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The Global ETD Search service is a free service for researchers
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Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 131 to 138 of 138 (0.024 seconds)| 131 |
[en] METHODS BASED ON SYNCHRONIZED PHASOR MEASUREMENTS FOR VOLTAGE STABILITY MONITORING / [pt] MÉTODOS BASEADOS EM MEDIÇÕES FASORIAIS SINCRONIZADAS PARA O MONITORAMENTO DA ESTABILIDADE DE TENSÃODIOGO CARDOSO LIMA 03 December 2020 (has links)
[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.
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Uma nova metodologia para estimação de estados em sistemas de distribuição radiais utilizando PMUsAlves, Guilherme de Oliveira 18 September 2015 (has links)
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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.
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Estimação de estados em sistemas de distribuição: uma abordadgem trifásica e descentralizadaOliveira, Bráulio César de 08 March 2016 (has links)
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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.
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A Networked Control Systems Framework for Smart Grids with Integrated CommunicationSivaranjani, S January 2014 (has links) (PDF)
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.
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Voltage Stability Analysis of Unbalanced Power SystemsSantosh Kumar, A January 2016 (has links) (PDF)
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.
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Analýza a návrh vinutí střídavých strojů / Analysis and design of the AC machines winding.Vorel, Luboš January 2014 (has links)
This diploma thesis is focused on an analysis and design of an AC machines windings. In the theoretical part of the thesis, differences between single-layer and double-layer windings are explained. Next, the properties of a stator winding of synchronous machines are described. Finally, the winding factor is determined by means of a standard calculation method and by means of a new progressive calculation method, too. In the experimental part of this thesis, the stator winding of a high-speed synchronous generator excited by permanent magnets on the rotor is designed. This generator is driven by a steam turbine.
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Výpočet jednofázového asynchronního motoru / Single-Phase Induction Motor CalculationVácha, Pavel January 2011 (has links)
The master´s thesis deal with the thesis of a single-phase induction motor that is more and more used all over the world. Its aim is assembling the information about this type of motor and its calculation. The content of the first part is the theoretical analysis of a single-phase induction motor and acquirement ways of the stroke moment. Than the work contains a project of basic schema of the single-phase induction motor with an auxiliary phase. The practical part is devoted to an elaboration of demonstration example of the single-phase induction motor with concrete parameters calculation, its method was projected before. Than there is practising successived measuring on the motor of the same parameters made firm EMP s.r.o. Slavkov by Brno in this part. In the conclusion there is the evaluation of the whole process with reached results.
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Minimization of Noise and Vibration Related to Driveline Imbalance using Robust Design ProcessesAl-Shubailat, Omar 17 August 2013 (has links)
Variation in vehicle noise, vibration and harshness (NVH) response can be caused by variability in design (e.g. tolerance), material, manufacturing, or other sources of variation. Such variation in the vehicle response causes a higher percentage of produced vehicles to have higher levels (out of specifications) of NVH leading to higher number of warranty claims and loss of customer satisfaction, which are proven costly. Measures must be taken to ensure less warranty claims and higher levels of customer satisfactions. As a result, original equipment manufacturers (OEMs) have implemented design for variation in the design process to secure an acceptable (or within specification) response. The focus here will be on aspects of design variations that should be considered in the design process of drivelines. Variations due to imbalance in rotating components can be unavoidable or costly to control. Some of the major components in the vehicle that are known to have imbalance and traditionally cause NVH issues and concerns include the crankshaft, the drivetrain components (transmission, driveline, half shafts, etc.), and wheels. The purpose is to assess NVH as a result of driveline imbalance variations and develop a tool to help design a more robust system to such variations.
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