1,720,955 research outputs found
Fixed-Switching Frequency Model Predictive Current Control: Closed-Form Solution in the Stationary Reference Frame
No full textCurrent control of three phase loads is a basic functionality in applications ranging from the control of electrical machines to grid-tied inverters. Commonly adopted approaches fail in case of low switching-to-fundamental frequency ratio, e.g., very high-speed motor drives (high fundamental frequency) and large power inverters (low switching frequency).Model Predictive Control (MPC) has been applied to overcome the limitations of the traditional approach and improve control performance in terms of dynamics and current distortion. The adopted MPC formulation considers the current error at the switching instants of the inverter.The main original contribution is the closed-form solution of the optimization problem, leading to simpler and more efficient implementation, which requires a fixed number of steps. Simulations results are reported for an isotropic Permanent Magnet Synchronous Machine (PMSM), confirming the validity of the approach. Implementation details such as execution time estimation and weight selection are addressed
Model Predictive Control for Wound Rotor Synchronous Machines Based on Closed-Form Solution and Fixed Switching Frequency
No full textWound rotor synchronous machine (WRSM), also known as electrically excited synchronous machine (EESM) and hybrid excited synchronous machine (HESM), can represent solutions to address the problem associated with the usage of rare earth materials for the construction of permanent magnets. When compared to other synchronous machines (e.g., permanent magnet or synchronous reluctance), they offer several benefits. However, the coupling between stator and rotor, although necessary for torque production, introduces a new degree of freedom, namely the rotor current, and complicates the current dynamics. Accurate and coordinated current control must be, therefore, designed. A novel fixed-switching frequency model predictive control (MPC) technique based on closed-form solution is proposed in this paper, aiming at improving the accuracy of current regulation, especially during rotor current transients (which are fundamental to be considered to minimize the overall machine Joule losses), while providing a simpler way to handle the available rotor and stator voltage, and keeping limited implementation requirements. Two versions, namely hybrid MPC and full MPC, have been investigated. The former allows for reducing the computational burden without almost no performance penalty. The description of the proposed strategies and complete analytical developments are reported. Relevant simulation results are included, proving the effectiveness of the proposal and better performance with respect to a standard PI-based FOC de-coupling controller. Implementation hints and preliminary results are also reported
Fixed-Switching Frequency Model Predictive Current Control of PMSM: Closed-Form Solution in the Rotating Reference Frame Suitable for Salient Machines
No full textA specific model predictive control (MPC) strategy is considered in this paper to improve transient and steady-state current control performance of permanent magnet synchronous machine drives at low values of switching to fundamental frequency ratio, being a typical design scenario for high-power systems and/or high-speed machines. Among the different MPC proposals that have been reported in literature in the last decade, which usually control the average current (as in standard PI-based systems), an original and promising approach can be found in some recent papers that consider controlling the actual phase current at each switching instant by selecting the application times of the 2-level inverter configurations (i.e., an optimal switching pattern) as a result of the optimization process involving a prediction mechanism. This paper considers this new approach, and some interesting and original developments are presented and validated with respect to former proposals. A closed-form solution to the optimization problem is proposed, resulting in a simpler and more efficient implementation and allowing deterministic execution times. The prediction model is considered in the rotating reference frame (RRF), allowing the control of salient rotor machines and differentiation of the weights (and control dynamics) between the two axes. Furthermore, a one-cycle delay is considered between the sampling instant and the control action update (application actuation of the optimal switching pattern), which allows for the implementation on low-cost control microcontrollers. The description of the proposed strategies and complete analytical developments are reported. Relevant simulation results are included, proving the effectiveness of the proposal and better performance with respect to a standard PI-based FOC de-coupling controller. Implementation hints and preliminary results are also reported
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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