Nonlinear observer-based state-of-charge balancing of networked battery energy storage systems

In this paper, we propose an observer-based algorithm for balancing the state-of-charge (SoC) among battery units in a battery energy storage system (BESS). The dynamical behaviour of a battery unit is approximated by an equivalent circuit model, based on which a nonlinear SoC observer can be constructed. Power distribution laws are designed for the battery units according to the states of the battery units, the average battery state, and the average power demand. Distributed estimation algorithms for the average battery state and the average power demand, as well as SoC observers, are constructed to implement them. The BESS is shown to achieve SoC balancing among all its battery units while satisfying the power demand, as long as mild conditions on the underlying communication network and on the power demand are met. Simulation results are presented to demonstrate the effectiveness of the proposed algorithm.