SECURE AND RESILIENT OPERATION OF CYBER-PHYSICAL POWER SYSTEMS
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For economic reasons, modern power systems are commonly operated close to their secure limits so that they are vulnerable to unexpected severe disruptions such as disastrous cyberattacks and extreme weather events. This thesis is aimed at enhancing the security and resilience of power supplies for facilitating the development of a Smart Grid, when power systems in various parts of the world have been undergoing transitions toward cyber-physical systems. First, this thesis discusses common cybersecurity vulnerabilities in modern power systems and presents physical implications of cyberattacks on power system operations. In particular, this thesis analyzes a specifc type of coordinated cyberphysical attacks that could lead to undetectable line outages. Coordinated with physical attacks causing line outages, cyberattacks comprising topology preserving and load redistribution attacks could mask and potentially exasperate the outages to trigger cascading failures. Such coordinated cyber-physical attacks are analyzed in a bi-level optimization model which is then transformed into a mixed-integer linear programming problem. The proposed model and the two-stage solution algorithm are examined by case studies based on the IEEE 14-bus and 118-bus test systems. Second, this thesis offers the pertinent studies on quantifying the risk of cybersecurity vulnerabilities in power system operations. A type of locally coordinated cyber-physical attacks is analyzed in detail, which would cause undetectable line outages in local areas without the need for complete network information. A risk-based optimization model in the mixed-integer linear programming form is presented for analyzing physical implications resulting from the power ow redistribution. An efficient greedy search-based heuristic method is then developed to offer satisfactory solutions for real-time applications, which are verified by case studies based on a six-bus system and the two-area IEEE RTS-96 system. Third, this thesis studies security measures for mitigating the cybersecurity risk in power system operations. A game-theoretic framework is built for determining the optimal combination of security measures based on the minimax-regret decision rule. The resulting multi-level optimization model is reformulated as a bilevel mixed-integer linear programming problem. An implicit enumeration algorithm is then developed to achieve an exact solution to this complex problem. Acceleration techniques are also provided to improve the computation efficiency for large-scale power system applications. The proposed model and solution methods are validated by case studies based on a six-bus test system and the two-area RTS-96 system. Fourth, this thesis extends the discussion of cybersecurity vulnerabilities to the operation of distributed power systems like microgrids. Since microgrids are regarded as building blocks of a Smart Grid, they strive for cyber-secure operations for sustaining power services to local customers. The assessment and mitigation of the cybersecurity risk in microgrid operations is then presented in depth. Additional opportunities provided by software-defined networking technologies to enhance the microgrid cybersecurity are also realized by the proposed defense-in-depth framework that comprises three lines of defense against cyberattacks. Last, this thesis investigates the role of networked microgrids in enhancing the power system resilience against extreme events. Since resilience is an intrinsically complex property which requires deep understanding of power system operations, a generic simulation-based framework is developed for power system operators to analyze the resilience comprehensively and respond effectively in emergency conditions. The notion that the deployment of networked microgrids catalyzes the resilience enhancement in a Smart Grid is discussed in detail. Besides, the management of networked microgrids for achieving a higher degree of resilience, reliability, and efficiency of power supplies is discussed based on the proposed hierarchical control framework.