1,720,957 research outputs found
A High-Power Medium-Voltage Open-Loop Induction Motor Drive for Industry Applications: Stability Analysis and Implementation
No full textDue to their several advantages, induction motors are widely used for industrial applications today. The present study focuses on developing a robust high-power induction motor variable frequency drive. In order to test the algorithms of the motor control on an actual induction motor, it is important to first carry out simulation tests to verify and troubleshoot the control strategy. One of the most common software used for such a need is MATLAB/Simulink. To run such experiments requires a significant simulation time and at the same time must satisfy a certain level of accuracy. Therefore, one of the objectives of the thesis is to carry out a study on some of the ODE solvers of MATLAB/Simulink to choose the most efficient solver for the simulation tests of the motor control strategy. The fixed step solvers ode1, ode2 and ode4 and the variable step solvers ode45, ode113 and ode23 are studied in terms of the actual time taken to complete the simulations and the relative tolerance of each solver. Comparing the performance of the fixed step and variable step solvers it is evident that the variable step solvers outperformed the fixed step solvers in terms of both speed and accuracy.
One of the most famous speed control strategies is the open loop V/Hz control. In this control method two modulation techniques were studied. This was the asynchronous modulation technique and the synchronous modulation technique. With the use of the asynchronous modulation technique subharmonics are introduced. To avoid the introduction of such harmful subharmonics the synchronous modulation technique is proposed. The synchronous modulation technique is implemented with the open loop V/Hz control strategy and simulation tests were carried out to verify the problem of subharmonics being removed. Another problem encountered with the open loop V/Hz control strategy is the presence of large current and torque oscillations of the motor at low to medium frequencies. This is due to the nonlinear interactions between the electrical and mechanical subsystems. To mitigate these unwanted oscillations a stability analysis of the open loop V/Hz control is carried out and a region of instability is determined. Two mitigation techniques are proposed in this thesis namely varying slope V/Hz control strategy and the active damping control strategy. The proposed techniques are verified and validated through simulation tests on a 7 MW medium voltage (MV) induction motor in MATLAB/Simulink and on a low voltage (LV) induction motor in laboratory without a mechanical load. Moreover, in this thesis it has been examined that with the consideration of the magnetic saturation of the motor, more stable operations are achieved. This is firstly verified in simulation where considering the magnetic saturation allowed the use of higher flux values providing more stable machine operations while at the same time allowing for a larger torque. With the experimental test on a 10-kW induction motor it was proved that the results obtained through simulations where more stable operations were seen as the value of the flux were increased were correct.
In the power applications such as the ac-dc conversion for the above mentioned 7 MW medium voltage induction motor, a high total harmonic distortion (THD) can be seen in the primary currents with the use of the conventional diode-based ac-dc conversion. In addition, such a conversion does not permit the control of the dc link voltage and has not power factor correction. To overcome these shortcomings the Active Front End rectifier which uses IGBTs that can be electronically controlled is used. In the AFE, the waveform of the input current is monitored and is shaped to be sinusoidal as a result decreasing the THD. Another significant advantage of the AFE rectifier is its capability to handle regenerative power. In this thesis, two configurations of the AFE rectifier are studied. These two configurations include firstly the development of the AFE rectifier using a two-level three-phase inverter and secondly the development of the AFE rectifier with single phase H-bridge cells. From the comparison of the performance of the two configurations of the AFE it is seen that the AFE realised with the H Bridge cells and phase shifted secondary was the best in terms of the THD and the dc link voltage ripple. From these results the AFE realised with H Bridge circuits and phase shifted secondary is chosen for the operation of a real high-power induction motor controlled with the open loop V/Hz control strategy and equipped with the active damping technique for mitigating the current and torque oscillations
Erle-copter Simulation using ROS and Gazebo
No full textThe recent decrease in the price as well as size of semi-conductor logic and due to significant advancements in technologies such as microcontrollers, motors and sensors, the application of quadcopters in several fields has been achieved. However, testing of quadcopter prototypes still has a risk of damage due to faults and unexpected behavior. Hence, a method of testing of quadcopters in simulation mimicking the actual conditions of the real environment in an actual hardware test has been proposed. For this purpose, Gazebo simulator integrated with ROS has been chosen for the simulation of the path of the quadcopter. Moreover, the software Matlab/Simulink has been interfaced with Gazebo in order for the simulation of the quadcopter to be achieved
Currents and Torque Oscillations Mitigation in High Power Induction Motor Drives
No full textInduction machines are always the most used machines in industry, due to the several advantages they offer. The quite simple V/Hz control strategy is one of the most commonly used strategies to control induction motors speed, due to its simplicity and ease of implementation. However, using this strategy for controlling high power induction motors may cause instability in some regions, leading to high oscillations in currents and in motor torque. Therefore, the authors propose an improved version of the V/Hz control strategy, which compensates for these oscillations by correcting the speed reference using the stator current. The results obtained are presented, showing excellent results in compensating for these oscillations in motor currents and torque
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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