An Adaptive Virtual Impedance control for improving Power Sharing among Inverters in Islanded AC Microgrids

Abstract

Inverter based distributed generators are increasingly being employed for feeding energy from renewable energy sources into the grid. The control of parallel inverters in a microgrid system can fall under: centralized (involving communication), decentralized (droop control) or distributed (sparse communication network) control. Droop control is an effective technique for ensuring parallel operation based on local measurements alone, ensuring plug and play capability, without the need for communication. However, several drawbacks of the conventional droop control technique are being addressed actively, over the years by various researchers. One of the prominent issues is the inaccurate power sharing among the distributed generators (DGs) due to the feeder/line impedances. This paper presents an adaptive 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 parameter estimations. The methodology is tested through simulations and the modelling for stability is verified through small signal eigenvalue analyses. Further, implementation on an experimental setup in the laboratory shows improved power sharing performance. The strategy is validated for both the conventional droop and the inverse droop cases.