Enhancing the quality of services in the distribution system is an important topic for power system research. It is imperative to employ precise network modeling and effective simulation tools, and a good system model is the key. This dissertation starts with modifying the building algorithms of Y-admittance and Z-impedance matrices. The Y-matrix will be built according to phase sequences. With the facts that the line self-impedance is significantly greater than the mutual-coupling terms and the existence of a high r/x ratio in distribution, two decoupled load flow methods (Phase-Decoupled¡BPD and Sub-Phase-Decoupled¡BSPD) with Current Injection Model(CIM) were developed. A new Z-matrix building algorithm was also developed in this dissertation. It decomposed the traditional Z into two sub-matrices, the upper and lower triangular matrices respectively. The matrices represent the relationships between the branch current and the bus injection current, and between the bus voltage and the branch current. Enhancing the quality of services will be effectively achieved by a proper capacitor placement technique. This dissertation develops a linear relationships of voltage changes versus the capacitor compensation, the branch current changes versus the capacitor compensation, and loss reductions versus the capacitor compensation. For loss reduction, a linear optimization function was defined to solve the capacitor placement problem. Tests have shown that the proposed methods were suitable for applications to an unbalance distribution system.

No / Due to high penetration of single-phase Photovoltaic (PV) cells into low voltage (LV) distribution networks, several impacts such as voltage unbalance, voltage rise, power losses, reverse power flow arise which leads to operational constraints violation in the network. In this paper, a time series Three Phase Optimal Power Flow (TPOPF) method is proposed to minimize the voltage unbalance in LV distribution networks with high penetration of residential PVs. TPOPF problem is formulated using the current injection method in which the PVs are modelled via a time-varying PV power profile with active and reactive power control. The proposed method is validated on a real LV distribution feeder. The results show that the reactive power management of the PVs helps mitigate the voltage unbalance significantly. Moreover, the voltage unbalance index reduced significantly compared to the case without voltage unbalance minimisation. / Innovate UK GCRF Energy Catalyst Pi-CREST project under Grant number 41358; British Academy GCRF COMPENSE project under Grant GCRFNGR3\1541; Mut’ah University, Jordan

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-02-11T10:15:45Z No. of bitstreams: 1 marciodecarvalhofilho.pdf: 1308253 bytes, checksum: ce4bec8646b462983e485a5bcad4f5c1 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-02-26T11:53:11Z (GMT) No. of bitstreams: 1 marciodecarvalhofilho.pdf: 1308253 bytes, checksum: ce4bec8646b462983e485a5bcad4f5c1 (MD5) / Made available in DSpace on 2016-02-26T11:53:11Z (GMT). No. of bitstreams: 1 marciodecarvalhofilho.pdf: 1308253 bytes, checksum: ce4bec8646b462983e485a5bcad4f5c1 (MD5) Previous issue date: 2014-08-13 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho desenvolveu-se uma ferramenta para análise de falhas, sendo os modelos de diversos equipamentos do sistema elétrico considerados de forma detalhada, permitindo a análise multifásica do sistema, representando-o da maneira mais generalizada e realista possível. A metodologia desenvolvida para análise de falhas baseia-se no método de injeção de correntes a n condutores em coordenadas retangulares, onde utiliza-se o método de Newton-Raphson no processo de solução e todas as grandezas são definidas diretamente em coordenadas de fase. A modelagem de todo o sistema elétrico é realizada baseando-se em elementos que compõem as estruturas dos equipamentos em seus modelos, sendo que estes elementos podem estar conectados das mais diversas maneiras. As próprias condições de curto-circuito são modeladas por meio de elementos, conectados em diferentes configurações. Também a inclusão dos controles é feita de forma otimizada. Com a modelagem considerada, o sistema a ser solucionado é o estritamente necessário, e, portanto, a metodologia apresenta-se bastante eficiente. A metodologia também se mostra bastante flexível, pois é capaz de representar equipamentos com qualquer número de condutores nas mais diversas configurações, permitindo representar desequilíbrios, acoplamentos mútuos, sistemas de aterramento e cabos neutros explicitamente, e permitindo modelar diversos tipos de falhas, dentre outras características. Desta forma, a metodologia possibilita análises bastante completas, sendo que a representação do sistema pode ser feita com o nível de detalhe que for possível e desejável em cada situação. A ferramenta desenvolvida é bastante abrangente sendo capaz de simular sistemas equilibrados ou desequilibrados, radiais ou reticulados, diversos tipos de falhas (como curtos-circuitos em derivação, interno e simultâneo, ou abertura série), podendo ser aplicada em sistemas de transmissão, subtransmissão, distribuição, e industriais, inclusive de grande porte. / In this work a tool for fault analysis was developed, and models of many electrical systems equipment were considered in detail, allowing the analysis of multiphase systems by representing it in a more general and realistic way possible. The methodology developed for fault analysis is based on the current injection method in rectangular coordinates, where the Newton-Raphson method is used in the solution process and all quantities are defined directly in phase coordinates. The modeling of the entire electrical system is made based on elements which assemble the structures of equipment in their models, and these elements can be connected in various ways. Even the short circuit conditions are modeled by elements connected in different configurations. Also the inclusion of controls is done optimally. With the considered modeling the system to be solved is the strictly necessary, and therefore, the method shows to be efficient. The methodology is also very flexible because it is able to represent equipments with any number of conductors in many different configurations, allowing the representation of imbalances, mutual couplings, groundings and neutral cables explicitly, and allowing to model various types of faults, among other features. Therefore, the methodology allows fairly complete analysis, and the representation of the system can be made with the level of detail that is possible and desirable in every situation. The tool developed is quite ample being able to simulate balanced or unbalanced, radial or meshed systems, various types of failures (such as shunt short circuits, internal faults, simultaneous fault, and series opening), it can be applied to the transmission, subtransmission, distribution and industrial systems, including large scale systems.

State estimation plays an important role in modern power systems. The errors in the telemetered measurements and the connectivity information of the network will greatly contaminate the estimated system state. This dissertation provides solutions to suppress the influences of these errors. A two-stage state estimation algorithm has been utilized in topology error identification in the past decade. Chapter II discusses the implementation of this algorithm. A concise substation model is defined for this purpose. A friendly user interface that incorporates the two-stage algorithm into the conventional state estimator is developed. The performances of the two-stage state estimation algorithms rely on accurate determination of suspect substations. A comprehensive identification procedure is described in chapter III. In order to evaluate the proposed procedure, a topology error library is created. Several identification methods are comparatively tested using this library. A remote measurement calibration method is presented in chapter IV. The un-calibrated quantities can be related to the true values by the characteristic functions. The conventional state estimation algorithm is modified to include the parameters of these functions. Hence they can be estimated along with the system state variables and used to calibrate the measurements. The measurements taken at different time instants are utilized to minimize the influence of the random errors. A method for auto tuning of measurement weights in state estimation is described in chapter V. Two alternative ways to estimate the measurement random error variances are discussed. They are both tested on simulation data generated based on IEEE systems. Their performances are compared. A comprehensive solution, which contains an initialization process and a recursively updating process, is presented. Chapter VI investigates the errors introduced in the positive sequence state estimation due to the usual assumptions of having fully balanced bus loads/generations and continuously transposed transmission lines. Several tests are conducted using different assumptions regarding the availability of single and multi-phase measurements. It is demonstrated that incomplete metering of three-phase system quantities may lead to significant errors in the positive sequence state estimates for certain cases. A novel sequence domain three-phase state estimation algorithm is proposed to solve this problem.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-06-09T12:11:11Z No. of bitstreams: 1 pedrodacruzloureiro.pdf: 1767688 bytes, checksum: 1fa1e4fbfaa6feaf5a5c88ea70df09d6 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-07-13T13:31:22Z (GMT) No. of bitstreams: 1 pedrodacruzloureiro.pdf: 1767688 bytes, checksum: 1fa1e4fbfaa6feaf5a5c88ea70df09d6 (MD5) / Made available in DSpace on 2016-07-13T13:31:22Z (GMT). No. of bitstreams: 1 pedrodacruzloureiro.pdf: 1767688 bytes, checksum: 1fa1e4fbfaa6feaf5a5c88ea70df09d6 (MD5) Previous issue date: 2012-04-16 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho é proposta a aplicação de redes neurais artificiais para ajuste de parâmetros de um compensador estático de reativos, para controle de tensão e harmônicos. Devido à intensa produção de correntes harmônicas e possíveis afundamentos de tensão em instalações industriais como o forno a arco, é necessário um sistema de controle eficiente e robusto. Além disso, os sistemas elétricos de potência se encontram em um cenário com a presença cada vez maior de geração distribuída, cargas não-lineares e forte tendência à operação no contexto das smartgrids e microgrids. Sendo assim, o suporte de reativos deve ser adequado a esses sistemas, podendo atuar de forma rápida, precisa e confiável. Uma possível solução é a utilização de um compensador estático de reativos (CER) com função adicional de filtragem no ponto onde se deseja controlar a tensão e a distorção harmônica. Entretanto, para o correto funcionamento, é necessário um sistema preciso para o ajuste dos parâmetros do CER, ou seja, determinar os ângulos de disparo dos tiristores e o número de bancos de capacitores a serem ligados. Neste trabalho é proposta uma estratégia de controle via redes neurais artificiais, treinadas para o reconhecimento de padrões de operação em regime permanente e definição da configuração do CER, conferindo inteligência ao equipamento. Os desenvolvimentos propostos foram implementados no ambiente MatLab®. A validação do método é feita através de simulações em sistemas-teste, presentes na literatura técnica, utilizando o fluxo de potência pelo método de injeção de correntes trifásico harmônico. Os resultados obtidos mostram as vantagens da utilização da estratégia proposta. / In this work, an artificial neural network-based static var compensator tuning is proposed for voltage and harmonic distortion control. Due to intense harmonic current injection and possible voltage sags produced by industrial facilities such as arc furnaces, an efficient robust control system is needed. Besides, electrical power systems face a new scenario with high penetration of distributed generation and non-linear loads and increased smart grid and microgrid trends. Therefore, the available reactive power sources must be able to provide system control in order to operate the system in a fast, accurate and reliable way. The application of a static var compensator (SVC) with additional filtering function at the controlled node is a possible solution. However, a precise SVC parameters tuning is needed, in order to make the system to work properly. In this work, a control strategy based on artificial neural networks is proposed. The neural networks are trained to recognize steadystate operating patterns and give the SVC adjustment. The proposed technique was implemented in the MatLab® environment. The methodology is validated by simulations in test-systems available in technical literature, using the three-phase harmonic current injection method power flow. Results show the advantages of the proposed methodology.