Adaptive Virtual Impedance Estimation by Fuzzy Logic Controller for Wireless Reactive Power Sharing in Islanded Microgrid

With microgrids gaining more popularity in effectively meeting the increasing power demand, the operational challenges keep on increasing hand-in-hand. Especially when the microgrid work in islanded mode, it has to supply its area loads and maintain the system parameters as per the standards. This requires systematic coordination among the distributed generators so that the real and reactive power sharing is proportional to their ratings, simultaneously maintaining the system voltage and frequency at the rated values. While a droop controller shares the real power accurately, it is ineffective for precise reactive power sharing. The errors in reactive power sharing are compensated by adding virtual impedance in series with the distributed generator. The key objective of the work is to estimate the virtual impedance value to nullify the reactive power sharing errors without the need for communication links. A fuzzy logic controller is proposed to estimate the value for virtual impedance based on the real and reactive power demand at that particular instant. The virtual impedance dynamically changes depending on the load demand in order to compensate for the feeder impedance mismatch and hence called adaptive virtual impedance. Thus with the proposed fuzzy logic controller, accurate reactive power sharing is made possible without the requirement of communication links and the knowledge of feeder impedance. A secondary controller is also included to restore the frequency and the voltage to the rated values. A microgrid with equally and unequally rated DGs has been simulated in Matlab Simulink with the proposed fuzzy controller and successfully validated.