1,720,970 research outputs found
Digital Implementation of Innovative Electric Drives
Get PDFNowadays high efficient electric drives are needed to achieve maximum performance of an electric motor. Moreover fault-tolerant capability of the drive has attracted great attention from research and industry world. Automotive sector for instance, is undergoing a radical shift from combustion engines to electric motors. Moreover, other sectors such as aircraft and navy, are moving towards the electrification of all the auxiliary services. An accurate motor control relies on the knowledge of the rotor position to achieve maximum performance of the electric drive. Sensors such as encoder or resolver are used to obtain the rotor position information, i.e. sensored control. In the last years, many algorithms have been developed and investigated to eliminate the position sensor which has some drawbacks. First of all the overall price is increased because additional hardware and cabling are needed. More importantly, the reliability of the drive is decreased since position sensor fault is common. In a sensorless drive, no position sensor is needed because the rotor position is estimated by processing stator currents or voltages according to the motor speed range. Sensorless control allows reducing the overall price, motor frame size and more importantly increasing the reliability of the drive. The latter, together with their fault-tolerant capability and high power density is increasing the attention on multiphase machines.
This dissertation aims at investigating sensorless control at standstill and low speed by using high frequency injection techniques. Motor anisotropy is depicted by analyzing the current response due to the high frequency injection. Since the motor parameters are different, several responses are obtained from different motors. As a consequence, the performance achievable in sensorless control are different for each machine. The ability of the motor to be controlled in sensorless control is defined as self-sensing capability.
The thesis can be divided into two main parts. In the first part, sensorless control applied to a multiphase machine with six phases is investigated. The machine is analyzed as two three-phase windings, each one supplied by a dedicated inverter. A fault-tolerant strategy is developed by studying the motor self-selfing capability. The novelty of the proposed research is that the self-sensing capability of the motor is enhanced and sensorless control without divergence is obtained. No complex compensation algorithms are applied and the fault tolerant capability is improved. Finally, an application of the Kalman fusion algorithm to the sensorless control of the machine is investigated. Sensor fusion is adopted to combine together more estimated positions from more winding sets. The purpose is to close all three-phase windings control loops on one fused position. By doing so, fault-tolerant of the machine is enhanced in the case of a fault in the position sensor.
The second part of the thesis is focused on the developing of a novel observer transfer function for the rotating voltage signal injection. The novelty is that the whole estimator transfer function is retrieved in the Laplace domain by exploiting the modulation/demodulation theory. With this approach, the demodulation effects on filters transfer functions are considered and a proper observer transfer function is retrieved. As a consequence the observer regulator tuning allows achieving both maximum performance and the desired closed loop bandwidth.
The whole thesis was fully validated through an intensive simulation and experimental stage, except the rotating voltage injection which was tested only by simulation. The aforementioned contents were presented by the author at several international conferences and IEEE Journal papers. The complete list of publications is reported at end of the dissertation
Fault-Tolerant Analysis of Kalman Filter Sensor Fusion for Sensorless Control of a Multiphase Machine
No full textModelling of a Rotating Signal Injection-Based Position Observer for Sensorless Synchronous Electric Drives
No full textInvestigation on the Self-Sensing Capability of a Dual Three-Phase Synchronous Reluctance Machine
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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