves that the voltage balancing is achieved for all the series cells and the inrush current of capacitors is declined at the turning on of power switches.