Date of Award

12-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering (Holcomb Dept. of)

Committee Chair/Advisor

Dr Sukumar Brahma

Committee Member

Dr Ramtin Hadidi

Committee Member

Dr Harlan Russell

Committee Member

Dr Zheyu Zhang

Committee Member

Dr Shuangshuang Jin

Abstract

With the increasing drive towards a greener and more sustainable electric infrastructure and the decreasing cost of residential rooftop solar panels, solar-enriched residential-level microgrids are gaining attention as building blocks for future power delivery paradigms. In such a microgrid, dc networks are being considered to be a better alternative than the traditional ac networks because of the operational simplicity of dc systems. Nevertheless, commercial Low Voltage Direct Current (LVdc) microgrids are yet to become a reality because of the unusual speed required for dc protection, typically of the order of tens of microseconds. Due to this speed constraint, protection schemes which use communication to collect remote end measurements are not desirable as communication can introduce delays and uncertainties. To overcome this hurdle, this dissertation formulates for the first time in closed form, a topology agnostic fault detection and location method for a dc feeder fed by converter sources from both ends. This method is immune to fault resistance and fast enough to be used for main protection of a dc feeder in a dc microgrid. As the buses of a dc microgrid are equipped with converters and their associated dc link capacitors, exploiting their discharge characteristics during a fault, a backup protection scheme using only single-ended measurements is developed and shown to coordinate with the main protection scheme designed using the fault location method. The protection schemes are shown to coordinate with the converter protection for fault inside the dc microgrid, as well as for faults on the ac side of the microgrid. The testing and validation of the proposed fault location and protection methods are per- formed on a detailed time-domain model of a 4-bus bipolar ac-dc hybrid microgrid, designed based on a real microgrid in the USA. Initially, the testing is done on PSCAD platform to provide proof of concept. Later, simulations are carried out using a time-step of 1 μs on a real-time simulation platform-RTDS, and the protection scheme is evaluated using software relays. Finally, after obtaining successful real time test results, the main protection scheme along with a filter to remove measurement noise is implemented on an external hardware device (TI TMS320F28379D), and successfully tested as a Hardware-in-the-Loop (HIL) with the RTDS, demonstrating that the implementation of filter as well as the fault location method can be executed within 1 μs, a noteworthy advantage over commercial products available today.

Author ORCID Identifier

0000-0003-1671-3024

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