Modularised non-isolated two-switch equaliser using full-wave voltage multiplier for series-connected battery/super-capacitor

Conventional battery/super-capacitor (SC) cell voltage equalisers require numerous switches and/or a multi-winding transformer, which are not desired in terms of circuit complexity and extendibility. In this study, a modularised non-isolated two-switch cell voltage equaliser for series-connected lithium-ion battery/SC is proposed. The proposed equaliser consists of a non-isolated front-end dc-dc converter and a full-wave voltage multiplier circuit. Without coupled-inductor, multi-winding transformer and multiple active switches, the proposed equaliser uses only two active switches and two magnetic components, thus it benefits from reduced complexity and circuit volume. Meanwhile, the modularised full-wave voltage multiplier circuit makes it flexible to extend to more battery/SC cells. Furthermore, it can work under open-loop without cell monitoring circuit, which makes its control simple. The equalisation current of the proposed equaliser can be limited automatically. Compared with conventional non-isolated equalisers using half-wave voltage multiplier, it benefits from faster equalisation speed and lower equalisation loss. High efficiency is achieved by zero voltage switching of all switches. Experimental results are provided to verify analysis results of the proposed equaliser.