Orientador: Carlos Alberto Canesin / Banca: Falcondes José Mendes de Seixas / Banca: Guilherme de Azevedo e Melo / Banca: João Batista Vieira Junior / Banca: Luiz Carlos de Freitas / Resumo: Esta proposta de tese se baseia na necessidade atual e tendência mundial na busca por sistemas cada vez mais eficientes e que se baseiem em fontes de energia alternativas menos poluentes, renováveis e que produzam pouco impacto ambiental. Desta forma, são desenvolvidos sistemas de geração de energia elétrica de pequeno porte baseado em painéis solares fotovoltaicos. Com o intuito de aumentar o rendimento e a densidade de potência dos sistemas, são apresentadas novas estruturas de inversores monofásicos e trifásicos integrados para aplicação como sistemas isolados e/ou conectados à rede de distribuição em corrente alternada (CA), operando como sistemas de geração distribuídos. Os inversores integrados são apresentados com o intuito de substituir os usuais sistemas de conversão de energia a duplo estágio. Incorporado aos inversores integrados são implementados métodos e dispositivos para extração da máxima potência possível dos painéis fotovoltaicos (algoritmo de MPPT), aumentando assim o aproveitamento de energia advinda destes painéis. Além disso, em virtude da necessidade de conexão segura destes sistemas à rede de distribuição de energia elétrica em corrente alternada, são realizadas análises e a implementação de métodos de sincronismo com a rede de CA em baixa tensão; além da análise e síntese de métodos híbridos para detecção e gestão do efeito de ilhamento, a fim de garantir a segurança do sistema. O controle dos conversores e as técnicas de MPPT, gestão e detecção de ilhamento, bem como de sincronismo com a rede em CA são implementadas de forma digital, com o objetivo de propiciar maior flexibilidade na concepção das lógicas de controle adequadas às aplicações propostas. Finalmente, destaca-se que o trabalho trouxe contribuições significativas para a melhoria na implementação... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work is based on the actual necessity and world tendency for high-efficiency systems based on renewable energy sources which are less pollutant and produces little environmental impact, and, for this purpose, it is developed some photovoltaic electrical generation systems to operate as a small distribution generation system (DG). With the purpose to increase efficiency and power density, new single-phase and three-phase integrated inverter topologies are presented for operating as stand-alone and/or grid-connected systems. The main idea of these inverters is the replacement of the conventional two-stage cascaded solutions. Main maximum power point tracking techniques are implemented and tested in order to increase energy utilization. Furthermore, because of safe-operation grid connection necessities this work presents analysis and implementation of active and hybrid anti-island detection techniques and synchronization methods with the AC low voltage grid. The converters control system and MPPT techniques, anti-island detection and management system together with the synchronization are implemented digitally, with the purpose of increasing flexibility for the overall control circuitry. Finally, this work has presented significant contributions regarding the P&O and IC based on PI MPPT techniques and has presented the integration procedures in order to obtain new families of single and three-phase inverters. Moreover, this is the first thesis that has presented the tri-state three-phase inverters injecting power into the grid. These inverters have inovations at its control and modulation that permit the input to... (Complete abstract click electronic access below) / Doutor

Advancements in power electronics to higher power levels and faster switching times allow new machine and systems designs, but also create higher stresses on electric machinery insulation. High performance, pulse-width modulated (PWM) inverters are now available for medium voltage drive systems, and are being considered by the U.S. Navy as they move to the "all-electric" ship. If this process is to be successful, a necessary component will be to understand the impact of partial discharge (PD) generation on electric drive systems. Out of the many PD influencing parameters, voltage level, voltage rise-time, switching frequency, and temperature were chosen to be investigated with regards to their influence on PD generation in a comprehensive research project in the Motor Systems Research Facility (MSRF) at Oregon State University (OSU). The tests were performed on representative propulsion coils employing two different 4160 V insulation systems and were evaluated by both an optical and electrical PD detection method. A highly flexible test configuration was developed, capable of adjusting each of the four test parameters independently over a wide range of appropriate values. The developed test program enabled the analysis of the influence of the parameters on the generation of PD, as well as an evaluation of the test coils and PD instrumentation used. It is concluded that, as expected, voltage level is the most significant parameter affecting PD production. However, there is a surprising interdependence of rise-time and pulse-width that requires further investigation. Multiple-cycling tests are seen as appropriate to determine the effect of temperature. Based on the subjective nature of the findings from the test program an improved PD instrument is proposed, which would increase the capabilities and objectivity of the PD detection process. / Graduation date: 2004

Adjustable Speed Drive (ASD) systems are widely used in industry to effectively improve process efficiency and control. Typically, an ASD system consists of a motor with its speed controlled by a power electronics converter via varying the amplitude and frequency of the input voltage. However, several abnormal insulation failures of random wound motors in ASD applications have been reported. These failures were related to voltage transients caused by inverters employing fast insulated Gate Bipolar Transistors (IGBTs) combined with long cables that connect motors to inverters. This thesis further analyzes the distribution of voltage waveforms generated by a pulse-width modulated (PWM) inverter at the motor terminals and windings. Experimental work was performed at the Motor Systems and Resource Facility (MSRF) at Oregon State University on a specially made 5hp induction motor with taps from the first and second coil and from the first four and last two turns in every phase. Tests were performed with long and short cables and results are compared. A simple simulation model was created in PSpice and used to predict maximum voltage transients across coils and turns. The validation of the model is demonstrated by its capability to predict most of the experimental results. / Graduation date: 2000

M. Tech. Electrical Engineering. / Aims to analyze, design and develop a transformer-less 5-level converter topology with an improvement in the output waveform and to investigate its suitability for AC/DC, DC/AC and back-to-back configuration.

Flexible AC Transmission Systems (FACTS) involves the incorporation of power-electronic controlled devices into ac power transmission systems in order to extend the power-transfer capability of these systems beyond their traditionally accepted boundaries. One particular category of FACTS devices makes use of high-powered voltage source inverters to insert near-sinusoidal ac compensating voltages into the transmission system. This thesis considers this particular category of inverter-based FACTS devices, namely the static synchronous compensator (STATCOM), static synchronous series compensator (SSSC) and unified power flow controller (UPFC). Although the potential for FACTS devices to enhance the operation of power systems is well known, a device such as a UPFC is itself a complicated subsystem of the overall power system. There is therefore also the possibility that the introduction of such devices could cause adverse interactions with other power system equipment or with existing network resonances. This thesis examines the interactions between inverter-based compensators and a particular form of system resonance, that of subsynchronous resonance between a generator turbine shaft and the electrical transmission network. The thesis presents a review of the theory of operation of high-power, multi-pulse inverter topologies actually used in transmission-level FACTS devices. Detailed simulation models are developed of both two-level and three-level multi-pulse inverters. With appropriate controls, simulation models of both the SSSC and STATCOM, and a full UPFC are then developed using these detailed inverter models and the results from these simulation models compared against other results from the literature. These comparisons show favourable agreement between the detailed FACTS models developed in the thesis and those used by other researchers. However, the models presented in this thesis include a more detailed representation of the actual power-electronic circuitry and firing controls of inverter-based FACTS devices than is the case with other models used in the literature. The thesis then examines the issue of whether the introduction of an SSSC to a transmission system could cause subsynchronous resonance (SSR). SSR is a form of dynamic instability that arises when electrical resonances in a series capacitively compensated transmission line interact with the mechanical resonances of a turbo-generator shaft system. The detailed SSSC simulation model developed in the thesis is used to determine the impedance versus frequency characteristics of a transmission line compensated by an SSSC. The results confirm earlier work by others, this time using more detailed and realistic models, in that the introduction of an SSSC is shown to cause subsynchronous resonance. The thesis then considers the addition of supplementary damping controllers to the SSSC to reduce subsynchronous oscillations caused both by the SSSC itself as well as by a combination of conventional series capacitors and an SSSC in a representative benchmark study system. The results show that subsynchronous oscillations in the transmission system compensated solely by an SSSC can successfully be damped out using a single-mode supplementary damping controller for a range of values of SSSC series compensation. However, in the case of the transmission system compensated by both conventional series capacitors and an SSSC, the nature of the subsynchronous oscillations is shown to be complex and strongly multi-modal in character. The thesis then proposes an extension to the single-mode supplementary damping controller structure that is better suited to damping the multi-modal resonances caused when an SSSC and conventional series capacitors are used together to compensate a transmission line. The results obtained from this multi-modal controller indicate that it is able to stabilise SSR for a range of compensation values, but that the controller design needs to be adjusted to suit different values of compensation. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2006.

Thesis (M.S.)--Ohio University, August, 1999. / Title from PDF t.p.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed February 18, 2009) Includes bibliographical references.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 388-392). Also available via the Internet.

Thesis (M.S.)--Ohio University, August, 1996. / Title from PDF t.p.

Thesis (M.S.)--Oregon State University, 2004. / Printout. Includes bibliographical references (leaves 39-40). Also available on the World Wide Web.