In the early 1980s, relaying engineers conceived a technology allowing a huge step forward in the monitoring of power system behavior: the synchrophasor, i.e. the estimation of a phasor representation - amplitude and phase - of a sinusoidal waveform at a given point in time thanks to highly accurate time synchronization of a digital relay. By measuring synchrophasors across the power system several times per second, and centralizing the appropriate information in a hierarchical way through a telecommunication network link, it is now possible to continuously monitor the state of very large systems at a high refresh rate. <p><p>At the beginning, the phase angle information of synchrophasors was used to support or improve the performance of classic monitoring applications, such as state estimation and post-mortem analysis. Later, synchrophasors were found to be valuable for the detection and analysis of phenomena that were not monitored previously, such as system islanding and angular stability. This allows a better understanding of system behavior and the design of remedial actions in cases where system security appears to be endangered. Early detection and even prediction of instabilities, as well as validation and improvement of the dynamic models used for studies, have thus become possible.<p><p>However, a power system is rarely stationary and the assumptions behind the definition of “phasor” are not completely fulfilled because the waveforms' frequency and amplitude are not constant over a signal cycle at fundamental frequency. Therefore, accuracy of synchrophasor measurements during dynamic events is an important performance criterion. Furthermore, when discontinuities (phase jumps and high magnitude variations) and harmonics disturb the measured analog signals as a consequence of switching actions or external disturbances, measurements provided to the “user” (the operator or the algorithms that will take decisions such as triggering alarms and remedial actions) require a certain robustness. <p><p>The efforts underpinning this thesis have lead to the development of a method that ensures the robustness of the measurement. This scheme is described and tested in various conditions. In order to achieve a closer alignment between required and actual measurement performance, it is recommended to add an online indicator of phasor accuracy to the phasor data. <p><p>Fast automated corrective actions and closed-loop control schemes relying on synchrophasors are increasingly deployed in power systems. The delay introduced in the measurement and the telecommunication can have a negative impact on the efficiency of these schemes. Therefore, measurement latency is also a major performance indicator of the synchrophasor measurement. <p><p>This thesis illustrates the full measurement chain, from the measurement of analog voltages and currents in the power system to the use of these measurements for various purposes, with an emphasis on real-time applications: visualization, triggering of alarms in the control room or remedial actions, and integration in closed-loop controls. It highlights the various elements along this chain, which influence the availability, accuracy and delay of the data. <p><p>The main focus is on the algorithm to estimate synchrophasors and on the tradeoff between accuracy and latency that arises in applications for which measurements are taken during dynamic events and the data must be processed within a very limited timeframe. <p><p>If both fast phasors and slower, more accurate phasors are made available, the user would be able to select the set of phasors that are the most suitable for each application, by giving priority to either accuracy or a short delay.<p><p>This thesis also tentatively identifies gaps between requirements and typical measurements in order to identify current barriers and challenges to the use of wide area measurement systems. <p><p>A specific application, the continuous monitoring of oscillatory stability, was selected in order to illustrate the benefits of synchrophasors for the monitoring, analysis and control of power system behavior. This application requires a good phasor accuracy but can allow for some measurement delay, unless phasor data are used in an oscillation damping controller. In addition, it also relies on modal estimators, i.e. techniques for the online identification of the characteristics of oscillatory modes from measurements. This field of ongoing research is also introduced in this thesis. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The future power grid will effectively utilize renewable energy resources and distributed generation to respond to energy demand while incorporating information technology and communication infrastructure for their optimum operation. This dissertation contributes to the development of real-time techniques, for wide-area monitoring and secure real-time control and operation of hybrid power systems. To handle the increased level of real-time data exchange, this dissertation develops a supervisory control and data acquisition (SCADA) system that is equipped with a state estimation scheme from the real-time data. This system is verified on a specially developed laboratory-based test bed facility, as a hardware and software platform, to emulate the actual scenarios of a real hybrid power system with the highest level of similarities and capabilities to practical utility systems. It includes phasor measurements at hundreds of measurement points on the system. These measurements were obtained from especially developed laboratory based Phasor Measurement Unit (PMU) that is utilized in addition to existing commercially based PMU’s. The developed PMU was used in conjunction with the interconnected system along with the commercial PMU’s. The tested studies included a new technique for detecting the partially islanded micro grids in addition to several real-time techniques for synchronization and parameter identifications of hybrid systems. Moreover, due to numerous integration of renewable energy resources through DC microgrids, this dissertation performs several practical cases for improvement of interoperability of such systems. Moreover, increased number of small and dispersed generating stations and their need to connect fast and properly into the AC grids, urged this work to explore the challenges that arise in synchronization of generators to the grid and through introduction of a Dynamic Brake system to improve the process of connecting distributed generators to the power grid. Real time operation and control requires data communication security. A research effort in this dissertation was developed based on Trusted Sensing Base (TSB) process for data communication security. The innovative TSB approach improves the security aspect of the power grid as a cyber-physical system. It is based on available GPS synchronization technology and provides protection against confidentiality attacks in critical power system infrastructures.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2015-12-16T11:21:48Z No. of bitstreams: 1 igordelgadodemelo.pdf: 4931795 bytes, checksum: cf03c45f0f2492c6cf9186af1b3866a2 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2015-12-16T11:57:23Z (GMT) No. of bitstreams: 1 igordelgadodemelo.pdf: 4931795 bytes, checksum: cf03c45f0f2492c6cf9186af1b3866a2 (MD5) / Made available in DSpace on 2015-12-16T11:57:23Z (GMT). No. of bitstreams: 1 igordelgadodemelo.pdf: 4931795 bytes, checksum: cf03c45f0f2492c6cf9186af1b3866a2 (MD5) Previous issue date: 2015-09-18 / Este trabalho objetiva apresentar uma metodologia capaz de estimar os componentes harmônicos em sistemas de distribuição com topologia radial utilizando PMUs (Phasor Measurement Units). Os estados a serem estimados serão as correntes passantes em todas as linhas do sistema em coordenadas retangulares. Uma vez que essas correntes são obtidas, torna-se possível o cálculo de outras grandezas elétricas através das equações de fluxo de potência e leis de Kirchhoff. A metodologia considera poucas unidades de medição fasorial (as PMUs) instaladas efetuando a leitura dos sinais de tensões nodais e correntes nas linhas com distorção harmônica. A fim de restaurar a observabilidade do sistema por completo, são considerados dados históricos de demanda de potência ativa/reativa, os quais serão tratados como restrições de desigualdades excursionando entre um valor mínimo e máximo considerados em um problema de otimização não linear que visa diminuir a diferença entre os valores monitorados pelas PMUs e os calculados pela metodologia. As mencionadas restrições permitem ao estimador o acompanhamento das variações sofridas ao longo do tempo na curva de carga para a frequência fundamental e também para as demais frequências. A abordagem proposta neste trabalho considera a modelagem trifásica de equipamentos e linhas de distribuição, portanto, são modelados os efeitos de acoplamento mútuo entre fases e a operação não linear de equipamentos de eletrônica de potência tiristorizados. O método demonstra eficiência não apenas em estimar os componentes harmônicos de um certo espectro considerado no estudo, como também se mostra uma ferramenta prática de detecção e identificação de fontes harmônicas no sistema elétrico de potência, além de explicitar um exemplo prático do uso de PMUs no que tange ao monitoramento de redes de distribuição, carentes de acompanhamento em tempo real. A metodologia ainda se mostra capaz de ser aliada a grandes estudos contextualizados em qualidade de energia, uma vez que permite a estimação de índices de distorção harmônica. / This work aims to present a methodology which is capable of estimating harmonic components for distribution systems with radial topology, using PMUs (Phasor Measurement Units). The estimated states will be all branch currents of the system expressed in rectangular coordinates. Once these currents are obtained, it is possible to calculate other electrical quantities using power flow equations and also Kirchhoff’s law. The methodology considers the installation of a few number of phasor measurement units which will measure voltage and branch currents signals distorted by harmonic sources. In order to make the whole system observable, historical data of active/reactive power demand will be treated as inequality constraints varying between minimum and maximum limits described in a non linear optimization problem, which aims to minimize the difference between the values monitored by PMUs and the ones calculated by the methodology. The already mentioned constraints allows the accompaniment of the variations occured in a typical load curve during a period of time for the fundamental frequency and also for their multiples, allowing the accompaniment of the harmonic load curve, normally unknown. The proposed approach considers a three-phase modelling of equipments and distribution lines, subject to their mutual coupling effects caused by mutual impedances between the lines. It will also be considered electronic-based devices using thyristors located along the distribution feeder, injecting harmonic currents in the system. The method demonstrates efficiency in estimating the harmonic states of the net and also in detecting and identifying harmonic sources in an eletric power system, besides showing a practical use of PMUs for the monitoring of distribution systems, lacking in information and real-time accompaniment. The method also enables the estimation of power quality indicators such as total harmonic distortion.

[pt] O fenômeno associado à estabilidade de tensão se caracteriza pela existência de valores máximos de potência ativa e reativa que podem ser transferidas a uma barra de carga, ou injetada na rede através dos geradores e compensadores síncronos. Sua relevância para o setor elétrico é constantemente reforçada pelo registro de ocorrências de colapsos de tensão em diversos países do mundo e, embora a instabilidade de tensão manifeste-se localmente, suas consequências se refletem na ampla deterioração do sistema. Impulsionado pelo crescente interesse a respeito dos métodos baseados em medições fasoriais sincronizadas para a detecção do máximo carregamento, este trabalho apresenta os principais modelos encontrados na literatura baseados em medições locais e no vasto monitoramento do sistema, com maior ênfase aos métodos de Corsi-Taranto e Circuito Acoplado de Porta-Simples Aprimorado (CAPS Aprimorado). Algumas contribuições são sugeridas ao modelo CAPS Aprimorado tendo em vista sua aplicação ao conjunto de barras de transferência e de geração. Explora-se a utilização dos equivalentes multi-portas como índice de avaliação das condições de estabilidade de tensão, comparando a identificação da barra crítica aos métodos da matriz D e dos autovalores e autovetores. São evidenciadas as principais limitações dos modelos mediante a um conjunto de análises estáticas e dinâmicas, considerando diferentes cenários de carregamento, a sensibilidade dos modelos ao ruído e a resposta dos métodos em face da atuação dos limitadores de sobre-excitação. / [en] The voltage stability phenomenon is characterized by the existence of a maximum active and reactive power that can be transferred to a load bus or injected into the network through the generators and synchronous compensators. Its relevance to the electric power sector is constantly reinforced by the record of occurrences of voltage collapses in several countries around the world. Although the voltage instability manifests itself locally, its consequences is reflected in the wide deterioration of the system. Driven by growing interest in methods based on synchronized phasor measurements for maximum loadability detection, this work presents the main models found in the literature based on local measurements and wide area monitoring, emphasizing the Corsi-Taranto method and Improved Coupled Single-Port Circuit (Improved CAPS). Some contributions are suggested to the Improved CAPS model considering its application to the set of transit and controlled buses. The use of the multi-port equivalents is explored as the evaluation index of voltage stability conditions, comparing the identification of the critical bus to the D matrix method and eigenvalues and eigenvalues method. The main limitations of the models are demonstrated through a static and dynamic studies, as well different loading scenarios, the sensitivity of the models to the noise and the response of the methods when the over-excitation limiters are considered.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-05-16T17:51:25Z No. of bitstreams: 1 guilhermedeoliveiraalves.pdf: 1293169 bytes, checksum: a76074780b2af177b66be7c6435b16d1 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-06-28T12:25:31Z (GMT) No. of bitstreams: 1 guilhermedeoliveiraalves.pdf: 1293169 bytes, checksum: a76074780b2af177b66be7c6435b16d1 (MD5) / Made available in DSpace on 2016-06-28T12:25:31Z (GMT). No. of bitstreams: 1 guilhermedeoliveiraalves.pdf: 1293169 bytes, checksum: a76074780b2af177b66be7c6435b16d1 (MD5) Previous issue date: 2015-09-18 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente trabalho tem por objetivo apresentar uma nova metodologia para estimação estática de estados em sistemas de distribuição de energia elétrica que estima as correntes nos ramos como variáveis de estado utilizando medições de tensão e corrente de ramo fasoriais oriundas de unidades de medição fasorial (Phasor Measurement Units - PMUs). A metodologia consiste em resolver um problema de otimização não linear minimizando uma função objetivo quadrática associada com as medições e estados estimados sujeito às restrições de carga das barras da rede que não apresentam PMUs instaladas baseadas em dados históricos, sendo esta a principal contribuição deste trabalho. Uma proposta de alocação de PMUs também é apresentada e que consiste em alocar duas unidades em cada ramificação do sistema, uma no começo e outra no final do trecho, procurando utilizar o menor número possível e que não comprometa a qualidade dos estados estimados. A resolução do problema de otimização é realizada de duas formas, através da ‘toolbox fmincon’ do software Matlab, que é uma ferramenta muito utilizada na resolução de problemas de otimização, e através da implementação computacional do Método de Pontos Interiores com Barreira de Segurança (Safety Barrier Interior Point Method - SFTB - IPM) proposto na literatura utilizada. Durante o processo de estimação de estados são utilizadas medidas obtidas através de um fluxo de potência que simulam as PMUs instaladas nos sistemas analisados variando o carregamento de cada sistema em torno da sua média histórica de carga até atingir os limites superior e inferior estabelecidos, sendo verificado o comportamento do estimador de estados perante a ocorrência de ruídos brancos nas medidas de todos os sistemas analisados. Foram analisados um sistema de distribuição tutorial de 15 barras e três sistemas encontrados na literatura contendo 33, 50 e 70 barras respectivamente. No sistema tutorial e no de 70 barras foram incluídas unidades de geração distribuída para se verificar o comportamento do estimador de estados. Todos os resultados do processo de estimação de estados são obtidos com os dois métodos de resolução apresentados e são comparados o desempenho de cada método, principalmente em relação ao tempo computacional. Todos os resultados obtidos foram validados usando um programa de fluxo de potência convencional e apresentam boa precisão com valor de função objetivo baixo mesmo na presença de ruídos nas medidas refletindo de maneira confiável o real estado do sistema de distribuição, o que torna a metodologia proposta atraente. / This work aims at presenting a new methodology for static state estimation in electric power distribution systems which estimates the branch currents as state variables using voltage measurements and current phasor branch obtained from phasor measurement units (Phasor Measurement Units - PMUs). The methodology consists of solving a nonlinear optimization problem minimizing a quadratic objective function associated with the estimated measurements and states, subject to load constraints for the non monitored loads based on historical data, which is the main contribution of this work. A PMU allocation strategy is presented which consists of allocating two PMUs for each system branch, one at the beginning and another at the end, trying to use as little PMUs as possible in such a way that the quality of the estimated states are not compromised. The solution of the optimization problem is obtained through two ways, the first is the toolbox ‘fmincon’ from Matlab solver software which is a widely used tool in the optimization problem. The second is a computer implementation of interior point method with security barrier (SFTB - IPM) proposed in the literature. Comparisons of computing times and results obtained with both methods are shown. A power flow program is used to obtain the voltages and branch currents in order to emulate the PMUs data in the state estimation process. Additionaly the non monitored loads are varied from the minimum bounds to their maximum, allowing white noise errors from the PMUs measurements. A tutorial test system of 15 buses is fully explored and three IEEE test systems of 33, 50 and 70 buses are used to show the effectiveness of the proposed methodology. For the tutorial and 70 bus systems, distribued generation units were included to see the state estimator behavior. All results from the state estimation process are obtained considering the two presented solving methods and the computing times performance compared. The results obtained were validated using a conventional power flow program and have good accuracy with low objective function value even in the presence of white noise errors in the measurements reflecting the reliability of the proposed methodology, making it very attractive for distribution system monitoring.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-01-09T11:36:05Z No. of bitstreams: 1 brauliocesardeoliveira.pdf: 2150243 bytes, checksum: 62faa254539b7873aa1393d8cd8f1bf2 (MD5) / Approved for entry into archive by Diamantino Mayra (mayra.diamantino@ufjf.edu.br) on 2017-01-31T11:23:24Z (GMT) No. of bitstreams: 1 brauliocesardeoliveira.pdf: 2150243 bytes, checksum: 62faa254539b7873aa1393d8cd8f1bf2 (MD5) / Made available in DSpace on 2017-01-31T11:23:24Z (GMT). No. of bitstreams: 1 brauliocesardeoliveira.pdf: 2150243 bytes, checksum: 62faa254539b7873aa1393d8cd8f1bf2 (MD5) Previous issue date: 2016-03-08 / O presente trabalho tem por objetivo apresentar uma metodologia para estimação de estados em sistemas de distribuição de energia elétrica. São utilizadas como variáveis de estado as correntes nos ramos. As medições são obtidas por meio de medições fasoriais sincronizadas(PhasorMeasurementUnits-PMUs),sendoqueostiposdemedidasadvindos desses equipamentos são as tensões nodais e as correntes nos ramos. A abordagem é trifásica, portanto representa as características próprias de um sistema de distribuição. A metodologia consiste em resolver um problema de otimização não linear cuja função objetivo associa o erro quadrático das medidas em relação aos estados estimados sujeito às restrições de carga das barras da rede que não possuem PMUs instaladas baseadas em estimativas de cargas obtidas para o instante “t-1”, partindo-se da premissa que em curtos intervalos de tempo a carga não sofre grandes variações, sendo esta em conjunto com a abordagem trifásica as principais contribuições deste trabalho. Outra contribuição do trabalho é a descentralização, com esta técnica pode-se dividir uma determinada rede em vários subsistemas que podem ser resolvidos de forma separada e independente. Isso torna o processo mais rápido do ponto de vista computacional além de permitir o uso do processamento paralelo, visto que já existe um paralelismo natural entre as tarefas que devem ser resolvidas. Outra vantagem da divisão em subsistemas reside no fato do monitoramento de áreas de interesse. Para utilizar a descentralização foi proposta uma alternativa de alocação de PMUs que consiste em posicionar duas unidades em cada ramificação do sistema, uma no começo e outra no final do trecho, procurando utilizar o menor número possível e que não comprometa a qualidade dos estados estimados. A resolução do problema de otimização é realizada através da implementação computacional do Método de Pontos Interiores com Barreira de Segurança (Safety Barrier Interior Point Method - SFTB - IPM) proposto na literatura especializada. As medidas das PMUs foram obtidas através de um Fluxo de Potência Trifásico via Injeção de Correntes (FPTIC). Foram realizadas diversas simulações variando-se o percentual da carga e os resultados obtidos foram comparados com outra metodologia existente na literatura e com os valores verdadeiros que foram obtidos através do FPTIC para as barras não monitoradas. Foram tambémcomparadosotempocomputacionalentreaexecuçãoserialeaexecuçãoutilizando o processamento paralelo. Os testes mostraram bons resultados o que torna a metodologia proposta aplicável na supervisão de sistemas de distribuição. / This work aims to present a methodology for static state estimation in electric power distribution systems. Branch currents are used as state variables. Measurements are obtained by means of Phasor Measurement Units (PMUs), in which voltage and current branches measurements are used. The approach is three-phase, thus represents the distribution system characteristics. The methodology consists of solving a nonlinear optimization problem minimizing a quadratic objective function associated with the estimated measurements and states subject to load constraints for the non monitored loads based on estimated load obtained from the ‘t-1’ instant, starting from the assumption that in short time intervals the load does not have large variations, which together with the the three-phase approach are the main contributions of this work. Another contribution of this work is the descentralided approach, with this assumption the network can be divided into several subnetworks that can be solved separately and independently. This speeds up the process of being solved from a computational point of view and allows the use of parallel processing, since there is already a natural parallelism among tasks to be solved. Another advantage of the division into subsystems is the fact that the monitoring areas of interest. With the aim of allowing the decentralization was proposed PMUs allocation strategy that consists of allocating two units for each lateral feeder, one at the beginning and one at the end, trying to use as little PMUs as possible in such a way that the quality of the estimated states are not compromised. The resolution of the optimization problem is done through a computer implementation of Interior Point Method with Security Barrier (SFTB - IPM) proposed in the literature. The PMUs measurements were emulated using a Three-PhasePowerFlowusingtheCurrentInjectionmethod(FPTIC).Severalsimulations were performed varying the load percentage and the results obtained were compared with other existing methodology in literature and also the true values that were obtained from the FPTIC to non monitored loads. The computational time using serial and parallel processing were also compared. Results show good results which makes the proposed methodology applicable in monitoring distribution systems.

Over the last decade, power systems have evolved dramatically around the world, owing to higher demand, stringent requirements on quality and environmental concerns that are becoming increasingly critical. With the introduction of new technologies like large-scale renewable energy, wide-area measurement based on phasor measurement units (PMUs) and consumer interaction in the distribution system, the power grid today has become more potent than ever before. Most of the defining features of the smart grid today rest on the integration of advanced communication capabilities into the grid. While communication infrastructure has become a key enabler for the smart grid, it also introduces new and complex control challenges that must be addressed. As we increasingly rely on information transmitted to distant areas over communication networks, it becomes imperative to model the effects of the communication system on the stability of the power grid. Several approaches exist in control theory to study such systems, widely referred to as Networked Control Systems (NCS). Networked control theory provides mathematical tools for system stability analysis and control in the presence of communication delays, packet dropouts and disordering due to transmission of sensor and actuator signals via a limited communication network. In this thesis, a networked control framework for smart grids with integrated commu-nication infrastructure (ICT) is developed. In particular, a networked control systems perspective is developed for two scenarios - wide-area monitoring control, and coordinated control of distributed generation sources. The effects of communication delays and packet dropouts on power system stability are modeled in detail. In the wide-area monitoring control problem, system state measurements are trans-mitted from remote locations through a communication network. The system is modeled as an NCS and a control design approach is presented to damp inter-area oscillations arising from various power system disturbances in the presence of communication constraints. In the coordinated control scenario, a power system with geographically dispersed sources is modeled as an NCS. A networked controller is designed to stabilize the system in the presence of small signal disturbances when system measurements are subject to communication delays and packet dropouts. A realistic output feedback networked control scheme that only uses voltage measurements from PMUs is also developed for practical implementation. The networked controllers designed in this thesis are validated against controllers designed by standard methods, by simulation on standard test systems. The networked controllers are found to enhance power system stability and load transfer capability even in the presence of severe packet dropouts and delays. Several extensions and theoretical problems motivated by this thesis are also proposed.

The modern day power system is witnessing a tremendous change. There has been a rapid rise in the distributed generation, along with this the deregulation has resulted in a more complex system. The power demand is on a rise, the generation and trans-mission infrastructure hasn't yet adapted to this growing demand. The economic and operational constraints have forced the system to be operated close to its design limits, making the system vulnerable to disturbances and possible grid failure. This makes the study of voltage stability of the system important more than ever. Generally, voltage stability studies are carried on a single phase equivalent system assuming that the system is perfectly balanced. However, the three phase power system is not always in balanced state. There are a number of untransposed lines, single phase and double phase lines. This thesis deals with three phase voltage stability analysis, in particular the voltage stability index known as L-Index. The equivalent single phase analysis for voltage stability fails to work in case of any unbalance in the system or in presence of asymmetrical contingency. Moreover, as the system operators are giving importance to synchrophasor measurements, PMUs are being installed throughout the system. Hence, the three phase voltages can be obtained, making three phase analysis easier. To study the effect of unbalanced system on voltage stability a three phase L-Index based on traditional L-Index has been proposed. The proposed index takes into consideration the unbalance resulting due to untransposed transmission lines and unbalanced loads in the system. This index can handle any unbalance in the system and is much more realistic. To obtain bus voltages during unbalanced operation of the system a three phase decoupled Newton Raphson load ow was used. Reactive power distribution in a system can be altered using generators voltage set-ting, transformers OLTC settings and SVC settings. All these settings are usually in balanced mode i.e. all the phases have the same setting. Based on this reactive power optimization using LP technique on an equivalent single phase system is proposed. This method takes into account generator voltage settings, OLTC settings of transformers and SVC settings. The optimal settings so obtained are applied to corresponding three phase system. The effectiveness of the optimal settings during unbalanced scenario is studied. This method ensures better voltage pro les and decrease in power loss. Case studies of the proposed methods are carried on 12 bus and 24 bus EHV systems of southern Indian grid and a modified IEEE 30 bus system. Both balanced and unbalanced systems are studied and the results are compared.