1,720,960 research outputs found
FAULT-TOLERANT GRID SYNCHRONIZATION OF THREE-PHASE PWM RECTIFIERS USING NEURAL NETWORK
No full textThis work focuses on the essential role of synchronous angle estimation in the conversion of three-phase AC to DC voltage. Accurately determining the synchronous angle is crucial for achieving optimal phasing in the abc/d-q transformation, aligning the synchronous reference d-q with the phase “a” voltage vector. This alignment ensures the efficient operation of the inner current loops in the d-q synchronous reference. However, estimating the synchronous angle becomes challenging during AC grid faults. Previous studies have employed phase-locked loops (PLLs) with specialized filters to handle parasitic harmonics. In contrast, this research proposes using neural networks to recognize fault types and estimate the phase with minimal perturbations. Comparative analyses of conventional PLL-based and neural network-based estimates of the converter bridge's output performance under fault conditions are presented using MATLAB/Simulink/PLECS
Neural Network Control of AC/DC Converters Robust to AC Grid Faults
No full textThis work presents the experimental application of artificial neural networks to improve the control of grid-connected AC/DC converters. The challenging context of AC grid faults is addressed and a general-purpose three-phase PWM rectifier equipped with IGBT technology, operating at 10 kHz switching frequency, is considered. A power supply facility with grid simulation capability emulates the most common failures. The estimation of the grid angle, critical for the efficient control in the synchronous d-q reference frame, is achieved by a set of neural networks depending on the type of fault, also identified by neural networks. The MATLAB/Simulink environment trains and simulates the neural networks and builds the control code for the target Texas Instruments Delfino F28379S microcontroller. The consolidated quadrature phase-locked-loop approach for grid synchronization is considered for comparison. The results demonstrate superior reliability when neural networks are used, especially when grid faults occur
Sub-Optimal Flux-Weakening Control of Synchronous Reluctance Motors
No full textThis paper deals with the control of the synchronous reluctance motors in the flux-weakening operating range. Given the difficulties of implementing truly optimal control strategies, sub-optimal solutions, which require minimal parametrization and set-up efforts, are proposed and experienced. First, the proposed solutions are presented and discussed, considering the uncoupled, constant-inductances model of the motor in d-q components as an analytical basis. Then, the influence of the flux non-linearities is taken into account, considering a 75 kW motor designed for an electric vehicle as a test case. The deviation in performance compared with the computed maximum torque-to-current and maximum torque-to-voltage optimization criteria are outlined. Finally, experimental results are presented, demonstrating the practical implementation in a micro-controlled drive
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
Simplified Linear Kalman Filter for Sensorless Oriented Control of PWM Rectifiers
No full textThis paper assesses the efficacy of a simplified Discrete-Time Linear Kalman Filter in estimating the grid voltages applied to a PWM Rectifier, thereby achieving sensorless Voltage-Oriented Control. Utilizing a typical dynamic system formulation, a different model is developed to reduce the number of state variables, thus minimizing the complexity and computational burden of the filter. The converter control ensures the power factor corrector functional mode through the phase angle of the grid derived from the estimated voltages. The proposed control method guarantees optimal converter performance while minimizing the required transducers, reducing costs, and enhancing reliability. Furthermore, its real-time-suitable algorithm enhances practical applicability. The effectiveness of the proposed solution is confirmed through MATLAB/Simulink simulations
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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