High-voltage bidirectional balancing structure and model predictive control for cell balancing of supercapacitors in heavy duty HEV applications

Supercapacitors, which offer unique high-power and fast charge/discharge operation performance, have emerged as a promising energy storage solution for heavy duty hybrid electric vehicle (HEV) applications. However, state-of-energy (SOE) inconsistency among supercapacitors would affect the safety and operating efficiency of the overall supercapacitor system. This study proposes a cell balancing method based on a novel high-voltage bidirectional balancing structure and a model predictive control (MPC) for supercapacitors in heavy duty HEV applications. To achieve high-efficiency energy balancing, the high-voltage bidirectional balancing structure with isolated DC-DC converters is developed. The isolated DC-DC converters can achieve special boost-buck balancing with a bidirectional flyback circuit. On this basis, the MPC is introduced for optimizing the balancing energy through the switch control of the bidirectional flyback circuit, which would achieve a fast and stable SOE balancing for supercapacitors. Simulation and experimental analyses are conducted to validate the proposed balancing method. Results show that the proposed balancing method can achieve fast balancing among supercapacitors in heavy duty HEV applications. Compared with the conventional constant current-constant voltage (CC-CV) control balancing method, it can reduce the balancing time by 34.4 %. Moreover, the proposed balancing method can achieve balancing accuracy up to 0.5 %.