1,720,958 research outputs found
Accurate and Computationally-Optimized Small-Signal Model Identification of LLC Resonant Converter Based on Machine Learning Techniques
No full textLLC small-signal model is often identified via FHA (First Harmonic Approximation) and/or EDF (Extended Describing Function) in order to analyse the dynamical behaviour of the converter and hopefully fine tune the controller. These approaches fail easily and force to consider a resistive load, which is a restrictive method since most of the times resonant converters are used to feed current or stabilize a voltage (e.g., in battery charging applications). In this paper the small-signal output current response of the converter is approximated by a second order discrete-time transfer function, whose numerator and denominator coefficients change with the operating condition (i.e., output voltage and switching frequency). The coefficients are fitted using a sparse linear combination of functions in data-driven fashion (via simulation) adopting a well-known machine learning operator (Least Absolute Shrinkage and Selection Operator, LASSO). The aim of this paper is to report the first attempts made to obtain an accurate and computationally-optimized approximation of the output current response of a generic resonant converter based on machine learning techniques
Adaptive High-Frequency Injection and Control Loops Design for Flying-Capacitor Passive Cross-Connected Modular Multilevel Converter Based Drive Systems
No full textOne of the main issues associated with the operation of Modular Multilevel Converters (MMC) as variable-speed drive is the voltage ripple developed across the sub-module (SM) capacitors at low speed and high torque conditions. A hybrid MMC topology, namely the Flying-Capacitor Passive Cross-Connected arms (FC-PCC) MMC has been recently introduced to cope with this issue. A comprehensive theoretical analysis, as well as a validation of both the power conversion topology and a new and optimized distributed digital control strategy are reported in this paper. An adaptive algorithm for the management of the high-frequency injection adopted to control the voltage ripple across the SM capacitors is proposed, allowing reduction of additional losses and guaranteeing enough voltage margin for proper current regulation in the whole speed/torque range in an adaptive fashion. The effectiveness of the proposal is demonstrated by a 22kW permanent magnet synchronous machine drive, even at rated torque from zero to rated speed
Advances on Analysis, Modeling and Accurate Self-Commissioning Compensation of Inverter Dead-Time Distortion Based on a Physical Model
No full textIn Pulse-Width-Modulated (PWM) inverters, dead-time and voltage drops lead to a distortion on the average output voltage. This effect is related to the system parameters and to the operating conditions and in many drives applications it can be intolerable. A number of modeling approaches and compensation methods have been proposed in the past literature. A recent approach adopts an accurate physical model of the inverter, aiming at investigating the effects of parasitic capacitances and devices voltage drops by a fitting analytical characteristic. Model parameters are derived from a self-commissioning procedure, based on proper voltage injection and processing, both affecting the accuracy of achievable compensation. In this paper, these issues have been considered and two original enhancements have been proposed and validated, demonstrating the superiority of the results over state-of-the-art. Finally, the effects of the mentioned inverter distortion on the accuracy of current sampling and control loops are also analyzed for the first time, and an original compensation strategy is proposed and validated. Theoretical analysis and developments are fully reported, together with accurate simulations and experimental results based on a commercial drive
Optimized Distributed Digital Control and Communication Architecture for Flying Capacitor Modular Multilevel Converter Based PMSM Drives
No full textAn optimized digital architecture exploiting distributed and multilayer hierarchical control and real-time communication for Flying Capacitor Passive Cross-Connected arms Modular Multilevel converter (FC-PCC MMC) based drive systems is proposed, designed and validated. The proposed solution, relies on two fundamental components: a Multi-Point Low Voltage Differential Signaling (M-LVDS) bus and a bi-directional optical wireless transceiver, recently introduced to the market. As a result, the necessary isolation barrier between ground and each Sub-Module (SM) can be crossed at a very high data rate. The real-time constraints and requirements have been analyzed and discussed in order to design a control strategy and communication infrastructure for proper, safe and reliable converter operation. Based on this analysis, a distributed control algorithm and the related communication infrastructure are proposed in this paper. Moreover, an innovative isolated communication bus is adopted, which aims at reducing the overall system size and cost. The effectiveness of the proposal is demonstrated by accurate simulation of a 22 kW Permanent Magnet Synchronous Machine (PMSM) drive, including the effect of communication and processing latency. The results show that proper operation is obtained even at rated torque from zero to rated speed, while the voltage ripple across the SM capacitors is kept limited thanks to the optimized control strategy proposed in [1]. A prototype of the converter has been designed and is ready to be manufactured
Integrated High-Frequency SiC Based Modular Multi Three-Phase PMSM Drive for Automotive Range Extender
No full textThe main issue limiting electric vehicles as viable partial solution to conventional mobility based on fossil fuels is the reduced range between charges. A possible solution is represented by range extender systems (RES), allowing to charge the main battery of the vehicle when needed, using a dedicated and reduced power internal combustion engine (ICE) coupled with an electric machine (EM) acting as a generator. In this paper a novel system architecture is proposed, based on an integrated multi three-phase PMSM, fed by high-frequency converter modules (HFCMs) employing silicon-carbide (SiC) power devices. Magnetic coupling of three-phase modules is managed by a proper decoupling control strategy requiring a real-time communication among modules. Design of the system, including the power and control electronics, and the electric machine, as well as simulation and experimental results are reported to demonstrate the effectiveness of this proposal
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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