Cooperative State-of-Charge Balancing of Supercapacitors: A Switched Systems Approach

State-of-charge (SoC) estimation and cell balancing are typically considered as two separate problems in the supercapacitor management systems. However, the SoC estimation accuracy decreases significantly when the cell balancing circuit is activated, which will further degrade the cell balancing performance. In this paper, we propose a switched systems approach to address this issue by integrating the two problems together in a unified switched systems framework. The proposed method consists of two stages: balancing-aware SoC estimation and observer-driven cell balancing. In the first stage, we propose a switching sliding mode observer to estimate the SoC of supercapacitor balancing systems, where two observers are designed for supercapacitors with cell balancing activated or deactivated. In the second stage, a cooperative SoC balancing method is proposed to synchronize the SoC of supercapacitors, which can effectively improve the energy efficiency during the charging process. An experimental platform is established, and the SoC estimation performance and SoC balancing performance are verified with experiment results. Experiment results indicate that the switching sliding mode observer improves the SoC accuracy by 4.96% than its non-switching counterpart and the cooperative balancing method improves the energy efficiency by 8.7% compared with the decentralized balancing method.