A Cell Balancing Circuit With a CLLC Converter and Reconfigurable Switch Banks for Supercapacitors

This paper proposes a supercapacitor cell balancing circuit employing a CLLC converter and reconfigurable switch banks. A prototype with four supercapacitors is designed and implemented to verify the static and dynamic balancing schemes. Specifically, two string-to-string (S2S) scenarios and one cell-to-cell (C2C) scenario are examined to show that the proposed circuit is capable of grouping the supercapacitors in a flexible manner even when they are physically far apart and implementing bidirectional power flows to balance the supercapacitors in two groups. For dynamic balancing, two cases are investigated to demonstrate that the proposed circuit can balance the supercapacitors during charging or discharging processes. Moreover, the proposed circuit is evaluated against other balancing circuits in two comparative studies. The first quantitative study shows that the balancing time of the proposed circuit is significantly shorter compared to the four baseline circuits: the buck-boost circuit, the LC resonant circuit, the LLC resonant circuit, and the coupled inductor-based circuit. The second qualitative study illustrates that the proposed circuit features a higher balancing speed, a smaller number of magnetics, and a better scalability while its hardware complexity and control complexity are relatively high compared to the balancing circuits based on switched resistors, switched capacitors, buck-boost converters, and multi-winding transformers.