Com o objetivo de determinar a eficiência da ação polinizadora de Apis mellifera L. no rendimento de sementes de Adesmia latifolia, estabeleceu-se três tratamentos na Estação Experimental Agronômica da UFRGS, em Eldorado do Sul (300 S, 510 W) nos anos de 2000, 2001 e 2002. A partir da floração, analisou-se a freqüência de visitas por A. mellifera e outros insetos nas flores de A. latifolia pelo teste de Qui-quadrado, já o número de inflorescências por área, número de flores, flores abortadas e lomentos por inflorescência foi através da análise de regressão. Os resultados indicaram que A. mellifera não é eficiente na polinização de A. latifolia, sendo esta cultura dependente de insetos nativos como Megachile sp. e Centris sp para produção de sementes. A média de produção de sementes na área controlada e livre foi 5,4 e 83,5 kg/ha, respectivamente, enquanto na área isolada não houve produção de sementes. A baixa freqüência (10%) de visitas de A. mellifera na área livre em comparação com os insetos nativos (90%) indica que o néctar não é atrativo para as abelhas A. mellifera pois tem uma baixa concentração de açúcares totais (5,7%).

The work detailed in the thesis compares the performance of single-phase thyristor bridge converters under different control strategies; considering in particular the efficiency, ac side power factor and harmonic content of the current and voltage waveforms. Extensive practical investigations were performed, in which, analogue and digital control circuits were developed to provide the drive signals necessary for a converter to operate in the different control modes for: a) A series -connected fully-controlled double thyristor bridge (used mainly in traction applications) operating under sequence control and; b) A fully controlled single-bridge operating under sequence and conventional control. A novel pulse-width modulation control strategy was developed for the single-bridge converter, using gate turn-off thyristors as the switching elements, whereby output voltage control is obtained by variation of the modulation index. Turn-on and turn-off signals for the power devices were obtained using an analogue control circuit. The advantages and disadvantages of this switching strategy compared with conventional and sequence control were studied, and results clearly showed that an improved input power factor and lower supply current and load voltage harmonics were all obtained. Mathematical models for single and double bridge converters operating under sequence and conventional control were developed using tensor techniques. Using these models, computer programmes were written in Fortran 77 on the University mainframe computer, to assemble automatically and solve the network equations as the converter topology changes. In addition, analytical models were also developed on the assumption that the load current is completely smooth. However, such an assumption is not justifiable with ac-to-dc converters and consequently a novel technique was developed to include the load current ripple in calculating the supply current harmonics. The results obtained are compared with both the computed and experimental ones.

This paper describes the design of DC/DC converters designed for charging supercapacitors and subsequent transformation of voltage to the desired value. In the text are presented decreasing and increasing switched-mode voltage converter including the calculation of the individual components and also the design of converter that combines both types. Using simulation software has been verified the function of each circuits, which can serves as a lower power backup supply.

This work builds on a semester project 2. from the winter semester of this academic year. The aim of this thesis is the design of converter using semiconductor components based on SiC technology. This converter is used in the construction of quick charger for electric vehicles. The design of this converter must be based on the requirements for compliance voltage safety. It describes the design of power components used in the construction of this facility, the determination of their losses and determines the overall efficiency of the converter. There is also proposed mathematical model of high-frequency transformer and made his simulation in Matlab-Simulink.

This thesis deals with a design, construciton and testing of a switch-mode power supply (SMPS) which is working as a LiFEPO4 battery charger with output current up to 100~A and output voltage up to 14,6~V. The output voltage and current can be regulated by the operator from zero to maximum value. For this SMPS Half-bridge asymmetrical forward converter with two transformers and common output inductor topology is chosen. The control circuits are run by the IC SG3525. Cascaded regulation of output voltage and current is implemented by two discrete operational amplifiers. Undervoltage protection of the control circuits and independent overcurrent protection on the primary side is also implemented.

This diploma thesis describes particular parts of power inverter such as gate driver, DSC, LC filter, low power supply, DC/DC converter and four-quadrant bridge and manner of its control by digital signal controller. Inverter is designated for generating of a mobile artificial electric grid (for example in a car).

The thesis deals with design and construction of low-power measurement device with power over optical fiber. This device should measure input signal in range of 50 mV to 50 V and the results of measurement sent through optical fiber into sensing module.

This work builds on a semester project 2 from the winter semester of this academic year. The aim of this thesis is the design of converter using semiconductor components based on SiC technology. This converter is used in the construction of quick charger for electric vehicles. The design of this converter must be based on the requirements for compliance voltage safety. It describes the design of power components used in the construction of this facility, the determination of their losses and determines the overall efficiency of the converter. There is also proposed mathematical model of high-frequency transformer and made his simulation in Matlab-Simulink.

This diploma thesis deals with elektrical power quality in DC grids. Electrical power is commodity and therefore it must be represented not just with quantitative, but also with qualitative parameters. Nowadays, there is an increasing demand for bigger implementation of renewable energy sources and more efficient power systems, which motivates installation of DC grids. However, development of DC grids is decelerated by lack of standardization alson in power quality. The work includes definition of power quality parameters and their measurement methodology.

Nous abordons dans cette thèse les approches de la Programmation DC et DCAen Data Mining (fouille de données). Plus particulièrement, nous nous intéressons aux problèmes de parcimonie en modélisation parcimonieuse de données. Le travail porte sur des recherches théoriques et algorithmiques et la principale approche utilisée est la programmation DC et DCA.Nous avons établi des propriétés intéressantes, des reformulations DC, voire quadratiques,équivalentes pour ces problèmes grâce à de nouvelles techniques de pénalité exacte développées durant cette thèse. Ces résultats donnent une nouvelle facette et une nouvelle manière de voir ces problèmes de parcimonie afin de permettre une meilleure compréhension et prise en main de ces problèmes. Ces nouvelles techniques ont été appliquées dans le cadre de la modélisation parcimonieuse pour le problème de la valeur propre maximale et dans le cadre de la modélisation parcimonieuse dans les modèles de régression linéaire.La structure simple des reformulations obtenues se prête bien à la programmation DC et DCA pour la résolution. Les simulations numériques, obtenues avec DCA et un algorithme combiné DCA et la procédure Séparation et Evaluation pour l’optimisation globale, sont très intéressantes et très prometteuses et illustrent bien le potentiel de cette nouvelle approche. / In this thesis, we investigate the DC Programming and DCA approaches in DataMining. More precisely, we are interested in the sparse approximation problems in sparse modelling. The work focuses on theoretical and algorithmic studies, mainly based on DC Programming and DCA. We established interesting properties concerning DC and quadratic reformulations for these problems with the help of new exact penalty techniques in DC programming. These results give new insights on these sparse approximation problems and so allow a better understanding and a better handling of these problems. These novel techniques were applied in both contexts of sparse eigenvalue problem and sparse approximation in linear models.The simple and nice structure of the obtained reformulations are suitably adapted to DC programming and DCA. Computational experiments are very interesting and promising, illustrating the potential of the novel approach.