Família de retificadores multipulsos com topologias diferenciais de transformadores

Multipulse rectifier topologies based on auto-connections or differential connections, are more and more applied as interface stages between the mains and power converters. These topologies are becoming increasingly attractive not only for robustness, but to mitigate many low order current harmonics in the utility, reducing the total harmonic distortion of the line currents (THDi) and increasing the power factor requirements. Unlike isolated connections (delta-wye, zigzag, etc.), when the differential transformer is employed, most of the energy required by the load is directly conducted through the windings. Thus, only a small fraction of the kVA is processed by the magnetic core. This feature increases the power density of the converter. This paper presents a mathematical model based on phasor diagrams, which results in a single expression able to merge all differential connections (wye and delta), for both step-up and step-down rectifiers for 12 or 18 pulses. The proposed family of converters can be designed for any relationship between the line input voltage and the DC voltage, unlike the conventional phase-shift voltage connections. An immediate application would be the retrofit, i.e. to replace a conventional rectifier with poor quality of the processed energy by the 12 or 18-pulse rectifiers with Wye or Delta-differential connections, keeping the original values for the input and load voltages. The simple and fast design procedure is developed and tested for a prototype rating 6 kW and 400 V on DC load.

Micro-inverter for integrated grid-tie PV module using resonant controller

Two-stage isolated converters for photovoltaic (PV) applications commonly employ a high-frequency transformer on the DC-DC side, submitting the DC-AC inverter switches to high voltages and forcing the use of IGBTs instead of low-voltage and low-loss MOSFETs. This paper shows the modeling, control and simulation of a single-phase full-bridge inverter with high-frequency transformer (HFT) that can be used as part of a two-stage converter with transformerless DC-DC side or as a single-stage converter (simple DC-AC inverter) for grid-connected PV applications. The inverter is modeled in order to obtain a small-signal transfer function used to design the PResonant current control regulator. A high-frequency step-up transformer results in reduced voltage switches and better efficiency compared with converters in which the transformer is used on the DC-DC side. Simulations and experimental results with a 200 W prototype are shown. © 2012 IEEE.

Efficiency analysis of an isolated high voltage gain converter operating in resonant and non-resonant mode

This paper presents an efficiency investigation of an isolated high step-up ratio dc-dc converter aimed to be used for energy processing from low-voltage high-current energy sources, like batteries, photovoltaic modules or fuel-cells. The considered converter consists of an interleaved active clamp flyback topology combined with a voltage multiplier at the transformer secondary side capable of two different operating modes, i.e. resonant and non-resonant according to the design of the output capacitors. The main goal of this paper is to compare these two operating modes from the component losses point of view with the aim of maximize the overall converter efficiency. The approach is based on losses prediction using steady-state theoretical models (designed in Mathcad environment), taking into account both conduction and switching losses. The models are compared with steady-state simulations and experimental results considering different operating modes to validate the approach. © 2012 IEEE.

Fault current limiter using transformer and modular device of YBCO coated conductor

In this work, we report on the evaluation of a superconducting fault current limiter (SFCL). It is consisted of a modular superconducting device combined with a short-circuited transformer with a primary copper winding connected in series to the power line and the secondary side short-circuited by the superconducting device. The basic idea is adding a magnetic component to contribute to the current limitation by the impedance reflected to the line after transition of the superconducting device. The evaluation tests were performed with a prospective current up to 2 kA, with the short-circuited transformer of 2.5 kVA, 220 V/660 V connected to a test facility of 100 kVA power capacity. The resistive SFCL using a modular superconducting device was tested without degradation for a prospective fault current of 1.8 kA, achieving the limiting factor 2.78; the voltage achieved 282 V corresponding to an electric field of 11 V/m. The test performed with the combined SFCL (xsuperconducting device + transformer) using series and toroidal transformers showed current limiting factor of 3.1 and 2 times, respectively. The test results of the combined SFCL with short-circuited transformer showed undesirable influence of the transformer impedance, resulting in reduction of the fault current level. © 2002-2011 IEEE.

Uma nova metodologia de projeto e controle para o inversor Boost (CSI) monofásico, para o aproveitamento de fontes alternativas e renováveis de energia elétrica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise e modelação de perdas em conversores CC-CC do tipo Boost entrelaçados

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Protocolos de adaptação a rações de alto teor de concentrados para bovinos nelore confinados

Pós-graduação em Zootecnia - FMVZ

Latin America and the Caribbean in the World Economy: 2005 Trends

The study recently published by the Division of International Trade and Integration of ECLAC considers that 2005 will be a good year for trade in the countries of the region. Despite a favourable international context, there are still serious problems of competitiveness. The region needs to increase productivity, promote technological innovation and take a proactive part in worldwide networks. The conclusions of the study include the need to update integration; to take a strategic view of the links to be constructed with China and the countries of the Pacific; to manage free-trade agreements so as to increase and diversify exports; to step up the pace of work and improve coordination with the developing countries on the Doha Round, and to gradually incorporate the demands of security into competitiveness policies, ensuring that they do not become protectionist barriers (traceability, food safety and maritime and port security).

Capital Flows to Latin America and the Caribbean: Recent Developments

For six years, the global economy has been driven by the U.S. Federal Reserve’s policies of easy money. Liquidity has flowed from developed to developing economies, financing infrastructure and corporate investment and allowing consumers to indulge in credit-fuelled retail spending. Thus the effective ending of the Fed’s third round of asset purchases (QE3) at the end of October represents both a watershed and the beginning of a new stage in the world economy. The end of asset-purchases comes at a challenging time for emerging markets, with China’s economy slowing, the Euro zone struggling to avoid a recession and the Japanese economy already in recession. The unwinding of the U.S. monetary stimulus, while the European Central Bank and the Bank of Japan step up their monetary stimulus, has underpinned an appreciation by the U.S. dollar, in which most commodities are priced. An appreciated dollar makes dollar-denominated commodities more expensive to buyers, thereby creating pressure for sellers to lower their prices. Latin American markets ended the third quarter of 2014 under pressure from a stronger U.S. dollar. In this changing external context, there are many signs that a slowdown in Latin American and Caribbean (LAC) financial markets, particularly debt markets, which have been breaking issuance records for the past six years, may slowdown from now on. Commodity prices – including those of oil, base metals and some goods – are in a prolonged slump. The Bloomberg commodity price index, a benchmark of commodity investments, has fallen to a five-year low as China’s economy slows down, and with it the demand for commodities. Investment into the LAC region has decelerated, in large part because of a deceleration of mining investments. Latin American currencies have suffered depreciations, as current account deficits have widening for a number of countries. And LAC companies, having issued record amounts of foreign currency bonds may now struggle to service their debt. In October, credit-rating agency Moody’s downgraded the bonds of Brazil’s Petrobras to tow notches above speculative grade because of the impact of falling oil prices and the weaker real on its debt. Growth prospects look brighter in 2015 relative to 2014, but a strengthening U.S. dollar, uneven global growth and weakness in commodity prices are skewing the risk toward the downside for the 2015 forecasts across the region. The Institute of International Finance expects the strengthening of the dollar to have a divergent impact across the region, however, depending on trade and financial linkages. The Institute of International Finance, Capital Flows to Emerging Markets, October 2, 2014. A stronger dollar lifts U.S. purchasing power, supporting exports, growth and capital inflows in countries with close trade links to the U.S. economy. However, rising dollar financing costs will increase pressure on countries with weak external positions. Given the effects of falling oil prices and a stronger dollar, some companies in the region, having issued record amounts of foreign currency bonds, may now struggle to service their debts. Prospects of Fed rate hikes resulting in tighter global liquidity amid the rapid rise in the corporate external bond stock has indeed raised concerns over some companies. However, there is still a shortage of bonds at a global level and the region still enjoys good economic policy management for the most part, so LAC debt markets may continue to enjoy momentum despite occasional bursts of high volatility – even if not at the record levels of recent years.

Macroeconomic trade-offs and external vulnerabilities of human development in Nicaragua

Nicaragua is making progress towards the Millennium Development Goals, but is set to miss a number of targets in 2015. This paper’s general equilibrium analysis shows that it is unfeasible for the government to step up spending in order to meet these targets by the 2015 deadline. Any boost to public spending and financing would have to be front-loaded, which would entail pernicious macroeconomic trade-offs. A more realistic scenario would be to postpone meeting the goals until 2020. In that case, the allocation of public spending would spur economic growth without causing macroeconomic hardships, although the country would nevertheless remain highly vulnerable to external shocks.

Micro-inverter for integrated grid-tie photovoltaic module using resonant controller

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Microinversor integrado ao módulo fotovoltaico para sistemas conectados à rede elétrica utilizando controlador ressonante

This paper shows the modeling and control of a single-phase full-bridge inverter with high-frequency transformer that may be used as part of a two-stage converter with transformerless DC-DC side or as a single-stage converter (simple DC-AC converter) for grid-connected PV applications. The inverter is modeled in order to obtain a small-signal transfer function used to design the P+Resonant current controller. A highfrequency step-up transformer results in reduced voltage switches and better efficiency compared with converters in which the transformer is used on the DC-DC side. Simulations and experimental results with a 200 W prototype are shown. 1

Weight and neuro-psycho-motor development in children discharged from neonatal intensive care unit

Background: Low birth weight affects child growth and development, requiring the intensive use of health services. There are conversely proportional associations between prematurity and academic performance around the world. In this study we evaluated factors involved in weight and neuropsychomotor profile in one and two years old discharged from Intensive Care Units (ICU). Methods/Design: We investigated 203 children from the ICU who were followed for 24 +/- 4 months. The research was conducted by collecting data from medical records of patients in a Follow-up program. We investigated the following variables: inadequate weight at one year old; inadequate weight at two years old and a severe neurological disorder at two years old. Results: We observed increase of almost 20% in the proportion of children which weighted between the 10th and 90th percentiles and decrease of around 40% of children below the 15th percentile, from one to two years old. In almost 60% of the cases neuropsychomotor development was normal at 2 years old, less than 15% of children presented abnormal development. Variables that remained influential for clinical outcome at 1 and 2 years old were related to birth weight and gestational age, except for hypoglycemia. Neurological examination was the most influential variable for severe neurological disturbance. Conclusion: Hypoglycemia was considered a new fact to explain inadequate weight. The results, new in Brazil and difficult in terms of comparison, could be used to identify risk factors and for a better approach of newborn discharged from ICUs.

Inactivating Mutations of the Human Luteinizing Hormone Receptor in Both Sexes

The human luteinizing hormone/chorionic gonadotropin receptor (LHCGR) plays a fundamental role in male and female reproductive physiology. Over the past 15 years, several homozygous or compound heterozygous loss-of-function mutations in the LHCGR gene have been described in males and females. In genetic males, mutations in LHCGR were associated with distinct degrees of impairment in pre- and postnatal testosterone secretion resulting in a phenotypic spectrum. Patients with the severe form of LH resistance have predominantly female external genitalia and absence of secondary sex differentiation at puberty. Patients with milder forms have predominantly male external genitalia with micropenis and/or hypospadias or only infertility without ambiguity. The undermasculization is associated with low basal, as well as human CG-stimulated, testosterone levels and elevated LH levels after pubertal age, without abnormal step-up in testosterone biosynthesis precursors. The testes have only slightly reduced size but mature Leydig cells are absent or scarce (Leydig cell hypoplasia). Genetic females with inactivating LHCGR mutations have female external genitalia, spontaneous breast and pubic hair development at puberty, and normal or late menarche followed by oligoamenorrhea and infertility. Estradiol and progesterone levels are normal for the early to midfollicular phase, but do not reach ovulatory or luteal phase levels. Serum LH levels are high whereas follicle-stimulating hormone levels are normal or only slightly increased. Pelvic ultrasound has demonstrated a small or normal uterus and normal or enlarged ovaries with cysts. The inactivating mutations of the LHCGR have provided important insights into distinct physiological roles of LH in reproduction of both sexes.

Addition of increasing doses of ricinoleic acid from castor oil (Ricinus communis L.) in diets of Nellore steers in feedlots

The aim of this study was to evaluate the performance and blood parameters of feedlot Nellore cattle fed increasing doses of ricinoleic acid (RA) in the diet. Ninety-six Nellore steers divided into 12 groups of 8 animals were used. The animals were randomly assigned to four treatments: 0, 1, 2, or 4 g of RA/animal/day, with three replicates per treatment. The experimental period consisted of 84 days divided into three 28-day periods preceded by three step-up diets. A quadratic effect was found for average daily gain and final body weight, as well as for leukocyte and lymphocyte counts, and for urea and blood urea nitrogen. A linear effect was observed for albumin, alkaline phosphatase, and gamma glutamyl transferase. The inclusion of 2 g of RA daily improved the performance of feedlot Nellore steers.