Date of Award
Master of Science (MS)
Dr. Sukumar Brahma
Dr. Sheikh Jakir Hossain
Dr. Ramtin Hadidi
As traditional, carbon-emitting power generation facilities are being retired, the future of the electric grid is being powered by renewable energy sources and supported by energy storage. Unlike centralized power generation, renewable energy can be installed in a distributed or local manner, leading to a restructuring of the distribution system towards a more modular design and the growth of microgrid technology.
Microgrids are small, locally fed power systems that supply electricity to a specific customer base. Utilities are using this technology to enhance the reliability and resilience of their distribution systems. These utility microgrids can provide grid support during normal operations and can also operate as a self-sustained island during grid outages.
With a growing commitment to carbon-neutrality, common forms of modular clean generation are solar photovoltaic arrays, battery energy storage systems, and wind turbines. These sources require an inverter to connect to the AC grid, and hence, are called inverter-based resources (IBRs). Advanced inverter-based microgrids with seamless transition can switch between grid-connected and island modes without any customer blinks, a unique feature not found in conventional inverters.
The addition of inverter-based microgrids to distribution systems introduces new protection challenges. If microgrid generation is providing grid-support, the multi-source distribution feeder will have bi-directional power flow and bi-directional fault current in the event of a short-circuit. The inverter-based resource is current-limited, providing limited fault current in the case of a short circuit. This requires the distribution protection design to be capable of handling a wider range of fault currents with bi-directional flow.
To overcome these challenges, protection designs utilize communication to interchange between two separate relay settings based on the microgrids mode of operation. However, for microgrids equipped with seamless transition, delays in change of settings and communication delays introduce risk to reliable protection.
By evaluating a Duke Energy microgrid system, this thesis illustrates the practical risks of seamless transition while using an inverter and the protection deficiencies that arise. Although conventional inverter design does not allow for seamless transition, inverter controls are designed on an actively deployed inverter to offer seamless transition functionality. Considering cost and the protection risks from seamless transition, an adaptive protection scheme has been designed without the need for change of settings or communication. The efficacy of the adaptive protection scheme has been successfully demonstrated through hardware-in-the-loop simulations and relay tests, which have validated the robustness of the protection design.
Sabet, Jason, "Adaptive Protection Scheme for Microgrids with Seamless Transition" (2023). All Theses. 4086.