Can photovoltaic battery energy storage systems BE self-balancing?

This paper proposes a novel approach for integrating battery storage into photovoltaic (PV) arrays. The approach relies on the integration of PV arrays with individual batteries to form "hybrid cells" that are then assembled into series strings. We use Lyapunov analysis to show that the proposed hybrid strings are globally asymptotically self-balancing, meaning that initial variations in state of charge (SOC), no matter how large, converge to zero. The PV subsystem serves as a negative feedback path that guarantees self-balancing without requiring dedicated balancing circuits. This significantly reduces the cost of the power electronics needed for integrating batteries into PV farms, compared to typical integration topologies. The paper uses local linearization to approximate the balancing rate, thereby highlighting its independence of battery pack length and elucidating its dependence on subsystem sizing. Finally, a simulation study validates the paper's theoretical insights regarding self-balancing, and examines its sensitivity to parameter heterogeneities.