Islanding Detection Techniques for Grid-Connected Microgrids and a Proposed Frequency–Reactive Power Hybrid Framework

Abstract

The increasing penetration of distributed generation (DG) based on renewable energy sources is transforming passive radial distribution networks into active, bidirectional microgrids. While this transition improves efficiency, reliability and environmental performance, it introduces the risk of unintentional islanding, whereby a DG unit continues to energize part of the network after the utility grid has been disconnected. Undetected islanding endangers maintenance personnel, can damage connected equipment, and disrupts protection coordination and power quality. Over the past two decades, researchers have proposed remote (communication-based), active, passive and hybrid islanding detection methods (IDMs), each involving trade-offs among the non-detection zone (NDZ), detection speed, power-quality impact, cost and robustness under multiple parallel-connected inverters. This paper organizes and critically compares these techniques with reference to the IEEE 1547 and UL 1741 anti-islanding requirements, and identifies two recurring limitations: the unreliable operation of passive schemes near zero power mismatch, and the continuous power-quality penalty imposed by active perturbation. Motivated by these gaps, a hybrid islanding detection framework is proposed that jointly monitors the frequency response of the point of common coupling (PCC) to a small, closed-loop reactive-power perturbation at the inverter output, with the perturbation gain increased through positive feedback once a passive stage first flags a suspected island. The proposed control architecture, detection algorithm, and a three-stage MATLAB/Simulink-based validation methodology, referenced against IEEE 1547 and UL 1741, are described.