Date of Award
12-2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Electrical and Computer Engineering
Committee Chair/Advisor
Dr. Sukumar Brahma
Committee Member
Dr. Mashrur Chowdhury
Committee Member
Dr. Christopher Edrington
Committee Member
Dr. Ramtin Hadidi
Abstract
The existing utility grid is experiencing a paradigm shift in electricity generation due to a significant penetration of renewable energy sources. This shift is primarily driven by the large-scale integration of solar and wind energy farms, particularly in the transmission network, where these farms are typically accompanied by battery energy storage in a hybrid configuration to overcome source intermittency and improve reliability. Such renewable farms comprise numerous inverters, pad-mounted transformers, collector feeders, and dc-side components depending on the generation-source type. Additionally, inverters within these farms exhibit distinct operating modes, such as `grid-following'(GFL) and `grid-forming'(GFM), as well as fault control modes, like momentary cessation (MC) and fault ride-through (FRT) mode, based on existing standards. To avoid the computational burden of detailed modeling of all components of such farms in an Electromagnetic Transient (EMT) program, this research lays out a physics-based argument to advocate the use of an aggregated model. This approach avoids the detailed modeling of all components of a renewable farm in an EMT program for short-circuit studies while maintaining acceptable accuracy. It also illustrates through EMT simulations how inverters operating under different modes within a farm can be aggregated. This is the addition to the state of the art proposed by this work in the area of fault modeling of bulk power systems with hybrid renewable farms including storage. For modeling of inverters in this work, generic inverters are modified to comply with the requirements of the recently published IEEE 2800 standard.
Next, the work focuses on the resolution of a well-documented security issue in the protection of power systems in presence of renewable farms. The distinct fault control approach of these farms' inverters has led to the tripping of multiple real-world solar and wind farms over the past few years in the USA. These trippings occurred while the inverter was recovering from the fault event following the MC or FRT as a control mode. It was due to `sub-cycle overvoltage', where the instantaneous ac voltage of inverters terminal rose above a hard threshold for a fraction of a cycle. Though, as shown through the literature survey, despite the problem being well-documented by NERC reports, a comprehensive solution that can be integrated with existing inverter controllers in the field has not been published. This research first recreates the sub-cycle overvoltage scenario in each fault control mode using a scaled farm model of a real-world farm, validating the simulation results using field data published in the NERC reports. Afterward, gaining insights from simulations and using physics based hypothesis supported by network properties, this research proposes distinct methods to comprehensively resolve the sub-cycle overvoltage issue in each fault control mode, which are rigorously tested in real-time in simulations. These methods can be implemented as firmware updates in the existing farms that are susceptible to such unwanted trippings due to sub-cycle overvoltage.
Recommended Citation
Hossain, Shah Mohazzem, "Short-Circuit Modeling and Instantaneous Overvoltage Protection of Renewable Farms" (2024). All Dissertations. 3846.
https://open.clemson.edu/all_dissertations/3846
Author ORCID Identifier
https://orcid.org/0000-0003-0206-6241