Date of Award
6-12-2024
Publication Type
Dissertation
Degree Name
Ph.D.
Department
Electrical and Computer Engineering
Keywords
Cyber resiliency;Directional overcurrent relays;Machine learning;Microgrids;Optimization;Synchronverters
Supervisor
Maher Azzouz
Supervisor
Mitra Mirhassani
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Abstract
Microgrids exhibit a cost-effective solution for expanding power systems due to their advantages such as flexible operation and control, limited emissions, and less dependence on fossil fuel. Like traditional distribution systems, microgrids should be protected during abnormal conditions, such as grid faults or cyber-attacks. Further, microgrids could be powered by inverter-interfaced distributed generators (IIDGs). These IIDGs have advantages, including reduced emissions and flexible operation during normal operation. However, IIDGs may generate currents with magnitudes that are high enough to damage the inverter switches. Also, the IIDG currents may affect the functionality and coordination of directional overcurrent relays (DOCRs) that protect microgrid distribution lines. Furthermore, the DOCRs are vulnerable to cyber-attacks that are intended to cause unwanted isolation of distribution lines. The ultimate objective of this dissertation is to enhance the resiliency of microgrids during grid faults and cyber-attacks. This objective investigates improving DOCRs' protection functions and proposing control algorithms for IIDGs. To improve DOCRs' performance, their susceptance to cyber-attacks that target their secure operation is analyzed. Then, a methodology that involves artificial intelligence is used to differentiate faults from cyber-attacks is proposed. Hence, the DOCRs will not trip their corresponding circuit breakers falsely. Also, improving DOCRs' protection encompasses investigating how to ensure DOCRs' reliable operation during grid faults. This is done by optimally coordinating the DOCRs to produce fast-tripping signals in a coordinated manner to cease microgrid faults from spreading to their healthy sections. Consequently, the cyber-secured and coordinated DOCRs guarantee the protection of microgrids by issuing tripping signals when required (i.e., during faults) and blocking those signals when the DOCRs should not produce them (i.e., during cyber-attacks). The second part of the dissertation's objective is the development of new control algorithms for IIDGs controlled as synchronous generators (i.e., synchronverters) that provide inertia and damping in addition to IIDGs advantages, such as providing frequency and voltage support. During grid faults, synchronverters generate currents that include two components: a transient component that decays with time and a steady-state component. In addition, the synchronverters generate active and reactive power that oscillate during faults. Furthermore, grid codes mandate synchronverters to regulate active and reactive power generation according to the grid frequency and voltage variation. Also, synchronverters should be adaptive to the microgrid mode of operation (i.e., grid-connected or islanded). Therefore, this dissertation proposes virtual impedance fault current limiters (VI-FCLs) to intercept the synchronverters transient currents by reducing their magnitudes and accelerating the decay time. Moreover, current controllers are proposed to regulate active and reactive power production, limiting peak current generation and ensuring microgrid operating mode adaptivity. In addition, three fault ride-through (FRT) strategies to reduce power oscillations are proposed. The first strategy significantly reduces power oscillation at the expense of generated distorted currents; the second strategy partially reduces power oscillations while maintaining sinusoidal current, and the third strategy eliminates power oscillations and maintains sinusoidal current. Finally, this dissertation examines the effect of synchronverters with the proposed control algorithms on the coordination of DOCRs. This examination helps select which synchronverter controller is more suitable to fulfill its tasks, such as power oscillation elimination and current limitation, and adaptivity to the microgrid mode without adversely affecting the DOCRs' coordination. Each study toward achieving the ultimate object is developed and tested using MATLAB/SIMULINK. The obtained results in each study demonstrate the efficacy of the proposed methodologies in enhancing microgrids' resiliency by ensuring reliable and secure DOCR operation and guaranteeing synchronverters performance that limited current generation, reduced power oscillations, and agility to the grid requirements.
Recommended Citation
Pola, Saad Arshed Elias, "Resiliency Enhancement of Active Distribution Networks During Grid Faults and Cyber Threats" (2024). Electronic Theses and Dissertations. 9406.
https://scholar.uwindsor.ca/etd/9406