A Geração Distribuída no Brasil tem crescido ao longo dos anos, especialmente na fonte fotovoltaica e na categoria que a ANEEL denomina microgeração distribuída, que são centrais geradoras de energia elétrica com potência instalada menor ou igual a 75 kW e conectada na rede de distribuição por meio de instalações de unidades consumidoras. Apesar dos problemas tradicionais que podem ocorrer com a inserção em larga escala, como maiores perdas e desvios de tensão, as placas fotovoltaicas, conectadas à rede de distribuição por meio de um inversor, trazem a possibilidade de controlar a tensão no ponto de conexão, manipulando-se o fator de potência de saída do inversor, controlando a potência reativa. Neste contexto, considerando o uso dos inversores inteligentes com possibilidade de envio de sinal remotamente ao operador e a possibilidade de criação de Centros de Despacho de Geração Distribuída (CDGD), este trabalho tem por objetivo propor uma metodologia de regulação de tensão centralizada utilizando unidades de microgeração fotovoltaicas, em redes de distribuição com larga inserção. A metodologia proposta utiliza o conceito de despacho de potência reativa e fluxo de potência reativa ótimo, por meio de uma abordagem centralizada da rede, utilizando-se o software OpenDSS e MatLab, equipado com Algoritmo Genético (AG) para solucionar o problema de otimização. Para avaliar o desempenho do modelo, foram feitos estudos de caso no sistema IEEE 123 barras e em uma rede real em Alegrete. Os resultados obtidos validam a abordagem proposta, demonstra a aplicabilidade e limitações em casos reais. / The distributed generation in Brazil has increased in the past years, specially in photovoltaic power generation, at the category that Brazilian Electric Regulator ANEEL classifies as "distributed micro-generation", i.e., generation units in which the active power capacity is equal or bellow 75kW and conected on distribution network by the consumers. Despite the traditional problems that might occur due to high penetration of the units, e.g., higher losses and voltage sags and swells, they are conected to the network through an inverter that can be controlled in order to provide or consume reactive power, providing voltage regulation. In that context, considering the use of intelligent inverters that can be remotely operated by a centralized utility operator, this work aims to propose a centralized voltage regulation methodology using distributed micro-generation in distribution networks. The proposed methodology uses the concept of reactive power dispatch and optimal power flow, from a centralized view of the network, using the software MatLab and OpenDSS with Genetic Algorithm to solve the optimization problem. To evaluate the model, simulations were performed with the IEEE 123 bus system and with a real distribution network from the Alegrete city, in the Brazilian state of Rio Grande do Sul. The results show the proposed is valid, despite some limitations on real cases.

Made available in DSpace on 2016-08-17T14:52:42Z (GMT). No. of bitstreams: 1 Airton Petinelli.pdf: 783096 bytes, checksum: 283e35e9f4e3e61ee0abe5860d9dcb08 (MD5) Previous issue date: 2002-05-29 / Static reactive power sources, such as shunt capacitors, have been commonly used to provide reactive compensation in distribution systems, minimizing losses and keeping voltage levels within operational limits. Heuristic algorithms for capacitor placement have been proposed in several works. However, the majority of these approaches converge to a local solution. This dissertation presents a hierarchical evolution strategy-based approach for solving the optimal reactive sources placement in radial distribution systems. The approach is based on the (m+l)-EE paradigm, improved by mutations control and by two types of mutations: the classical Gaussian mutation and the Cauchy-based mutation. Discrete standard capacitor values with non-linear cost are considered. Constraints such as the maximum number of parallel banks and installations cost are included. Validation tests have been performed using a real industrial feeder. / Fontes estáticas de potência reativa, tais como os capacitores, têm sido comumente usados para a compensação de potência reativa em sistemas de distribuição de energia elétrica. Capacitores são instalados para minimizar as perdas de potência e manter os níveis de tensão dentro de limites operacionais aceitáveis. Algoritmos heurísticos têm sido propostos na literatura para a alocação de capacitores, entretanto, a maioria deles converge para uma solução local. Nesta dissertação, é apresentado um algoritmo hierárquico utilizando uma estratégia evolutiva para solucionar a alocação ótima de fontes de reativos em sistemas de distribuição radiais. O enfoque é baseado no paradigma (m+l)-EE, melhorado pelo controle de mutação com a utilização de dois tipos: a mutação clássica de Gauss e a mutação de Cauchy. Considera-se também a discretização de banco de capacitores com a utilização de tamanho de células disponíveis comercialmente e respectivos custos de aquisição, assim como restrições do tipo número máximo de capacitores em paralelo e custos de instalação. O algoritmo é testado usando-se um alimentador industrial da Companhia Energética do Maranhão - CEMAR

Made available in DSpace on 2016-08-17T14:52:57Z (GMT). No. of bitstreams: 1 Yuri Percy Molina Rodriguez.pdf: 1031212 bytes, checksum: 17d44bafcedcf0ffe29f1cc733e0904a (MD5) Previous issue date: 2005-03-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In the operation of the power transmission system the problems of voltage/reactive power can occur at any time due the contingencies and/or alterations in the demand. Therefore, reactive services are necessary to perform the control in relatively small time periods to improve the operation state and avoid the degradation of the security and the reliability of the system.The ancillary service of reactive power can be contracted by the System Independent Operator of agents connected to the Electrical system, such as generators, capacitor/reator banks, static VAR compensators static, compensators synchronous, among others.The present work proposes a methodology for minimizing the price of the reactive power service considering the coupling between this ancillary service and the power reserve service and the power market as well. For evaluation of the performance, it is considering the method of payment for reserve allocated for service of reserve power, and tests to evaluate its impact in the cost of the reactive power by using the IEEE 14-buses and IEEE 30-buses test systems, are performed. Discussions and relevant conclusions are also reported. / Na operação dos sistemas de transmissão de potência os problemas de tensão/potência reativa podem ocorrer a qualquer momento devido a contingências e/ou alterações na demanda. Portanto, são necessários serviços ancilares de suporte de potência reativa para realizar o controle em períodos de tempo relativamente pequenos para melhorar o estado de operação de modo a não comprometer a segurança e a confiabilidade do sistema elétrico. Esse serviço pode ser contratado pelo Operador Independente do Sistema de agentes conectados ao sistema elétrico, tais como geradores, banco de capacitores/reatores, compensadores estáticos, compensadores síncronos, entre outros. O presente trabalho propõe uma metodologia para minimizar o preço total do serviço ancilar de suporte de potência reativa, considerando o acoplamento existente entre este serviço ancilar com o serviço de reserva de potência, assim como com o mercado de energia. Para a avaliação do desempenho, é considerando o método de pagamento por reserva atribuída no serviço de reserva de potência. Testes com os sistemas IEEE 14-barras e IEEE 30-barras, simulando-se vários cenários são apresentados.

[pt] A falta de recursos e a questão ecológica tem limitado a expansão do sistema de transmissão. Esta realidade, em conjunto com o crescimento da carga, faz com que os sistemas elétricos trabalhem bastante carregados. Esta nova condição pode levar a situações de colapso de tensão. O desenvolvimento de métodos para a avaliação do carregamento da rede de transmissão tornou-se necessário e imprescindível para que se possa entender o funcionamento do sistema nestas condições e possibilitar a sua operação de modo correto. O carregamento da rede de transmissão pode ser avaliado 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, e uma medida de dificuldade de transmissão. O controle de tensão influi diretamente nas condições de operação e portanto, deve ser incluído na modelagem do problema. Usualmente são: controle de tensão por ajuste de tap de LTCs e controle de tensão (local e remota) por injeção de potência reativa. O controle é restrito pelos limites dos taps de transformadores, limites de injeção de potência reativa e limites de tensão. Neste trabalho é mostrada a forma como se deve incluir os controles e limites relacionados com a tensão, na ferramenta analítica de avaliação do carregamento da rede de transmissão. O índice calculado apropriadamente é nulo no ponto de máxima transferência de potência. É mostrado que os controles e limites de tensão do sistema podem e devem ser representados na matriz Jacobiano do sistema linearizado de equações que modelam o sistema, exceto os da barra em análise, mesmo se esta tiver sua tensão controlada. / [en] The lack of investiments and the ecological matter have limited the expansion of the transmission system. This reality, together with the growth of the load, makes the electric systems to work heavy loaded. This new condition can lead to situations of voltage collapse. The development of methods for evaluation the loading of the transmission network became necessary and indispensable in understanding the performance of the system under these conditions and in making possible the operating in a correct way. The transmission system loading can be evaluated by nodal conditions associated to the maximum active and reactive power flow that can be transmitted from generators to loads. These nodal conditions are assessed by an analytic tool based on a a mathematical model. Simple but powerful, derived directly from a physical interpretation of the phenomenon. Meaningful and comprehensive indexes are obtained from a partition of the jacobian matrix of the system. They indicate the operation area in the V x P, Q curve, the margin in MVA for the maximu loading, the relative importance among the busbars, and a measure of transmission difficulty. The voltage control is of paramount importance on operating consitions and therefore should be included in the problem modeling. Usually they are voltage control by tap adjstment of LTCs and voltage control (local and remote) by injection of reactive power. The control is constrained by limits on the taps of transformers, on reactive power injection and on voltage magnitudes. In this work it is shown how the controls and limits related with the voltage should be include in the analytical tool for the evaluation of the transmission system loading. The index calculated adequately is null in the point of maximum power transfer, positive in the upper half and negative in the lower half of the V x P, Q curve. It is shown that the voltage controls and limits of the system can and should be represented in the Jacobian matrix of the linearised system of equations, except on bus under analysis, even if it is a voltage controlled bus.

Orientador: Edméa Cássia Baptista / Banca: Geraldo Roberto Martins da Costa / Banca: Edilaine Martins Soler / Resumo: Este trabalho propõe uma abordagem que utiliza uma combinação de métodos baseados na função barreira logarítmica e barreira logarítmica modificada para a resolução do problema de Fluxo de Potência Ótimo Reativo. Na abordagem proposta as restrições de desigualdade são transformadas em igualdade introduzindo as variáveis de folga, as quais são tratadas pela função barreira logarítmica ou pela função barreira logarítmica modificada e as restrições de igualdade são tratadas pelos multiplicadores de Lagrange. Estes métodos são utilizados em duas etapas. Inicialmente aplica-se o método baseado na função barreira logarítmica até que um critério de transição seja satisfeita. Depois aplica-se o método baseado na função barreira logarítmica modificada até que a condição de convergência seja satisfeita. Testes numéricos utilizando os sistemas elétricos de 3 barras e IEEE 14, 30, 57 e 118 barras indicam que o método é eficiente na resolução do problema Fluxo de Potência Ótimo Reativo. Uma comparação dos resultados obtidos pela abordagem proposta com os dos métodos de barreira logarítmica e de barreira logarítmica modificada separadamente é realizada. / Abstract: This work proposes an approach that uses a combination of methods based on loga-rithmic barrier function and modi˝ed logarithmic barrier function for the resolution of the reactive optimal power ˛ow problem. In this proposed approach the inequality cons-traints are transformed into equalities by adding the slack variables, which are handled by logarithmic barrier function or modified logarithmic barrier function, and the equality constraints are handled by means of Lagrange multipliers. These methods are used in two steps. Initially, the method based on the logarithmic barrier function is applied until the stop condition is satisfied. After the method based on modified logarithmic barrier function is used until the convergence condition is satisfied. Numerical tests carried out with the 3 bus, IEEE 14, 30, 57 and 118 bus electrical systems indicate that the proposed approach is efficient in the resolution of the reactive optimal power flow problem. The results obtained by the proposed approach were compared with the logarithmic barrier method and the logarithmic barrier method modified, separately. / Mestre

Falbygdens Energi AB is a local grid owner in Västra Götaland county and have had an increase in the amount of cable in the grid during the last decades. This increase in cable length, combined with a lack of reactive power monitoring, has led to the reactive power situation in the grid not being fully investigated. This paper aims to examine where the reactive power in the grid is being consumed and produced, how the increase in capacitance affects the company's current arc supression coils, and how the reactive power affects contract limits towards the regional grid owner. Finally, appropriate reactive power compensation is suggested.   By creating a network model that excludes minor contributions to reactive power, including line inductance and resistance, a simplified one phase-thevenin equivalent circuit is developed that only includes the capacitance of 10 kV-cables, leakage reactance of distribution transformers and load reactance.    The results show that the contract limits are exceeded during summer when there is low or no load connected, but comparisons with contract data show that the developed model overestimates the reactive power consumed in 10/0.4 kV-distribution transformers. The arc supression coils being used today are determined to be under-dimensioned, with coils in stations T2 and T5 being nearly 50 % of the size required with regards to cable length. Furthermore, the simulation shows that a variable shunt reactor located at the furthest node in each line yields the lowest over voltage during low load conditions and can compensate for the reactive power exceeding the contract limit, with a reactor of 175 kVAr being appropriate for station T5.   The method used to determine the production and consumption of reactive power in each outgoing line is shown to be accurate regarding the reactive power produced in cables, but inaccurate regarding the reactive power consumed in distribution transformers. An inquiry with more accurate transformer leakage reactance data, as well as an investigation concering the economical aspects of the shunt reactor compensation is recommended.

[pt] O problema geral de minimizar os custos operativos de um sistema de potência mediante escolha acertada de geração ativa e reativa, é formulado como um problema matemático de programação não linear. O problema geral é particularizado para o de minimização das perdas ativas em transmissão, com decisões judiciosas quanto a geração de potência reativa e posicionamento de taps de transformadores. Rotinas computacionais eficientes baseadas na resolução do fluxo de potência pelo método de Newton-Raphson e nas variáveis duais (lagrangeanas) do teorema de Kuhn-Tucker são discutidas. As possibilidades de se estender o fluxo de potência com otimização de reativo para a potência ativa são também discutidas. Verifica-se que o trabalho adicional envolvido é bastante simples, resultando no problema economicamente mais importante do despacho otimizado da potência ativa e reativa. / [en] The general problem of minimizing the operating cost of a power system by proper selection of active and reactive productions is formulated as a nonlinear programming problem. The general problem is particularized to the minimization of transmission line losses by suitable selection of the reactive productions and tranformer tap settings. An efficient computational producedure based on the Newton- Raphson method for solving the power flow equations ando n the dual (lagranggian) variables of the Kuhn and Tucker theorem is discussed. The possibilities of extending the optimum reactive power flow to consider the real power are also discussed. The extra work to be done is very simple, resulting in the economically more important problem of combined active and reactive dispatch optimication.

Yes / This paper presents a robust framework for active and reactive power management in distribution networks using electric vehicles (EVs). The method simultaneously minimizes the energy cost and the voltage deviation subject to network and EVs constraints. The uncertainties related to active and reactive loads, required energy to charge EV batteries, charge rate of batteries and charger capacity of EVs are modeled using deterministic uncertainty sets. Firstly, based on duality theory, the max min form of the model is converted to a max form. Secondly, Benders decomposition is employed to solve the problem. The effectiveness of the proposed method is demonstrated with a 33-bus distribution network.

The electric power grid is operated with exceptionally high levels of reliability, yet recent large-scale outages have highlighted areas for improvement in operation, control, and planning of power systems.  Synchrophasor technology may be able to address these concerns, and Phasor Measurement Units (PMUs) are actively being deployed across the Western Interconnection and North America.  Initiatives such as the Western Interconnection Synchrophasor Program (WISP) are making significant investments PMUs with the expectation that wide-area, synchronized, high-resolution measurements will improve operator situational awareness, enable advanced control strategies, and aid in planning the grid. This research is multifaceted in that it focuses on improved operator awareness and alarming as well as innovative remedial controls utilizing synchrophasors.  It integrates existing tools, controls, and infrastructure with new technology to propose applications and schemes that can be implemented for any utility.  This work presents solutions to problems relevant to the industry today, emphasizing utility design and implementation.  The Bonneville Power Administration (BPA) and Western Electricity Coordinating Council (WECC) transmission systems are used as the testing environment, and the work performed here is being explored for implementation at BPA.  However, this work is general in nature such that it can be implemented in myriad networks and control centers. A Phase Angle Alarming methodology is proposed for improving operator situational awareness.  The methodology is used for setting phase angle limits for a two-tiered angle alarming application.  PMUs are clustered using an adapted disturbance-based probabilistic rms-coherency analysis.  While the lower tier angle limits are determined using static security assessment between the PMU clusters, the higher tier limits are based on pre-contingency operating conditions that signify poorly damped post-contingency oscillation ringdown.  Data mining tools, specifically decision trees, are employed to determine critical indicators and their respective thresholds.  An application is presented as a prototype; however, the methodology may be implemented in online tools as well as offline studies. System response to disturbances is not only dependent on pre-contingency conditions but also highly dependent on post-contingency controls.  Pre-defined controls such as Special Protection Schemes (SPSs) or Remedial Action Schemes (RAS) have a substantial impact on the stability of the system.  However, existing RAS controls are generally event-driven, meaning they respond to predetermined events on the system.  This research expands an existing event-driven voltage stability RAS to a response-based scheme using synchrophasor measurements.  A rate-of-change algorithm is used to detect substantial events that may put the WECC system at risk of instability.  Pickup of this algorithm triggers a RAS that provides high-speed wide-area reactive support in the BPA area.  The controls have proved effective for varying system conditions and topologies, and maintain stability for low probability, high consequence contingencies generally dismissed in today's deterministic planning studies. With investments being made in synchrophasor technology, the path of innovation has been laid; it's a matter of where it goes.  The goal of this research is to present simple, yet highly effective solutions to problems.  Doing so, the momentum behind synchrophasors can continue to build upon itself as it matures industry-wide. / Ph. D.

One of the greatest technological challenges of the world today is reducing the size and weight of the existing products to make them portable. Specifically, in electric vehicles such as electric cars, UAVs and aero planes, the size of battery chargers and inverters needs to be reduced so as to make space for more parts in these vehicles. Electromagnetic Interference (EMI) filters take up a more than 80 % of these power converters, the size of these filters can be reduced by pushing the switching frequency higher. High frequency operation (> 300 kHz) leads to a size in reduction of EMI filters though it also leads to an increase in switching losses thus compromising on efficiency. Thus, soft switching becomes necessary to reduce the losses, adding more electrical components to the converter to achieve soft switching is a common method. However, it increases the physical complexity of the system. Hence, advanced control methods are adopted for today's power converters that enable soft switching for devices specifically ZVS turn-on as the turn-off losses of next generation WBG devices are negligible. Thus, the goal of this research is to discover novel switching algorithms for soft turn-on. The state-of the-art control methods namely CRM and TCM achieve soft turn-on by enabling bi-directional current such that the anti-parallel body diode starts conducting before the device is turned on. CRM and TCM result in variable switching frequency which leads to asynchronous operation in multi-phase and multi-converter systems. Hence, TCM is modified in this dissertation to achieve constant switching frequency, as the goal of this research is to be able to achieve ZVS turn-on for a three-phase converter. Further, Triangular Current Mode (TCM) to achieve soft switching and phase synchronization for three-phase two-level converters is proposed. It is shown how soft switching and sinusoidal currents can be achieved by operating the phases in a combination of discontinuous conduction mode (DCM), TCM and clamped mode. The proposed scheme can achieve soft switching ZVS turn-on for all the three phases. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kW with a density of 110 W/in3. The discussion of TCM in current literature is limited to unity power factor assumption, however this limits the algorithm's adoption in real world applications. It is shown how proposed TCM algorithm can be extended to accommodate phase shift with all the three phases operating in a combination of DCM+TCM+Clamped modes of operation. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kVA with a density of 110 W/in3. TCM operation results in 33 % higher rms current which leads to higher conduction losses, as WBG devices have lower on-resistance, these devices are the ideal candidates for TCM operation, hence to accurately obtain the device parameters, a detailed device characterization is performed. Further, proposed TCM+DCM+Clamped control algorithm is extended to three-level topologies, the control is modified to extract the advantage of reduced Common Mode Voltage (CMV) switching states of the three-level topology, the switching frequency can thus be pushed to 3 times higher as compared to state-of-the-art SVPWM control while maintaining close to 99 % efficiency. Two switching schemes are presented and both of them have a very small switching frequency variation (6%) as compared to state-of-the-art methods with >200% switching frequency variation. / Doctor of Philosophy / Power supplies are at the heart of today's advanced technological systems like aero planes, UAVs, electrical cars, uninterruptible power supplies (UPS), smart grids etc. These performance driven systems have high requirements for the power conversion stage in terms of efficiency, density and reliability. With the growing demand of reduction in size for electromechanical and electronic systems, it is highly desirable to reduce the size of the power supplies and power converters while maintaining high efficiency. High density is achieved by pushing the switching frequency higher to reduce the size of the magnetics. High switching frequency leads to higher losses if conventional hard switching methods are used, this drives the need for soft switching methods without adding to the physical complexity of the system. This dissertation proposes novel soft switching techniques to improve the performance and density of AC/DC and DC/AC converters at high switching frequency without increasing the component count. The concept and the features of this new proposed control scheme, along with the comparison of its benefits as compared to conventional control methodologies, have been presented in detail in different chapters of this dissertation.