Agricultural practices may influence stream biological communities by removing riparian vegetation and modifying stream channel morphology, both which may reduce water retention time. I collected benthic invertebrates and fishes in seven headwater agriculturally-influenced streams in central Indiana, to quantify controls on invertebrate and fish community assemblage variation. Invertebrates were collected at 14 sites and fish were collected at 12 sites in Buck Creek watershed. The abundances of invertebrates and fishes were analyzed in Detrended Correspondence Analyses (DCA) in PC-ORD software and correlated with abiotic and biotic factors. The sites located in close proximity to Buck Creek have increased stability of biotic (fish assemblages) and abiotic (flow and water depth) factors. Abundances of invertebrates of headwater streams in east-central Indiana agricultural landscapes are influenced by distance between sites, distance to Buck Creek, and presence of fish species. Abundances of fishes were correlated with water quality and distance to Buck Creek. / Department of Biology

In the thesis, a LED driver circuit that is applied in low power LED lighting with constant output current and Power Factor Correction (PFC) is presented. For power stage of LED driver, a non-insulated switching Buck power converter without transformer is used, and develop equivalent mathematical model and block diagram of Buck converter while its inductor current operating in Continuous Conduction Mode(CCM). Furthermore, the closed loop PFC control circuit is designed by time-domain and frequency-domain analysis. In addition, because of the classical PFC control configuration needs the expensive multiplier, a LED driver circuit with PFC without multiplier is presented in this thesis in order to reduce the system cost and space of the circuit. Then, we confirm the designed circuit by simulation and experiment. By the results, the proposed system achieves constant output current control and power factor can reach to 0.92.

A twin-buck converter with zero-voltage-transition (ZVT) is proposed in this thesis. The converter comprises two identical buck conversion units connected in parallel by an interleaved inductor. The ZVT is accomplished by the resonating the currents between the interleaved inductor and the parasitic capacitances of the power MOSFETs. The circuit efficiency can be further improved by introducing synchronous rectification to reduce the condition loss on the diodes. The detailed circuit analysis and operation characteristics are provided. A laboratory circuit rated at 300 W is designed and tested. Experimental results show that the switching losses can be effectively reduced by smoothly transiting the currents of the active power switches.

This thesis is to design an LED driver circuit with constant output current and Power Factor Correction(PFC) control. Switching power converter is applied for power stage of the LED driver circuit, a non-insulated Buck converter without transformer is used, and the inductor current of Buck converter is operating in Continuous Conduction Mode(CCM). According to the operating principle of Buck converter, the equivalent mathematical model and system block diagram is developed to establish the traditional closed loop PFC control circuit. The controller parameters are set up by time-domain and frequency-domain analysis to achieve the goal with constant output current and PFC control. Furthermore, the thesis presents a more effective PFC control method to reduce the cost of multiplier used in traditional PFC control method and overcome the congenital defect of Buck converter. Both two PFC control methods are confirmed and compared by simulation and experiment. The results show that the proposed control method has more effective performance and achieve constant output current for LED with high power factor by 0.966 under full-load condition.

DC/DC buck converters are cascaded in order to generate proper load voltages. Rectified line voltage is normally converted to 48V, which then, by a bus voltage regulating converter also called the line conditioner converter, is converted to the bus voltage, e.g. 12V. A polynomial controller converter transforms the 12V into to a suitable load voltage, a fraction of or some few voltages. All cascaded converters are individually controlled in order to keep the output voltage stable constant. In this presentation focusing on the polynomial controller converter implemented as Ericsson’s buck converter BMR450. In this paper modeling, discretization and control of a simple Buck converter is presented. For the given DC-DC-Converter-Ericsson BMR 450 series, analyzing the disturbance properties of a second order buck converter controllers by a polynomial controller. The project is performed in Matlab and Simulink. The controller properties are evaluated for measurement noise, EMC noise and for parameter changes. / +46-762795822

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 154-168).

Made available in DSpace on 2018-08-02T00:00:38Z (GMT). No. of bitstreams: 1 tese_10498_dissertacao_Netalianne.pdf: 5417301 bytes, checksum: 5f643d84188fcaeb6044feefa4b71257 (MD5) Previous issue date: 2016-12-08 / Devido à necessidade do emprego de técnicas de rastreamento do ponto de máxima potência no estudo de energia solar fotovoltaica, e considerando a dificuldade de viabilizar ensaios e testes em laboratório, este trabalho consiste em modelar um arranjo fotovoltaico representando o efeito do sombreamento parcial em arranjos como referência para emuladores de módulos PVs. As características nominais de um módulo fotovoltaico são descritas por meio de um modelo matemático que, por simulação computacional, estabelece uma corrente de referência para emulação de um conjunto de módulos conectados em série. O modelo matemático utilizado é adaptado para representar os efeitos de sombreamento parcial a que são expostos os arranjos fotovoltaicos, e a corrente de referência disponibilizada é utilizada como referência de corrente do laço de controle de um conversor CC que deve conseguir imitar o comportamento de um arranjo fotovoltaico com sombreamento parcial. O algoritmo para adequação aos efeitos de sombreamento parcial, o projeto do emulador e os resultados obtidos são apresentados considerando diferentes níveis de radiação do Sol e para diferentes condições de sombreamento parcial. A partir dos resultados apresentados e comparados com um sistema de referência foi possível obter uma resposta satisfatória para a representação de arranjos série de módulos em situação de sombreamento parcial. Os resultados de cálculo de desvios se mantiveram abaixo da faixa de tolerância prevista pelo fabricante do módulo comercial utilizado. O conversor projetado e a sintonia do controlador obtiveram bom funcionamento para todas as condições de irradiância mostradas com um bom comportamento dinâmico, sendo capaz de representar as características elétricas do arranjo de maneira adequada.

Made available in DSpace on 2018-08-02T00:01:58Z (GMT). No. of bitstreams: 1 tese_3848_Tese_TiaraRSFreitas.pdf: 3688998 bytes, checksum: e95e71bd31d909af188216252316081e (MD5) Previous issue date: 2015-12-11 / Apresentam-se duas topologias retificadoras controladas, aplicadas em aerogeradores síncronos a ímã permanente, de baixa potência. Para sistemas de baixa potência, ou sistemas de operação isolada (stand-alone), onde a energia proveniente da geração eólioelétrica é parte significante da energia total do sistema, os geradores e os conversores têm o papel de manter a tensão e a frequência da rede constantes, apesar das oscilações de potência na turbina eólica. Em geradores síncronos a ímã permanente (GSIP) com velocidade variável, a solução preferencial tem sido a conversão em duas etapas: CA-CC-CA. Diversas topologias de conversores têm sido exploradas, porém, o que se tem observado, é que essa conversão dispõe de muitos elementos controlados na conversão CA-CC, a maioria a seis chaves, dificultando e encarecendo o seu controle. Cada nova topologia apresenta novos aspectos, sempre buscando um conversor que melhor se adapte ao sistema e influenciando minimamente possível a qualidade da potência de geração. As topologias apresentadas pela literatura são eficientes para as potências maiores, mas quando se trata de sistemas com potências menores, conversores mais simples (com uma ou três chaves controladas) podem atender ao objetivo de retificação com um custo menor, e sem que a qualidade da conversão seja reduzida. A contribuição desta tese de doutorado é o desenvolvimento de uma nova topologia retificadora SEPIC, a três chaves controladas, e a análise e a aplicação de uma topologia Buck-ressonante, a uma chave controlada, para aerogeradores. São soluções retificadoras mais simples, aplicadas à geração eólioelétrica de baixa potência com gerador síncrono de ímãs permanentes, oferecendo simplicidade e facilidade de controle. Apresentam-se o projeto dos conversores, as equações que os definem, os resultados de simulação e os resultados experimentais. Verificou-se que ambas as soluções conseguem operar com alto fator de potência e conteúdo harmônico reduzido empregando um único sinal de comando, em ampla faixa de velocidade do vento e sem laço de controle da corrente do gerador.

Hydrogen is a potential future energy storage medium to supplement a variety of renewable energy sources. It can be regarded as an environmentally-friendly fuel, especially when it is extracted from water using electricity obtained from solar panels or wind turbines. The focus in this thesis is on solar energy, and the theoretical background (i.e., PSCAD computer simulation) and experimental work related to a water-splitting, hydrogen-production system are presented. The hydrogen production system was powered by a photovoltaic (PV) array using a proton exchange membrane (PEM) electrolyser. The PV array and PEM electrolyser display an inherently non-linear current-voltage relationship that requires optimal matching of maximum operating power. Optimal matching between the PV system and the electrolyser is essential to maximise the transfer of electrical energy and the rate of hydrogen production. A DC/DC converter is used for power matching by shifting the PEM electrolyser I-V curve as closely as possible toward the maximum power the PV can deliver. By taking advantage of the I-V characteristics of the electrolyser (i.e., the DC/DC converter output voltage is essentially constant whereas the current increases dramatically), we demonstrated experimentally and in simulations that the hydrogen production of the PV-electrolyser system can be optimised by adjusting the duty cycle generated by the pulse-width modulation (PWM) circuit. The strategy used was to fix the duty cycle at the ratio of the PV maximum power voltage to the electrolyser operating voltage. A stand-alone PV energy system, using hydrogen as the storage medium, was designed. The system would be suitable for providing power for a family's house located in a remote area in the Libyan Sahara.

Les Alimentations Sans Interruption (ASI) ont pour rôle de protéger les charges sensibles. Leur utilisation nécessite l’usage de convertisseur de puissance AC/DC triphasé abaisseur et/ou élévateur de tension. Les ASI utilisent généralement une chaîne de conversion DC/DC+DC/AC ayant un rendement aux alentours de et sont souvent employées de façon continue. L’objectif de cette thèse est donc d’étudier un convertisseur DC/AC triphasé réversible en puissance susceptible de fonctionner en abaisseur et en élévateur de tension pour atteindre un rendement souhaité de 98% avec un minimum de 97,5%. L’étude s’oriente vers des architectures de convertisseurs peu conventionnelles, l’utilisation de semi-conducteurs grand gap (SiC) et de composants passifs à faible pertes. Une méthode de comparaison rapide qui est à la fois analytique et numérique est présentée pour dimensionner ces architectures en se basant sur les caractéristiques fournies par les constructeurs. La solution ‘Gradateur Onduleur Différentiel’ a été jugée comme la plus adaptée à nos besoins. Les choix techniques pour ce convertisseur sont détaillés, puis une étude de faisabilité présentée. Le convertisseur retenu est non linéaire et sa commande utilise des principes de fonctionnement atypiques, différentes stratégies de régulation sont donc présentées. Des tests sont effectués pour valider la commande mise en place et réaliser les essais fonctionnels et mesures de rendement. Enfin les résultats sont comparés aux prévisions et la solution proposée est finalement globalement comparée à la chaîne de conversion AC/DC+DC/DC classique.