An Improved SOC Equalization Control Strategy for Distributed Energy Storage System in DC Microgrid

Distributed energy storage system (DESS) plays a vital role in energy management, voltage regulation, and reliable power supply in hybrid energy system. However, the inconsistent operation between energy storage units (ESUs) often results in an imbalance in the state of charge (SOC), which may greatly shorten the DESS life. To address these issues, this paper proposes an improved droop control strategy to realize the SOC equalization of the DESS. In the primary control layer, the droop coefficient is adaptively adjusted based on the real-time SOC of each ESU, and two balancing factors are introduced to improve the convergence speed and equalization accuracy. In addition, a bus voltage recovery method is developed to compensate for the voltage deviation caused by droop control. At the communication level, a dynamic diffusion algorithm is employed to enable stable estimation of global average SOC through sparse neighbor-to-neighbor information exchange. Finally, the hardware-in-the-loop platform is built to verify the effectiveness of the proposed strategy. The results show that compared to conventional droop-based methods, the proposed method significantly improves the SOC equalization speed and the current sharing accuracy, and is able to restore the bus voltage. Besides, the proposed method maintains effective performance under load fluctuations, and even in the case of ESU failure, the proposed method can ensure SOC balancing among the remaining ESUs, accurate current sharing proportional to capacity, and stable voltage regulation.