1,721,010 research outputs found
Extended State Observer Based Stator Flux Linkage Estimation of Nonlinear Synchronous Machines
No full textInstantaneous conduction and switching losses in two-level voltage source inverters
Full text linkA mathematical model is derived which allows to compute instantaneously the conduction and switching losses in two-level voltage source inverters (2L-VSIs) regardless of the employed modulation scheme. The model is based on the use of switching vectors applied to the considered VSI, taking into account the instantaneous conduction and switching losses of the semiconductor devices. The advantages of this method are, (i) it can be extended to any type of VSI and any modulation scheme, (ii) it can be applied to analyze the power losses of VSIs during any desired period, and (iii) it can be easily implemented in any kind of the simulation software (e.g. Matlab/Simulink)
Continuous Control Set Model Predictive Torque Control of Electrically Excited Synchronous Motors
No full textThis paper presents a Continuous Control Set Model Predictive Torque Control (CCS-MPTC) strategy for Electrically Excited Synchronous Machines (EESMs). The proposed control algorithm aims to minimize copper losses. By leveraging a precise discrete-time motor model, the CCS-MPTC algorithm optimizes control inputs over a finite horizon, ensuring torque reference tracking and current vector amplitude minimization. The algorithm autonomously identifies the Maximum Torque Per Ampere (MTPA) condition, eliminating the need for precalculated trajectories. Simulation results demonstrate the effectiveness of the proposed strategy in both stand-still and nominal speed conditions, highlighting its ability to maintain minimal excitation current and adhere to current constraints. The CCS-MPTC control algorithm provides a robust solution for advanced EESM applications, particularly in high efficiency, high dynamic performance scenarios such as electric vehicles and traction systems
Electrical launch catapult and landing decelerator for fixed-wing airborne wind energy systems
No full textThis paper presents a (pre)feasibility study of the rail-based ultra-short launch and landing system ElektRail for fixed-wing airborne wind energy systems, such as Ampyx Power. The ElektRail concept promises airborne mass reductions through the elimination of landing gear as well as decreased landing stresses and ground stability requirements, opening possibilities for improved aerodynamics through a single fuselage configuration. Initially designed for operating fixed-wing drones from open fields, the ElektRail concept had to be significantly shortened for application in an airborne wind energy (AWE) context. This shorter size is required due to the much more limited space available at AWE sites, especially on offshore platforms. Hence, a performance enhancement using the integration of a bungee launching and landing system (BLLS) was designed and a system dynamics model for the launch and landing was derived. The results demonstrated the possibility for the ElektRail to be shortened from 140 m to just 19.3 m for use with an optimised tethered aircraft with a mass of 317 kg. A system length below 20 m indicates that an enhanced ElektRail launch and landing concept could be viable for airborne wind energy operations, even with relatively low-tech bungee cord boosters. Linear motor drives with a long stator linear motor actuator could potentially shorten the system length further to just 15 m, as well as provide better control dynamics. An investigation into improved AWE net power outputs due to reduced airborne mass and aerodynamic improvements remains to be conducted.This paper presents a (pre)feasibility study of the rail-based ultra-short launch and landing system ElektRail for fixed-wing airborne wind energy systems, such as Ampyx Power. The ElektRail concept promises airborne mass reductions through the elimination of landing gear as well as decreased landing stresses and ground stability requirements, opening possibilities for improved aerodynamics through a single fuselage configuration. Initially designed for operating fixed-wing drones from open fields, the ElektRail concept had to be significantly shortened for application in an airborne wind energy (AWE) context. This shorter size is required due to the much more limited space available at AWE sites, especially on offshore platforms. Hence, a performance enhancement using the integration of a bungee launching and landing system (BLLS) was designed and a system dynamics model for the launch and landing was derived. The results demonstrated the possibility for the ElektRail to be shortened from 140 m to just 19.3 m for use with an optimised tethered aircraft with a mass of 317 kg. A system length below 20 m indicates that an enhanced ElektRail launch and landing concept could be viable for airborne wind energy operations, even with relatively low-tech bungee cord boosters. Linear motor drives with a long stator linear motor actuator could potentially shorten the system length further to just 15 m, as well as provide better control dynamics. An investigation into improved AWE net power outputs due to reduced airborne mass and aerodynamic improvements remains to be conducted.This paper presents a (pre)feasibility study of the rail-based ultra-short launch and landing system ElektRail for fixed-wing airborne wind energy systems, such as Ampyx Power. The ElektRail concept promises airborne mass reductions through the elimination of landing gear as well as decreased landing stresses and ground stability requirements, opening possibilities for improved aerodynamics through a single fuselage configuration. Initially designed for operating fixed-wing drones from open fields, the ElektRail concept had to be significantly shortened for application in an airborne wind energy (AWE) context. This shorter size is required due to the much more limited space available at AWE sites, especially on offshore platforms. Hence, a performance enhancement using the integration of a bungee launching and landing system (BLLS) was designed and a system dynamics model for the launch and landing was derived. The results demonstrated the possibility for the ElektRail to be shortened from 140 m to just 19.3 m for use with an optimised tethered aircraft with a mass of 317 kg. A system length below 20 m indicates that an enhanced ElektRail launch and landing concept could be viable for airborne wind energy operations, even with relatively low-tech bungee cord boosters. Linear motor drives with a long stator linear motor actuator could potentially shorten the system length further to just 15 m, as well as provide better control dynamics. An investigation into improved AWE net power outputs due to reduced airborne mass and aerodynamic improvements remains to be conducted
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
Modellierung, Regelung und Betrieb im Fehlerfall von doppelt drei-phasigen elektrischen Antriebssystemen für Flugwindkraftanalgen
Full text linkThis thesis proposes the utilization of DT interior permanent magnet synchronous machines. Compared to the available body of literature, the main contributions of the carried-out work are: (i) identifying the machine non-linearities; (ii) modeling and simulating the machine dynamics; (iii) efficient operation coupled with a zero steady-state error current regulator; and (iv) deriving a post-fault optimization without exceeding the machine ratings (i.e. currents and voltages). Experimental results are provided for the sake of validation.In dieser Arbeit wird die Verwendung einer doppelt drei-phasigen permanenterregten Synchronmaschine mit vergrabenen Magneten für Flugwindkraftanlagen vorgeschlagen. Die Hauptbeiträge sind (i) Identifikation der Maschinen-Nichtlinearitäten; (ii) Modellierung und Simulation der Maschinendynamik; (iii) verlustminimaler Betrieb und asymptotisch genaue Stromregelung; und (iv) Entwicklung einer optimierten Betriebsstrategie im Fehlerfall unter Berücksichtigung der Maschinennenngrößen. Alle Beiträge werden experimentell im Labor validiert
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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