Rafael Beltrame

Simplified Zero-Voltage-Transition Circuits Applied to Bidirectional Poles: Concept and Synthesis Methodology

This paper proposes the concept and the synthesis methodology of simplified zero-voltage-transition (ZVT) circuits applied to bidirectional pulsewidth modulation poles. The main goal of simplified ZVT circuits is to make possible the use of conventional modulation schemes to accomplish better converter performance and to eliminate the synchronous-switching requirements imposed by ZVT integrated multipole topologies. To derive the simplified ZVT circuits, a synthesis methodology is proposed based on the generalization of the ZVT technique, where the restrictions to achieve the zero-voltage switching for the main converter switches are identified. Thereafter, a set of simplified semiconductor switches composed by only one high-frequency switch is defined to be used in the simplified ZVT auxiliary circuits. Thus, using the proposed synthesis methodology, any simplified ZVT topology can be derived, whether or not they have appeared in a previous publication. In order to validate the proposed approach, experimental results for a three-phase ZVT inverter, employing the minimum-loss space vector modulation and operating at 1.5 kW and 20 kHz are presented. The prototype presented an efficiency of 98% at full load representing an improvement of 0.5% when compared to its hard-switched counterpart and 1.8% when compared to an integrated ZVT topology.

THERMAL MODIFICATION OF Eucalyptus grandis WOOD: VARIATION OF COLORIMETRIC PARAMETERS

The color modifications in Eucalyptus grandis thermally modified wood were investigated. One hundred eighty specimens (10 x 10 x 200 mm) were prepared and thermally modified in an electric kiln for 4 and 8 h at 180-240oC. The color parameters (L*, a*, b*, C*, h* and ΔE) were determined by the CIE-L*a*b* method on radial and tangential sections of untreated and treated wood. The results indicated the darkening of specimens in the radial and tangential sections. Both sections showed variation of L* between 73 and 30, a* between 9 and 5 and b* between 20 and 8. The thermally modified wood at 180 and 200oC showed similar patterns, equally at 220 and 240oC. The time of exposure indicated significance just in treatment at 200oC.

Implementation of a stand-alone photovoltaic system based on decentralized dc-dc converters

This paper presents an alternative for standalone PV systems that performs a decentralized input energy processing with maximum power point tracking and a bidirectional converter to manage the power flux control of the battery bank. Previous works demonstrate that the gain in efficiency can reach up to 16% in situations where one or more photovoltaic panels are shaded, damaged or aged. Simulation analyses and experimental results are provided to demonstrate the prospects of the proposed system.

Desempenho silvicultural e seleção precoce de clones de híbridos de eucalipto

The objective of this work was to evaluate the genetic variability and silvicultural performance of clones from interspecific hybrids of Eucalyptus urophylla, E. globulus, E. maidenii, E. saligna, E. grandis, E. pellita, E. resinifera, E. kirtoniana and E. dunnii, and to determine the feasibility of early selection in selecting superior clones. The stem diameter at breast height at three (DAP3) and seven years (DAP7) and the total tree height at seven years were evaluated. A randomized complete block design, with138 clones, ten replicates and six plants per plot was used. Data were subjected to analysis of variance and clustered by the k-means method; the means were compared, and the Pearson correlation (r) was determined between variables. Clustering validation was performed using analysis of variance and Tukeys test. Clones of interspecific Eucalyptus hybrids showed genetic variability. Five groups of clones were established based on their silvicultural performance (DAP3, DAP7 and height). The DAP3 is highly correlated to DAP7 and height at seven years. The selection based on DAP3 can be used to identify superior clones of Eucalyptus with good growth vigor.

Modification of static bending strength properties of Eucalyptus grandis heat-treated wood

The present study describes the effect of thermal rectification on physical and mechanical properties of Eucalyptus grandis wood at different levels of temperature and time. Samples of Eucalyptus grandis wood (10 × 10 × 200 mm) were heat-treated at 180, 200, 220 and 240 °C during 4 and 8 hours. The mechanical properties of heat-treated and untreated samples were determined by static bending tests. The physical properties were determined by weight loss and swelling tests. The results showed that modulus of elasticity, modulus of rupture, weight loss, volumetric swelling and linear swelling were affected significantly by the thermal rectification. However, the length of exposure influenced just weight loss, while the temperature influenced all the studied properties of heat-treated wood. More significant modifications with treatments at a temperature of 200 °C or higher were found in the properties of heat-treated wood.

Hybrid AC Power Source Based on Modular Multilevel Converter and Linear Amplifier

This paper presents a hybrid amplifier for an ac power source (ACPS). The topology is composed of a modular multilevel converter (MMC), operating as main amplifier, connected in series with a linear power amplifier (LPA), which operates as correction amplifier. This way, it is possible to gather the modularity, reliability, and high efficiency provided by the MMC and the high waveform fidelity provided by the LPA. Additionally, it is possible to reproduce a voltage waveform with a high bandwidth and, differently from previous works, with a topology that requires a unique dc voltage source for the main amplifier. The inner current and the submodule capacitor voltages are controlled in the MMC. Meanwhile, the LPA is controlled to define the output voltage. A design methodology and experimental results are included to demonstrate the operation of the ACPS topology.

D-STATCOM applied to single-phase distribution networks: Modeling and control

This paper proposes a digital control system for a voltage-controlled D-STATCOM applied to single-phase low voltage distribution networks. This system is especially suited for long rural distribution lines with problems to comply with voltage levels standards. The voltage regulator consists of a single-phase voltage-source PWM (Pulse Width Modulation) inverter connected in parallel with the point of common coupling (PCC) through a second-order low-pass filter. The proposed control system is composed of three loops: an active damping loop, a control loop to regulate the PCC voltage and a dc bus voltage control loop. Experimental results are included to demonstrate the performance of the proposed system.

Determinação das deformações residuais longitudinais decorrentes das tensões de crescimento em Eucalyptus spp.

This study was carried out to determine the longitudinal residual strain (DRL) resulting from growth stress in standing trees, in different clones of Eucalyptus spp. Twelve clones of 9-year-Eucalyptus spp. were selected by basal area (G). From each clone, 12 trees of each clone were selected, and the following variables were measured: basic density (DB), bark thickness (EC), diameter at breast height (DBH) and total height (H). The measurements of DRL were performed in living trees, using an extensometer(Growth Strain Gauge), according to the CIRAD-Foret method. Readings were taken at four locations around the tree trunk. In relation to the levels of DRL, the results obtained in the study indicated that the clones showed large variations among themselves, presenting values considered high ones when compared with the results found in literature. The clone 8 was distinguished by having the lowest levels of strain and was considered as a suitable and recommended material for the production of solid wood and for breeding programs. On

Hybrid power amplifiers - a review

With the aim of synthesizing high-fidelity voltage waveforms without penalizing the system efficiency, several works have proposed hybrid power amplifiers (HPAs) composed of linear and switching amplifiers, combining the features of each approach. The HPAs can be classified as envelope, parallel and series configurations, depending on how the connection between the linear and switching amplifiers is implemented. This way, through a fair review of literature, this work identifies the features of each configuration and presents the main topologies and control techniques proposed hitherto. Therefore, this paper can be useful for selecting an adequate hybrid arrangement for a given application. Finally, future trends in research in hybrid power amplifiers are also addressed.

Resistência ao impacto da madeira de açoita-cavalo em diferentes condições de umidade

Neste estudo, objetivou-se comparar a resistencia ao impacto da madeira de acoita-cavalo (Luehea divaricata Mart. et Zucc Mart.) ensaiada em condicoes de equilibrio a 12% de umidade e saturada em agua. Para tanto, foram utilizadas arvores procedentes de duas regioes fisiograficas do estado do Rio Grande do Sul. Os corpos-de-prova foram submetidos ao impacto, utilizando-se pendulo de Charpy e avaliados quanto a resistencia oferecida a aplicacao da carga nos planos radial e tangencial e nas posicoes de retirada (medula -casca) das toras, para as duas regioes fisiograficas em cada condicao de umidade. Para auxiliar na interpretacao dos dados determinou-se a densidade aparente a 12% e saturada, teor de umidade, trabalho absorvido, resistencia ao impacto, coeficiente de resiliencia e a cota dinâmica. Os resultados evidenciaram que a madeira de acoita-cavalo testada na condicao saturada apresentou maior resistencia, indicando que a especie e mais resistente ao impacto quando verde, absorvendo grande parte da forca aplicada sobre ela, quando comparada a resistencia a 12% de umidade.