This thesis aims to establish computer methods for the transient stability analysis of electric power systems which operate isolated from the large interconnected system. A typical isolated system is characterized by a compact network in which the size of the load is relatively large when compared to the total, installed generation capacity. The stability problems are thus more severe for this system than for the grid-type system. This results in the need for more accurate representations for the system components in the computer studies. This work considers particularly the prime mover and the induction motor modelling. The accurate modelling for turbo-charged diesel engines and single shaft gas turbines is considered first due to the significative presence of these types of prime movers in the isolated systems. The quasi-steady approach is adopted in the development of these models. The induction motor modelling is then dealt with and an accurate model which accounts for the deep-bar effects and includes the stator transients is presented. In addition, this work also investigates the possibility of substituting all these detailed models by simple, reduced models in the computer simulations since the latter pose less problem in assembling the necessary data than the former ones. Furthermore, some theoretical aspects for the representation of synchronous machines, automatic voltage regulators and transformers are included in the thesis. Some insight on the numerical integration method used in the stability program - the Trapezoidal implicit - is also given in the text with the advantages and disadvantages being stated. Several studies are shown in the thesis which aim firstly to compare the various models for prime mover and induction motor representations and secondly to test the complete simulation package when dealing with stability analyses of typical isolated systems.

This thesis describes the implementation of microprocessor controlled single-phase and three-phase inverters for UPS applications. A carrier frequency of 18 kHz is employed in both cases, and the PWM pulses are generated directly by the microprocessor using the regular-sampled symmetric PWM strategy. Single-edge modulation as well as double-edge modulation has been implemented for single-phase and three-phase systems. Since in general, software implementation of PWM strategies require precalculated pulse width values, a scheme is proposed which enables the large quantity of such data to be handled efficiently. The scheme involves the use of a small program for calculating and transferring the data to the memory of the controller.

Smart inverters have been considered the primary fast solution for voltage regulation in power distribution systems. Optimizing the coordination between inverters can be computationally challenging. Reactive power control using fixed local rules have been shown to be subpar. Here, nonlinear inverter control rules are proposed by leveraging machine learning tools. The designed control rules can be expressed by a set of coefficients. These control rules can be nonlinear functions of both remote and local inputs. The proposed control rules are designed to jointly minimize the voltage deviation across buses. By using the support vector machines, control rules with sparse representations are obtained which decrease the communication between the operator and the inverters. The designed control rules are tested under different grid conditions and compared with other reactive power control schemes. The results show promising performance. / With advent of renewable energies into the power systems, innovative and automatic monitoring and control techniques are required. More specifically, voltage regulation for distribution grids with solar generation is a can be a challenging task. Moreover, due to frequency and intensity of the voltage changes, traditional utility-owned voltage regulation equipment are not useful in long term. On the other hand, smart inverters installed with solar panels can be used for regulating the voltage. Smart inverters can be programmed to inject or absorb reactive power which directly influences the voltage. Utility can monitor, control and sync the inverters across the grid to maintain the voltage within the desired limits. Machine learning and optimization techniques can be applied for automation of voltage regulation in smart grids using the smart inverters installed with solar panels. In this work, voltage regulation is addressed by reactive power control.

Power quality is an issue of ever increasing importance, and with ever increasingcustomer expectations on such issues, the significance of supplying customers withhigh quality power can never be underestimated. One of the most important mattersthat define power of good quality is the voltage level each customer is supplied with.Most appliances are designed to operate satisfactorily only within a narrow range ofsupply voltages. Inappropriate supply voltages can not only result in poor performingappliances, it can also cause equipment damage, increase distribution losses anddecrease the revenue for the power supplier.The point that is electrically closest to the consumers, where the voltage is activelyregulated and monitored, is usually in a zone substation, where on load tap changerson the zone substation transformers ensure that the voltage in the distribution networkis kept within appropriate limits. The supply voltage is therefore directly reliant oncorrect operation and functionality of the on load tap changers and their controllingautomatic voltage regulators. The main objective that this thesis seeks to achieve is todetermine the most effective method of voltage control to be utilised with differenttypes of zone substations, primarily with respect to the algorithms utilised in theautomatic voltage regulator.Metering data from the distribution network has been utilised to examine the presentvoltage performance of the distribution network. Different reasons that can causevoltage fluctuations and unpredictable voltage performance are investigated anddiscussed. Voltage levels that are investigated are steady-state voltages, hencetransients, flicker, and sags and swells of short duration have not been taken intoconsideration. The present voltage levels are also examined in network models, withthe aim to investigate the impact of altered methods of voltage control in zonesubstations. The accuracy of the utilised network models is also investigated, bycomparing metering data to modelled voltage levels.This thesis is undertaken with the assistance of Ergon Energy Corporation Limited, acorporation owned and operated by the Queensland Government. Ergon Energy ownsand operates the subtransmission and distribution network in regional Queensland. Itis intended that this thesis will aid understanding of the voltage performance of thedistribution network, and that it will bring clarity to how the voltage in thedistribution network should be controlled in order to achieve optimum voltageperformance. / Uppsatsnivå: C

No description available.

Para que a instalação de geração distribuída possa de fato beneficiar a operação das redes de distribuição e de subtransmissão de energia elétrica, seus impactos técnicos devem ser cuidadosamente estudados, sobretudo em redes de distribuição, as quais foram inicialmente planejadas para operar com fluxo de potência unidirecional. Dentre esses impactos, a influência da geração distribuída na regulação da tensão é um aspecto de suma importância, pois está diretamente relacionada à qualidade do fornecimento da energia elétrica aos consumidores. Neste contexto, é importante conhecer e dispor de meios para controlar a interação entre esses geradores e os dispositivos convencionais de regulação de tensão (transformadores com comutadores de tap sob carga, bancos de capacitores e reguladores de tensão) para que a tensão de suprimento permaneça dentro da faixa de valores admissíveis. Assim, este projeto de pesquisa propõe uma análise comparativa entre diferentes estratégias de operação de dispositivos reguladores de tensão em sistemas de distribuição com a presença de geradores distribuídos. Algumas das metodologias discutidas aqui são bastante consolidadas e usualmente aplicadas na operação de sistemas de distribuição de energia elétrica e em trabalhos acadêmicos, enquanto outras são sugeridas por este mesmo trabalho. Tais estratégias são propostas como problemas de otimização não linear inteira mista em que se consideram diferentes modos de operação dos geradores distribuídos e duas funções-objetivo distintas, tratadas de forma independente: minimização dos desvios de tensão nas barras e minimização das perdas elétricas. Os resultados da aplicação de cada estratégia de operação são apresentados e é realizada uma análise qualitativa das vantagens e desvantagens de cada uma. Tem-se até o momento um conjunto de informações que podem servir de suporte na configuração de características operativas e definição de parâmetros de controle para o sistema de regulação de tensão das redes de distribuição de energia elétrica. / In order to assure that the installation of distributed generation would improve the operation of distribution and subtransmission networks, its technical impacts should be carefully studied, especially in distribution networks, which were originally designed to operate with unidirectional power flow. Among these impacts, the influence of distributed generation on voltage regulation is a very important aspect because it is directly related to the quality of electricity supply to the consumers. In this context, it is important to know and employ means of controlling the interaction between these generators and conventional voltage regulation devices (transformers with on-load tap changers, shunt capacitor banks and voltage regulators) assuring that the voltage supply remains within the range of permissible values. Thus, this work proposes a comparative analysis among different operational strategies of voltage regulation devices in distribution systems in the presence of distributed generators. Some of the methodologies discussed here are fairly consolidated and usually applied in power industry and academic researches, while others are suggested by this work. Such strategies are proposed as mixed integer nonlinear programming problems considering different operation modes of distributed generators and two different objective functions, treated independently: minimization of voltage deviations and minimization of power losses. The results of each operation strategy application are presented and a qualitative analysis of the advantages and disadvantages of each one is performed. So far, a set of information that may provide support to configure operating characteristics and define control parameters of voltage regulation system in power distribution networks has been generated.

Para que a instalação de geração distribuída possa de fato beneficiar a operação das redes de distribuição e de subtransmissão de energia elétrica, seus impactos técnicos devem ser cuidadosamente estudados, sobretudo em redes de distribuição, as quais foram inicialmente planejadas para operar com fluxo de potência unidirecional. Dentre esses impactos, a influência da geração distribuída na regulação da tensão é um aspecto de suma importância, pois está diretamente relacionada à qualidade do fornecimento da energia elétrica aos consumidores. Neste contexto, é importante conhecer e dispor de meios para controlar a interação entre esses geradores e os dispositivos convencionais de regulação de tensão (transformadores com comutadores de tap sob carga, bancos de capacitores e reguladores de tensão) para que a tensão de suprimento permaneça dentro da faixa de valores admissíveis. Assim, este projeto de pesquisa propõe uma análise comparativa entre diferentes estratégias de operação de dispositivos reguladores de tensão em sistemas de distribuição com a presença de geradores distribuídos. Algumas das metodologias discutidas aqui são bastante consolidadas e usualmente aplicadas na operação de sistemas de distribuição de energia elétrica e em trabalhos acadêmicos, enquanto outras são sugeridas por este mesmo trabalho. Tais estratégias são propostas como problemas de otimização não linear inteira mista em que se consideram diferentes modos de operação dos geradores distribuídos e duas funções-objetivo distintas, tratadas de forma independente: minimização dos desvios de tensão nas barras e minimização das perdas elétricas. Os resultados da aplicação de cada estratégia de operação são apresentados e é realizada uma análise qualitativa das vantagens e desvantagens de cada uma. Tem-se até o momento um conjunto de informações que podem servir de suporte na configuração de características operativas e definição de parâmetros de controle para o sistema de regulação de tensão das redes de distribuição de energia elétrica. / In order to assure that the installation of distributed generation would improve the operation of distribution and subtransmission networks, its technical impacts should be carefully studied, especially in distribution networks, which were originally designed to operate with unidirectional power flow. Among these impacts, the influence of distributed generation on voltage regulation is a very important aspect because it is directly related to the quality of electricity supply to the consumers. In this context, it is important to know and employ means of controlling the interaction between these generators and conventional voltage regulation devices (transformers with on-load tap changers, shunt capacitor banks and voltage regulators) assuring that the voltage supply remains within the range of permissible values. Thus, this work proposes a comparative analysis among different operational strategies of voltage regulation devices in distribution systems in the presence of distributed generators. Some of the methodologies discussed here are fairly consolidated and usually applied in power industry and academic researches, while others are suggested by this work. Such strategies are proposed as mixed integer nonlinear programming problems considering different operation modes of distributed generators and two different objective functions, treated independently: minimization of voltage deviations and minimization of power losses. The results of each operation strategy application are presented and a qualitative analysis of the advantages and disadvantages of each one is performed. So far, a set of information that may provide support to configure operating characteristics and define control parameters of voltage regulation system in power distribution networks has been generated.

Recent portable electronic technologies require the power management circuit be efficient, small and cost effective. The switched-capacitor (SC) converter provides a trade-off between the efficiency, the size and the cost that is desirable in many of these new portable technologies. This dissertation investigates different circuit techniques and SC converter topologies to make the SC converters fully adapt to the portable system requirements. To make the SC converter efficient over a wide range of input and output voltages, a family of SC power stages with multiple gain ratio (GR) is developed. Multiple GR allows the converter to provide step-down or step-up voltage conversion while increasing the average efficiency of the converter. These power stages are also capable of providing interleaving regulation that has been proved to be effective in reducing the input and the output noise of the converter. Unlike conventional interleaving, the technique developed in this research uses fewer switches and capacitors. The research also contributes in developing circuit techniques such as charge recycling in the bottom plate parasitic capacitors, local gate driving and adaptive body biasing to reduce the power loss in monolithic SC converter implementation. To control the SC power stage for accurate regulation and fast transient response, a control scheme named adaptive gain/pulse control is developed. The research also investigates the use of multipath compensation scheme in SC converters for ultra fast and low noise performance. The techniques and the topologies developed for SC converters in this research can be effectively implemented in the portable devices to reduce cost, and improve efficiency which leads to longer battery life and circuit implementation using smaller areas.

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.

The general trends in the past decade of increasing solar cell efficiency, decreasing PV system costs, increasing government incentive programs, and several other factors have all combined synergistically to reduce the barriers of entry for PV systems to enter the market and expand their contribution to the global energy portfolio. The shortcomings of current inverter functions which link PV systems to the utility network are becoming transparent as PV penetration levels continue to increase. The solution this thesis proposes is an approach to control the inverters real and reactive power output to help eliminate the problems associated with PV systems at their origin and in addition provide the grid with ancillary support services. The design, modeling, and analysis of a grid-tied PV system was performed in the PSCAD software simulation environment. Results indicate that in the presence of grid disturbances the smart inverter can react dynamically to help restore the power system back to its normal state. A harmonic analysis was also performed indicating the inverter under study met the applicable power quality standards for distributed energy resources.