This thesis has proposed two types of real time System Integrity Protection Schemes(SIPS) using Emergency Single Machine Equivalent (E-SIME) and Model PredictiveControl (MPC) approaches respectively. They are aiming to resolve the transientstability problems in power systems. Synchronous measurements, fast communicationnetwork and FACTS are deployed in the two SIPSs. The Thyristor Controlled SeriesCompensation (TCSC) is applied as the control action in both SIPSs.In the E-SIME based SIPS, the SIME approach is used to evaluate the transient stabilityof the system and then a decision is made about the control actions needed to stabilizethe system. During emergency conditions, a fast response time is very important andthis requires a security guideline to be used in the decision making process. Theguideline is developed by analyzing offline multiple fault scenarios using an automaticlearning approach. This ensures appropriate control actions can be performed withoutcompromising the response time required on a real system.The MPC based SIPS optimizes the control action at every discrete time instant byselecting the control action that leads to the minimized cost function value. Automaticlearning (AL) is utilized to predict power system dynamics by assuming each controlaction has been taken. Furthermore, a feature selection technique, that chooses themost relevant variables, is used to improve the performance of the AL prediction. Themodel predictive control (MPC) technique is performed every discrete time interval, sothe optimal control action is always selected.Two types of SIPS are tested and verified in the benchmark systems. Simulation resultsshow they can effectively protect the system from loss of synchronism in the aftermathof a large disturbance. This thesis also compares the two SIPSs and concludes thebenefits and shortcomings of each approach.

Dynamic simulation of a large-scale electric power system involves solving a large number of differential algebraic equations (DAEs) every simulation time-step. With the ever-growing size and complexity of power grid, dynamic simulation becomes more and more time-consuming and computationally difficult using conventional sequential simulation techniques. This thesis presents a fully distributed approach intended for implementation on High Performance Computer (HPC) clusters. A novel, relaxation-based domain decomposition algorithm known as Parallel-General-Norton with Multiple-port Equivalent (PGNME) is proposed as the core technique of a two-stage decomposition approach to divide the overall dynamic simulation problem into a set of sub problems that can be solved concurrently. While the convergence property has traditionally been a concern for relaxation-based decomposition, an estimation mechanism based on multiple-port network equivalent is adopted as the preconditioner to enhance the convergence of the proposed algorithm. The algorithm is presented in detail and validated both in terms of accuracy and capability

This thesis investigates and develops a direct method for transient stability analysis using the energy approach [1] and the Phasor Measurement Units (PMUs). The originality of this new method results from a combination of a prediction of the post-fault trajectory based on the PMUs and the Transient Energy Function of a multimachine system. Thanks to the PMUs, the weakness of the direct methods, which is the over-simplification of the generator model, is overcome. This new method consists of fitting a curve to the data of the post-fault path provided by PMUs and identifying the controlling unstable equilibrium point (c.u.e.p.). Two second-order linear models have been estimated and evaluated from a prediction viewpoint. These are a polynomial function and an auto-regressive model. These parameters have been estimated by means of the least-squares estimator. They have been compared to the model proposed by Y. Ohura et al. [6], which has been upgraded into an iterative algorithm. The post-fault trajectory is predicted until the exit point located on the Potential Energy Boundary Surface (p.e.b.s.) is reached. In order to detect with efficiency this exit point and to find the c.u.e.p., it is proposed a combination of the so called "Ball-Drop" method [22] and an improved version of the Shadowing method. These combined procedures give accurate results when they are compared to the step-by-step method, which directly integrates the differential equations using a fourth-order Runga-Kutta method. The simulations have been carried out on a 3-machine system and on the 10-machine New-England power system. / Master of Science

The increasing penetration of inverter based renewable generation in the form of solar photo-voltaic (PV) or wind has introduced numerous operational challenges and uncertainties. Among these challenges, one of the major ones is the impact on the transient stability of the grid. On the other hand, the direct methods for transient stability assessment of power systems have also fairly evolved over the past 30 years. These set of techniques inspired from the Lyapunov's direct method provide a clear insight into the system stability changes with a changing grid. The most attractive feature of these types of techniques is the heavy reduction in the computational burden by cutting down on the simulation time. These advancements were still aimed at analyzing the stability of a non-linear autonomous dynamical system and the existing power system perfectly fits that definition. Due to the changing renewable portfolio standards, the power system is undergoing serious structural and performance alterations. The whole idea of power system stability is changing and there is a major lack of work in the field of direct methods in keeping up with these changes. This dissertation aims at employing the pre-existing direct methods as well as developing new techniques to visualize and analyze the stability of a power system with an added subset of complexities introduced by PV generation. / Ph. D.

Modular multilevel converter type voltage source converter (MMC-VSC) is a potential candidate for present and future HVdc projects. The d-q decoupled control system is widely used to control MMC-VSC systems. Selection of PI-controller parameters for MMC-VSC systems is a challenging task as control loops are not completely decoupled. Since there is no widely accepted method to tune these control loops, the industry practice is to use the trial and error approach that requires a great amount of time. Therefore, it is required to develop a systematic procedure to tune PI-controllers considering necessary system dynamics and also to propose guidelines for control system design. This thesis introduces a systematic procedure to determine PI-controller parameters for the d-q decoupled control system. A linearized state-space model of an MMC-VSC system is developed to calculate the frequency-domain attributes. The control tuning problem is formulated as an optimization problem which is general and any meta-heuristic method can be used to solve the problem. In this thesis, the simulated annealing is applied to solve the problem. The efficacy of the tuned parameters is tested on the electromagnetic transient model of the test system on the real-time digital simulators (RTDS). In addition, it is shown that the proposed method is suitable to tune PI-controller parameters for MMC-VSC systems connected to strong as well as weak ac networks. Further, this thesis investigates the effects of d-q decoupled controller parameters, phase-locked loop (PLL) gains, and measuring delays on the stability and performance of the MMC-VSC test system. It is shown that the converter controllers have greater influence on the system stability and the impact of PLL gains is negligible unless very high PLL gains are used. In addition, the negative impact of measuring delays in instantaneous currents and voltages is also analysed by performing eigenvalue and sensitivity analysis. Finally, a set of guidelines for control design of MMC-VSC systems is summarized. In general, the proposed control tuning procedure would be useful for the industry to tune PI-controllers of MMC-VSC systems. Furthermore, the proposed methodology is generic and can be adapted to tune of any dynamic device in power systems. / February 2017

Stability analysis methods may be categorized by two major stability analysis methods: small-signal stability and transient stability analyses. Transient stability methods are further categorized into two major categories: numerical methods based on numerical integration, and direct methods. The purpose of this thesis is to study and investigate transient stability analysis using a combination of step-by-step and direct methods using Equal Area Criterion. The proposed method is extended for transient stability analysis of multi machine power systems. The proposed method calculates the potential and kinetic energies for all machines in a power system and then compares the largest group of kinetic energies to the smallest groups of potential energies. A decision based on the comparison can be made to determine stability of the power system. The proposed method is used to simulate the IEEE 39 Bus system to verify its effectiveness by comparison to the results obtained by pure numerical methods.

Cette thèse porte sur les convertisseurs des liaisons à courant continu (HVDC- High Voltage Direct Current). Une nouvelle méthodologie de synthèse des régulateurs des convertisseurs basée sur un modèle de commande a été développée. Ce dernier prend en considération non seulement les deux convertisseurs de la liaison HVDC mais aussi l'ensemble des principaux éléments impactant la stabilité transitoire du système électrique dans lequel la liaison est insérée. Une commande robuste coordonnée est proposée pour, à la fois, répondre au cahier des charges de la liaison et améliorer la stabilité de la zone AC voisine à la liaison. La coordination de la synthèse de régulateurs pour les convertisseurs se fait à deux niveaux : le premier concerne les deux stations de conversion d'une même liaison HVDC et un second consistant en la coordination de plusieurs liaisons HVDC. De plus, seules les mesures disponibles localement (i.e., au niveau des stations de conversion) sont utilisées. Ce nouveau cadre de commande est une alternative à la commande vectorielle classique. L'approche a été validée à la fois sur des benchmarks académiques et en grande taille sur des cas concrets de renforcement du réseau de transport européen. / This thesis focuses on the control of converters of high voltage direct current (HVDC) links. A new methodology of synthesis of the controllers of the HVDC converters based on a control model has been developed. The latter takes into consideration not only the two converters of HVDC link but all the main dynamics affecting the transient stability of the power system in which the link is inserted. In order to improve the stability of the AC zone neighboring the HVDC link, in addition to the local objectives like power and voltage control, a coordinated robust control is proposed. The coordination of the synthesis controllers for converters is done at two levels: the first one is the coordination of the two stations of an HVDC link the second is consisting on the coordination of several HVDC links. In addition, only measures available locally (i.e., at the converter stations) are used. This new control frame is an alternative to the conventional vector control. The approach was validated on both academic benchmark and a large-scale dynamic model of the whole European power system.

O objetivo principal deste trabalho é o desenvolvimento de algoritmos para análise de estabilidade transitória com esforço computacional reduzido. Com este propósito é desenvolvido uma metodologia para o equivalente dinâmico, a qual é um resultado da eliminação das barras de cargas providas com diferentes modelagens: PQ como constante, PQ como função de tensão e PQ como função de tensão e frequência. O sistema elétrico de potência é reduzido à barras geradoras internas através do método clássico de determinação de equivalentes desenvolvidos por Ward. Uma versão melhorada do equivalente de Ward atualiza a injeção de corrente equivalente nas barras geradoras internas através da utilização das Unidades Medidoras de fasores (PMU\'s) que fornecem os desvios angulares de potência das unidades geradoras e ele uma matriz ele sensibilidade W. A atualização da injeção ele corrente equivalente nas barras geradoras internas é efetuada através da matriz de sensibilidade W para cada novo ponto ele operação. A técnica utilizada para o desenvolvimento da matriz de sensibilidade W foi feita atráves da linearização da equação do fluxo de carga não linear e considerando diferentes modelagens das cargas. Programas que levam em consideração os aspectos acima foram desenvolvidos onde as diferentes modelagens de cargas são incorporadas. Para isto, o sistema AEP de 14 barras foi utilizado como teste para este projeto. / The development of algorithms for analysis of transient stability with reduced computational effort is the main objective of this work. With that purpose a methodology to build reduced equivalents of a power system in a dynamic way is developed. The expression for the injected equivalent currents at the generator buses, is a result of load buses elimination corresponding to different load models, that is: constant PQ loads, PQ as voltage dependency model,as well as PQ as voltage and frequency dependency models. The electric power system is reduced to the generator buses only, using the classic methodology for equivalents developed by Ward. An improved version for the Ward equivalent updates the injected equivalent currents at the generator buses through the use of the phasor measurement units (PMU\'s) and a sensitivity matrix W; those units give the power angle deviation of the generators when some perturbation is applied to the system. In the process of correcting the injected equivalent currents the sensitivity matrix W is updated every time the operating point changes significatively. The technique used in developing the sensitivity matrix W was made through linearization of the load flow equations applied to the different load models. Computer programs taking the considerations above mentioned were developed. The AEP-14 bus power system was used to test the models proposed on this work.

No estudo de estabilidade transitória, as não linearidades inerentes aos sistemas aliadas a grande dimensão do problema, contribuem para que as análises dos sistemas de potência sejam muito complexas. O estudo clássico de estabilidade transitória utiliza soluções numéricas iterativas de um conjunto de equações diferenciais associadas à dinâmica do sistema, visando a obtenção do tempo crítico de abertura. Porém, este não é o processo mais adequado à aplicações em tempo real devido ao esforço computacional exigido em tais iterações numéricas. Os métodos diretos são adequados para análises em tempo real, já que obtêm as informações necessárias sem a solução explícita de equações diferenciais. Dentre os métodos diretos existentes, as idéias de Lyapunov associadas ao princípio de invariância de LaSalle destacam-se por serem métodos energéticos e diretos adequados ao estudo de estabilidade em sistemas não lineares. Baseados em tais idéias, diversos métodos de estimativa da região de estabilidade foram propostos. Dentre estes, o BCU tem sido aceito como o mais eficiente para a determinação do tempo crítico de abertura. Apesar do BCU ser bastante eficiente, existem casos de falha do mesmo. Este trabalho visa eliminar dois problemas relacionados ao BCU: o primeiro problema advém do fato de que nem sempre o máximo de energia potencial ocorre nas vizinhanças do PEBS. O segundo problema está associado aos casos em que a trajetória do sistema gradiente reduzido não passa nas vizinhanças do ponto de equilíbrio de controle. Para solucionar estes dois problemas utiliza-se um método dinâmico para a deteção do “exit point" e o “Shadowing Method" para cálculo do ponto de equilíbrio de controle. Testes com os dois algoritmos mostram que eles encontram soluções para casos de falha do PEBS e BCU, porém problemas de deteção dos pontos de interesse ainda persistem. Alguns métodos alternativos, baseados nos algoritmos citados são propostos, bem como aspectos de melhoria de convergência dos mesmos. / In transient stability assessment, the nonlinearities of the systems and the dimension of the problem contribute to the complexity of the analysis in power systems. The classical numerical solution to obtain the critical clearing time (cct) has been used, but it is time-consuming and not adequate for real-time applications. The direct methods have the adequacy for real-time analysis because they get the necessary information for stability without the explicit solution of the set of differential equations associated to the system dynamics. Among the existing methods of power system transient stability analysis, Lyapunov ideas associated to LaSalle´s invariance principle are very important. Inspired by these ideas, methods to estimate the stability region have been obtained. One of them is the BCU, that has been accepted as the most efficient method in the determination of the critical cct. Despite BCU´s efficiency, it fails in many cases. The main objective of this research is to solve two problems associated to the BCU: the first problem is the fact that not always the maximum of potential energy occurs in the neighborhood of PEBS. The second problem is the fact that in many cases the trajectory of the reduced gradient system does not pass in the neighborhood of the controlling unstable equilibrium point. For the solution of these problems it will be used a dynamic method for the exit point detection and the Shadowing Method to calculate the controlling unstable equilibrium point. Tests have shown that the aforementioned robust algorithms find the solutions for many cases for which BCU and PEBS method fails, but many cases of fail persist. Some alternative methods, based in the mentioned algorithms are proposed, and so, aspects to improve its convergency.

Os métodos diretos são adequados à análise de estabilidade transitória em sistemas de potência, já que não requerem a resolução, integração numérica, do conjunto de equações diferenciais que representam o sistema. Os métodos diretos utilizam as idéias de Lyapunov associadas ao princípio de invariância de LaSalle para estimar a área de atração dos sistemas de potência. A grande dificuldade dos métodos diretos está em encontrar uma função auxiliar V, denominada função de Lyapunov que satisfaça as condições estabelecidas pelo Teorema de Lyapunov. Neste trabalho é realizada uma revisão bibliográfica das funções de Lyapunov utilizadas para análise de estabilidade transitória em sistemas de potência. Analisa-se o problema da existência de funções de Lyapunov quando as condutâncias de transferência são consideradas. Utilizando-se de uma extensão do princípio de Invariância de LaSalle, apresenta-se uma nova função a qual é uma função de Lyapunov no sentido mais geral da extensão do princípio de invariância de LaSalle quando as condutâncias de transferência da matriz admitância da rede reduzida são consideradas. Estudou-se também a existência de funções de Lyapunov no sentido mais geral de extensão do princípio de invariância de LaSalle para modelos que preserva a estrutura da rede. Neste caso, infelizmente não encontramos uma função satisfazendo todas as hipóteses requeridas. / The direct methods are well-suited for transient stability analysis to power systems, since they do not require the solution of the set of differential equations of the system model. The direct methods use the Lyapunov\'s ideas related to the LaSalle\'s invariance principle to estimate the power system attraction area. The great difficulty of the direct methods is to find an auxiliar function V, called Lyapunov function, which satisfies the conditions of Lyapunov\'s theorem. In this work, a bibliographic review of the Lyapunov functions used in transient stability analysis of power systems is done. The problem of existence of Lyapunov functions, when the transfer conductances are considered, is analysed. Using LaSalle\'s invariance principle extension, a Lyapunov function considering the transfer conductances is presented. The existence of Lyapunov functions for models that preserv the network structure was studied using the LaSalle\'s invariance principle. Unfortunately, in these cases, we did not find a function satisfing all the required hypothesis.