1,720,966 research outputs found
Early detection of photovoltaic system inverter faults
Full text linkPhotovoltaic (PV) systems are increasingly adopted as a source of green energy. The reliability of PV systems mainly depends on the reliability of the power MOSFETs of their inverter(s). It has been shown that short and open faults are the most frequent power MOSFET faults. They may compromise the inverter reliability, with consequent significant impact on the PV system energy efficiency. It has been proven that the likelihood of such faults is related to the value of the MOSFET ON-state resistance, which may increase over time due to aging mechanisms. When the value of such a resistance reaches a critical value, the likelihood of the MOSFETs subsequently failing as open or short becomes very high. In this paper, we first evaluate the effects of the MOSFETs' ON-state resistance increase on the harmonic components of the inverter input and output currents. Then, based on the obtained results, we propose an innovative strategy for the early detection (also referred to as condition monitoring [1]) of inverter faults, which enables to generate an alarm message when the ON-state resistance of any inverter MOSFET reaches the critical value. Upon the generation of such an alarm message, proper recovery strategies can be activated, to enable the online replacement of the affected transistors before they actually become faulty. Our detection strategy does not require to interrupt the inverter normal operation in the field and can be implemented using the microcontroller typically embedded within the control circuitry of PV systems
Fault-Tolerant Inverters for Reliable Photovoltaic Systems
No full textPhotovoltaic (PV) systems are increasingly adopted as a source of green energy. Due to the high economic investment that they usually involve, their reliability is becoming of concern. Recent studies have proven that faults likely to affect the inverters of PV systems in the field can dramatically reduce the energy delivered to the load. We first present a self-checking monitor to detect faults affecting the inverter in the field, as well as faults affecting the monitor itself. Then, we propose a hardware reconfiguration scheme that activated upon the monitor's generation of an alarm message after the occurrence of faults, enables to avoid their impact on the energy efficiency of the PV system. Our recovery scheme is also self-checking with respect to faults affecting itself. Therefore, our monitoring and reconfiguration schemes provide inverters with fault-tolerance ability, thus enabling to meet the increasing demand for reliable PV systems
New Approaches for Power Binning of High Performance Microprocessors
No full textThe significant process parameter variations occurring during fabrication of high performance sequential circuits, such as microprocessors, are posing relevant uncertainties on the power that such circuits will consume in the field, while executing workloads typical for the diverse products they are oriented to (e.g., cellular phones, notebooks, servers, etc). On the other hand, different kinds of products have different constraints on the maximal power that could be consumed during the execution of typical workloads, due to diverse needs in terms of charge autonomy, heat dissipation, etc. Consequently, the power that will be consumed by microprocessors during the execution of typical workloads in the field needs to be accurately characterized at the end of fabrication. Such a power consumption characterization (hereinafter referred to as “power binning”), will enable to classify microprocessors in “power bins”, each one containing microprocessors suitable for different kinds of products, thus enabling to introduce them all into the market for different kinds of products. Based on these considerations, in this paper we propose an approach to characterize accurately at the end of fabrication, and at low-cost (in terms of characterization time), the power that microprocessors will consume in the in-field during the execution of workloads typical for different kinds of products. Our approach exploits scan-based Logic Built-In Self-Test (LBIST) to apply to microprocessors' sequential blocks test vectors that induce on their internal nodes an activity factor (AF) similar to that experienced during the in-field execution of workloads typical for different kinds of products, thus enabling to perform power binning by simply measuring their consumed power. Our approach enables to scale the AF from 0 percent up to 97.6 percent (on average for the considered benchmark circuits) compared to conventional LBIST, with a granularity of the 2 percent, thus enabling to emulate accurately the AF induced by workloads typical of a wide range of products. We propose a hardware implementation for our approach requiring a limited area overhead (lower than 3 percent) over conventional LBIST
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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