CAPES / O desenvolvimento de um conversor CC-CC de três portas é proposto neste trabalho. Através da combinação de um conversor bidirecional Ćuk e um transformador de alta frequência com um circuito retificador em ponte completa, duas portas de energia não isoladas e uma porta de energia isolada são obtidas. Um circuito LC série ressonante é empregado, resultando em comutação suave nos interruptores de potência. O conversor bidirecional Ćuk, controlado por modulação de largura de pulso (PWM) e o circuito tanque ressonante, controlado por modulação de frequência (PFM) acima da frequência de ressonância, permitem duas variáveis de controle para a topologia. Além disso, os interruptores de potência são compartilhados nas etapas de operação, reduzindo o número de componentes ativos. Regulação de suas portas é realizada para aplicações com elementos armazenadores de energia. São apresentados os modos de operação, a análise matemática e a estratégia de controle do conversor proposto. Os resultados experimentais são expostos para discutir a viabilidade da estrutura. / The development of a DC-DC three-port converter is proposed in this work. Through the combination of a bidirectional Ćuk converter and a high frequency transformer with a full-bridge rectifier circuit, two non-isolated energy ports and one isolated energy port are achieved. A LC series resonant circuit is employed, resulting in soft-switching in the power switches. The bidirectional Ćuk converter, controlled by pulse width modulation (PWM), and the tank resonant circuit, controlled by pulse frequency modulation (PFM) above the resonance frequency, allow two control variables for the topology. Furthermore, the power switches are shared for the operation of both circuits, reducing the number of active components. Port regulations are performed for applications with energy storage elements. Operation modes, math analysis and control strategy of the proposed converter are presented. Experimental results are exposed to discuss the feasibility of the structure.

NHS / Este trabalho apresenta o desenvolvimento e a implementação de um retificador Ponte Completa isolado em alta frequência com elevado fator de potência para aplicações em UPS. Este conversor é composto por um conversor Boost multi-fase operando em modo contínuo (CCM) integrado a um conversor ZVS CC-CC Ponte Completa sem o indutor de saída operando em modo descontínuo (DCM). A topologia apresenta comutação suave intrínseca, permitindo a operação com baixas perdas por comutação em altas frequência. Este conversor também apresenta operação multi-fase e redução da ondulação da corrente de entrada com o uso de dois indutores de entrada. A estrutura sem ponte de diodos possibilita a redução do número de componentes da etapa de potência, apresentando baixas perdas por condução. A implementação de uma nova malha de controle de potência, adicional ao controle convencional, permite melhor resposta dinâmica do conversor. Os detalhes da estratégia de controle, bem como o projeto dos componentes do circuito são apresentados. Os resultados são obtidos através de um protótipo com frequência de chaveamento de 43,2 kHz e comprovados através da simulação, sendo o rendimento máximo é igual a 92,2 % com potência nominal, 1,7 kW. Um novo controle com duas modulações independentes também é proposto, permitindo o conversor também operar como abaixador de tensão. Esta modificação possibilita maior faixa de tensão de saída do conversor e consequentemente para a saída do UPS. / This paper presents the development and implementation of a high power factor full-bridge rectifier with high frequency isolation for UPS applications. This converter is composed by a multiphase boost converter operating in continuous mode (CCM) integrated with a ZVS DC-DC full-bridge converter without the output inductor and operating in discontinuous mode (DCM). The topology presents intrinsic ZVS commutation allowing the operation with lower switching losses at higher frequencies. It also presents multiphase operation and input current ripple reduction by using two input inductors. The structure bridgeless rectifier reduces the number of semiconductors in conduction of power circuit, presenting lower conduction losses. The implementation of a new power loop control, allows a better dynamic converter response. Details of the control strategy and circuits components design are presented. The results are verified through a prototype with switching frequency equal to 43,2 kHz and the maximum efficiency is equal to 92,2 % at nominal power, 1,7 kW. A new control with two independent modulations is also proposed, allowing the converter operating also as step-down voltage. This modification provides greater range of converter output voltage and thus the output of the UPS.

Este trabalho apresenta o desenvolvimento de um sistema trifásico para a carga rápida de baterias de veículos elétricos, com elevado fator de potência, isolação em alta frequência e reduzidos esforços de corrente. O sistema proposto baseia-se em uma estrutura de estágio único, integrando a etapa retificadora trifásica com um conversor CC–CC isolado em alta frequência. Esta estrutura utiliza dois conjuntos de retificadores bidirecionais trifásicos de dois níveis operando com controle da defasagem entre eles. São inseridos transformadores de alta frequência entre os braços de comutação, no total de três transformadores e um retificador e um indutor de filtro na saída. Esta estrutura permite a utilização da modulação PWM clássica para o controle das correntes de entrada, com elevado fator de potência, além de controlar a tensão do barramento primário. O controle do ângulo de defasagem entre os dois módulos retificadores permite controlar o fluxo de potência entre o barramento primário e o secundário, possibilitando o controle independente da corrente de saída do conversor. A operação integrada dos módulos retificadores e transformadores de alta frequência, permite obter algumas características importantes como redução das ondulações de corrente de entrada e de saída devido a operação multifase dos retificadores, divisão dos esforços de corrente entre os semicondutores, entre os indutores de entrada e divisão da potência nos transformadores de alta frequência (importantes para a operação em alta potência), um único estágio de processamento de energia com controles independentes das correntes de entrada e saída, operação com comutação suave na maioria dos interruptores e possibilidade de operação bidirecional entre a rede e outra fonte CC, tais como painéis fotovoltaicos, permitindo a redução do impacto dos sistemas de carga rápida no sistema elétrico, e também possibilitando a injeção de energia em períodos ociosos. O trabalho apresenta a análise da topologia, projeto e implementação de um protótipo de 10 kW para a carga rápida de baterias. / This work presents the development of a three-phase system for fast charging electric vehicle batteries, with high power factor, insulation at high frequency and low current stresses. The proposed system is based on a single-stage structure, by integrating the three-phase rectifier stage with a DC–DC converter isolated at high frequency. The proposed structure is based on the use of two sets of two levels bidirectional three-phase rectifiers operating with phase shift control between them. High–frequency transformer are inserted between the arms of each switching set, for a total of three transformers and a rectifier and a filter inductor on the output. This structure allows the use of classical PWM to control the input currents, obtaining high power factor, besides controlling the voltage of the primary bus. The phase shift control angle between the two rectifier modules allows to control the flow of power between the primary and the secondary bus, allowing independent control of the output current. The integrated operation of rectifier modules and high frequency transformers, allow to obtain some important operating characteristics such as reducted input current ripple and output by multi-phase operation of the rectifiers, division of the current efforts of the semiconductor between the input inductors and power division in the high-frequency transformers (important for operation with high power), single power processing stage with independent control of input and output currents, soft switching operation on most switches and possibility of bidirectional operation between the power grid and other DC source, such as photovoltaic panels, allowing the reduction of the impact of fast charge systems in the electrical system, and also enabling injection of energy in idle periods. his work presents the analysis of the topology, design and implementation of a 10 kW prototype for the fast charging batteries.

Neste trabalho é proposto o desenvolvimento de um novo microinversor de estágio único para aplicação em sistemas fotovoltaicos. A topologia apresentada é baseada na combinação do conversor Cuk com uma estrutura de indutores chaveados para obtenção de um maior ganho estático e um circuito inversor em ponte completa conectado à rede. A estrutura de indutores chaveados apresentada nesse trabalho reduz esforços de tensão e corrente nas chaves semicondutoras. Com o objetivo de facilitar o controle, a etapa CC do microinversor opera em modo de condução descontínua (DCM). Para injetar corrente senoidal com baixa distorção harmônica à rede, é aplicado às chaves semicondutoras da etapa CC uma modulação por largura de pulso senoidal (SPWM). As chaves semicondutoras do circuito inversor em ponte completa são comandadas na frequência da rede, reduzindo perdas por chaveamento. Por se tratar de uma topologia inédita, são apresentados os modos de operação e a análise matemática do conversor CC-CC Cuk com alto ganho estático. Posteriormente, são realizadas a análise teórica e a estratégia de controle do microinversor proposto. Os resultados experimentais são expostos para discutir o funcionamento da topologia proposta, através de simulações e da implementação de um protótipo de 180 W. / The development of a novel single stage microinverter is proposed. The presented topology is based on the combination of the Cuk converter with a switched inductor structure to obtain a higher static gain, and a full-bridge inverter circuit. The presented switched inductor structure reduces voltage and current stresses on the power switches. In order of simplify the control, the stage CC of the microinverter operate in discontinuous conduction mode (DCM). To inject sinusoidal current with low harmonic distortion to the grid, a sinusoidal pulse width modulation (SPWM) is applied in the power switches. The switches of the full-bridge invertes are commanded in low frequency, in order to reduce switching losses. Operation modes and math analysis of the novel CC-CC converter are presented. Moreover, the math analysis and control strategy of proposed microinverter topology are exposed. Furthermore, experimental results are performed to analyze the proposed topology operation, by software simulations and implementation of a 180 W prototype.

The densification mechanisms of polycrystalline α-alumina by spark plasma sintering are highly contradictory, with different research groups suggesting diffusion to dislocation controlled mechanisms to be rate controlling. The specific objective of this work was to investigate densification mechanisms of α-alumina during the intermediate and final stages of sintering by SPS, analyze the microstructural development and establish sintering trajectories. In addition, zirconia and yttria were added in different weight percentages to study the effect of solute concentration on the densification kinetics of spark plasma sintered alumina. The present work adopts a different approach from the classical method adopted previously to analyze the sintering kinetics and densification mechanisms of alumina in SPS, although existing models for hot pressing were adopted for the basic analysis. The densification behavior was investigated in the temperature range 1223-1573 K under applied stresses of 25, 50 and 100 MPa and grain sizes between 100 and 250 nm. The SEM micrographs reveal equiaxed grains with no abnormal grain growth in the dense samples. The ‘master sintering curve’ shows grain size to be primarily dependent on density, irrespective of the applied stresses or temperature. The stress exponent of 1 along with an inverse grain size exponent of 3 and activation energy of 320-550 kJ mol-1 suggests Al3+ grain boundary diffusion as the rate controlling densification mechanism in alumina. The densification rates are marginally slower in compositions with 0.1% Y2O3 and ZrO2 content possibly due to the smaller grain sizes used in this study which leads to faster rates compared to earlier reports. However, higher Y2O3 and ZrO2 content led to decrease in densification rate by more than an order of magnitude possibly due to presence of a second phase which increases the effective path length for diffusion, thereby reducing the densification rates. Presence of Y2O3 and ZrO2 in the compositions with 0.1% Y2O3 and ZrO2 were confirmed by TEM studies. The Y3Al5O12 (YAG) phase developed between 1223 and 1273 K and suppressed densification and grain growth in alumina. In spite of higher temperatures required for alumina-YAG and alumina-zirconia composites to attain density ~99%, the alumina grain size in the composites was smaller than that in pure alumina due to the Zener drag effect. The stress exponents obtained for Y2O3 and ZrO2 composites at both the concentrations yield a value of n~ 2, which indicates a change in densification mechanism from pure alumina. The higher stress dependence of these composites could be due to presence of solute and second phase formation, both of which retard densification rates. The inverse grain size exponents obtained are between 1 and 2; both stress exponent and grain size exponent values suggest an interface reaction controlled diffusion mechanism occurring in these composites, independent of the Y2O3 and ZrO2 content. Higher activation energies are obtained with the Y2O3 and ZrO2 composites of higher content, respectively, due to presence of second phase particles at grain boundaries. The presence of solutes at grain boundaries hinders grain boundary diffusion of alumina, leading to interface reaction controlled process; this is confirmed by superimposing standard aluminum grain boundary and lattice diffusion data on to stress-densification rate data obtained in this work. A comparison of stress exponents using current experimental data adopting the present and the classical approaches show a wide difference in their values indicating a change in the rate controlling diffusion path, necessitating a review of the assumptions made on the basic equations used in previous SPS studies.

The need for efficiency, reliability and continuous operation has lead over the years to the development of fault-tolerant electrical drives for various industrial purposes and for transport applications. Permanent-magnet synchronous machines have also been gaining interest due to their high torque-to-mass ratio and high efficiency, which make them a very good candidate to reduce the weight and volume of the equipment.<p><p>In this work, a multidisciplinary approach for the design of fault-tolerant permanent-magnet synchronous machine drives is presented. <p><p>The drive components are described, including the electrical machine, the IGBT-based two-level inverter, the capacitors, the sensors, the controller, the electrical source and interfaces. A literature review of the failure mechanisms and of the reliability model of most of these components is performed. This allows understanding how to take benefit of the redundancy generally introduced in fault-tolerant systems.<p><p>A necessary step towards fault tolerance is the modelling of the electrical drive, both in healthy and faulty operations. A general model of multi-phase machines (with a number of phases equal to or larger than three) and associated converters is proposed. Next, control algorithms for multi-phase machines are derived. The impact of a closed-loop controller upon the occurrence of faults is also examined through simulation analysis and verified by experimental results.<p><p>Condition monitoring of electrical machines has expanded these last decades. New techniques relying on various measurements have emerged, which allow a better planning of maintenance operations and an optimization of the uptime of electrical machines. Regarding drives, a number of sensors are inherently present for control and basic protection functions. The utilization of these sensors for advanced condition monitoring is thus particularly interesting since they are available at no cost. <p><p>A novel fault detection and isolation scheme based on the available measurements (phase currents, DC-link voltage and mechanical position) is developed and validated experimentally. Change-detection algorithms are used for this purpose. Special attention is paid to sensor faults as well, what avoids diagnosis errors.<p><p>Fault-tolerant control can be implemented with passive and active approaches. The former consists in deriving a control scheme that gives acceptable performance for all operating conditions, including faulty conditions. The latter consists in applying dedicated solutions upon the occurrence of faults, i.e. by reconfiguring the control. Both approaches are investigated and implemented. <p><p>Finally, design considerations are discussed throughout the thesis. The advantages and drawbacks of various topologies are analyzed, which eventually leads to the design of a five-phase fault-tolerant permanent-magnet synchronous machine. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

No description available.

Tématem této práce je počítačové modelování organického elektrochemického tranzistoru (OECT). Pro vytvoření modelu bylo třeba vypočítat rozložení elektrického pole a koncentrace iontů elektrolytu. Výpočet byl proveden numericky pomocí metody konečných prvků. Bylo vypočítáno rozložení elektrického potenciálu na povrchu kanálu OECT, dále byly vypočítány změny vodivosti a výstupní proud OECT. Výpočty byly provedeny na osobním počítači pomocí komerčního softwaru COMSOL Multiphysics. Kvůli nedostatečnému výpočetnímu výkonu musel být model rozdělen na části a drasticky zjednodušen. Prezentované výsledky se liší od literatury, protože se nepodařilo správně modelovat saturaci tranzistoru. Odchylky od reálného chování OECT jsou pravděpodobně způsobeny zjednodušením modelu.

Indiana University-Purdue University Indianapolis (IUPUI) / The substantial increase demand for electrical energy requires high efficient apparatus dealing with energy conversion. Several technologies have been suggested to implement power supplies with higher efficiency, such as multilevel and interleaved converters. This thesis proposes an energy conversion unit with an optimized number of output voltage levels per number of switches nL=nS. The proposed five-level four-switch per phase converter has nL=nS=5/4 which is by far the best relationship among the converters presented in technical literature. A comprehensive literature review on existing five-level converter topologies is done to compare the proposed topology with conventional multilevel converters. The most important characteristics of the proposed configuration are: (i) reduced number of semiconductor devices, while keeping a high number of levels at the output converter side, (ii) only one DC source without any need to balance capacitor voltages, (iii) high efficiency, (iv) there is no dead-time requirement for the converters operation, (v) leg isolation procedure with lower stress for the DC-link capacitor. Single-phase and three-phase version of the proposed converter is presented in this thesis. Details regarding the operation of the configuration and modulation strategy are presented, as well as the comparison between the proposed converter and the conventional ones. Simulated results are presented to validate the theoretical expectations. In addition a fault tolerant converter based on proposed topology for micro-grid systems is presented. A hybrid pulse-width-modulation for the pre-fault operation and transition from the pre-fault to post-fault operation will be discussed. Selected steady-state and transient results are demonstrated to validate the theoretical modeling.

As fontes renováveis de energia, em especial a energia solar fotovoltaica vem ganhando espaço nos últimos anos devido ao avanço da tecnologia, redução dos custos e redução das fontes não-renováveis. Os painéis fotovoltaicos isoladamente ou para pequenas aplicações geram uma baixa tensão de saída e a adequação dos níveis de tensão fornecidos em sua saída aos requeridos pela concessionária de energia elétrica é um desafio. Neste trabalho é apresentada uma nova estrutura modificada da topologia do conversor SEPIC que usa as técnicas de acoplamento magnético série e células multiplicadoras de tensão em conjunto, afim de obter um elevado ganho de tensão, visando a aplicação em fontes renováveis de energia. Optou-se pela solução não isolada, pois esta apresenta diversas vantagens em relação a solução isolada, como: menor peso, volume, custo e maior eficiência energética devido a menores perdas de potência nos indutores acoplados. Também, a utilização da indutância de dispersão, que é um parâmetro intrínseco de um acoplamento magnético, permite a operação com comutação suave ZCS (ZCS, do inglês Zero Current-Switching) no interruptor, aumentando a eficiência da estrutura com a redução das perdas por comutação. No decorrer do trabalho são realizadas as análises das etapas de operação de diversos conversores a partir do conversor SEPIC modificado, evolui-se pela adição de técnicas elevadoras de tensão até a estrutura proposta neste trabalho. Por fim, é realizado o controle em malha fechada utilizando um controlador PID analógico que fornece uma resposta rápida e consequente correção a possíveis mudanças na variável controlada. Os resultados teóricos e experimentais do conversor proposto são descritos neste trabalho para validar as análises desenvolvidas e demonstrar a eficiência da estrutura. O protótipo é desenvolvido para uma aplicação com potência nominal de 200 W, tensão nominal de saída igual a 450 V e uma tensão de entrada variando entre 20 V e 40 V. O rendimento obtido para o conversor proposto operando na frequência de 35 kHz na potência nominal é de 91,28% e eficiência igual a 89,04% para a potência nominal de 200 W na frequência de 90 kHz. / The renewable energy resources, in special the photovoltaic energy has been achieve more space in last years due to technology advances, cost reduction and decrease of the non-renewable energy sources. The photovoltaic panels in isolation or to small applications generate a low output voltage and to comply with of voltage levels provided in panel’s output to those required by electric power concessionaire is a challenge. In this work is presented a new structure modified of the SEPIC converter topology who uses the coupling magnetic series and voltage multiplier cell techniques together, in order to obtain a high voltage gain aiming at application in renewable energy resources. It was has been choosen non-isolated solution, because this present several advantages in relation to the isolated solution, such as: lower weight, volume, cost and high energy efficiency due to smaller power losses in the coupled inductors. The use leakage inductance, who is an intrinsic parameter of the a magnetic coupling, allows soft-switching operation ZCS in switch, increasing the structure’s efficiency with reduction of switching losses. During the work are perform the analysis of the operation steps of several converters as of the modified SEPIC converter and evolves by addition high voltage techniques until the structure proposed in this work. Finally, is performed the closed loop control using the analog PID controller who provides a fast response and consequent correction to possible changes in the controlled variable. The theoretical and experimental results of the proposed converter are described in this work to validate the developed analysis and demonstrate the structure’s efficiency. The prototype is developed to a application with nominal power of 200 W, nominal output voltage equal 450 V and an input voltage varying between 20 V and 40 V. The efficiency obtained to proposed converter operating in frequency of the 35 kHz in nominal power is 91,28% and efficiency equal 89,04% to nominal power in frequency of the 90 kHz.