Distributed adaptive droop control for DC microgrids

Conventional droop controls have been widely studied for load sharing in dc Microgrids. However, unlike ac Microgrids, transmission line impedances can undermine the controller´s performance, and it might fail to provide regulated rated voltage and proportional load sharing. Herein, a distributed secondary controller is introduced that includes two modules; a voltage regulator and a current regulator. A sparse cyber network is also spanned through the converters for data exchange wherein, each converter is in contact with a few others as its neighbors. A cooperative algorithm is introduced and used in a voltage observer that estimates the average voltage across the Microgrid. This estimation is further used in the voltage regulator to locally adjust the voltage set point, compensating the voltage drop caused by the droop mechanism. Simultaneously, the current regulator compares local per-unit current with the neighbors´ per-unit currents and, accordingly, adjusts the droop virtual impedance to balance the per-unit supplied currents. Thus, the voltage and current regulators together provide the best choice of voltage set point and virtual impedance that leads to the global voltage regulation and tight load sharing. Simulation studies on a low-voltage dc Microgrid verify the performance of the proposed control methodology.