Developing microgrids is an attractive solution for integrating inverter-based resources (IBR) in the power system. Distributed control is a potential strategy for controlling such microgrids. However, a major challenge toward the proliferation of distributed control is cybersecurity. A false data injection (FDI) attack on a microgrid using distributed control can have severe impacts on the operation of the microgrid. Simultaneously, a microgrid needs to be protected from system faults to ensure the safe and reliable delivery of power to loads. However, the irregular response of IBRs to faults makes microgrid protection very challenging. A microgrid is also susceptible to faults inside IBR converters. These faults can remain undetected for a long time and shutdown an IBR. This dissertation first proposes a method that reconstructs communicated signals using their autocorrelation and crosscorrelation measurements to make distributed control more resilient against FDI attacks. Next, this dissertation proposes a protection scheme that works by classifying measured harmonic currents using support vector machines. Finally, this dissertation proposes a protection and fault-tolerant control strategy to diagnose and clear faults that are internal to IBRs. The proposed strategies are verified using time-domain simulation case studies using the PSCAD/EMTDC software package. / Doctor of Philosophy / Renewable energy resources, such as wind, solar, and geothermal, are interfaced with the grid using DC-to-AC power electronic converters, popularly known as inverters. These “inverterbased resources (IBR)” are mostly distributed and located near consumers. During outages, IBRs can be used to provide power to customers. This gives developers the idea of integrating IBRs in microgrids. A microgrid is a miniature grid that consists of IBRs and customers. A microgrid is normally connected to the grid but can disconnect from the grid and operate on its own. To run efficiently, a microgrid uses fast and reliable communication between IBRs to create a high-performance distributed control strategy. However, this creates cybersecurity concerns for microgrids. This dissertation proposes a cybersecure distributed control strategy to make sure microgrids can keep their advantages. This dissertation also proposes a protection method that relies on machine learning to clear short circuits in the microgrid. Finally, this dissertation proposes a strategy to diagnose failures inside IBRs and ride through them. The proposed solutions are verified using the industry-grade simulation software PSCAD/EMTDC.

Traditionally, power system protection describes detecting, clearing, and locating faults in the power system. Traditional methods for detecting and locating faults may not be sufficient for inverter-based resources (IBR) as the fault response of an IBR differs from the response of a synchronous generator. As the composition of the power grid continues to evolve to integrate more IBRs that employ communication-based control algorithms; the power system is also exposed to cyberattacks. Undetected cyberattacks can disrupt normal system operation causing local outages. Therefore, power system protection must evolve with the changes in the grid to not only detect, locate, and clear faults with IBR generation but also detect and mitigate cyberattacks on IBR controllers. This thesis proposes methods for protecting an IBR-based transmission system from: (i) GPS spoofing cyberattacks on a power sharing controller; (ii) open-circuit faults. The GPS spoofing detection algorithm is a decision tree that enables either the proposed state observer--based mitigation technique or the proposed long short-term memory (LSTM)-based mitigation algorithm. The proposed logic for detecting open-circuit faults addresses each subcategory of open-circuit faults: breaker malfunctions, broken conductors, and series arc faults. PSCAD/EMTDC simulations are performed to test the effectiveness of the proposed methods. / Master of Science / The desire to reduce carbon emissions from electric power generation is resulting in the simultaneous retirement of fossil-fuel-burning electric power generation and increase in the number of renewable energy resources. These renewable energy resources, or inverter-based resources, respond differently to disturbances than traditional generators, and; therefore, require the development of new strategies to improve the disturbance response of an inverter-based resource. Disturbances in the power system can be divided into two types: (i) normal disturbances; (ii) abnormal disturbances. The response of an IBR to normal disturbances is improved with reliable control, further improved with communication, which ensures the stable operation of the power system. The abnormal conditions can also be split into two categories: (i) cyberattacks; (ii) faults. A cyberattack is when an adversary gains access a system with the goal of causing harm. In IBRs, cyberattacks can degrade power quality and lead to local outages. Faults are events that cause a change in the normal current flow in the power system. Undetected faults can cause local outages, lead to forest fires, and personnel injury; therefore, must be detected, located, can cleared in a timely manner. This work explores methods for detecting and mitigating cyberattacks and detecting faults in the presence of inverter-based resources.

The U.S. movement toward clean energy generation has increased the number of installed inverter-based resources (IBR) in the grid, introducing new challenges in IBR control and cybersecurity. IBRs receive their set point through the communication link, which may expose them to cyber threats. Previous work has developed various techniques to detect and mitigate cyberattacks on IBRs, developing schemes for new inverters being installed in the grid. This work focuses on developing model-free control techniques for already installed IBR in the grid without the need to access IBR internal control parameters. The proposed method is tested for both the grid-forming and grid-following inverter control. Separate detection and mitigation algorithms are used to enhance the accuracy of the proposed method. The proposed method is tested using the modified CIGRE 14-bus North American grid with 7 IBRs in PSCAD/EMTDC. Finally, the performance of the detection algorithm is tested under grid normal transients, such as set point change, load change, and short-circuit fault, to make sure the proposed detection method does not provide false positives. / Master of Science / Due to the increasing presence of renewable energy resources such as photovoltaic and solar has introduced new challenges to the grid as the United States shifts towards clean energy. Those resources rely on devices called inverters to transform the energy to match the conditions of the grid. Inverters receive instructions to change their values before making the connection, making them potentially vulnerable to cyberattacks. While there has been progress in developing protection methods for inverters, existing inverters require additional protection to ensure their safe and reliable function. This work proposes a way to improve the reliability of existing inverters without changing the values of their internal settings. The method, tested under several conditions, successfully detects and counters potential cyberattacks without mistaking normal grid operations such as adjustments in demand and short circuit events.

The global trend towards electrifying the grid has positioned power electronics at the forefront of modern power systems. To control power electronics in grid-connected applications, Grid Forming (GFM) control has become a focal point of research. GFM control utilizes control laws derived from steady-state relationships in the phasor domain. Although these control methods have historically performed well in traditional power systems dominated by electrical machines, they exhibit unexpected control issues in power electronics-dominant power systems. The root of these unexpected behaviors lies in the foundational assumptions of these control methods (Droop control and Virtual Synchronous Machine) i.e. frequency is considered to be a steady state quantity which is constant within the fundamental line cycle. This thesis critically examines these assumptions and elucidates their potential inapplicability in power electronics-dominated power systems. This thesis also introduces vectors as an alternative representation of voltages and currents. Unlike phasors, vectors are instantaneous and time-varying representation of electrical quantities at any point in time, defined by three time-varying values: Magnitude, Polar angle, and Azimuthal angle, using the spherical coordinate system. An initial attempt to demonstrate the capability of using these vectors to control the active and reactive power in inverters connected to the grid has also been presented in this thesis. The proposed vector-based control is able to track the commanded power setpoints within a fraction of the fundamental AC voltage cycle. / Master of Science / As the world moves towards cleaner, greener energy, power electronics have become a key technology in modern electrical grids. One of the main ways to control power converters in grid- connected systems is through a method called Grid Forming (GFM) control. GFM control has been effective in traditional grids with large rotating machines, but it faces unexpected problems in grids that rely more on power electronics. This is because the basic assumptions of GFM control, such as treating frequency as a steady value, do not always hold true in power electronics-driven systems. This thesis explores these issues and proposes a new approach to improve control. Instead of using traditional methods based on steady-state values, it introduces the idea of using vectors to represent electrical quantities like voltage and current. Unlike traditional methods, vectors can describe electrical signals at any moment in time. The thesis demonstrates how this vector-based approach can be used to control important parameters of power converters in the grid, like active and reactive power, in a way that responds quickly and accurately to changes and disturbances. This new method could help make power systems more reliable and efficient as they evolve to incorporate more power electronics.

The introduction of Distributed Energy Resources such as energy storage systems, solar, and wind create system dynamics which modern electric grids cannot reliably handle in such large quantities without properly coordinated protections. One such tool is the concept of Fault Ride Through, which allows a system to continue operation during a long-term minor or short-term major disturbance. Standards are in place to control and monitor the operation and recovery of this capability but are meant to be minimum or maximum requirements. Since these standards must be used nationally, or sometimes internationally, they tend to be left very flexible. The rise of inverter-based devices, however, means that stricter standards which provide better grid protections can be more easily achieved. This thesis presents a comprehensive review of the inverter requirements inside IEEE 1547 regarding Voltage Fault Ride Through, power quality, and recovery of these devices during fault conditions. It examines the technical requirements, discusses various techniques of implementation, and compares IEEE 1547 to other national and international standards. Several real-world case studies are included to highlight the consequences of inadequate Fault Ride Through protocols, emphasizing the importance of robust inverter design and proper controller settings.

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Rapidly growing Inverter- Based Resources (IBR) have different fault properties compared to Synchronous Generators (SG). Therefore, it is necessary to study the fault behavior of systems that contain different types of IBR and compare it to the conventional system responses in order to understand what steps should be taken to adapt conventional protection settings for new types of sources. For a two bus model, it is found out that sequence profiles in a system with one IBR are different from those observed in conventional system. Thermal and electrical limitations of the power electronics reduce the fault current from the IBR significantly, driving negative sequence current to small values compared to conventional sources. This is true for all studied types of IBR. Moreover, if IBR is connected to the grid through one line only, during Three Phase Fault (3hp) it is possible to lose synchronism with grid due to erroneous estimation of the grid angle through the Phase-Locked Loop (PLL). Verification of the obtained results is made through comparison to the Fault Recordings taken from the protection relays placed at substations. It is shown that for some faults simulation results can predict the behavior of symmetrical components in the network whereas for others they do not. To explain the latter behavior modifications to the sequence networks are proposed. / Snabbt växande inverterbaserade resurser (IBR) har olika felinmatningsegenskaper jämfört med synkrongeneratorer (SG). Därför är det nödvändigt att studera felbeteende hos system som innehåller olika typer av IBR och jämför det med konventionella källor för att kunna förstå vilka steg som ska göras för att anpassa konventionella skyddsinställningar för nya typer av källor. Under litteraturöversikten introduktion till det fast jordade systemet och dess speciella fall med isolerad transformatorjordning är klar. Kort introduktion till den studerade IBR och typer av simulerade fel görs också. För en tvåbussmodell har det visat sig att sekvensprofiler i ett system med en IBR skiljer sig från de som observerats i konventionella system. Termisk och elektrisk begränsningar i kraftelektroniska komponenter minskar felströmmen från IBR avsevärt och driver negativ sekvensström till små värden jämfört med konventionella källor. Detta gäller för alla studerade typer av IBR. Dessutom, om IBR är ansluten till nätet endast genom en linje, är det möjligt under trefasfel (3hp) att tappa synkronisering med nätet på grund av felaktig uppskattning av fasvinkeln genom styrsystemets faslåst slinga (PLL). Verifiering av de erhållna resultaten görs genom jämförelse med Fel Inspelningar från reläet placerade på transformatorstationer. Det visas att för vissa fel simuleringsresultat kan förutsäga symmetriska komponenters beteende i nätverket medan andra inte gör det. För att förklara de senare beteendena föreslås modifieringar i sekvensnätverket.