Balanced Control Strategy of Distributed Energy Storage SOC Considering Line Impedance

Due to the uncertainty of distributed generation (DG) in islanding DC microgrids, it is necessary to add an energy storage unit for a supplement. In traditional droop control, the output current cannot be accurately distributed due to line impedance difference, which affects the balancing effect of the energy storage unit's state of charge (SOC). Besides, the convergence rate slows down as SOC decreases. Also, the influence of DG fluctuation on bus voltage is not considered. Therefore, an improved droop control strategy is proposed. By calculating the output current deviation, the authors introduce an integrator for the current deviation to eliminate the influence of the line impedance difference. Acceleration term and adaptive acceleration factor are also designed to increase the SOC balancing speed. When the DG fluctuates, the output current increment is adjusted to meet the load power balance and keep the voltage stable. The simulation results show that the SOC convergence error of the proposed control strategy is less than 0.1% when considering the line impedance. Convergence speed increases by 20% compared with the method referred, and the voltage drop is less than 3%.