Consensus-Based Delay-Tolerant Distributed Secondary Control Strategy for Droop Controlled AC Microgrids

Shafaat Ullah,Nasim Ullah,Laiq Khan,Irfan Sami

doi:10.1109/access.2020.3048723

Abstract

This article formulates a fully-distributed and delay-tolerant secondary control scheme for droop-controlled AC microgrids. The proposed strategy is inspired by the cooperative control concept of multi-agent systems (MASs). It considers the hierarchical control structure of the distributed energy resource (DER) units. It ensures equal active power sharing between three DER units, where each unit tracks the time-varying average load, with a finite-time convergence. As a result, the frequencies of the DER units are regulated to their nominal values. Furthermore, it offers plug-and-play capability for DER units, demonstrates significant robustness against load disturbances, and successfully tolerates, small as well as large, communication time-delays. Due to the fully-distributed configuration of the proposed control strategy, each DER unit in the test microgrid requires only its own information and information of its neighbors. The benefit is two-fold: not only this configuration assists in minimizing the overall bandwidth requirement, and cost of the corresponding communication network, but also it increases the reliability of the microgrid operation. The performance and effectiveness of the proposed technique is supported by exhaustive numerical simulations performed in Matlab/Simulink on an AC microgrid testbench comprising three DER units. The proposed strategy renders the superior performance in several aspects as compared to the existing developments in the literature in this area.

Highlights

GENERALLY, a low voltage, small-scale electric power grid is termed as a microgrid
The major contributions of the article are summarized below: 1) A fully-distributed and robust secondary frequency and equal active power sharing control framework is proposed for an AC microgrid that ensures equal active power sharing between distributed energy resource (DER) units, and in turn regulates their frequencies to the nominal value in a finite-time
2) The proposed control scheme ensures equal active power sharing and frequency regulation using a single control protocol for each DER unit as compared to the concepts reported in [13], [30]–[32], where a separate control methodology has been used for both purposes

Summary

Introduction

GENERALLY, a low voltage, small-scale electric power grid is termed as a microgrid. It comprises distributed generation (DG) units (such as photovoltaic systems, solar-thermal systems, wind turbines, fuel cells, geothermal systems, low-head hydro units, internal combustion engines and miniand micro-gas-turbines), distributed energy storage (DES, such as battery energy storage, super capacitor or ultra capacitor storage, superconducting magnetic energy storage systems and low- and high-speed flywheel systems) and loads interconnected through power lines. The authors in [24] have proposed a finite-time robust distributed secondary voltage and frequency control technique for inverter-interfaced DGs in an islanded AC microgrid that demonstrated accurate active power sharing between four DGs. The proposed technique has been found to offer plug-and-play feature, and robustness to reconfiguration of the communication network structure, parametric uncertainties and unmodeled system dynamics.

Results

Conclusion