An Adaptive Virtual Impedance Control for Improving Power Sharing Among Inverters in Islanded AC Microgrids

Several drawbacks of the conventional and inverse droop control based decentralized techniques for islanded microgrids are being addressed actively, over the years by various researchers. One of the prominent issues is the inaccurate power sharing (reactive power in the conventional droop and real power in the inverse droop) among the distributed generators (DGs) due to the feeder/line impedances. Virtual impedance (VI) is a popular technique to overcome impedance mismatches but the challenge is in the setting of the appropriate value. This paper presents an adaptive decentralized technique for adjusting the virtual impedance in the controller of a DG, based on its output current, without the need of communication, extra sensors or network parameter/load estimations. The methodology is tested through simulations for a wide variety of cases including unbalanced, harmonic, constant power and induction motor loads, DG plug and play functionality and performance in larger networks (modified 13 and 33 bus systems) under meshed configurations. The range for parameter stability is verified through modelling and small signal eigenvalue analyses. Further, improved power sharing performances using the proposed scheme is validated through implementation on a laboratory experimental setup.