Distributed Control Scheme for Package-Level State-of-Charge Balancing of Grid-Connected Battery Energy Storage System

For the battery energy storage system (BESS) consisting of multiple battery packages, package-level state-of-charge (SOC) balancing can provide safety redundancy in protecting battery packages from overcharging or overdischarging, and maintain the maximum power capacity of the overall BESS. In this paper, a distributed control scheme is proposed for package-level SOC balancing of a grid-connected BESS. The proposed control scheme comprises three parts. First, each battery package shares its SOC with its neighboring battery packages over the communication network. Based on the SOCs of its own and its neighbors, each battery package is equipped with an energy coordinator. Second, for each battery package, a distributed observer is employed to estimate the average desired power output, which is used to determine the local reference power output together with the energy coordinator. Third, local current controller is synthesized for each battery package to achieve local reference power output tracking. Comprehensive case studies are conducted to evaluate the effectiveness of the proposed control scheme.