1,720,983 research outputs found
Effect of parasitic components in the Integrated Boost-flyback high step-up converter
No full textThe increasing interest for renewable energy sources like those based on photovoltaic panels and fuel-cells have driven the power electronics community toward the study and development of high step-up DC-DC converters, able to efficiently interface the low voltage side of such energy sources with the high-voltage dc link side of the grid connected inverter. Between the different investigated topologies, those based on the combination of a boost section and a flyback one are quite interesting, thanks to the possibility to boost the output voltage while keeping the switch voltage stress at a reasonable level. However, the analysis reported in literature always neglect the effect of parasitic components that strongly modify the converter behavior. In this paper, the analysis of the integrated boost-flyback converter with voltage multiplier is presented that includes the effect of the parasitic components. It is shown that a resonance occurs that helps to increase the converter's voltage gain. Experimental results taken from a 300 W rated prototype are included, showing a good agreement with the theoretical expectations
Analysis of a High Step-Up Ratio Flyback Converter with Active Clamp and Voltage Multiplier
No full textIn this paper, an isolated high step-up ratio dc-dc converter aimed to be used in interface systems between low voltage renewable energy sources, like photovoltaic panels and fuel-cells, and the utility grid is presented. The converter is based on the active clamp flyback topology with a voltage multiplier at the transformer secondary side. Such configuration, while naturally clamping the rectifier diode voltages thus avoiding the use of dissipative snubber circuits, allows to reduce the circulating current during the active clamp operation, thanks to the resonance involving the transformer leakage inductances and the diode parasitic capacitances. Experimental results taken from a 300W rated prototype are reported, showing a good agreement with the theoretical expectations
High Step-Up Ratio Flyback Converter With Active Clamp and Voltage Multiplier
No full textIn this paper, an isolated high step-up ratio dc–dc converter
aimed to be used in interface systems between low-voltage
renewable energy sources, such as photovoltaic panels and fuel
cells and the utility grid, is presented. The converter is based on
the active clamp flyback topology with a voltage multiplier at the
transformer secondary side. Such configuration, while naturally
clamping the rectifier diode voltages thus avoiding the use of dissipative snubber circuits, allows the reduction of the circulating
current during the active clamp operation due to the resonance
involving the transformer leakage inductances and the diode parasitic capacitances. Experimental results taken from a 300-W-rated prototype are reported, showing the absence of parasitic oscillations after diodes and switch transitions and high efficiency, in agreement with the theoretical expectations
Parameter-Independent Time-Optimal Digital Control for Point-of-Load Converters
No full textIn this paper, a digital control approach is investigated
for time-optimal load step response of dc–dc synchronous
buck converters intended for point-of-load (PoL) applications and
employing low-equivalent series resistance ceramic output capacitors.
Unlike previously reported approaches, the proposed technique
is insensitive to converter parametric variations and design
uncertainties, as its operation does not rely on the knowledge of the
output filter inductance or capacitance. The time-optimal response
is achieved through a single ON/OFF switching action undertaken
as soon as a load transient is detected. In its most general formulation,
the proposed technique automatically incorporates adaptive
voltage positioning (AVP) regulation, according to the typical droop
design guidelines for powering modern microprocessors. A simpler
version, suitable for voltage-mode controlled PoL converters not
requiring AVP positioning, is also presented. The technique employs
an asynchronous A/D conversion scheme, which quantizes
the converter state variables and triggers a nonlinear, event-based
digital controller whenever a quantization level transition is detected.
Additional sensing requirements are not needed, since the
time-optimal transient is achieved through the measurement of
the output voltage and, whenever AVP regulation is needed, of the
phase currents. Effectiveness and properties of the proposed robust
time-optimal approach are validated through both computer simulations
and experimental tests on a synchronous buck converter
prototype and a VHDL implementation of the control algorithm
on an field programmable gate array device
Convergence analysis and tuning of ripple correlation based MPPT: A sliding mode approach
No full textThe development of fast MPPT (Maximum Power Point Tracking) algorithms for photovoltaic (PV) systems able to track variable irradiation conditions with high bandwidth is becoming attractive, especially for mobile applications. This paper focuses on the well known ripple correlation technique, proposing an analysis that provides an upper bound to the convergence time in response to solar irradiation steps. The availability an upper bound enables the prediction of the dynamic behaviour of the MPPT, and gives a set of guidelines for a proper tuning of the controller to fit specific requirements. The analysis is based on a simple application of sliding mode theory, and it also includes chattering phenomena and the effects of parasitic reactive elements of the PV module. Matlab simulation and experimental tests are provided on a 35W panel interfaced to a 24V battery through a boost converter. A controllable LEDs illuminator has been used as solar generator, able to provide irradiation step changes with a bandwidth of 1kHz. The results confirm the effectiveness of both the analysis and tuning
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
