1,721,421 research outputs found
Model predictive control of NPC inverters for different scenarios
No full textMultilevel inverters have undergone a period of rapid development recently and, as a result of the progression of contemporary industry, a range of commercial applications have attained the megawatt standard, thereby meaning that there is a requirement for medium- or high-power conversion mechanisms. At the same time, several energygenerating technologies that can be renewed including solar power, bio-energy, tidal power, wind power, and geothermal power have emerged as critical areas of development in global energy production initiatives, hence creating a situation where the multilevel inverter is becoming increasingly investigated by scholars. It is possible to use multilevel inverters with renewable energy sources and, at the same time, these devices can contribute to high-power rating standards. In light of these considerations, the purpose of the present thesis is to address the control algorithms of multilevel inverters and, to be specific, the thesis will chiefly examine the neutral point clamped (NPC) inverters. The main challenge regarding the modulation and control of NPC inverters is that the entire system is nonlinear due to the utilisation of power switches. Conventional approaches are mainly based on the average state space modelling and related modulation techniques such as pulse width modulation (PWM) and sinusoidal pulse width modulation (SPWM). However, the limitations of these conventional methods are clear. The model must be linearised based on a specific operating point. The tuning procedure of the controller is complex, and this complexity increases yet further when the operating point is adjusted. Due to the development of the fast microprocessor and digital signal processors (DSP), some novel control methods such as hysteresis current control, sliding mode control and model predictive control (MPC) have been applied to NPC inverters. Among these methods, MPC stands out for its fast response and handling multiple constraints, and MPC has achieved great success in power electronics applications. Therefore, novel MPC algorithms for 3-level NPC inverters have been proposed to improve energy efficiency for different scenarios in this thesis. Firstly, an MPC algorithm with reduced switching frequency for 3-level NPC inverters is proposed. The proposed method can reduce the switching frequency through the optimisation of switching sequences while keeping the advantages of the conventional MPC method, such as its fast response and ability to handle multiple constraints. The performance of this proposed method is verified by simulation results with 3-level NPC inverters. Based on this MPC algorithm, two additional extended MPC algorithms are proposed to reduce computational burden, including a multistep model predictive control (MMPC) algorithm and a model predictive control algorithm for grid-connected NPC inverters. The effectiveness of the proposed MPC algorithms has been identified.Furthermore, an MPC algorithm for NPC grid-connected inverters is proposed with automatic selection of weighting factors. The main objective of this proposed algorithm is to reduce switching frequency and to provide for the automatic selection of weighting factors without the need for trial and-error across different working conditions. The algorithm can also achieve active power tracking and maintain neutral point balancing. These various objectives are achieved through the use of a modified three-part cost function and the adoption of a two-dimensional fuzzy logic control scheme. The effectiveness of the proposed algorithm is verified using the results of grid-connected NPC inverters simulations, which show that the switching frequency can be reduced by at least 30% when compared to conventional MPC methods. In addition, a new proposed current slope-related control objective is added to the cost function of the proposed MPC algorithm. This control objective aims to make predicted slope values approach slope reference values. By doing this, the proposed algorithm can reduce the total harmonic distortion (THD) of the output currents and, when compared to a conventional MPC algorithm, can reduce the switching frequency by more than 30%. A case study of a grid-connected NPC inverter system is used to assess the effectiveness of the proposed MPC algorithm under conditions of nominal operation and dynamic operation (with the active power reference, P∗, being stepped down from 31kW to 24kW at 0.3s, then increased to 41kW at 0.5s) and with different degrees of parameter sensitivity (at +25%, +50%, and −75% variation in inductance)
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
Newton hard thresholding pursuit for sparse LCP via a new merit function
No full textSolutions to the linear complementarity problem (LCP) are naturally sparse in many applications such as bimatrix games and portfolio section problems. Despite that it gives rise to the hardness, sparsity makes optimization faster and enables relatively large scale computation. Motivated by this, we take the sparse LCP into consideration, investigating the existence and boundedness of its solution set as well as introducing a new merit function, which allows us to convert the problem into a sparsity constrained optimization. The function turns out to be continuously differentiable and twice continuously differentiable for some chosen parameters. Interestingly, it is also convex if the involved matrix is positive semidefinite. We then explore the relationship between the solution set to the sparse LCP and stationary points of the sparsity constrained optimization. Finally, Newton hard thresholding pursuit is adopted to solve the sparsity constrained model. Numerical experiments demonstrate that the problem can be efficiently solved through the new merit function
Model Predictive Control of Neutral Point Clamped Inverter with Reduced Switching Frequency
No full textThis paper proposes a novel model predictive control (MPC) algorithm with reduced switching frequency for Neutral Point Clamped (NPC) inverters. The proposed method can reduce the switching frequency through the optimization of switching sequences, while keeping the advantages of the conventional MPC method such as fast response and handling multiple constraints. The performance of this proposed method is verified by simulation results with a three-level NPC inverter. © 2019 The Korean Institute of Power Electronics (KIPE
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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