Distributed Voltage Equalization Design for Supercapacitors Using State Observer

The switched shunting resistor circuit is a classical and practical passive equalization scheme that nevertheless suffers from the voltage imbalance after the charging process. It results from the discrepancy of the shunting resistor and the physical characteristics of supercapacitor (SC) cells. In this paper, the distributed voltage equalization control strategies with the proportional-integral (PI) observer for the switched shunting resistor circuit are analyzed and compared. First, the charging and equalizing system is modeled as the switched system and the system observability is proved. The decentralized control and consensus control are analyzed and their shortages are presented. Then, the leader-follower cooperative control is proposed to improve the charging time while keeping the equalization performance. Meanwhile, the PI observer is designed to estimate the internal capacitance voltage of an SC precisely to avoid the effect of equal series resistance. The control convergence is proved by using the Lyapunov stability and switched system theory. The experimental results show that the proposed method has much superiority and wide applicability than the existing methods for equalizing voltages of SCs.