Doctoral Dissertations

Orcid ID

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Energy Science and Engineering

Major Professor

Leon Tolbert

Committee Members

Seddik M. Djouadi, Fangxing Li, Aleksandar Dimitrovski


This dissertation proposes protection solutions to challenges introduced in power systems with high penetration of renewable energy sources. The distinct protection challenges that emerge in both islanded and grid-tied systems are explored.

For islanded systems, the main protection challenge relates to the low-short circuit currents of inverter-based resources (IBRs). As a solution, a novel approach that addresses the root problem is proposed that can increase the short-circuit contribution of a generic voltage source converter. The proposed design allows the inverter to provide sustained short-circuit current to achieve fuse-relay and relay-to-relay coordination. Adaptive relaying for microgrid protection in islanded and grid-tied mode is analyzed. An adaptive relay adjusts the relay curves based on the available generation and the network topology. The model-adaptive relay is validated in hardware and hardware-in-the-loop (HIL) and was deployed at EPB control center microgrid. A power amplifier is designed to interface protective relays with protective relays, which is used to evaluate the model-adaptive relay in the laboratory.

For grid-tied systems, this dissertation explores the impact of voltage dips in wind turbine doubly fed induction generator (DFIG) and photovoltaic (PV) systems while also presenting solutions to improve their low-voltage ride through (LVRT) capabilities. The development of a real-time simulator is validated against a physical DFIG testbed. The DFIG machine model is compared with physical measurements during balanced and unbalanced grid conditions. The validated model is then used to study the DFIG system during symmetrical and asymmetrical voltage sags and to evaluate LVRT strategies. Hardware modifications are applied to significatively increase the reactive power support of PV inverters and demonstrates that increasing the semiconductor’s current rating allows the PV inverter to ride through faults while enhancing their reactive power support during voltage sags. Through detailed electrothermal simulations, this design is shown to be capable of injecting three-times the inverter rated current for enough time to comply with established LVRT requirements.

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