Keywords

power system protection, microgrids, superimposed quantities, dynamic phasors, negative sequence, symmetrical components

Abstract

The global electric power system is undergoing a transition which has resulted in the proliferation of inverter-based resources (IBRs), mainly renewable energy resources and battery energy storage. These offer the advantage of decarbonization targets in electricity generation while potentially improving resilience and overall efficiency of the electric grid. Furthermore, this has led to the development of inverter-interfaced microgrids at the sub-transmission, and especially, distribution levels.

An effective protection system is a prerequisite for any power system operation. However, the departure of modern power systems, in this regard, from conventional sources and topologies presents new challenges to effective protection from power system faults. Active distribution networks formed by integration of IBRs introduce bi-directionality in fault current flow. This is a major departure from the radial nature of fault currents in conventional distribution systems. This impacts the selectivity and security of existing protection systems.

Similarly, the sensitivity and dependability of existing protection systems are impacted by in modern systems due to the fault current magnitudes of IBRs. Based on the state-of-the-art, these current levels are significantly lower than current contribution from conventional sources. In fact, the general characteristics of IBR fault signatures tend to depart from traditional sources. In order to accommodate high penetration of IBRs in distribution networks, modern solutions have to be developed to deal with the protection challenges introduced by their integration.

This dissertation presents a a series of research works aimed at addressing the aforementioned sensitivity and selectivity challenges in detecting faults in modern distribution systems. The works employ various models using symmetrical components. The first work models a superimposed quantity to provide a new fault detection element for unbalanced faults. The element also provides a way to determine the direction of faults detected to improve selectivity. The second work introduces a dynamic phasor model as measured quantity for fault detection. A sub-cycle version of the dynamic phasor is further decomposed into symmetrical quantities to investigate potential improvement in the sensitivity and speed of fault detection. Finally, the final work addresses coordination of protection devices in an inverter-interfaced distribution system. This new model is based on positive sequence voltage to reduce the impact of IBR low fault current in coordinating relays during fault detection. Hadware-in-the-Loop and offline computer simulation results demonstrate the effectiveness of the proposed methods in improving protection systems in inverter-interfaced distribution networks.

Completion Date

2025

Semester

Spring

Committee Chair

Dimitrovski, Aleksandar

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Electrical and Computer Engineering

Identifier

DP0029364

Document Type

Dissertation/Thesis

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