Protection challenges and emerging solutions in renewable-integrated microgrids: a critical review

This study presents a critical and structured review of protection challenges and emerging solutions in renewable-integrated microgrids. The proliferation of distributed energy resources (DERs) has introduced complex protection issues, including bidirectional power flow, low fault currents, mode-dependent dynamics, and communication dependencies. This review systematically examines fault detection, classification, and coordination strategies for both grid-connected and islanded operating conditions from 2020 to 2025. A qualitative comparative analysis is conducted across diverse protection approaches, including conventional relay-based methods, artificial intelligence (AI)-based schemes, fuzzy logic systems, time-frequency analysis, phasor measurement unit (PMU)-assisted techniques, and communication-assisted multi-agent frameworks. The analysis identifies dominant trends toward hybrid, adaptive, and data-driven protection strategies while highlighting persistent gaps in scalability, experimental validation, cybersecurity, and real-world deployment. By synthesizing current research and identifying unresolved challenges, this review provides a clear roadmap for future work toward robust, standardized, and practically deployable microgrid protection systems.