Intelligent Virtual Impedance Based Control to Enhance the Stability of Islanded Microgrid

Abstract

This paper focuses on the voltage stability issue of an islanded microgrid in a cost-effective way adding the concept of adaptive virtual impedance. In the islanded microgrid structure, the mis-match of line impedance between the Distributed Generation (DG) units and imbalance of inverter local load are two critical factors to be dealt with carefully. These can result in serious circulating current and unreasonably reactive power sharing among DG units by using the conventional droop control method. In practical engineering, line inductance is often increased to eliminate the impedance mismatch. However, such a method would lead to an increase in cost, weight, and volume. To solve this problem, an adaptive virtual impedance droop control strategy based on fuzzy controller is proposed. Instead of DG units are equipped with series inductors, an adaptive virtual impedance is introduced to adaptively eliminate the reactive power error caused by the inconsistency of the line impedance through the fuzzy controller. At the same time, in order to deal with the droop control and the voltage drop at the inverter output caused by the addition of virtual impedance, a voltage compensation link is introduced to maintain the voltage within an acceptable range. The simulations were performed in Matlab/Simulink and RT-LAB experiments to verify the validity of the proposed control strategy.