Cyber-Physical Security of Wide-Area Frequency-based Applications in Power Systems

Modern power systems are continuously developing into large and interconnected ones. However, at the same time, restructuring within the power industry and reduced investment in transmission system expansions mean that power systems are operating closer and closer to their limits, leaving them more vulnerable to fault outages than before. The aspects of protection and control within power systems have thus become increasingly important as well as complicated. Concurrently, the continuous technological development in communication and measurement has accelerated the occurrence and application of Wide-Area Monitoring, Protection and Control (WAMPAC), a new kind of advanced scheme based on wide-area measurements. The blackouts happening in North America as well as in other countries over the past few years are also providing more incentives to scientists and engineers to study wide-area protection and control systems. Communication networks in smart grids bring increased connectivity at the cost of increased security vulnerabilities and challenges. A smart grid can be a prime target for cyber terrorism because of its critical nature. As a result, smart grid security has already attracted significant attention from governments, the energy industry, and consumers, leading to several important studies. WAMPAC is the concept of using system-wide information via a centralized control center or Energy Management System (EMS) to monitor and control the whole system. Based on the situation and the required control action, the control center shares selected data with specific remote locations that are in need of the data. The utilization of system-wide information makes it easier to monitor the entire system and make better control and protection decisions by the EMS. Although the communication system is the backbone of these recent schemes, it makes them vulnerable to different types of cyber attacks. This thesis aims to investigate the problem of cyber security in frequency-related WAMPAC schemes. Two main schemes are considered as case studies: Automatic Generation Control(AGC) and Wide-Area Under-Frequency Load Shedding (WAUFLS) protection schemes. In addition, the cyber security of Power System State Estimation (PSSE), as a Wide-Area Monitoring (WAM) scheme, has been revisited. As WAMPAC schemes are so varied in their purpose and implementation, there is no general analysis to illustrate the potential impact of a cyber attack on all such schemes. However, some general types of system responses are considered in this work. First, with regard to AGC systems, a Kalman filter-based approach is proposed to detect False Data Injection (FDI) in AGC systems. Because detecting FDI and removing the compromised measurements are not enough in practical situations, the use of a simultaneous input and state estimation-based algorithm to detect and concurrently compensate for FDI attacks against the measurements of AGC systems is investigated. Throughout the use of this algorithm, the FDI attack signal is dealt with as an unknown input and its value is estimated accordingly. Then, the estimated value for the FDI is used to compensate for the effect of the attack so that the control center makes its decisions based on the corrected sensor signals, not the manipulated ones. Unlike other approaches, and as an extension to this work, the effect of AGC nonlinearities is studied during the attack time. Recurrent Neural Networks (RNN)-based approach is proposed to detect FDI during a time where any of the nonlinearities is affecting the system. The RNN-based approach is used to classify and identify the attacks according to their behavior. Second, with regard to WAUFLS protection schemes, this thesis investigates the problem of cyber attacks on WAUFLS. This is followed by a detailed analysis showing that an adversary can launch an FDI attack against existing WAUFLS schemes in three different ways depending on they access level to system data, which may lead to equipment damage and/or system-wide blackout. To address this issue, a new mitigation scheme, that is ro-bust against cyber attacks, is proposed to mitigate the effect of FDI attacks on WAUFLS. The proposed scheme depends on trusted system states to run power flow, so the power mismatch in the system is calculated. Finally, the calculated magnitude of disturbance is used to decide on the amount and locations of the load shedding. All proposed detection and mitigation methods in the thesis are tested using simulations of practical systems. In addition, sensitivity analysis is given after each method

Attributes of Big Data Analytics for Data-Driven Decision Making in Cyber-Physical Power Systems

Big data analytics is a virtually new term in power system terminology. This concept delves into the way a massive volume of data is acquired, processed, analyzed to extract insight from available data. In particular, big data analytics alludes to applications of artificial intelligence, machine learning techniques, data mining techniques, time-series forecasting methods. Decision-makers in power systems have been long plagued by incapability and weakness of classical methods in dealing with large-scale real practical cases due to the existence of thousands or millions of variables, being time-consuming, the requirement of a high computation burden, divergence of results, unjustifiable errors, and poor accuracy of the model. Big data analytics is an ongoing topic, which pinpoints how to extract insights from these large data sets. The extant article has enumerated the applications of big data analytics in future power systems through several layers from grid-scale to local-scale. Big data analytics has many applications in the areas of smart grid implementation, electricity markets, execution of collaborative operation schemes, enhancement of microgrid operation autonomy, management of electric vehicle operations in smart grids, active distribution network control, district hub system management, multi-agent energy systems, electricity theft detection, stability and security assessment by PMUs, and better exploitation of renewable energy sources. The employment of big data analytics entails some prerequisites, such as the proliferation of IoT-enabled devices, easily-accessible cloud space, blockchain, etc. This paper has comprehensively conducted an extensive review of the applications of big data analytics along with the prevailing challenges and solutions

Scenarios for the development of smart grids in the UK: literature review

Smart grids are expected to play a central role in any transition to a low-carbon energy future, and much research is currently underway on practically every area of smart grids. However, it is evident that even basic aspects such as theoretical and operational definitions, are yet to be agreed upon and be clearly defined. Some aspects (efficient management of supply, including intermittent supply, two-way communication between the producer and user of electricity, use of IT technology to respond to and manage demand, and ensuring safe and secure electricity distribution) are more commonly accepted than others (such as smart meters) in defining what comprises a smart grid. It is clear that smart grid developments enjoy political and financial support both at UK and EU levels, and from the majority of related industries. The reasons for this vary and include the hope that smart grids will facilitate the achievement of carbon reduction targets, create new employment opportunities, and reduce costs relevant to energy generation (fewer power stations) and distribution (fewer losses and better stability). However, smart grid development depends on additional factors, beyond the energy industry. These relate to issues of public acceptability of relevant technologies and associated risks (e.g. data safety, privacy, cyber security), pricing, competition, and regulation; implying the involvement of a wide range of players such as the industry, regulators and consumers. The above constitute a complex set of variables and actors, and interactions between them. In order to best explore ways of possible deployment of smart grids, the use of scenarios is most adequate, as they can incorporate several parameters and variables into a coherent storyline. Scenarios have been previously used in the context of smart grids, but have traditionally focused on factors such as economic growth or policy evolution. Important additional socio-technical aspects of smart grids emerge from the literature review in this report and therefore need to be incorporated in our scenarios. These can be grouped into four (interlinked) main categories: supply side aspects, demand side aspects, policy and regulation, and technical aspects.

PMU-Based ROCOF Measurements: Uncertainty Limits and Metrological Significance in Power System Applications

In modern power systems, the Rate-of-Change-of-Frequency (ROCOF) may be largely employed in Wide Area Monitoring, Protection and Control (WAMPAC) applications. However, a standard approach towards ROCOF measurements is still missing. In this paper, we investigate the feasibility of Phasor Measurement Units (PMUs) deployment in ROCOF-based applications, with a specific focus on Under-Frequency Load-Shedding (UFLS). For this analysis, we select three state-of-the-art window-based synchrophasor estimation algorithms and compare different signal models, ROCOF estimation techniques and window lengths in datasets inspired by real-world acquisitions. In this sense, we are able to carry out a sensitivity analysis of the behavior of a PMU-based UFLS control scheme. Based on the proposed results, PMUs prove to be accurate ROCOF meters, as long as the harmonic and inter-harmonic distortion within the measurement pass-bandwidth is scarce. In the presence of transient events, the synchrophasor model looses its appropriateness as the signal energy spreads over the entire spectrum and cannot be approximated as a sequence of narrow-band components. Finally, we validate the actual feasibility of PMU-based UFLS in a real-time simulated scenario where we compare two different ROCOF estimation techniques with a frequency-based control scheme and we show their impact on the successful grid restoration.Comment: Manuscript IM-18-20133R. Accepted for publication on IEEE Transactions on Instrumentation and Measurement (acceptance date: 9 March 2019