Accurate Reactive Power Sharing Strategy for Droop-based Islanded AC Microgrids

In islanded AC microgrids, the mismatched impedances of the interfacing feeders between the inverters and the load bus cause poor reactive power-sharing when the conventional frequency and voltage droop control technique is employed. Such operation endangers the whole microgrid reliability as it may lead to overloading certain inverters and, consequently, triggering protection relays and causing cascaded failure in the microgrid. Thus, this paper proposes an accurate reactive power sharing strategy that considers the mismatched feeder impedances in islanded AC microgrids. It is based on optimal tuning of the virtual complex impedance for each inverter. The proposed strategy has several advantages. it has a physical meaning as it establishes an explicit relationship between the mismatched values of the actual resistive-inductive feeders and the assigned values for the proposed optimal virtual complex impedance for each inverter. Third, there is no need for prior knowledge in the design stage about the actual feeder impedances as they are estimated online from the available measurements. Lastly, the proposed control is reliable and fault-tolerant which copes with sudden failure in some inverters and with the communication disruptions/delays as it ensures accurate reactive sharing even under the primary controller. Simulation and experimental verification results are presented to validate the performance of the proposed technique.