1,721,086 research outputs found
A Novel MPPT technique for single stage grid-connected PV systems: T4S
No full textIn this paper, a novel maximum power point tracking (MPPT) technique, which has been named T4S (a technique based on the proper setting of the sign of the slope of the photovoltaic voltage reference signal), is presented and discussed. It is specifically designed with reference to a single-stage grid-connected PV system. Its performance is numerically compared with that of the well-known and widely used perturb and observe (P&O) MPPT technique. The results of the numerical simulations confirm the validity of the proposed MPPT technique which exhibited a slightly better performance, under stationary and also time-varying irradiance conditions. In addition, the T4S technique is characterized by the following features: it does not require explicit power detection or calculation and, moreover, it allows the tracking of the maximum average power injected into the grid rather than the tracking of the maximum instantaneous power extracted by the PV source
Maximum Power Transfer in Electromagnetic Vibration Energy Harvesters driven by Non-Sinusoidal Vibrations
No full textIn this paper, the problem of the Maximum Power Extraction is discussed with reference to Resonant Electromagnetic Vibration Energy Harvesters driven by non-sinusoidal vibrations. It is well known that, in order to maximize the harvested power in case of purely sinusoidal vibrations, the Maximum Power Transfer Theorem must be exploited. Instead, in case of non-sinusoidal vibrations, the Nonlinear Dynamic Maximum Power Transfer Theorem must be exploited. An active power electronics AC/DC architecture is considered and two different control algorithms are proposed and discussed. They are respectively used for the implementation of the Maximum Power Transfer Theorem and of the Nonlinear Dynamic Maximum Power Transfer Theorem. The differences existing between the two proposed controls techniques in terms of performances and implementation complexity are discussed and analyzed with the help of suitable numerical simulations
Two-Dimensional PO MPPT Technique for Piezoelectric Vibration Energy Harvesters
No full textThis paper is focused on resonant Piezoelectric Vibration Energy Harvesters (PVEHs). In all energy harvesting applications, and in particular in PVEH applications, the maximization of the extracted power is mandatory. It is well known that, in order to maximize the harvested power, it is necessary to get the optimal matching between the harvesting device and the load. In particular, in PVEH applications under purely sinusoidal input vibrations, in order to maximize the harvested power, the impedance of the load must be coincident with a well-defined optimal impedance ZOPT. However, in practical applications, the load of PVEHs is not a linear impedance, but it is nearly always represented by a non-linear AC/DC converter. In this paper, the full-bridge based active AC/DC architecture, that is theoretically able to emulate just the optimal impedance ZOPT, is analyzed in detail. In particular, a Two-Dimensional Perturb and Observe (TD-P&O) algorithm is proposed and discussed for the emulation of such an optimal impedance. Simulation results confirming the validity of the proposed TD-P&O algorithm and the increase of the extracted power with respect to the simpler case of a diode bridge rectifier source/load electronic interface are presented and discussed
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
Partial discharge testing on resin insulated voltage transformers
No full textThe lifetime of resin insulated voltage transformers
(RIVT) can be considerably shortened due to
partial discharge activity taking place inside the insulation
close to the active parts of the component. In that region
the presence of voids, due to manufacturing processes, and
the enhanced electric field stress lead to an intense partial
discharge activity which determines accelerated degradation
processes and eventually the ultimate failure of the
device. Partial discharge measurements together with an
estimation of the electric field distribution in RIVT seem
to be indispensable in order to fully understand transformer
performances. In this paper, a study of the electric
field distribution inside the RIVT, together with results of
partial discharge tests are presented. The influence of the
various test arrangements and methods on the experimental
results are investigated
Resonant electromagnetic vibration harvesters applications: Optimization of P&O MPPT technique parameters
No full textIn this paper it is shown that Resonant Electromagnetic Vibration Energy Harvester (REVEH) systems nearly always need to be equipped with suitable MPPT (Maximum average Power Point Tracking) controllers due to the fact that the characteristics of vibrations (frequency, amplitude etc.) change with time. The particular (but frequent) case of Constant Frequency Time Varying Amplitude (CFTVA) vibrations will be considered. In particular, the guidelines for the optimization of the P&O MPPT technique to adopt in REVEH systems in the case of CFTVA vibrations are provided. It is demonstrated that both the sampling frequency íp&o and the amplitude Ad of the P&O duty cycle perturbation need to fulfill suitable inequalities in order to get an efficient REVEH system
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