1,720,967 research outputs found
Innovative Architecture of dc-dc Converters for High Efficiency Applications in Harsh Automotive Environment
Get PDFIn the last years the strive for car emission reduction produced several changes in the automotive environment, which led to a significant increase of power electronics presence on cars. Linear dc-dc converters are being replaced by higher efficiency switching-mode power converters also in the standard 12 V-to-5 V application, while hybrid electric and full electric vehicles require bidirectional high power dc-dc converters for their powertrains. To decrease the car fuel consumption, a reduction of the copper cable weight is required.
For these reasons car manufacturers propose to shift the battery voltage from 12 V to 48 V and to deliver this single bus throughout the car, while deriving all the required voltages locally. This scenario pushes for high step-down converters.
The goal of this thesis is to optimize the operation of automotive dc-dc switching converters through the use of digital regulators and controllers. As a general philosophy no additional devices are added to the power stage and the topology modulation degrees of freedom are exploited to regulate and optimize its operation. This research activity is conducted through a collaboration between the Power Electronics Group of the Department of Information Engineering (DEI) and Infineon Technologies Italia S.r.l.
In the first part the minimum rms current trajectory (MCT) for a highpower bidirectional series-resonant dual-half bridge (SR-DHB) is analytically calculated, approximated and implemented on a digital controller which makes the converter to act as an optimized building block driven by a power command.
Secondly the 12 V-to-5 V application is analyzed and a non-resonant dual half-bridge – also called non-inverting buck-boost – is selected. Its efficiency is optimized on-the-fly by measuring the input current while a low-complexity hardwired simplex algorithm acts on the modulation quantities to find the highest efficiency point. This approach is robust against operating condition variation.
In the third chapter the SCTI converter topology is considered because of its increased duty cycle range and the zero voltage switching turn-on for all devices. The SCTI is a promising topology but suffers from a potential voltage spike during transient events, which poses a reliability issue for the converter. Both a snubber and a control solution are proposed. With the former a careful design is required taking into account several parasitics, which could be challenging to be measured. For this reason a solution based on a finite state machine which only requires analog comparators is then proposed and developed. Since SCTI topology is not a wide-spread topology, there is a shortage of commercially available ad-hoc inductors. During a research period in Infineon Technologies A.G. under the supervision of prof. Pelz, the SCTI converter efficiency was studied and optimized by considering off-theshelf inductors only. To perform this optimization, Cadence R simulations are run and machine learning algorithm are employed in order to have a good understanding of the converter efficiency on the full design space and providing preliminary inductor design guidelines
Synchronous Series Capacitor Tapped Inductor (SCTI) Converter with Auxiliary Snubber Winding
No full textA Low-Complexity Trajectory Controller for Reduced Conduction Losses in Series-Resonant Dual Half-Bridge Converters
No full textThis paper describes a low-complexity trajectory controller for near-optimal minimization of conduction losses in series resonant, dual half-bridge converters (SR-DHB). The technique builds on the concept of minimum current trajectory (MCT) of a resonant converter, and formulates a piecewise-linear approximation of the MCT (PWL-MCT) for a SR-DHB topology which can be implemented digitally via standard arithmetic operations. The low-complexity realization of such technique makes it suitable to be easily implemented in a commercial microcontroller, or even inside a custom-designed digital IC, depending on the target application requirements. Even more importantly, the MCT-based control trajectory can be formulated independently of the converter parameters, resulting in a control approach of the broadest applicability. When equipped with such simple trajectory controller, the SR-DHB converter becomes an efficient, controllable bidirectional dc-dc power unit which can be employed in a number of scenarios, including dc power distribution systems and battery-to-battery power interfaces. Compared with traditional phase shift modulation, the proposed trajectory controller yields higher efficiency at intermediate-to-light load levels, and equal efficiency at heavy load. Furthermore, the proposed PWL-MCT concept can be implemented to accommodate
wide variations in the converter voltage conversion ratio, making the resulting power unit versatile and voltage-programmable. The proposed approach is validated on a 800 W, 200 V-to-
145 V, SR-DHB converter prototype. Efficiency comparisons are discussed highlighting the benefits of the PWL-MCT controller over traditional modulation approaches, and the strong efficiency
improvement achievable at voltage conversion ratios away from the nominal one
Control technique for reliable operation of the synchronous series capacitor tapped inductor converter
No full text
Two-dimensional online efficiency optimization technique for dual active bridge converters
No full textThis paper proposes an online efficiency optimization technique for Dual Active Bridge (DAB) Converters. Simultaneous output voltage regulation and efficiency optimization are achieved through an advanced modulation scheme by exploiting the degrees of freedom offered by the DAB topology and with no requirements of preliminary calibration or converter characterization. A digital closed-loop controller implements voltage regulation and a two-dimensional optimization algorithm which continuously tracks the converter optimal efficiency point. The optimization loop relies on the simplex algorithm, which can be implemented in a hardware-efficient manner and without involving gradient calculations. Experimental results on a digitally controlled 196 kHz, 12 V-to-5 V, 10 W DAB prototype are reported confirming the effectiveness of the technique
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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