[pt] Um dos meios utilizados par aumentar a capacidade de transmissão das linhas é a compensação de parte da reatância indutiva dessas linhas através de capacitores série. Entretanto compensação série causa o aparecimento de freqüências de ressonância subsíncrona no sistema. Tendo como principal objetivo neste trabalho apresentar um método para a análise da Ressonância Subsíncrona devida a auto-excitação, começa-se por fazer um breve estudo sobre o problema da Ressonância Subsíncrona em geral e apresenta- se alguns dos seus efeitos. Desenvolve-se em seguida o modelo de gerador proposto por Kilgore er al. Para estudos de Ressonância Subsíncrona e apresentam-se os modelos da rede e dos equivalentes utilizados. O método de análise utilizado neste trabalho é então apresentado assim como os programas de cálculo desenvolvidos. Por fim são apresentados os resultados obtidos com estes programas utilizando-se um Sistema Teste e comparam-se estes resultados com aqueles conhecidos de um sistema semelhante. / [en] One of the methods used to increase power transfer capability is the partial compensation of the inductive reactance of lines through the use of series capacitors. This compensation, however, gives rise to subsynchronours resonance frequencies to appear in the system. Having as main objective of this work to present a method for subsynchronours resonance analysis due to self- excitation, one starts by making a short study about the subsynchronours resonance problem in general and presents some of its effects. One develops then the generator model proposed by kilgore and al for subsynchronours Resonancec studies and presents the network and equivalent models utilied. The analysis method used in this work as well as the calculation programmes developed are then presented. Finally results obtained with these programmes using a Test System are presented and compared with those known from a similar system.

<p>During the last two decades, increase in electricity demand and environmental concern resulted in fast growth of power production from renewable sources. Wind power is one of the most efficient alternatives. Due to rapid development of wind turbine technology and increasing size of wind farms, wind power plays a significant part in the power production mix of Germany, Spain, Denmark and some other countries.</p><p>Wind power has to be built in areas with good wind potential. The best conditions for installation of wind power are, thus, in remote areas free of obstacles, and consequently with low population density. The transmission system in such areas might not be dimensioned to accommodate additional large-scale power plants. Insufficient transmission capacity problem, however, would emerge for any type of new generation, planned in similar conditions, although wind power has some special features that should be considered solving this problem.</p><p>In this thesis the four possibilities are considered. One possibility is to revise the methods for calculation of available transmission capacity. Another solution for large-scale integration of wind power in such areas is to reinforce the network. This alternative however may be expensive and time consuming. Since wind power production depends on the wind speed, the wind farm utilization time is only 2000-4000 hours a year, and power production peaks not necessarily occur during periods with insufficient transmission capacity. Therefore wind energy curtailment may be considered as an alternative for large-scale wind power integration. It is also possible to store excess wind energy during the periods with insufficient transmission capacity. Conventional power plants with possibilities of fast production control (e.g. hydro power plants or gas power plants) may also be employed for this purpose.</p><p>There is a lot of research regarding first two measures, therefore, this thesis provides a review and summarized conclusions from the existing work and further concentrates on development of the methods for estimation of wind energy curtailment and evaluation of wind energy storage possibility in hydro reservoirs.</p><p>Methods similar to probabilistic production cost simulation are developed for estimation of wind energy curtailment. The developed methods are applicable to discrete variables (measurements) and also generalized for continuous variables with known distribution.</p><p>For evaluation of wind energy storage possibility the optimization problem is formulated, the objective of this evaluation is to minimize the costs for power production under consideration of the future water value. The developed method allows us to analyze previous years of operation of the power system (e.g. dry, wet and normal year) and evaluate physical possibilities for wind energy storage. The developed methods are than tested for Swedish power system and the results are also summarized in this thesis.</p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p> / QC 20100607

Interference is a defining feature of a wireless network. How to optimally deal with it is one of the most critical and least understood aspects of decentralized multiuser communication. This dissertation focuses on distributed transmission strategies that a transmitter can follow to achieve reliability while reducing the impact of interference. The problem is investigated from three directions : distributed opportunistic scheduling, multicast outage and transmission capacity, and ergodic transmission capacity, which study distributed transmission in different scenarios from a transmission-capacity perspective. Transmission capacity is spatial throughput metric in a large-scale wireless network with outage constraints. To understand the fundamental limits of distributed transmission, these three directions are investigated from the underlying tradeoffs in different transmission scenarios. All analytic results regarding the three directions are rigorously derived and proved under the framework of transmission capacity. For the first direction, three distributed opportunistic scheduling schemes -- distributed channel-aware, interferer-aware and interferer-channel-aware scheduling are proposed. The main idea of the three schemes is to avoid transmitting in a deep fading and/or sever interfering context. Theoretical analysis and simulations show that the three schemes are able to achieve high transmission capacity and reliability. The second direction focuses on the study of the transmission capacity problem in a distributed multicast transmission scenario. Multicast transmission, wherein the same packet must be delivered to multiple receivers, has several distinctive traits as opposed to more commonly studied unicast transmission. The general expression for the scaling law of multicast transmission capacity is found and it can provide some insight on how to do distributed single-hop and multi-hop retransmissions. In the third direction, the transmission capacity problem is investigated for Markovain fading channels with temporal and spatial ergodicity. The scaling law of the ergodic transmission capacity is derived and it can indicate a long-term distributed transmission and interference management policy for enhancing transmission capacity. / text

Wireless networks are increasingly interference-limited, which motivates the development of sophisticated interference management techniques. One recently discovered approach is interference alignment, which attains the maximum sum rate scaling (with signal-to-noise ratio) in many network configurations. Interference alignment is not yet well understood from an engineering perspective. Such design considerations include (i) partial rather than complete knowledge of channel state information, (ii) correlated channels, (iii) bursty packet-based network traffic that requires the frequent setup and tear down of sessions, and (iv) the spatial distribution and interaction of transmit/receive pairs. This dissertation aims to establish the benefits and limitations of interference alignment under these four considerations. The first contribution of this dissertation considers an isolated group of transmit/receiver pairs (a cluster) cooperating through interference alignment and derives the signal-to-interference-plus-noise ratio distribution at each receiver for each stream. This distribution is used to compare interference alignment to beamforming and spatial multiplexing (as examples of common transmission techniques) in terms of sum rate to identify potential switching points between them. This dissertation identifies such switching points and provides design recommendations based on severity of the correlation or the channel state information uncertainty. The second contribution considers transmitters that are not associated with any interference alignment cooperating group but want to use the channel. The goal is to retain the benefits of interference alignment amid interference from the out-of-cluster transmitters. This dissertation shows that when the out-of-cluster transmitters have enough antennas, they can access the channel without changing the performance of the interference alignment receivers. Furthermore, optimum transmit filters maximizing the sum rate of the out-of-cluster transmit/receive pairs are derived. When insufficient antennas exist at the out-of-cluster transmitters, several transmit filters that trade off complexity and sum rate performance are presented. The last contribution, in contrast to the first two, takes into account the impact of large scale fading and the spatial distribution of the transmit/receive pairs on interference alignment by deriving the transmission capacity in a decentralized clustered interference alignment network. Channel state information uncertainty and feedback overhead are considered and the optimum training period is derived. Transmission capacity of interference alignment is compared to spatial multiplexing to highlight the tradeoff between channel estimation accuracy and the inter-cluster interference; the closer the nodes to each other, the higher the channel estimation accuracy and the inter-cluster interference. / text

During the last two decades, increase in electricity demand and environmental concern resulted in fast growth of power production from renewable sources. Wind power is one of the most efficient alternatives. Due to rapid development of wind turbine technology and increasing size of wind farms, wind power plays a significant part in the power production mix of Germany, Spain, Denmark and some other countries. Wind power has to be built in areas with good wind potential. The best conditions for installation of wind power are, thus, in remote areas free of obstacles, and consequently with low population density. The transmission system in such areas might not be dimensioned to accommodate additional large-scale power plants. Insufficient transmission capacity problem, however, would emerge for any type of new generation, planned in similar conditions, although wind power has some special features that should be considered solving this problem. In this thesis the four possibilities are considered. One possibility is to revise the methods for calculation of available transmission capacity. Another solution for large-scale integration of wind power in such areas is to reinforce the network. This alternative however may be expensive and time consuming. Since wind power production depends on the wind speed, the wind farm utilization time is only 2000-4000 hours a year, and power production peaks not necessarily occur during periods with insufficient transmission capacity. Therefore wind energy curtailment may be considered as an alternative for large-scale wind power integration. It is also possible to store excess wind energy during the periods with insufficient transmission capacity. Conventional power plants with possibilities of fast production control (e.g. hydro power plants or gas power plants) may also be employed for this purpose. There is a lot of research regarding first two measures, therefore, this thesis provides a review and summarized conclusions from the existing work and further concentrates on development of the methods for estimation of wind energy curtailment and evaluation of wind energy storage possibility in hydro reservoirs. Methods similar to probabilistic production cost simulation are developed for estimation of wind energy curtailment. The developed methods are applicable to discrete variables (measurements) and also generalized for continuous variables with known distribution. For evaluation of wind energy storage possibility the optimization problem is formulated, the objective of this evaluation is to minimize the costs for power production under consideration of the future water value. The developed method allows us to analyze previous years of operation of the power system (e.g. dry, wet and normal year) and evaluate physical possibilities for wind energy storage. The developed methods are than tested for Swedish power system and the results are also summarized in this thesis. / <p>QC 20100607</p>

[pt] Na medida em que as redes de transmissão de energia elétrica ficaram mais malhadas, os limites térmicos de linhas e transformadores passaram a restringir menos a transmissão de potência. Similarmente, o uso de sistemas estáticos de compensação de potência reativa e estabilizadores na excitação dos geradores aumentou a capacidade de transmissão de potência nos sistemas antes limitados por problemas de estabilidade angular. Hoje as linhas de transmissão estão mais carregadas e isto deu origem ao problema da instabilidade de tensão.Neste trabalho, as condições de estabilidade de tensão são avaliadas por condições nodais associadas ao máximo fluxo de potência ativa e reativa que pode ser transmitida dos geradores para as cargas. Estas condições nodais são avaliadas por uma ferramenta analítica com base em modelo matemático, simples mas poderoso, de uma direta interpretação física do fenômeno.Índices abrangentes e significativos são obtidos a partir da matriz Jacobiano do sistema. Eles indicam a região de operação na curva V x P, Q , a margem em MVA para o máximo carregamento, a importância relativa entre as barras, uma medida de dificuldade de transmissão, e o índice de influência que relaciona as margens de potência entre dois pontos de operação, o que caracteriza a eficácia ou não, por exemplo, de uma ação de controle. O método proposto nesta tese para reforçar as condições de estabilidade de tensão consiste de três etapas seqüenciais. Primeiramente, avalia-se as condições de estabilidade de tensão determinando-se a barra crítica da rede através do cálculo da margem de potência. Determinase o caminho de transmissão crítico, conceito novo usado neste trabalho, entre os vários existentes para transportar potência de geradores para aquela barra crítica. Determina-se então o ramo crítico deste caminho, conceito introduzido neste trabalho. Um programa de fluxo de potência ótimo é usado para aliviar o carregamento desse ramo crítico. A seqüência começa novamente com a avaliação das condições no novo ponto de operação. Todas as etapas são repetidas até que as margens resultantes sejam julgadas adequadas.Barras de carga, de geração e de tensão controlada por compensadores de potência reativa em paralelo com a rede podem ser eleitas como a barra crítica. Somente o método de avaliação nodal usado é capaz de lidar com qualquer tipo de barra. Da mesma forma, o procedimento proposto para reforçar as condições de estabilidade de tensão é adequado para qualquer tipo de barra.São mostrados inúmeros testes, tanto ilustrativos como com sistemas reais, em pontos de operação também reais, inclusive na situação de iminente colapso de tensão. Verifica-se que o método proposto realmente produz os resultados desejados. / [en] As the electric power transmission networks became more interconnected, the thermal limits of lines and transformers restrict less the power transmission. Similarly, the use of static systems of reactive power compensation increases the power transmission capacity in systems whereas before they were limited by problems of angular stability. Actually, transmission lines are more loaded and create the voltage stability problem. In this work, voltage stability conditions are assessment by nodal conditions associated to the maximum active and reactive power flow that can be transmitted from generators to loads.These nodal conditions are assessment using an analytical tool, based on a simple but sound mathematical background, modelling a straightforward physical haracterisation of the phenomena. Comprehensive and meaningful indices are obtained from system Jacobean matrix. They indices indicate the operating region in V x P,Q curve, the MVA margin to the maximum load, the relative importance among buses, the buses loading ranking, a measure of difficult for power transmission, and the influence indices that relates power margins between two operating points, which characterises efficiency or not, for example, of a control action.In order to reinforce voltage stability condition, the thesis proposes a method consisting of three sequential stages. Firstly, voltage stability is analysed, deciding network critical bus using the power margin calculation. Next, the critical transmission path is decided, which is a new concept used in this work, in between several existing used to transport generators power for that critical bus. Then, critical branch is obtained through this path, concept introduced in this work. An optimal power flow program is used to alleviate load flow in the critical branch. The sequence starts again with the stability condition assessment in the new operating point. All stages are repeated until resultant margins are judged suitable. Load, generation and voltage-controlled bus by shunt reactive power compensators could be considered critical bus. The nodal method used is the only one capable of handling any bus type.Several cases are shown, illustrative as well as real systems using real operating points,including imminent voltage collapse situations. It is verified that the proposed method really produces the desired results.

På den svenska järnvägen används två olika återledningssystem på kontaktledningen, autotransformatorsystem och boostertransformatorsystem. De flesta sträckor i Sverige har idag boostertransformatorsystem. I takt med utvecklingen av järnvägen så ställs det andra krav på banorna, till exempel införandet av höghastighetståg. Problemformuleringen blev således frågan om vilket system som föredras vid upprustning eller nybyggnad av järnvägen. Beräkningar på överföringsförmåga beroende på spänningshållningen i systemen samt en modell för en livscykelkostnadsanalys gav svaren på hur skillnaden ser ut i dessa system från ett tekniskt och ekonomiskt perspektiv. Resultaten visar att båda systemen fungerar på den svenska järnvägen. Beroende på hur trafiken, banutformningen samt kostnaderna för ett enskilt system ser ut kan båda systemen användas. Resultatet visar också att vid låg trafiktäthet har AT-systemet större energiförluster än ett BT-system. Vid hög trafiktäthet har ett BT-system större energiförluster än ett AT-system. Resultaten visar också att autotransformator-systemet har en bättre överföringsförmåga av effekt men är dyrt. Boostertransformatorsystemet å andra sidan har en sämre överföringsförmåga av effekt men är billigare. / On the Swedish railway, two different return systems are used on the overhead line, autotransformer systems and booster transformer systems. Most routes in Sweden today have booster transformer systems. In step with the development of the railway, other requirements are placed on the lines, for example the introduction of high-speed trains. The problem formulation thus became the question of which system is preferred for upgrading or new construction of the railway. Calculations of transmission capacity depending on the voltage control in the systems and a model for a life cycle cost analysis gave the answers to what the difference looks like in these systems from a technical and economic perspective. The results show that both systems work on the Swedish railway. Depending on the traffic, track design and costs of an individual system, both systems can be used. The results also show that at low traffic density, the AT system has greater energy losses than a BT system. At high traffic density, a BT system has greater energy losses than an AT system. The results show that the autotransformer system has a better transmission capacity of power but is expensive. The booster transformer system, on the other hand, has a poorer transmission capacity of power but is cheaper.