A universal centralized protection scheme for feeders of AC microgrids using IEC-61869-9 digital instrument transformers

Abstract

This thesis underscores the escalating importance of microgrids powered by renewable energy sources and inverters in modern power systems. Despite offering significant environmental and economic advantages, their decentralized and dynamic nature poses unique protection challenges. Traditional protection methods struggle to adapt to the diverse conditions within microgrids. Past protection techniques relying on current or voltage detection have limitations affecting system reliability and security. To address this, the thesis proposes a pioneering protection approach based on ’discrepant impedance.’ This concept calculates impedance disparities using both feeder ends’ positive sequence voltage and current measurements. This value approximates zero during normal operation but deviates during a fault, enabling effective fault detection. The proposed protection philosophy was rigorously tested through simulations, real-time experiments using RTDS®, and validation on the IEEE-9 bus system with inverter-based resources, a benchmark system by the National Renewable Energy Laboratory National Renewable Energy Laboratory (NREL). Comparative assessments with traditional methods underscore the effectiveness and adaptability of the discrepant impedance-based protection scheme. The thesis concludes by discussing practical implementation options, showcasing the approach’s versatility across varied microgrid configurations and control strategies, and ultimately demonstrating the feasibility and effectiveness of discrepant impedance-based feeder protection for modern microgrid systems.