1,720,982 research outputs found
Contributions to Secure Electric Power System Operation
No full textElectric power system is a fundamental infrastructure of modern society. A magnicent property of electric power system { security, is achieved by keeping it operated in a secure state at most of the time. Security means the ability to withstand imminent disturbances or contingencies, such as electric short circuits or unanticipated loss of system elements, without interruption of customer service. This thesis proposes methods to secure power system operation from classifying threat origins to power system security, analyzing power system steady-state security, splitting power system network intentionally to increase power system transient stability. Maintaining electric power system secure is a very challenging interdisciplinary multidimensional problem, which is impacted by a large amount of factors, such as extreme weather conditions and unexpected disturbances. In order to achieve keeping the system secure, pursuing a better understanding of all kinds of origins of threats to electric power system is meaningful. Identifying and classifying potential threats to electric power system help to design corresponding measures to tackle them. Moreover, due to impossibility of considering countless threats with nite resource, quantifying and ranking the risks of threats contribute to level up eciency and eectiveness. When power system in a normal, alert, or emergency state, steady-state security analysis, as a branch of power system security analysis, is an eective tool to provide information for operators to design control to mitigate power system progressing into a extremis state. Conventionally, most analysis methods for steady-state security are "point-wised", which means that they considering operational points by checking all components' electrical quantities. However, this sort of method has obvious disadvantages, such as heavy numerical computation and lacking global information. Therefore, "region-wised" method, such as nodal power injections security region and interface power ow security region, with the ability to provide global security information to operators, is promising. Normal, preventive and emergency control measures are eective tools to keep power system security. However, if these measures fail, power system will be placed into a extremis state. Extremely, a cascading spreading of system components outages would result in partial or systemwide blackout (loss of supplied load). In this case, intentional islanding, the ultimate control to preserve as many stable areas as possible, is an eective and promised measure to prevent blackout. In designing a islanding scheme, fast and eectively searching out the optimal MC (minimum cut-set) to split power system network is a conundrum. Moreover, for the large-scale power system, it is even impossible to nd out the best scheme but surrender to suboptimum ones. Genetic algorithm, with excellent optimization capacity, is suitable in this optimization problem to search the optimal MC from the collection of possible cut-sets. However, a considerable portion of meaningless individuals would be produced at the stages of population initialization and genetic operation in the original algorithm, some supplementary modications must be employed to improve its eciency and eectiveness. For each survived island, resynchronization, one aspect of restoration, is a prior issue should be considered. A threat to jeopardize the resynchronization of the survived island is power system 1 transient instability. The mechanism of transient instability can be described as a part of generators in power system deviating from the remaining ones. The deviation of the group from the remaining groups causing power system instable is called critical pattern. The strategy of designing controllers to increase the coherency between the two groups of generators is promising to reduce, even eliminate in some case, the risk of the threat to power system transient stability. In order to implement the control strategy, Lyapunov trajectory tracking control is eective to calculate the mechanical torque to track power system's desired stat
An Outage Risk Oriented Dynamic Distribution Network Reconfiguration Methodology Considering the Effects of Weather Conditions on Power Line Failure Rate
No full textA dynamic network reconfiguration methodology consid-
ering time-varying weather conditions is proposed. The aim of the
proposed methodology is to minimize outage risk. To fully reflect
actual weather severity, a classification method for weather states
based on weather variables analysis is presented. Considering time-
varying nature of weather, an approach to determine the optimal time
for reconfiguration by comparing reliability change between adjacent
intervals is provided. Then, applying the Quantum Genetic Algo-
rithm to solve reconfiguration optimization problem is introduced.
Simulation results on the IEEE 33-node test systems show that the
proposed dynamic reconfiguration method can reduce distribution
network’s outage risk. In addition, weather conditions have impacts
on outage risk of distribution network and should be considered in
reconfirmation problems
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
Demand Response Scheduling Considering Pollutant Diffusion Uncertainty of Industrial Customers
Full text linkThe demand response scheduling scheme requires the consideration of both the industrial customers’ economic cost and the environmental influences from pollutants. However, the diffusion process of the latter, although of paramount importance, is typically ignored in the existing literature. To address this issue, we propose a demand response scheduling scheme that not only precisely simulates the diffusion process through a spatio-temporal diffusion model, but incorporates the uncertainty into the diffusion trajectories via a Markov decision process. This enables the schedule-maker optimally select the industrial customers to participate in the demand response with a minimum cost while reducing the environmental influences of the pollutants simultaneously. Using it, a deep reinforcement learning approach is further advocated in the optimization procedure to improve the scalability of the proposed method. Simulation results on the modified IEEE-118 test system reveal the validity of the proposed method
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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