Electrical power systems are vulnerable to contingencies due to the possibility of fault or damage. When a serious fault (which cannot be removed immediately) occurs in the power system, the fault needs to be isolated, and the remaining system should be reconfigured to make efficient use of available energy. Reconfiguring the system by making an island can be one of the strategies to continue the energy supply using the remaining generation capacity. By analyzing the effect of contingencies on power systems in terms of voltage support, reliability and stability, survivability of the system can be predicted. A survivability index of the system can be developed based on voltage support, reliability and the stability index with predefined weight given to each performance criterion. These weights may vary for different system conditions. The purpose of this research work is to develop a survivability index for shipboard power system and rank reconfiguration choices based on the developed index.

In this research, the impacts of installing DG on a residential distribution circuit are explored. The work is focused on analyzing the impact of DG installation on distribution network operation including voltage analysis, electric losses and reliability of the system. First, various DG penetration levels and the impact of distributing the DG across several locations are explored. Secondly, the impacts of installing DG on any one phase on the voltage profiles of the unbalanced three-phase distribution network are investigated. Thirdly, the losses of the system are analyzed. Next, the reliability analysis (SAIDI, CAIDI, ENS, and AENS) of the system is performed by installing DGs as backup generators. Different DG penetration levels, locations and the impacts of installing one large-scale DG on the main distribution line vs. several small-scale randomly distributed DGs are explored. A residential distribution circuit in Blacksburg, VA was built using its one-line diagram in DEW (Distributed Engineering Workstation) to perform detailed analysis. The research involves several case studies that explore the impacts of installing distributed generation (DG) on residential distribution network operation including the voltage profile, losses, and reliability indices of the system. / Master of Science

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / O constante aumento da demanda energÃtica de um paÃs à sempre alvo de preocupaÃÃo para os operadores de sistemas. Isto implica diretamente no aumento do grau de exigÃncia dos novos procedimentos de rede. Dentre outros tipos de exigÃncia, o ONS (Operador Nacional do Sistema ElÃtrico), solicita, por exemplo que a tensÃo contratada seja controlada pelo solicitante em nÃveis entre 0,95 e 1,05 p.u. (230kV). Quando existem no sistema, centrais eÃlicas de geraÃÃo baseados em mÃquina de induÃÃo duplamente alimentada, esta preocupaÃÃo à ainda maior. Isto porque este tipo de mÃquina, possui seu estator conectado diretamente à rede, tendo, por sua vez, maior sensibilidade a oscilaÃÃes de tensÃo. Sabendo disto, nos Ãltimos anos a eletrÃnica de potÃncia tem estado cada vez mais presente no setor elÃtrico, a exemplo do Static Synchronous Compensator, o STATCOM, que atravÃs do gerenciamento da potÃncia reativa, pode melhorar e muito a ponto de atà anular efeitos causados por oscilaÃÃo de tensÃo. Visando uma aplicaÃÃo semelhante a esta, este trabalho investiga a operaÃÃo conjunta entre o STATCOM e centrais eÃlicas no que diz respeito ao suporte à tensÃo do sistema no qual esta incorporaÃÃo à conectada. Decidiu-se basear o estudo num cenÃrio existente no nordeste brasileiro pois desta forma, à possÃvel ter noÃÃo dos reais efeitos que um STATCOM pode trazer, positivamente, ao sistema. Este trabalho apresenta uma tÃcnica para dimensionamento do STATCOM bem como discussÃes gerais sobre possÃveis desvantagens desta aplicaÃÃo. AlÃm disso, à utilizado dois softwares para elaboraÃÃo dos resultados: MatLab, que atravÃs de scripts calcula todos pontos de interesse para a anÃlise; e ANAREDE, para verificaÃÃo e comparaÃÃo dos resultados obtidos atravÃs do primeiro software. E ainda, este estudo mostra que o script desenvolvido à capaz de designar resultados que se aproximam bastante das respostas do ANAREDE, que sÃo conferidos atravÃs do comportamento do erro das respostas de ambos os programas. Por fim, com objetivo de mostrar o funcionamento dos modos de operaÃÃo do STATCOM conectado ao sistema, sÃo explicitados resultados retirados pelo software PSCAD para um cenÃrio diferente do estudado. / The constant increase in energy demand of a country is always the target of concern for system operators. This implies directly in increasing degree of requirement of the new grid procedures. Among other types of requirement, the ONS (National Electricity System Operator), requests, for example that the tension is controlled by contractor requestor is always controlled between 0.95 and 1.05 p.u.. When there are in the system, wind generation plants based on doubly fed induction machine, this concern is even greater. This is because this type of machine, has its stator connected directly to the network, and in turn more sensitive to voltage fluctuations. Knowing this, in recent years the power electronics is being increasingly present in the electricity sector to mitigate these failures, the example of Static Synchronous Compensator, the STATCOM, that through the management of reactive power, can improve and the point until oscillation effects of annular tension. Targeting an application similar to this, this work brings an idea of STATCOM operating in conjunction with wind farms on serviceability of the desired bar voltage. It was decided to base the study on existing scenario in northeastern Brazil because this way, you can get a sense of the real effects of a STATCOM can bring, positively, to the system. This paper presents a technique for STATCOM sizing as well as general discussions about possible disadvantages of this application. In addition, is used two softwares for preparation of results: MatLab, which through scripts calculates all points of interest for analysis; and ANAREDE, for verification and comparison of the results obtained through the first software .

In recent years, both a significant increase in electrical demand and a large influx of intermittent renewable energy sources have put a considerable stress on the nation’s electrical grid. Conventional power flow control techniques such as capacitor banks and tap-changing transformers are incapable of adequately handling the rapid fluctuations in power supply and demand that today’s grid experiences. Flexible AC Transmission System (FACTS) controllers are a practical way to compensate for such rapid power fluctuations. One type of shunt FACTS controller is the Static Synchronous Compensator (STATCOM), which uses fully controllable switches to source or sink reactive power to a point on the grid, thus reducing voltage fluctuations due to load changes. The purpose of this thesis is to model and simulate the operation of two Distribution STATCOMs (D-STATCOMs) operating on the same point on the grid. These D-STATCOMs also utilize parallel full-wave rectifiers that directly connect the ac grid to the dc capacitor of the D-STATCOMs. Parameters such as power loss, reaction time, stability, and THD are measured for several test scenarios. Results from this thesis show that two D-STATCOMs operating on the same point can be stable and effective under a wide range of conditions. This thesis also concludes that the inclusion of parallel rectifiers with the D-STATCOMs results in no performance improvement of the D-STATCOMs.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This thesis addresses the main issues regarding the operation of full power converters wind turbines connected to the grid under balanced and unbalanced voltage sags. In the past, the grid codes allowed wind turbines to be disconnected during voltage and frequency disturbances. However, recently, grid codes updates often require that wind turbines remain connected during voltage sags aiming to provide voltage back-up support. Furthermore, some specific criteria establish that wind turbines should be able to utilize part of its current capability to promote the voltage back-up during unbalanced voltage sags. To guarantee the grid connected converter operation, even with voltage sags that lead to zero-voltage situations and unbalanced voltage conditions, a synchronous frame PLL with a very low time constant is designed and adapted with a Kalmam filter synchronization system. This thesis propose a two stages synchronization for grid connected converters that is able to ensure proper operation of the converter even when voltage on the converter terminals has temporarily falling down to zero. This goal is meet with a synchronous frame PLL with a very low time constant adapted with a Kalmam filter synchronization system. This composed synchronization system allows the converter control system to get the positive and negative sequences voltages components, that are necessary to the output power control even under severe voltage dips. Moreover, an anti windup is adapted to operate with a resonant current controller enabling the minimization of the saturation in the control action during voltage transients. During unbalanced voltage dips, the injection of unbalanced currents to the voltage back-up support becomes a good alternative to reduce the imbalance factor of the grid voltages. However, it is necessary to limit the maximum current output of the converter to avoid undesirable protection trips. This thesis proposes a strategy that limite the output currents allowing the use of the converter full current capacity during unbalanced voltage sags support. To achieve this goal, the current references are divided into three parts. The former is associated with the active power reference synchronized with the positive sequence voltage. The second is the reactive power synchronized with the positive sequence voltage and the third is the reactive power synchronized with the negative sequence voltage. The strategy propose the computation of th reactive power references by the positive and negative sequence voltages on the PPC in order to not overpass the converter current limits. Experimental and simulation results corroborate the contributions of this thesis. / Esta tese trata do problema de operação de aerogeradores com conversores plenos conectados à rede durante afundamentos de tensão equilibrados e desequilibrados. Inicialmente, os códigos de rede permitiam a desconexão dos aerogeradores durante distúrbios de frequência ou durante afundamentos de tensão. Entretanto, a presente tendência dos requisitos de conexão em diversos países obriga os aerogeradores a permanecerem conectados a contribuição destes com injeção de corrente reativa visando dar suporte à tensão. Além disso, alguns critérios especifícos estabelecem que aerogeradores devem ser capazes de utilizar parte de sua capacidade de corrente para promover o suporte de reativos também durante afundamentos desequilibrados. Nesta tese é apresentado um método de sincronismo composto baseado em filtro de Kalman e aplicado para conversores conectados à rede durante afundamentos de tensão que possam levar a tensão a zero no ponto de conexão. Este possibilita a obtenção das componentes de sequência e as suas tensões em quadratura de maneira simples, além de apresentar um bom desempenho dinâmico durante afundamentos desequilibrados. Além disso, uma estrutura anti windup é adaptada para operar com um controlador ressonante de corrente possibilitando a minimização da saturação da ação de controle na síntese das correntes de saída. Uma vez que o conversor do lado da rede é capaz de operar em condições severas de maneira adequada, a injeção de corrente reativa de forma a minimizar a tensão se sequência negativa no ponto de conexão é uma possibilidade para a diminuição do fator de desequilíbrio. Entretanto é necessário limitar as correntes máximas de saída do conversor. Esta tese propõem uma estratégia de limitação de corrente para conversores conectados à rede que possibilita o uso da plena capacidade de corrente do conversor na injeção de correntes desequilibradas para o suporte de tensão. Para atingir esse objetivo, as referências de corrente são dividas em três partes e com objetivos distintos. A primeira é associada a potência ativa sincronizada com a tensão de sequência positiva. A segunda representa a parcela de potência reativa sincronizada com a tensão de sequência positiva e a terceira parcela representa a potência reativa sincronizada com a tensão de sequência negativa. Pelo cômputo da norma máxima das correntes por uma expressão genérica é possível determinar as correntes de referência que respeitam os limites de corrente do conversor. Resultados de simulação e experimentais corroboram as contribuições desta tese.