1,720,952 research outputs found
Brushless Doubly-Fed Induction Machines for Wind Turbine Drive-Train Applications
No full textThe research leading to these results has received funding from the European Union’s Seventh framework Programme (FP7/2007_2013) for theWindrive project under Grant Agreement 315485.Electrical Power Processin
The Development of Range Extender Generator By Evaluating The Eddy Current Losses and End Effect Using FE Method
No full textPeec-Power B.V. is developing high power range extender for hybrid electric vehicles. The first generator designs for range extender have been built and tested in the laboratory. The prototype generators use a permanent magnets with a radial flux type. These prototypes use two kinds of fractional-slot concentrated winding. The slot pole combinations that were chosen are a multiple of 9 coils around 9 teeth with 8 magnet poles and a multiple of 3 coils around 3 teeth with 2 magnet poles. There are two types of permanent magnet constructions in the rotor, which are the Surface Mounted Permanent Magnet (SMPM) and Inset Permanent Magnet (IPM). This thesis deals with further development of the range extender generator. Two topics will be further investigated by using 2D and 3D FEM model. The first topic is the investigation of eddy current losses in the permanent magnets and rotor back iron. The second topic is the investigation of the influence of the machine ends and end windings on the flux distribution and inductivity. The rotor eddy current losses in the prototypes machine are calculated using analytic model, 2D FEM and 3D FEM model. The 3D FEM model is used to investigate the finite length effect in 2D FEM magnet loss calculations. This investigation needs to be done since the prototype generators have a short axial length. The lamination effect on the magnet loss also will be investigated in 3D FEM model. From this investigation, a correction factor to the 2D FEM magnet loss calculation is introduced. 3D FEM models are built to investigate the influence of the machine ends and end windings. With these models, the flux leakages, end inductances and the eddy current losses in the stator end are calculated.Electrical power processingElectrical Power EngineeringElectrical Engineering, Mathematics and Computer Scienc
Brushless Doubly Fed Induction Generator Based Wind Turbine Drivetrain Under Grid Fault Conditions
No full textWith growing interest in sustainable forms of energy, the wind industry is growing rapidly. The Doubly Fed Induction Generator is the most popular choice for the drivetrain because it is cost effective. However, it suffers from reliability and maintenance issues due to the slip rings and brushes it requires. The Brushless Doubly Fed Induction Generator (B-DFIG) aims to address these drawbacks. With increased wind power penetration, tripping of wind turbines during grid disturbances is no longer acceptable for the power system. Therefore, it is important to study the performance of such wind turbine drivetrain under low voltage events. This thesis studies the Low Voltage Ride Through (LVRT) characteristics of the B-DFIG for its application in wind turbines. This thesis first looks at the modelling and control of the Brushless Doubly Fed Induction Generator (B-DFIG) to be used in a wind turbine drivetrain. It develops the steady state model using circuit theory to study the steady state characteristics of the machine. The dynamic model is developed to form the basis of the study of the machine during low voltage events. Further, the controller is developed based on vector control. The second part of the thesis looks at the performance of a B-DFIG based wind turbine under symmetric low voltage dips. It compares the performance of this generator with that of the Permanent Magnet Synchronous Machine (PMSM) and Doubly Fed Induction Generator (DFIG) - two of the most prevalent generators used in wind turbine drivetrains today. The thesis also looks at protection methods for these generators. It has been seen that the issue with LVRT performance of the PMSM is the rise in the DC link voltage which is due to the mismatch in power generated by the machine and the power transferred to the grid. It has also been found that apart from offering better reliability through the exclusion of slip rings and brushes, the B-DFIG also has an improved LVRT performance when compared with the DFIG - the protection is simpler and can be built into the control algorithm of the machine controller.Electrical Power ProcessingElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Control Algorithm for a BDFIG based Wind Turbine Drivetrain including Rotor Position Estimation.
No full textAs the need for electrical power from sustainable energy sources is continually increasing, electrical power generation from wind turbines continues to grow. A common type of electrical generators used in wind turbines is the Doubly Fed Induction Generator. However, this type of generator suffers from reliability issues associated with slip rings and brushes. The Brushless Doubly Fed Induction Generator (BDFIG) is an attractive choice to eliminate the drawbacks associated with slip rings and brushes. To commercialize the first BDFIG wind turbine a high performance control algorithm must be designed. This thesis focuses on the development of a control algorithm for a BDFIG based Wind Turbine Drivetrain (WTDT) system including sensorless position estimation. To explore the characteristics of the BDFIG, an equivalent circuit is developed to determine the machine steady state behavior. From the BDFIG equivalent circuit, a dynamic model of the machines is derived to form the basis for the control algorithm development. The control algorithm is based on a Field Orientated Control using a two cascaded control loops for control of active- and reactive power. WTDT reliability can be further improved by eliminating the rotor position sensor. In place of a position sensor, a method of estimating rotor position is required, such that a senorless control algorithm is achieved. Two methods for position estimation are investigated and theoretically validated. Indirect position estimation, though speed estimation, using Model Reference Adaptive System is developed and compared to direct position estimation through induced Back-Electromotive Force (B-EMF) in the stator windings. The developed sensorless control algorithm provides maximum wind power extraction during the expected operating range, where active- and reactive power control loops response are limited by mechanical inertia. The control algorithm uses the induced stator B-EMF for rotor position estimation. To test the validity of a sensorless control algorithm for a BDFIG, an experimental setup has been constructed. A sensorless current control of the Control Winding (CW) active- and reactive power has been experimentally validated, where the CW frequency is made to follow the CW stator flux. The experimental controller maintains synchronous mode of operation, for a limited speed range, due to presence of space harmonics.Electrical Power ProcessingElectrical Power EngineeringElectrical Engineering, Mathematics and Computer Scienc
Design of a permanent magnet radial flux concentrated coil generator for a range extender application
No full textThe main disadvantages of currently available electric vehicles can be overcome by integrating range extenders in short range electric vehicles. Peec-Power is developing a new prototype range extender, integrating combustion engine and generator. For this purpose a generator had to be developed. The generator constructions best suited for this range extender application are discussed. Of these generator constructions models have been derived. The resulting designs will be presented along with a comparison of the analytical calculation results and finite element method (FEM) calculation results.Electrical Power ProcessingElectrical Engineering, Mathematics and Computer Scienc
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
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