Control strategy to improve load/power sharing, DC bus voltage restoration, and batteries SOC balancing in a DC microgrid

DC microgrids are well known as a proper solution to link different DC sources, such as photovoltaic panels and wind turbines, directly to DC loads. Along with their advantages, they suffer from an imbalance state of charge (SOC) in their energy storage units (ESUs), improper current-sharing between ESUs, and DC bus voltage deviation. This study proposes a novel control strategy for DC microgrids, which not only balances ESUs SOC and shares current between ESUs proportional to their capacity but also, reduces DC bus voltage deviation significantly. In this way, the same droop curve is defined. Then, three virtual resistances are considered. The first one is set based on the lines resistance and ESUs capacity to share current among the ESUs properly. As the lines resistance changes affect the proportional current-sharing, the second virtual resistance is intended to relieve this effect. The third one is suggested to balance the ESUs SOC. The small-signal stability analysis is performed, which demonstrates that the proposed method has stability in all operating conditions. Simulation results in MATLAB/Simulink confirm that with the aid of the proposed control method, not only proper current-sharing and ESUs SOC balancing are obtained, but also DC bus voltage deviation is effectively diminished.