Impedance-Based Adaptive Droop Control for Islanded AC Microgrids and Overview

Abstract

Recent improvements in the application of distributed energy resources (DERs) and microgrids (MGs) have made controlling these resources very important. However, there are still many challenges in this field. One of the anticipated challenges in islanded MGs (IMGs) is the mismatched output impedance of DERs, which affects the volt-var regulation, shortly after the occurrence of islanding mode. Ignoring these events creates consecutive power quality challenges such as circulating currents and reactive power sharing error, voltage variations, increased power loss, and overcurrent. Even though the microsources that make up the MG are located near loads, MGs often require receiving control commands from the central controller through low-/high-bandwidth communication networks to achieve the most stable operating point. Depending on the type of control structure, the information of the units including current, voltage, and active and reactive power is received/sent between one and three control levels. This paper aims to analyze the state-of-the-art techniques that are often developed based on adaptive virtual impedance droop control (AVIDC). Hierarchical structure and multiagent system (MAS) are the most coherent class of three-level infrastructures implemented by the consensus protocol. In this survey, the opportunities and threats of the islanded AC MGs controlled by the enhanced droop method using virtual impedance have been analyzed. At the same time, these have been implemented in centralized, decentralized, hierarchical, and MAS-based distributed coordination structures. Finally, the simulation results of an IMG controlled by AVIDC and based on line X/R ratio have been analyzed in PSIM Altair software.