Renewable energy and distributed generation are getting more and more popular, including photovoltaic modules (PV), wind turbines, and fuel cells. The renewable energy sources need the power electronics interface to the utility grid because of different characteristics between the sources and the grid. No matter what renewable energy source is utilized, inverters are essential in the microgrid system. Thanks to flexible modular design, transformerless connection, extended voltage and power output, less maintenance and higher fault tolerance, the cascade inverters are good candidates for utility interface of various renewable energy sources. This dissertation proposes a new type of cascade inverters based on dual-buck topology and phase-shift control scheme. Compared to traditional cascade inverters, they have enhanced system reliability thanks to no shoot-through problems and lower switching loss with the help of using power MOSFETs. With phase-shift control, it theoretically eliminates the inherent current zero-crossing distortion of the single-unit dual-buck type inverter. In addition, phase-shift control can greatly reduce the ripple current or cut down the size of passive components by increasing the equivalent switching frequency. An asymmetrical half-cycle unipolar (AHCU) PWM technique is proposed for dual-buck full-bridge inverter. The proposed approach is to cut down the switching loss of power MOSFETs by half. At the same time, this AHCU PWM leads to current ripple reduction, and thus reducing ripple-related loss in filter components. Therefore, the proposed PWM strategy results in significant efficiency improvement. Additionally, the AHCU PWM also compensates for the zero-crossing distortion problem of dual-buck full-bridge inverter. Several PWM techniques are analyzed and compared, including bipolar PWM, unipolar PWM and phase-shifted PWM, when applied to the proposed cascade dual-buck full-bridge inverter. It has been found out that a PWM combination technique with the use of two out of the three PWMs leads to better performance in terms of less output current ripple and harmonics, no zero-crossing distortion, and higher efficiency. A grid-tie control system is proposed for cascade dual-buck inverter with both active and reactive power flow capability in a wide range under two types of renewable energy and distributed generation sources. Fuel cell power conditioning system (PCS) is Type I system with active power command generated by balance of plant (BOP) of each unit; and photovoltaic or wind PCS is Type II system with active power harvested by each front-end unit through maximum power point tracking (MPPT). Reactive power command is generated by distributed generation (DG) control site for both systems. Selective harmonic proportional resonant (PR) controller and admittance compensation controller are first introduced to cascade inverter grid-tie control to achieve better steady-state and dynamic performances. / Ph. D.

Although the locomotive of a train is energized, in general, other railcars are not. This prevents commercial rail companies from installing sensor equipment on the railcars. Thus, several different solutions have been proposed to provide energy for commercial railcars. One such solution is a vibration-based energy harvester which can be mounted in the suspension coils of the railcar. The harvester translates the linear motion of the suspension vibration into rotational motion to turn a 3-phase AC generator. When subjected to real-world suspension displacements, the harvester is capable of generating peak energy levels in excess of 70 W, although the average energy harvested is much lower, around 1 W. A battery pack can be used to store the useful energy harvested. However, a power conditioning circuit is required to convert the 3-phase AC energy from the harvester into DC for the battery pack. The power converter should be capable of extracting maximum power from the energy harvester as well as acting as a battery manager. Experimental results with the energy harvester conclude that maximum power can be extracted if the harvester is loaded with 2 . In order to maintain a constant input impedance, the duty cycle of the power converter must be fixed. Conversely, output regulation requires the duty cycle to change dynamically. Consequently, there is a tradeoff between extracting maximum power and prolonging the battery life cycle. The proposed converter design aims to achieve both maximum power transfer and battery protection by automatically switching between control modes. The proposed converter design uses an inverting buck-boost converter operating in discontinuous conduction mode to maintain a constant input impedance through a fixed duty cycle. This constant input impedance mode is used to extract maximum power from the harvester when the battery is not close to fully charged. When the battery is near fully charged, extracting maximum power is not as important and the duty cycle can be controlled to regulate the output. Specifically, one-cycle control is used to regulate the output by monitoring the input voltage and adjusting the duty cycle accordingly. Finally, the converter is designed to shut down once the battery has been fully charged to prevent overcharging. The result is a power converter that extracts maximum power from the energy harvester for as long as possible before battery protection techniques are implemented. Previous related studies are discussed, tradeoffs in converter design are explained in detail, and an experimental prototype is used to confirm operation of the proposed control scheme. / Master of Science

As laptop mobile users expect more application features and long battery life, the processor current has to increase to response the demanding while the voltage has to decease to save the power loss. Therefore, it is necessary for a system designer to improve the efficiency of the voltage regulator converter (VRC) for the processor. Laptop processor architecture is more complicated than desktop because of different mode operations and their transitions. The laptop processor runs at different voltage levels for each operation mode to save the battery life. Therefore, the VRC needs to supply the correct and stable voltage to the processor. In this thesis, an analysis of power loss is derived to estimate the efficiency and switching frequency, three widely current sensing methods are discussed, two methods to compensate for the thermal resistance in loss less current sense methods are proposed, the tolerance of load line base on the component's tolerance in the converter is analyzed, the equation to estimate the output capacitance is derived, and the small signal analysis of multiphase synchronous buck converter with the droop current loop is derived. A hardware prototype was implemented base on 4-phase synchronous buck topology to provide high efficiency and lower cost solution. The results of load line meets the Intel specification in different modes of operation, provides the best transient responses, and meets the specification during the load transient. The control loop lab measurement is also matched with the analysis and simulation. / Master of Science

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Neste trabalho à apresentado o estudo, modelagem e projeto de uma nova topologia de conversor CC-CC, o Conversor Buck QuadrÃtico CC-CC nÃo isolado (QBC). Inicialmente, foi realizada a anÃlise qualitativa e quantitativa da topologia proposta para operaÃÃo em modo de conduÃÃo contÃnua (MCC), verificando-se as etapas de operaÃÃo e obtendo-se as relaÃÃes de tensÃo e corrente para dimensionar os componentes de projeto do conversor, tambÃm foi realizada a modelagem do sistema atravÃs da representaÃÃo no espaÃo de estados. Em seguida, a fim de validar a topologia proposta, utilizou-se simulaÃÃo via PSpice. ApÃs essa etapa, iniciou-se a construÃÃo de um protÃtipo com 500 W de potÃncia total de saÃda, operando em 20 kHz. Os resultados experimentais obtidos confirmam que a topologia proposta pode ser utilizada em atividades prÃticas, como por exemplo, para o carregamento de baterias. / In this paper is presented the study, modeling and design of a new DC-DC converter topology, the Converter Quadratic Buck DC-DC non-isolated (QBC). Initially, was made the qualitative and quantitative analysis of the proposed topology of continuous conduction mode operation (MCC), the steps of operation and thus the relationship of voltage and current to size the components converter project, was also held the system modeling through representation on the State space. Then, in order to validate the proposed topology, was used simulation via PSpice. After this step, began the construction of a prototype with 500 W total power output, operating at 20 kHz. The experimental results obtained confirm that the proposed topology can be used in practical activities, for example, for battery charging.

This thesis evaluate the state of art ROHM SCT3080KR silicon carbide mosfet in a synchronous buck converter. The converter was using the ROHM P02SCT3040KR-EVK-001 evaluation board for driving the mosfets in a half bridge configuration. Evaluation of efficiency, waveforms, temperature and a theoretical comparison between a silicon mosfet (STW12N120K5) is done. For the efficiency test the converter operate at 200 V input voltage and 100 V output voltage at output currents of 7 A to 12 A, this operation was tested at switching frequencies of 50 kHz, 80 kHz and 100 kHz. The result of the efficiency test showed an efficiency of 98-97 % for 50 kHz, 97.7-96.4 % for 80 kHz and 97-96.2 % for the 100 kHz test. The temperature test shows a small difference in comparison of the best case scenario and the worst case scenario, temperature ranges from 25.5 to 33.5 °C for the high side mosfet while the low side mosfet temperature ranges from 29.8 to 35 °C. The waveform test was conducted at 50 kHz and 100 kHz for output currents of 4 A and 12 A (at 200 V input and 100 V output). The result of the waveform test shows a rise and fall time of the voltages in range of 10-12 ns while the current rise and fall time was 16 ns for the 4 A test and 20 ns for the 12 A test. Overall SiC mosfet show a clear advantage over silicon mosfet in terms of efficiency and high power capabilities.

No description available.

This study has attempted to model and quantify the impacts of Beneficial Management Practices (BMP) like buffer strips on the phosphorus concentration and loading in the Buck Creek Watershed of Central Indiana. The GIS based modeling was done using the Soil and Water Assessment Tool (SWAT) developed by the U.S. Department of Agriculture-Agricultural Research Services (USDA-ARS). The results from the EPA funded two year (2002-2004) Upper White River Watershed Project (UWRWP) for the Buck Creek Watershed were used as the measured base data for the modeling evaluation. These measured data were compared against the data generated out of the model simulation based on two different scenarios which took into consideration the combinations of land use, agricultural management practices, point source pollutions and BMPs. Scenario-1 simulated all the aspects of land use intensity, moderate agricultural management practices and moderate point source pollutions taking place in the Buck Creek watershed. While running the model in scenario-1, there was a noticeable increase in the phosphorus loading to the sub-watersheds ranging from 10% in the lowland sub-watershed of BC-4 to 39% in the highland sub-watershed of BC-7. In scenario-2, BMPs were implemented in the model which added 100 acres of vegetated buffer strips uniformly in all sub-watersheds and 3 acres of grassed buffers along the streams except BC-3. On re-running the model in scenario-2, there was a drastic decline in the phosphorus loading to the stream. It has been noted that there was at least 15% reduction in the loading of phosphorus to the stream where buffer strips were implemented. The present GIS modeling study helped to quantify the changes in the loading of sediments and nutrients which are induced by any parametric changes in the watershed including soil, slope, land use, agricultural management practices and BMPs. / Department of Geography

This study is an analysis of images of Chinese women in five of Pearl S. Buck's novels: East Wind: West Wind, The Good Earth, The Mother, Pavilion of Women, and Peony. Buck's female characters, with their different degrees of individuality and typicality, form a realistic picture of Chinese women.In terms of thematic content, the study shows that all Buck's female characters use their limited power within the constraints of their society to achieve what they deserve, often employing different, covert ways, some manipulation, and even a little deception.The significance of this is that it reveals, in an artistic way, the social conditions under which Chinese women at Buck's times lived. Chinese women had been very much oppressed. In order to survive, they had to act in ways acceptable by their society. However, they had, just as their male counterparts, the desire to love, to be happy, to maintain dignity, and to be free. What is more important, they were intelligent, courageous, and capable of fighting to achieve their goals for themselves.Buck portrays her female characters both as typical of Chinese women in general and as strong individual figures, each facing different conflicts, in a variety of social, familial situations, with unique characteristics. In order for the Western readers to understand the cultural content in which the individuals function, Buck gives her Chinese characters enough typicality as a solid foundation for the Westerners to interpret their behaviors.It is not difficult for the reader to see how the Confucian doctrines and the social conditions concerning Chinese women are truthfully reflected in the novels herein analyzed. Therefore, different degrees of individualization of these characters result from differing themes of the novels in which they appear. / Department of English

The present papers deals with three variable analogue of Boas and Buck [14] type generating functions forpolynomials of two variables and then the same has been extended for m-variable analogue. The results obtained are extensions of those obtained by us in our earlier paper [14]. / El presente artículo trata el anólogo de tres variables de la función generatriz de Boas and Buck [14] para polinomios de dos variables y lo mismo se puede extender para el análogo de m variables. Los resultados obtenidos son extensiones de un artículo previo [14].

L’équipe de conception de Freescale à Toulouse développe des circuits intégrés dédiés au marché de l’automobile pour des applications châssis, sécurité ou loisir. Les contraintes associées à l’embarquement des circuits sont nombreuses : niveau d’intégration, fiabilité, températures élevées, et compatibilité électromagnétique. Les produits conçus par Freescale intègrent des convertisseurs à découpage pour l’alimentation en énergie des microcontrôleurs. Cette thèse a pour objet l’étude de nouvelles topologies de convertisseur d’énergie pour la baisse de l’encombrement et des perturbations électromagnétiques. La structure multiphase répond à la problématique dans son ensemble. Un prototype est réalisé dans une technologie silicium Freescale haute tension 0.25µm. Le volume des composants externes de filtrage est optimisé et réduit. Les mesures sur le prototype montrent des performances en accord avec les objectifs, et des émissions électromagnétiques particulièrement faibles. / The Freescale design team in Toulouse develops integrated circuits for automotive application such as chassis, safety or infotainment. Constraints associated with the embodiment of such circuits are many: die-size, safety, EMC (Electromagnetic Compliance). Switching Mode Power Supplies are integrated in these products to supply power to microcontrollers. This PhD thesis is to study new topologies of power supply to reduce the volume and electromagnetic disturbances. The multiphase structure responds to the raised issue. A prototype is produced in a Freescale 0.25µm high voltage silicon technology. Volume of the external components for filtering is optimized and reduced. Measures show upgrades in performance and reduced electromagnetic emissions.