1,720,958 research outputs found
Secure operation of a stand-alone wind energy system based on an incommensurate fractional-order chaotic system
No full textCybersecurity for wind energy conversion systems, such as Stand-Alone Wind Energy Conversion Systems (SAWECSs) that use Self-Excited Induction Generators (SEIGs), has been a growing area of focus recently. Despite their advantages such as robust structure, low cost, minimal maintenance, and the ability to operate at varying wind speeds, SEIG-based SAWECSs rely on effective reactive power management to maintain output voltage stability. As modern technologies become more integrated into SAWECS, controlling the output voltage becomes increasingly challenging, which makes the system more vulnerable to cyber-attacks. To ensure the cybersecurity of SEIG-based SAWECS, this study proposes a novel approach, a chaotic system-based secure communication algorithm derived from the interaction between dark matter and dark energy (DM-DE). This algorithm utilizes fractional calculus to increase the complexity of chaotic flows, thereby strengthening the robustness of secure communication. The effectiveness of the proposed approach is verified through detailed analyses and simulation studies, demonstrating its capability to maintain system stability and security. The chaos-based secure operation algorithm is then tested and validated using a SAWECS comprising a 3-phase, 400V, 50 Hz SEIG with resistive-inductive loads. It is observed that the experimental results are consistent with the simulation results. This work demonstrates that chaotic system-based approaches can be used to enhance the cybersecurity of renewable energy systems
Masking of measurements in a photovoltaic system using an incommensurate fractional-order chaotic system based on string dynamics around the Bardeen-AdS black hole
No full textConsidering environmental factors and global warming, the use and installation of photovoltaic (PV) systems have become widespread. However, the integration of these PV systems into smart grids raises concerns regarding cybersecurity. Since PV systems rely on communication networks, remote monitoring, and grid-connected inverters, they exhibit a cyber–physical structure and are therefore vulnerable to cyber-attacks. Cyber threats targeting PV infrastructure can lead to system failures, energy theft, grid instability, and financial losses. While many studies focus on cyber-attack detection for PV system cybersecurity, this paper aims to design a cybersecure PV system by employing a novel chaos-based encryption method. Due to their unpredictable and highly sensitive nature, chaotic algorithms are utilized to ensure secure communication within PV systems. The encryption algorithm is derived from the incommensurate fractional analysis of the “strings around the Bardeen-AdS black hole surrounded by quintessence dark energy”, a cosmological system. Simulation results performed in MATLAB/Simulink confirm the effectiveness of the proposed encryption framework. The underlying pseudo-random number generator (PRNG) successfully passed all 15 standard NIST SP800-22 statistical tests, validating its strong statistical randomness and unpredictability. Furthermore, the encrypted signals consistently exhibit high information entropy (e.g., encrypted entropy = 5.3213 compared to actual entropy = 4.0931), indicating strong randomization and obscurity of original patterns. The decrypted outputs precisely recover the original measurements, with entropy values perfectly matching the actual signals (e.g., decrypted entropy = 4.0931), thereby validating the reliability, reversibility, and cyber resilience of the approach
A robust LQR-(FOPID mu)-D-lambda controller design for output voltage regulation of stand-alone self-excited induction generator
No full textThis paper presents several optimal controllers compared with a robust control method for the terminal voltage regulation of a stand-alone self-excited induction generator (SEIG) with fixed capacitor and thyristor controlled reactor (FC-TCR). The major challenge of designing process of the controllers is the nonexistence of perfect model of SEIG. Therefore, small-signal based models for the output voltage and frequency are carried out using real input-output data. Accordingly, Linear Quadratic Regulator (LQR), Linear Quadratic Integral (LQI) and Linear Quadratic Fractional Order Integral (LQFOI(lambda)) controllers are designed to regulate output voltage. Moreover, novelty and main contribution of the paper is to design a hybrid controller which combines LQR and Fractional Order Proportional Integral Derivative (LQR-(FOPID mu)-D-lambda) controller to ensure the best tracking dynamics, robustness against disturbances and sensor noise suppression. The proposed hybrid LQR-(FOPID mu)-D-lambda controller is obtained by solving H-infinity weighted mixed sensitivity problem. Optimization process of the controller parameters is implemented by using particle swarm optimization (PSO) algorithm. Matlab/Simulink program is used to compare the effectiveness of the proposed controllers. Furthermore, the experimental results show that robust LQR-(FOPID mu)-D-lambda controller has the best tracking dynamics among them with less overshoot, settling time as well as the robust structure against external disturbances and sensor noises
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
Fault Tolerant Sliding Mode Controller Design Subject to Sensor Faults for Output Voltage Regulation of a Self-Excited Induction Generator
No full textThis paper aims to improve the performance of the output voltage regulation of the Self-Excited Induction Generator (SEIG) with fixed capacitor-thyristor controlled reactor (FC-TCR) structure in case of sensor faults. A sliding mode controller (SMC) is designed to generate the triggering angle of the FC-TCR to regulate the output voltage. The performance of proposed SMC is firstly tested without sensor faults and high success in tracking the reference is obtained. Since an additive fault occurs on the sensor, SMC performs well tracking dynamic but is on the incorrect reference. Therefore, Radial Basis Function Neural Network (RBFNN) is trained accurately with the 2% mean squared error (MSE) by taking the stator currents, triggering angle and generator speed as inputs, whereas the output voltages of the SEIG are outputs. Further, fault detection architecture is well designed with a voltage error index calculated by subtracting the sensor output from the estimated output. The threshold based selector reconfigures the controller well. The simulation results show that in case of sensor faults and various loading conditions, proposed fault tolerant SMC remains the actual output voltage of the SEIG at real reference with maximum 2.2% steady state error in a finite time
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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