Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work investigates the influence of operation point (Δi @ fs) in the final volume of PFC boost converter. The boost inductor, EMI filter and thermal heatsink are the elements which main influences in the converter volume. These elements are strongly influenced by the chosen operation point, showing a direct relationship among them. With the increase of switch frequency and of the input current ripple occurs reduction of the boost inductor volume. On the other hand, it increases the switching losses in semiconductors, and influence on the EMI filter volume. It should be highlight that the optimum designs of individual devices or parameters of a system could not take the optimization of the overall system. In this form it is strongly recommended that the engineers and designers take into account the overall system, as well available technologies, standard and recommendation, and finally market commitments. The methodology presented realize the converter design in a integrate form, selecting the operation point that the converter finds the minimal total volume, starting from input variable output power, input and output voltage. The design takes into account different semiconductors technologies, different input filter topologies, different heart sinks profile, different magnetic cores technologies further of international standards that the converter must be adapt. Based on an integrate design of converter parameters is possible optimize the design finding the operation point for the minimal volume. / Esse trabalho investiga o impacto do ponto de operação (Δi @ fs) no volume final do conversor boost operando como pré regulador com correção do fator de potência (PFC). Os elementos de maior influência no volume do conversor são o indutor boost, o filtro de entrada e os dissipadores térmicos. O volume destes elementos é diretamente influenciado pelo ponto de operação, mostrando uma relação direta entre eles. Com o aumento da freqüência de comutação e da ondulação da corrente de entrada ocorre a diminuição do indutor boost, porém, aumentam as perdas nas comutações dos semicondutores e aumenta o volume do filtro de entrada. Com a diminuição da freqüência e da ondulação da corrente ocorre o inverso, sabendo disto, fica claro que projetar individualmente cada um destes três elementos pode resultar em um bom projeto individual, contudo penaliza os outros parâmetros. Assim, a metodologia apresentada realiza o projeto do conversor de forma integrada, escolhendo o ponto de operação em que o conversor encontre o volume final mínimo, partindo de algumas variáveis de entrada, como potência de saída e tensões de entrada e saída. O projeto leva em consideração diferentes tecnologias de semicondutores, topologias de filtros de entrada, perfis de dissipadores térmicos, tecnologias de núcleos magnéticos além das normas internacionais a que o conversor deve se adequar. Baseado no projeto integrado dos parâmetros do conversor é possível otimizar o projeto encontrando o ponto de operação para o volume total mínimo do conversor.

This thesis aims to investigate an active power factor correction (PFC) circuit and its mathematical model, in order to develop a reliable and efficient simulation platform. By using the PI controller, we can control the inductor current and the output voltage of the boost converter. Finally, we constructed the circuit and analyzed the results to verify that our mathematical model is valid.

The thesis aims at investigating an active power factor correction circuit. In boost power converter, we ser up average large signal model with Matlab and derive control¡Voutput function for pole assignment of control loop with ac small signal model. In controller, control circuit of conventional active power factor correction and modified PI control circuit are adopted, separately. Through simulation results and experimental responses of hardware circuit show that under variation of load or alternating input voltage, modified PI control circuit has better regulating capacity than that of conventional control circuit .

This paper presents the results of an experimental study aimed at determining the impact of porous asphalt on the quality of stormwater runoff on highways with a curb and gutter drainage system. A porous overlay, also known as permeable friction course (PFC), is a layer of porous asphalt applied to the top of conventional asphalt highways at a thickness of 50 mm to improve safety and water quality and reduce noise. The quality of highway stormwater runoff was monitored before and after the installation of PFC on an eight-lane divided highway in the Austin, Texas area for 15 months. Observed concentrations of total suspended solids from PFC are more than an 80% lower than from the conventional pavement. Concentration reductions are also observed for nitrate/nitrite and total amounts of phosphorus, copper, lead, and zinc. The data shows that the results with curb and gutter are consistent with past results where runoff sheet flowed onto vegetated shoulders. / text

<p>The PFC plays an important role in memory tasks in organizing free recall. However, very little is known about the exact mechanisms underlying PFC function. Many researchers, like Morris Moscovitch (1994) believe the PFC supplies cues to other memory areas but details concerning this hypothetical function are vague. Anderson (2003), in contrast, believes that the PFC directly suppresses semantic memory traces. These potential functions of the PFC were explored in the following work. A model of non-strategic memory was built using a TCM framework, and a number of different implementations were evaluated. The model was then applied to Anderson's RIF work, to determine whether an item inhibition account of memory was necessary to explain RIF results. Finally, the model was applied to semantic memory strategies in free recall results to guide empirical research. It was found that no direct inhibition was necessary to explain RIF, and that, in a timed and categorized free recall task, the PFC best performs a semantic strategy by generating category labels at recall. Implications of this work were then discussed. </P> / Thesis / Doctor of Philosophy (PhD)

In a conventional electronic ballast for a fluorescent lamp, inductor-capacitor-transformer tank circuit is used. A Piezoelectric Transformer (PT) can potentially be used to replace such a tank circuit to save space and cost. In the past, ballast design using a PT requires selecting a PT from available samples which are normally not matched to specific application and therefore resulting in poor performance. In this thesis, a design procedure was proposed for designing a PT tailored for a 120-V 32-W electronic ballast with high power factor, high efficiency and Zero-Voltage-Switching (ZVS) of the inverter transistors that drive the lamp. This involves selection of PT materials, determination of geometries and the number of physical layers of the PT. A radial mode piezoelectric transformer prototype based on this design process was fabricated by Face Electronics Inc. and was tested experimentally, the results showed that the ballast using this custom-made PT achieved high power factor, Zero-Voltage-Switching and a 83% overall efficiency. / Master of Science

Although suitable CAD tools for thermal and electrical analyses in power electronic systems are available, traditional stand-alone simulation method seldom takes into consideration of the inter-dependency of semiconductor device power loss and junction temperature in an iterative process. However these dependencies are important, especially for applications where both cooling and power losses are driven by complex mechanisms. For a power supply system, a dynamic design process is necessary to address both electrical and thermal issues. It is because the steady state temperatures of the system are obtained from loss-and-temperature iteration. Once a system solid body model is built, iterations between power loss and junction temperature calculations are performed to obtain the steady state temperature distribution. Since reliability and failure rate of components are directly related to temperatures, an accurate model is critical to provide proper thermal management, which achieves maximum power density. All cooling-related data such as placement of components, airflow rate, heat sink size, and device types are subjected to design changes in order to meet ultimately the temperature requirements. The goal of this thesis is to demonstrate the benefits of integrated analysis and design tools applied in distributed power supply systems designs. First, it will significantly speed up the design process and eliminate the errors resulting from repeated manual data entry and information exchange. Second, the integrated electrical-thermal design tools encompass electrical, thermal, layout, and packaging design to obtain the optimal system design. / Master of Science

The research presents two novel high power factor ac-to-dc resonant converters with symmetrical topologies and zero-voltage-switching (ZVS) operation. The derived circuits are obtained from the integration of a dual-switch boost-type or buck-boost-type power factor corrector (PFC) into a half-bridge resonant converter. With symmetrical topology, the circuit is simple and the voltage and current stresses on the two active power switches are identical to each other. The PFC is operated at discontinuous conduction mode (DCM) to achieve unity power factor. The resonant energy tank of half-bridge resonant converter is designed to be inductive to retain ZVS operation. The design equations are derived based on fundamental approximation. Prototypes of the two proposed converters designed for 100 W and 50 W, respectively, were built and tested to verify the computer simulations and analytical predictions. Satisfactory results are obtained experimentally.

Memory is a complex and multifaceted entity. Cognitive psychology has adopted terminology to help simplify the study of memory. For example, one can consider the cognitive process the brain is engaged in, such as encoding versus retrieval. Similarly, one can consider the content of information, such as words, faces, or scenes. Content and process can also interact such as with instructions to view a face that happens to be situated next to a house (item memory) versus instructions to evaluate whether the face 'belongs' in the house (relational memory). Although neuropsychology, animal lesion studies, and cognitive neuroscience have identified brain structures that are consistently associated with memory performance, such as the medial temporal lobes (MTL) and prefrontal cortex (PFC), the specifics of when and why such regions participate in memory is still largely unexplored. Theoretical standpoints are often at odds about whether regions such as the MTL operate as a functional unit, supporting memory in general, or whether subregions within the MTL support specific types of memory (e.g. item versus relational memory). To investigate how memory processes might recruit unique and common brain regions, three functional magnetic resonance imaging (fMRI) studies were conducted. Each study involved comparisons of successful encoding (trials later remembered versus forgotten) and successful retrieval (hits versus misses). Experiment 1, using semantic and perceptual word pairs, found unique contributions for subregions in the MTL and PFC, dependent on memory phase and stimulus class. One region in the left hippocampus was associated with memory success, regardless of either memory phase or stimulus class. Experiment 2, using faces and scenes, found unique contributions for 'stimulus sensitive' subregions of the fusiform gyrus and parahippocampal gyrus, as well as for the PFC, and MTL that were dependent on content-process interactions, or independent of content and process. Experiment 3, using faces, scenes, and face-scene pairings, found unique contributions for subregions of the MTL and PFC based on item versus relational processing and memory phase. Together, the results of the three experiments provide support for dichotomies in brain structures based on specific processes, specific content, or process-content interactions. / Dissertation

This thesis aims at investigating the technologies of the active power-factor correction (PFC) circuit. The system originally in the article is based on a boost converter circuit as the structure, the control method is to adopt the average current mode. We doesn¡¦t only narrate the circuit principle of the systematic circuit in the article but also use the OrCAD PSpice A/D software to simulation. Finally, we implemented make a prototype circuit and verified the proposed method. The experimental result shows that it can reach the goal for the power-factor correction.