Saudi Cultural Missions Theses & Dissertations
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Item Restricted A State Observer Based Protection System for Microgrids: Theory and Implementation(Saudi Digital Library, 2025) Alzahrani, Saad A; Mitra, JoydeepThe protection of microgrids (MGs) is an emerging research topic due to the increasing integration of distributed generation (DG) based renewable energy resources (RES). Although a microgrid can operate in two modes: grid—connected and islanded, protection against unexpected disturbances and faults in microgrid systems faces significant challenges due to the high penetration of RES, dual operation modes, and fluctuations in fault currents. Moreover, as microgrids proliferate and become increasingly smaller in size, the use of conventional protection methods can become unreliable and cost-prohibitive. This dissertation investigates the development of a protection system to alleviate the aforementioned issues. First, an integrated control and protection framework based on a state observer is developed and demonstrated. This framework enables the microgrid to detect faults and limit fault-current contributions. As the DGs are connected to the MG through power converters and the MG primarily supplies critical loads, the technical benefits of incorporating external fault-current limiters (FCLs) into the integrated protection framework are investigated to ensure power continuity and stable, reliable operation under all conditions. Second, the dissertation introduces a modern multi-function protection technique, where a decentralized Multi-Agent System (MAS) control strategy is utilized to enable reliable data exchange over the MG network. This framework can accommodate various functions, such as fault detection, isolation, and auto-reconfiguration. Third, this dissertation develops a dynamic state estimation based protection method using a linear state space model for each protection zone and real-time measurements, where a weighted least absolute value (WLAV) estimator implemented via linear programming estimates the system state. The protection logic is developed based on the residuals of the state estimation and the operational limits of the system to detect and isolate the faulted zone. Finally, a prototype digital relay-based control and protection integration scheme is developed, in which the relay is modeled using residuals from a state observer, phase-voltage continuity, and the circuit-breaker (CB) status of the protected component. The proposed digital relay is designed and tested in real time using the Real-Time Digital Simulator (RTDS), providing a high-fidelity environment for evaluating its performance under various fault scenarios. Its communication framework is based on the IEC 61850 standard.16 0