A buck-boost converter with extended duty-cycle range in the buck voltage region for renewable energy sources

Buck-boost DC-DC converters are useful as DC grid interfaces for renewable energy resources. In the classical buck-boost converter, output voltages smaller than the input voltage (the buck region) are observed for duty cycles between 0 and 0.5. Several recent buck-boost converters have been designed to present higher voltage gains. Nevertheless, those topologies show a reduced duty-cycle range, leading to output voltages in the buck region, and thus require the use of very low duty cycles to achieve the lower range of buck output voltages. In this work, we propose a new buck-boost DC-DC converter that privileges the buck region through the extension of the duty-cycle range, enabling buck operation. In fact, the converter proposed here allows output voltages below the input voltage even with duty cycles higher than 0.6. We present the analysis, design, and testing of the extended buck-boost DC-DC converter. Several tests were conducted to illustrate the characteristics of the extended buck-boost DC-DC converter. Test results were obtained using both simulation software and a laboratory prototype.info:eu-repo/semantics/publishedVersio

Cointegration and Asymmetric Adjustment between Output and Unemployment: an Application to the U.S. Economy

This paper focuses on the properties of the adjustment between the real output and the unemployment rate for the U.S. economy in the period from 1975 to 2006. It starts by checking the order of integration of the two series and then tests for the presence of asymmetry in the Okun’s law relationship through a cyclical equation, a first differences equation and an ADL(p,q). Using the threshold cointegration approach this study also accounts for the possible existence of a long-run equilibrium relationship and it is ability to test for the asymmetric adjustment hypothesis. It is found that Okun’s coefficient ranges between -0.41 and -0.59, being the latter estimated by the cointegrating equation. Furthermore, the unemployment rate behaves differently along the business cycle and increases faster in recessions than it recovers in expansions. A long-run equilibrium relationship is established where adjustment is made asymmetrically. Positive deviations away from equilibrium are corrected slightly faster than negative ones. Our explanation concerns the higher speed of flows within the labor market during a recession than during an expansion which may also be related to the existence of nominal rigidities in the US economy that causes imperfectly flexible prices.Okun’s Law, Threshold Cointegration, Asymmetric Adjustment, Monte Carlo Simulations, U.S. Economy

Stability Condition Based Sliding Mode Modulators for Multilevel Power Converters

Sliding mode controllers for power converters usually employ hysteresis comparators to directly generate the power semiconductors switching states. This paper presents a new sliding mode modulator based on the direct implementation of the sliding mode stability condition, which for multilevel power converters shows advantages, as branch equalized switching frequencies and less distortion on the ac currents when operating near the rated converter power. The new sliding mode multilevel modulator is used to control a three-phase multilevel converter, operated as a reactive power compensator (STATCOM), implementing the stability condition in a digital signal processing system. The performance of this new sliding mode modulator is compared with a multilevel modulator based on hysteresis comparators. Simulation and experimental results are presented in order to highlight the system operation and control robustness

Domain wall dynamics in an optical Kerr cavity

An anisotropic (dichroic) optical cavity containing a self-focusing Kerr medium is shown to display a bifurcation between static --Ising-- and moving --Bloch-- domain walls, the so-called nonequilibrium Ising-Bloch transition (NIB). Bloch walls can show regular or irregular temporal behaviour, in particular, bursting and spiking. These phenomena are interpreted in terms of the spatio-temporal dynamics of the extended patterns connected by the wall, which display complex dynamical behaviour as well. Domain wall interaction, including the formation of bound states is also addressed.Comment: 15 pages Tex file with 11 postscript figures. Resubmitted to Phys. Rev.

Symmetry Constrained Two Higgs Doublet Models

We study Two-Higgs-Doublet Models (2HDM) where Abelian symmetries have been introduced, leading to a drastic reduction in the number of free parameters in the 2HDM. Our analysis is inspired in BGL models, where, as the result of a symmetry of the Lagrangian, there are tree-level scalar mediated Flavour-Changing-Neutral-Currents, with the flavour structure depending only on the CKM matrix. A systematic analysis is done on the various possible schemes, which are classified in different classes, depending on the way the extra symmetries constrain the matrices of couplings defining the flavour structure of the scalar mediated neutral currents. All the resulting flavour textures of the Yukawa couplings are stable under renormalisation since they result from symmetries imposed at the Lagrangian level. We also present a brief phenomenological analysis of the most salient features of each class of symmetry constrained 2HDM.Comment: 30 pages, 5 Table

Plano de desenvolvimento desportivo municipal

Esta comunicação não pretende ser a apresentação de um qualquer projecto de investigação, mas sim motivar todos os responsáveis municipais pelo desporto e lazer a aderirem com as suas câmaras municipais ao projecto PLANO DE DESENVOLVIMENTO DESPORTIVO MUNICIPAL – PDDM – do Núcleo de Investigação em Políticas Económicas da Universidade do Minho. O PDDM vem reunir num só projecto dois interesses legítimos: (1) o legítimo interesse que a universidade tem na concepção, na elaboração e no teste de novos modelos e instrumentos de planeamento sustentado, no sentido da implementacao de uma política de ordenamento local racional, e (2) o legítimo interesse das câmaras municipais em verem esses modelos e instrumentos aplicados aos seus territórios, a fim elaborarem políticas o mais próximas possível dos interesses e opções dos seus munícipes. Resumidamente, o PDDM pretende desenvolver uma metodologia científica que permita reconhecer, a médio-longo prazo, a evolução das formas de organização do desporto e dos diferentes hábitos/comportamentos desportivos da população portuguesa, permitindo alicerçar as decisões políticas em favor do desporto para todos, já que o grupo da população activa no lazer e desporto se encontra em directa concorrência com outros grupos sociais no que diz respeito a espaços/ terrenos municipais, suas localizações e respectivas fontes de financiamento. O PDDM pretende ainda garantir uma aplicabilidade fácil e uma utilização prática dos dados a obter, traduzindo as necessidades e realidades de cada localidade na perspectiva de formulacao de objectivos políticos, desportivos e de ordenamento do território

Study of the HVDC dual transmission system under faults in the power converters

Trabalho apresentado no Speedam 2016, 22-24 de junho de 2016, Capri, ItáliaHVDC transmission systems based on voltage source converters have lately emerged as a good alternative to conventional AC transmission. In these transmission systems multilevel converters have become a promising energy conversion technology. The reliability of the power converters are extremely important since a fault in these equipments may lead to an unavailability for a long period of the transmission system. Thus, this paper will focuses in HVDC dual transmission system under semiconductor failure conditions. As presented in this paper this structure presents interesting characteristics under the point of view the reliability considering a power semiconductor failure. It will present the consequences for the transmission system when there is a semiconductor fault. A study for the change of the modulation system in order to ensure DC link capacitors voltage balance under a fault condition is also presented. Simulation studies are shown in order to confirm the characteristics of the proposed methodology in normal and fault condition mode.N/