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Orientador: Carlos Alberto Canesin / Resumo: Considerando o atual crescimento dos sistemas baseados em fontes de energia renováveis para a Geração Distribuída (GD), novas estruturas de potência estão sendo desenvolvidas para os sistemas de conversão. O presente estudo propõe a utilização do Inversor Integrado Cuk para o processamento da energia solar fotovoltaica proveniente de um conjunto de módulos fotovoltaicos. Este inversor é o resultado da integração de um conversor Cuk e um inversor de ponte completa, sendo capaz de realizar as funções de elevação e redução de tensão, e a função de converter a corrente continua em alternada, possuindo um grande potencial para a obtenção de uma estrutura de potência de reduzido volume e alto rendimento, garantindo uma baixa distorção harmônica da corrente injetada à rede. Neste trabalho de dissertação são apresentadas as análises quantitativa e qualitativa do inversor com o objetivo de mostrar em detalhes o seu funcionamento e apresentar as principais equações elétricas dos componentes reativos e semicondutores. Além disso, para a obtenção do modelo dinâmico em pequeno sinal do inversor, o método de média do circuito e modelagem média de interruptores é utilizado a fim de projetar os controladores do modo de controle adotado, o qual consiste em dois laços de corrente retroalimentados. Por outro lado, uma comparação das diferentes configurações de módulos fotovoltaicos conectados ao inversor é realizada através dos dados de simulação, a fim de obter a configuração com as melhores c... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Considering the current growth of the renewable energy sources-based systems for Distributed Generation (DG), new power structures are being developed for the conversion systems. The present study proposes the use of the Cuk Integrated Inverter for the processing of photovoltaic solar energy from a set of photovoltaic modules. This inverter is the result of the integration of a Cuk converter and a Full Bridge inverter, being able to perform the functions of raise and reduce voltage, and the function of converting the direct current (DC) to alternating current (AC), possessing a great potential for obtaining a power structure of reduced volume and high performance, guaranteeing a low harmonic distortion of the current injected into the electric grid. In this research work, the quantitative and qualitative analysis of the inverter are presented in order to show in detail its operation and present the main electrical equations of the reactive and semiconductor components. In addition, to obtain the dynamic model in small signal of the inverter, the method of Circuit Averaging and Averaged Switch Modeling is used in order to design the controllers of the adopted control mode, which consists of two feedback loops of current. On the other hand, a comparison of the different configurations of photovoltaic modules connected to the inverter is performed by simulation data, in order to obtain the configuration with the best performance characteristics of the system. The maximum power p... (Complete abstract click electronic access below) / Mestre

The study involves the following stages: First, coupled-inductor and integrated magnetic structure used in Cuk converter circuit topologies are analyzed and the necessary information about these elements in circuit design is gathered. Also, benefits of using these magnetic elements are presented. Secondly / steady-state model, dynamic model and transfer functions of coupled-inductor Cuk converter topology are obtained via state-space averaging method. Third stage deals with determining the design criteria to be fulfilled by the implemented circuit. The selection of the circuit components and the design of the coupled-inductor providing ripple-free input current waveform are performed at this stage. Fourth stage introduces the experimental results of the implemented circuit operating in open loop mode. Besides, the controller design is carried out and the closed loop performance of the implemented circuit is presented in this stage.

Lighting consumes approximately 20-25% of the energy produced worldwide. LED based lighting is rapidly becoming the preferred choice over incandescent and fluorescent based lighting. LEDs have advantages such as high efficacy, long operating lifetime and excellent lumen maintenance. Therefore, to gain benefits from LEDs for lighting purposes, they must be driven with efficient drivers which maintain high LED efficacy and long LED lifetime. A review of existing LED drivers is done, and their advantages and drawbacks are identified. Existing fault-tolerant drivers are also reviewed. Several dimming methods and their effects on the LED efficacy and lifetime are investigated. As a result, a converter with coupled inductors, suitable as an LED driver which has high efficiency and can maintain high LED efficacy, incorporated with a high efficiency dimming method, is chosen. For the proposed LED driver, a comprehensive analysis on the effects of coupling type and coupling coefficient on converter performance is done. This is carried out to establish the best coupled inductor structure and coupling coefficient, for the proposed LED driver. The coupled inductor obtained is used to achieve high LED efficacy and also used to eliminate the need for an output filtering capacitor. This results in a highly compact, high efficiency and low cost LED driver. A lossless method of LED string current sensing is proposed, so that driver efficiency is not negatively impacted. The LED driver and a digital control system are designed, with the fault-tolerant feature incorporated. The LED driver and the control system are simulated and practically implemented. The results obtained show excellent LED driver performance. The fault-tolerant feature can enable the driver to operate under fault conditions, saving repair costs and down time. Additionally, a novel digitally controlled LED driver, which can drive several independent multiple LED loads, is proposed. This novel driver is simulated and practically implemented; with the results showing excellent driver performance. The novel LED driver can simplify and reduce costs of existing LED lighting systems. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Electrical, Electronic and Computer Engineering / Unrestricted

This work consists of the study, design and implementation of DC-DC converters, used in lighting systems based on light emitting diodes (LEDs). Can be powered by an universal AC voltage source or battery, and the current in the LEDs is controlled digitally. The main objective is to present a proposal of new step-up/down converters topologies with full conversion much higher than that of conventional converters. So, is initially presented an overview of solid-state lighting (SSL). Following is presented the study on the dynamic behavior of converters based on modeling by the method of varying state-space average, ending with the design of a digital PI controller. This work resulted in the application for a patent PI-0801425-6 filed with the INPI, which presents a new family of converters with full conversion extremely wide, called cubic converters. / O presente trabalho consiste do estudo, projeto e implementação de conversores CCCC, aplicados em sistemas de iluminação de estado sólido baseado em diodos emissores de luz (LEDs). Podem ser alimentados por uma fonte de tensão alternada universal ou por uma bateria sendo que a corrente nos LEDs é controlada digitalmente. O objetivo principal é apresentar uma proposta de novas topologias de conversores abaixadores/elevadores com faixa de conversão muito maior que a dos conversores convencionais. Portanto, inicialmente é apresentada uma visão geral sobre iluminação de estado sólido (SSL). Na sequência, é apresentado o estudo sobre o comportamento dinâmico dos conversores baseado na modelagem através do método de variáveis de espaço de estados médio, finalizando com o dimensionamento de um controlador PI digital. Este trabalho resultou no pedido de patente de invenção PI-0801425-6 depositado junto ao INPI, o qual apresenta uma nova família de conversores com faixa de conversão extremamente larga, denominados de conversores cúbicos. / Doutor em Ciências

In this dissertation the ac-link universal power converters, which are a new class of power converters, are introduced and studied in detail. The inputs and outputs of these converters may be dc, ac, single phase, or multi-phase. Therefore, they can be used in a variety of applications, including photovoltaic power generation, wind power generation, and electric vehicles. In these converters the link current and voltage are both alternating and their frequency can be high, which leads to the elimination of the dc electrolytic capacitors and the bulky low-frequency transformers. Therefore, the ac-link universal power converters are expected to have higher reliability and smaller size. Moreover, these converters are soft switching, which results in negligible switching losses and minimized current and voltage stress over devices. In the first part of the dissertation, the parallel ac-link universal power converter is studied in detail. This converter is an extension of the buck-boost converter. The series ac-link universal power converter, which is dual of the parallel ac-link universal power converter, is proposed in the second part of this dissertation. This converter is an extension of the Cuk converter. A modified configuration with fewer switches, named sparse ac-link universal power converter is proposed in the third part of this dissertation. The sparse ac-link universal power converters can appear as parallel or series. The performance of all these configurations is evaluated through simulations and experiments.

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This theses analyzes Cuk converter, that is one of the dc to dc switching converters. For continuous inductor current mode and discontinuous inductor current mode, stedy state operation is analysied. Characteristic parameters are determined. Through State Space Averge Models, Small Signal Models are obtained. Parasitic Resistance effects on steady state and small signal models are determined. Efficency of the switching converter is derived. Open loop transfer functions for continous and discontinuous inductor curret mode are obtained. Parmeters for small signal behaviour is determined and stability is analysied. Parasitic resistance effects on transfer functions is determined. Therotecial analysis are verified with a simulations of designed converter.

Growing concerns about climate change have led to the world experiencing an unprecedented push towards renewable energy. Economic drivers and government policies mean that small, distributed forms of generation, like solar photovoltaics, will play a large role in our transition to a clean energy future. In this thesis, a novel DC-DC converter known as the Coupled Inductors Combined Cuk-SEPIC' (CI-CCS) converter is explored, which is particularly attractive for these photovoltaic applications. A topological modification is investigated which provides several benefits, including increased power density, efficiency, and operational advantages for solar energy conversion. The converter, which is based on the combination of the Cuk and SEPIC converters, provides a bipolar output (i.e. both positive and negative voltages). This converter also offers both step-up and step-down capabilities with a continuous input current, and uses only a single, ground-referenced switching device. A significant enhancement to this converter is proposed: magnetic coupling of the converter's three inductors. This can substantially reduce the CI-CCS converter's input current ripple - an important benefit for maximum power point tracking (MPPT) in photovoltaic applications. The effect of this coupling is examined theoretically, and optimisations are performed - both analytically and in simulations - to inform the design of a 4 kW prototype CI-CCS converter, switched at a high frequency (100 kHz) with a silicon carbide (SiC) MOSFET. Simulation and experimental results are then presented to demonstrate the CI-CCS converter's operation and highlight the benefits of coupling its inductors. An efficiency analysis is also undertaken and its sources of losses are quantified. The converter is subsequently integrated into a domestic photovoltaic system to provide a practical demonstration of its suitability for such applications. MPPT is integrated into the CI-CCS DC-DC converter, and a combined half bridge/T-type converter is developed and paired with the CI-CCS converter to form an entirely transformerless single-phase solar energy conversion system. The combination of the CI-CCS converter's bipolar DC output with the combined half bridge/T-type converter's bipolar DC input allows grounding at both the photovoltaic panels and the AC grid's neutral point. This eliminates high frequency common mode voltages from the PV array, which in turn prevents leakage currents. The entire system can be operated in grid-connected mode - where the objective is to maximise power extracted from the photovoltaic system, and is demonstrated in stand-alone mode - where the objective is to match solar generation with the load's power demands.

The dissertation deals with simulations of the DC-DC converters in their basic configurations (Buck, Boost, Buck-boost, Cuk, SEPIC). In the first part of the thesis derivation of transfer functions Line-to-Output (LTO) and Control-To-Output (CTO) can be found. These symbolic responses are derived for three types of basic converters (Buck, Boost, Buck-boost) using well-known average model [1]. Derived expressions are very complicated. For reduction of these expressions symbolic approximation method was used, however the generality is lost. The average model was used to for decreasing the computational effort of analysis of DC-DC converters in the time domain. For these simulations VHDL-AMS language was used. The main topic of the thesis is harmonic balance method, which was adapted to DC-DC converters. Because conditions and assumptions for LTO and CTO functions are very different, harmonic balance method was derived into two variants. For obtaining of LTO response, duty cycle of switching signal can be considered as constant in time. Spectrum of this signal is simple as follows from well-known sinc function. For obtaining of CTO response PWM modulation must be used. Compared to sinc function spectrum of PWM modulation is richer (contains more combination frequencies). Many types of PWM modulation is described in [31]. For simulation PWM modulation with uniform sampling in two variants (single and double edge) was used. Non-ideal switching of PWM switch was modeled by PWM pulse with defined slew rate. Last section deals with comparison of all derived functions (LTO, CTO, modulation type, defined slew rate) with well-known averaged model.