Fuzzy control-based hierarchical active equalization strategy for lead-carbon energy storage systems

Energy storage systems are fundamental to ensuring the stability of power grids with a high share of renewable energy sources. However, the inconsistency in the State of Charge (SOC) within the energy storage system can accelerate capacity degradation and increase the risk of thermal runaway. To mitigate SOC inconsistency during operation, this paper proposes a fuzzy control-based hierarchical active equalization strategy, specifically designed for lead–carbon battery energy storage systems. To overcome the limitation of insufficient equalization speed in traditional Buck-Boost circuit topologies, a hierarchical circuit structure is first designed and analyzed. Based on this, a multi-parameter cooperative fuzzy equalization criterion is developed, incorporating the SOC of the lead carbon battery pack, external current ( I ), and switching duty cycle ( D ). This approach not only achieves SOC equalization but also effectively prevents overcharge/overdischarge risks while minimizing unnecessary energy consumption. Experimental results show that, under constant current charging conditions, the proposed method improves the equalization speed by 28.84 % compared to the traditional multi-inductor equalization topology. Further tests in multiple scenarios, including dynamic periodic charging, constant current discharging, and dynamic periodic discharging, validate that the proposed hierarchical active equalization strategy effectively adapts to nonlinear parameter variations and demonstrates strong practical feasibility for engineering applications.