An accurate reactive power sharing strategy for an islanded microgrid based on online feeder impedance estimation

The mismatched feeder impedances in islanded microgrids result in poor reactive power sharing when the conventional frequency and voltage droop control technique is deployed. Thus, adaptive/improved droop control schemes should be adopted. This paper proposes a novel reactive power sharing for resistive-inductive islanded microgrids. The proposed control scheme relies on the online estimation of feeder impedances to accurately and adaptively tune the virtual complex impedances of parallel-connected inverters. After the virtual impedance is tuned for a given operating point, it is required to be tuned again only if the microgrid load changes. This advantage makes the proposed control scheme tolerant of communication disruptions/delays. The proposed technique perfectly compensates the voltage drops across various feeder impedances in real-time. Consequently, it is ensured that load demands are taken up among parallel-connected inverters in proportion to their power ratings by only adopting the conventional droop control method and the proposed adaptive virtual complex impedance. Simulation results of an islanded microgrid consists of two parallel single-phase inverters are presented to validate the performance of the propose technique.