Analysis and Design of Zero-Current Switching Switched-Capacitor Cell Balancing Circuit for Series-Connected Battery/Supercapacitor

To overcome the problem that the balancing performance of existing switched-capacitor (SC) cell balancing systems drops along with the increase in the number of series-connected battery cells, a novel SC cell balancing circuit is presented in this paper. The same as other SC balancing systems, only a pair of complementary square-wave signals is required to control the proposed circuit. With resonant SC design, all switches employed in the proposed balancing circuit operate under zero-current switching. The equivalent model is derived to reveal the balancing performance of the proposed balancing circuit. The system feasibility and theoretical analysis are verified by both of simulation and experimental results.

I. Introduction

With global warming and fossil fuel depletion, various electric vehicles (EVs) have drawn great attention from vehicle manufacturers, consumers, and governments as their advantages of lower carbon emissions and transportation costs [1]–[4]. Challenges introduced by the intensive use of plug-in EVs in distribution networks and the corresponding optimization method have been discussed in detail in the literatures [1]– [3]. In EVs, battery or supercapacitor strings have become one of the key components and they operate in charging and discharging modes alternately [5]. Battery or supercapacitor strings are usually made up of a large number of series-connected cells. Because of non-uniform individual cell properties, united operation of battery strings causes a small imbalance among cell voltages during charging and discharging periods. Overcharging, as well as deep discharging, will cause battery cells to be deteriorated forever or even worse, thereby affecting the operation and safety of the entire battery string [6]. The cell balancing, also known as voltage equalization, is therefore necessary to prevent this phenomenon and to prolong battery life [7].