1,720,993 research outputs found
A real-time harmonic monitoring aimed at improving smart grid power quality
No full textIt is well known that network analyzers perform reliable estimations of the Total Harmonic Distortion (THD). A distorted signal is actually decomposed in real time into its harmonic components using the Fourier transform. The implemented algorithm requires a 200ms observation window in order to meet both the necessary accuracy and standard requirements. Though the adopted observation time is compatible with the dynamic behavior of large generators, it is however not acceptable for small distributed generators (DG). Moreover, DGs are usually intermittent energy sources connected to a distribution network through inverters with time constants of dozens of microseconds. For this reason, smart grids with a massive presence of distributed renewable generation have to be monitored by fast algorithms in order to guarantee high levels of power quality. Actually, a remarkable distortion of the voltage waveform, which may also be due to a malfunctioning inverter, can cause for instance an incorrect behavior of digital protection systems. Herein a fast algorithm for the estimation of voltage harmonics is introduced, which, contrarily to algorithms currently adopted for the discrete Fourier transform, can be implemented also in non-updated, low-performing microprocessors. The proposed method uses a second order generalized integrator that refers to the SOGI-based Frequency Locked Loop (SOGI-FLL). A number of simulations were performed in order to validate the method, and the results showed that the time response of the algorithm is less than 20 ms, which means the method can be profitably used to improve smart grid power quality
One-Cycle Controlled Active Rectifier for Full Digital Implementation
No full textThis paper presents a discrete implementation of a Triangular One Cycle Control for three phase active rectifiers. The algorithm is characterised by triangular modulation carrier and can be implementated using a programmable logic device, thus obtaining increased feasibility and performance over analog OCCs systems. Simulation results and comparisons with another three-phase active rectifier control method show that the proposed MT-OCC offers satisfactory performance in terms of high power factor control, low harmonic pollution, fast and accurate dc output voltage regulation and high stability during regenerative operations
Qualitative information-based heuristic for districting problems
No full textDistricting problems are of high importance in many real-world applications. When multiple criteria are considered, enumerating all the efficient solutions in these problems is known as being Non-Polynomial (NP)-hard. The objective of this paper is thus to introduce a heuristic to solve this type of problem. The proposed heuristic relies on a tree data structure, previously constructed based on a qualitative evaluation of the study area. This evaluation is grounded on several criteria and takes the form of a qualitative scale with a finite set of evaluation levels. The paper introduces the qualitative assessment approach, the mathematical formulation and the resolution heuristic
Capitoli I (I beni) e II (Le funzioni)
No full textSono considerati i beni culturali nella tipologia in cui si articolano nonché le funzioni (tutela e valorizzazione) che li concernono
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
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