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In an effort to curb climate change, the electric power system in many countries is transitioning from fossil fuels to more renewable power sources such as wind. At the same time, other countries are decommissioning their old nuclear power, and replacing it with wind power. When replacing synchronous machines with wind power the inertia in the system is decreased. If nothing is done about this the performance of electric power grids will deteriorate. For example, the frequency deviation at a disturbance in power balance will increase. In this thesis the effects of more wind power in the Swedish electric power system was investigated. This was carried out by building two models of the Swedish electric power system in Matlab Simulink®. The first model was a one node representation of the Swedish system, and the second was a two node representation. For the two models both today’s system, and a future scenario without nuclear power was tested. Simulations with different losses of generation were preformed and the results examined. The usage of wind turbines for frequency control was investigated. To do this, 10% of the power in the wind was curtailed to enable increased power output when needed. A controller was introduced for the wind turbine, with the grid frequency as the measurement signal. This was tested for different amounts of the wind turbines contributing to the frequency control. The stability of the two node model was also investigated with theory for distributed control. The effects of replacing nuclear power with wind power in Sweden was also investigated by simulations in the existing Nordic 32 model, implemented in the dynamic power system simulation software PSS®E. The different simulations, and the control theory, showed that if more wind power is being built without controlling the frequency of the grid, the performance at a disturbance will deteriorate as the inertia in the system is reduced. If wind turbines are used for frequency control the perfo

The study of nonlinear dynamical systems via the spectrum of the Koopman operator has emerged as a paradigm shift, from the Poincaré's geometric picture that centers the attention on the evolution of states, to the Koopman operator's picture that focuses on the evolution of observables. The Koopman operator-theoretic framework rests on the idea of lifting the states of a nonlinear dynamical system to a higher dimensional space; these lifted states are referred to as the Koopman eigenfunctions. To determine the Koopman eigenfunctions, one performs a nonlinear transformation of the states by relying on the so-called observables, that is, scalar-valued functions of the states. In other words, one executes a change of coordinates from the state space to another set of coordinates, which are denominated Koopman canonical coordinates. The variables defined on these intrinsic coordinates will evolve linearly in time, despite the underlying system being nonlinear. Since the Koopman operator is linear, it is natural to exploit its spectral properties. In fact, the theory surrounding the spectral properties of linear operators has well-known implications in electric power systems. Examples include small-signal stability analysis and direct methods for transient stability analysis based on the Lyapunov function. From the applications' standpoint, this framework based on the Koopman operator is attractive because it is capable of revealing linear and nonlinear modes by only applying well-established tools that have been developed for linear systems. With the challenges associated with the high-dimensionality and increasing uncertainties in the power systems models, researchers and practitioners are seeking alternative modeling approaches capable of incorporating information from measurements. This is fueled by an increasing amount of data made available by the wide-scale deployment of measuring devices such as phasor measurement units and smart meters. Along these lines, the Ko

In this paper is presented a semi-active fault-tolerant control (SAFTC) as an alternative to reconfigurable or self-repairing fault-tolerant architectures with application to power systems. The final goal is to achieve stability and a minimum level of system performance following the completely loss of the feedback signals in the controller, which in this case are remote wide-area signals. The proposed controller is designed under the framework of Linear Matrix Inequalities (LMIs) to achieve pole placement. The semi-active design is compared against and ordinary or non-fault-tolerant control design to highlight that following the loss of a wide-area signal in the control, the closed loop response can lead to instability in the non-fault-tolerant case. The results are validated through nonlinear simulations results using a reduced version of the Nordic power system where the effectiveness of the proposed approach is demonstrated.

Two trends are emerging from modern electric power systems: the growth of renewable (e.g., solar and wind) generation, and the integration of information technologies and advanced power electronics. The former introduces large, rapid, and random fluctuations in power supply, demand, frequency, and voltage, which become a major challenge for real-time operation of power systems. The latter creates a tremendous number of controllable intelligent endpoints such as smart buildings and appliances, electric vehicles, energy storage devices, and power electronic devices that can sense, compute, communicate, and actuate. Most of these endpoints are distributed on the load side of power systems, in contrast to traditional control resources such as centralized bulk generators. This thesis focuses on controlling power systems in real time, using these load side resources. Specifically, it studies two problems. (1) Distributed load-side frequency control: We establish a mathematical framework to design distributed frequency control algorithms for flexible electric loads. In this framework, we formulate a category of optimization problems, called optimal load control (OLC), to incorporate the goals of frequency control, such as balancing power supply and demand, restoring frequency to its nominal value, restoring inter-area power flows, etc., in a way that minimizes total disutility for the loads to participate in frequency control by deviating from their nominal power usage. By exploiting distributed algorithms to solve OLC and analyzing convergence of these algorithms, we design distributed load-side controllers and prove stability of closed-loop power systems governed by these controllers. This general framework is adapted and applied to different types of power systems described by different models, or to achieve different levels of control goals under different operation scenarios. We first consider a dynamically coherent power system which can be equivalently mod

Distributed generation, decentralized and local control, self organization and autonomy are evident trends of today's electric power systems focusing on innovative control architectures such as MicroGrids, Virtual Power Plants, Cell based systems, plug-in electric vehicles and real time markets. Situation in Denmark is even more interesting, with a current 20% penetration of wind energy it is moving towards an ambitious goal of 50% penetration by the year 2050. Realization of these concepts requires that power systems should be of distributed nature { consisting of autonomous components and subsystems that are able to coordinate, communicate, cooperate, adapt to emerging situations and self organize in an intelligent way. At the same time, rapid development in information and and communication technologies (ICT) have brought new opportunities and elucidations. New Technologies and standards have been developed particularly in the area of communication and distributed control. Electric power industry is eager to explore, evaluate and adopt these new advancements in ICT for improving its current practices of automation and control in order to cope with above mentioned challenges. This thesis focuses on making a systematic evaluation of using intelligent software agent technology for control of electric power systems with high penetration of distributed generation. The thesis is based upon a requirement driven approach. It starts with investigating new trends and challenges in Electric power systems brought by introduction of distributed generation (DG). It reviews innovative control architectures and precisely identies the requirements in these control architectures which are interesting for application of the inteliiligent agents and maps them to the capabilities of the intelligent agents. It suggests a multiagent based exible control architecture (subgrid control) suitable for the implementation of the innovative control concepts. This subgrid control architecture i

In this paper is presented a semi-active fault-tolerant control (SAFTC) as an alternative to reconfigurable or self-repairing fault-tolerant architectures with application to power systems. The final goal is to achieve stability and a minimum level of system performance following the completely loss of the feedback signals in the controller, which in this case are remote wide-area signals. The proposed controller is designed under the framework of Linear Matrix Inequalities (LMIs) to achieve pole placement. The semi-active design is compared against and ordinary or non-fault-tolerant control design to highlight that following the loss of a wide-area signal in the control, the closed loop response can lead to instability in the non-fault-tolerant case. The results are validated through nonlinear simulations results using a reduced version of the Nordic power system where the effectiveness of the proposed approach is demonstrated., QC 20150703