A Decentralized Control Method of Battery Energy Storage Units With Different State of Charge

Power capacity of battery energy storages (BESs) should be large to stabilize microgrids. To maximize the total available power capacity of the BESs, state of charge (SoC) balancing control is essential. Therefore, several SoC- adaptive droop control methods have been developed to balance the SoC among the BESs. However, the conventional control methods have slow balancing speed due to limited droop gain, potentially reducing the available power capacity. To address the limitation, this paper employs a novel adaptive nonlinear droop control method. The proposed control method uses output power as an additional variable to adjust the droop gain, leading to a nonlinear relationship between output voltage and output power. Using the nonlinearity, the proposed control method can have larger droop gains, ultimately improving SoC balancing speed. The effectiveness of the proposed control method was demonstrated through both theoretical analysis and lab-scale experiments.