1,720,958 research outputs found
A two-stage online inertia estimation: Identification of primary frequency control parameters and regression-based inertia tracking
Full text linkIn recent years, power system inertia has significantly decreased and has become more variable due to the massive integration of converter-interfaced renewable energy sources. Real-time awareness of the inertia present in the system is essential for operators to take preventive actions and mitigate potential instability risks. Online inertia tracking methods based on field data have been used to accomplish this task. However, most existing methods are disturbance-based and few have proven effective under normal operating conditions. In addition, some methods require prior knowledge of the primary frequency control dynamics, which are usually unknown, especially in presence of power converters. To overcome these limitations, this paper proposes a two-stage online inertia estimation method. The first stage estimates the primary frequency control parameters. The second stage uses a regression-based approach to track the inertia in real time. A sensitivity analysis of the parameters of the regression model is used to determine the conditions under which the primary frequency control parameters must be updated. The performance of the method is validated using the IEEE 39-bus benchmark network under normal operating conditions and under the occurrence of large disturbances. The algorithm is also tested in the presence of converter-interfaced sources controlled in both grid-following and grid-forming modes. Real-time tests validate the applicability of the method
On-line Inertia Estimation in Presence of Distributed Energy Resources
No full textProper levels of inertia guarantee the stable and secure operation of power systems. Due to the increasing deployment of distributed resources, most of which are converter-interfaced sources (CISs), the inertia level is decreasing and can vary significantly depending on the connection of renewable energy sources. It is hence useful to monitor the system inertia close to real-time. This paper proposes an improved online inertia estimation method based on a non-linear least squares (LSQ) optimization technique and the Dynamic Regressor Extension and Mixing (DREM) procedure. The LSQ optimizer periodically characterizes the aggregated dynamics of the units involved in the primary frequency control, while the DREM continuously estimates the inertia of the system. Both units with directly connected synchronous generators and CISs are considered in the tests based on the 39-bus IEEE system. The CIS models include a droop control together with a virtual inertia scheme to represent their participation in the frequency regulation. The impact of rotating load dynamic is also considered
Optimal Operation of Renewable Energy Communities Through Battery Energy Systems: A Field Data-Driven Real-Time Simulation Study
No full textGoing 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
DC Microgrids for Industrial DC Application: Focus on Energy Management and Storage Optimization
No full textThis paper deals with a DC microgrid powered by a photovoltaic (PV) system, supported by a Battery Energy Storage System (BESS) to supply DC loads of specific industrial processes and tertiary applications. These microgrids are of interest for industries characterized by high energy consumption (energy-intensive). The relevant objective is to reduce energy import from the grid, lower energy procurement costs, and minimize current ripple affecting the DC loads. The system includes an interface with the AC grid through a bidirectional DC/AC converter in order to export surplus of PV energy to the grid and guarantee electricity supply when needed. It also integrates a charge controller to manage the BESS system using a dedicated energy management system (EMS). This study focuses on determining the optimal BESS capacity to maximize the Net Present Value (NPV) of investments-originated savings. Industrial electricity load profiles, PV generation data derived from 18 years of average hourly irradiation, and three years of electricity price profiles are used for the optimization inputs. BESS power is optimized over a one-year period to minimize grid energy exchange, with annual cost curves used to maximize the NPV. In addition, an optimization algorithm implemented in the EMS useful for the daily scheduling of the system is also proposed
- …
