State-of-Charge Balance Using Adaptive Droop Control for Distributed Energy Storage Systems in DC Microgrid Applications

TLDR

This study proposes coordinated control of distributed energy storage systems in DC microgrids to balance their state‑of‑charge. An SoC‑based adaptive droop control is introduced, where the droop coefficient scales inversely with a chosen power of SoC, causing units with higher SoC to supply more power and enabling adjustable load‑sharing speed; the control model is formulated and its stability proven. The method reduces SoC disparities, achieving equal load sharing among units, and simulations and experiments on a 2×2.2 kW parallel‑converter system confirm its effectiveness.

Abstract

This paper presents the coordinated control of distributed energy storage systems (DESSs) in DC micro-grids. In order to balance the state-of-charge (SoC) of each energy storage unit (ESU), an SoC-based adaptive droop control method is proposed. In this decentralized control method, the droop coefficient is inversely proportional to the nth order of SoC. By using SoC-based droop method, the ESUs with higher SoC deliver more power, while the ones with lower SoC deliver less power. Therefore, the energy stored in the ESU with higher SoC decreases faster than that with lower SoC. The SoC difference between each ESU gradually becomes smaller and finally the load power is equally shared between the distributed ESUs. Meanwhile, the load sharing speed can be adjusted by changing the exponent of SoC in the adaptive droop control. The model of SoC-based adaptive droop control system is established and the system stability is thereby analyzed by using this model. Simulation and experimental results from a 2×2.2 kW parallel converter system are presented in order to validate the proposed approach.