1,720,957 research outputs found
Optimal aggregation and disaggregation for coordinated operation of virtual power plant with distribution network operator
No full textVirtual power plants (VPPs) offer an effective approach for managing distributed energy resources (DERs), including microturbines, distributed generators, demand response aggregators, and energy storage systems. This technology significantly enhances the economic efficiency and flexibility of distribution network systems. This study aims to facilitate a flexible power exchange between the distribution network system and the upper-level grid by aggregating the power flexibility of heterogeneous DERs via a VPP. Additionally, it introduces a methodology for optimal aggregation and disaggregation within a coordinated operation framework between the VPP and distribution network operator (DNO). On one hand, the VPP can determine its day-ahead feasible region and real-time flexible regulation power based on operational constraints of DERs and representative data provided by the DNO, circumventing the need for detailed network information. On the other hand, day-ahead and real-time correction procedures for the DER cost functions are proposed, effectively neutralizing the impact of network operational constraints on these cost functions. Consequently, precise cost functions for both the active power and the flexible regulation power aggregated by the VPP are derived. Employing this aggregated cost function enables the determination of a cost-minimized optimal scheduling solution in real-time by solving a fundamental economic dispatch problem, significantly alleviating computational demands. Finally, case studies demonstrate that the proposed method achieves an error in aggregated power of only 0.77%, compared to the precise computation method that requires comprehensive system information. The proposed optimal VPP disaggregation scheme exhibits power discrepancies of 0.63% and cost discrepancies of 0.91% relative to the precise method. Additionally, when implementing the most cost-effective demand response plan based on the proposed cost function, the average costs for aggregators are reduced by 19.7%
Optimal Aggregation Method of a Virtual Power Plant Based on a Nash-Stackelberg Game
No full textThe aggregation of massive heterogeneous distributed energy resources (DERs) is a crucial challenge in the optimal operation of a virtual power plant (VPP). To effectively exploit the flexibility and economy of DERs, this study proposed a novel method to aggregate DERs belonging to different stakeholders into a VPP based on a Nash-Stackelberg game. The DER-based generators act as leaders in the game and decide their output to maximize profits, while the VPP acts as a follower on the lower level to maximize the profit in the market. Moreover, the network constraints and uncertainties are considered in the lower model. Subsequently, a method to find the Pareto-optimal equilibrium points is proposed. The bi-level model can be transformed into a single-level model via the Karush-Kuhn-Tucker conditions. Thus, the proposed Nash-Stackelberg game model is transformed into a non-cooperative multi-objective optimization problem. Furthermore, the Nash equilibrium point can be obtained by the modified column-and-constraint generation algorithm. Finally, case studies demonstrated that the method can efficiently find the Nash equilibrium solution of the VPP aggregation model and provide more comprehensive Nash equilibrium points than other methods. Moreover, the distribution of Nash equilibrium points can be used to guide the dispatching scheme of the VPP
A long-term congestion management framework through market zone configuration considering collusive bidding in joint spot markets
No full textThe zonal market (ZM) adopted in Europe, in contrast to the nodal market (NM), reconciles the inconsistency between physical networks and administrative management. However, the growing integration of renewable energy sources (RESs) has introduced zonal supply-demand imbalances that exacerbate congestion and the need to re-dispatch. Furthermore, different clearing mechanisms between the day-ahead and real-time markets provide further opportunities for collusive bidding, decreasing total social welfare (TSW). Thus, this paper is the first to propose a long-term congestion management (CM) framework through a market zone (MZ) configuration approach with CM assessment considering collusive bidding in the joint spot markets. More specifically, a topology-based location division (TLD) method is proposed to partition optimal MZs, ensuring the minimum number of MZs based on critical branches. Then, a bi-level evolutionary model is developed to analyze the collusive bidding of producers in the day-ahead and ancillary service markets. Finally, the established framework is applied to a 20-bus test and simplified European systems. Our simulation on the 20-bus system shows that compared with the initial ZM and NM, the congestion cost of the optimized ZM decreased by 90% and 33%, respectively, while the TSW increased by around 13% and 1%, respectively
Market zone configuration under collusive bidding among the conventional generators and renewable energy sources in the day-ahead electricity market
No full textThe European cross-zonal day-ahead (DA) electricity market is transitioning to the flow-based market coupling model for market clearing. With the increasing integration of renewable energy sources (RESs), market participants have opportunities for collusive bidding, resulting in decreased social welfare (SW). Thus, this paper is the first to propose an approach to configure the market zone (MZ) considering collusive bidding among conventional generators (CGs) and RESs in the DA market. Specifically, a bi-level model is developed to analyze collusive bidding among the CGs and RESs. Then, multi-dimensional market performance indices are used to determine the critical branches (CBs), on which the configuration of MZs is based. Finally, test 6-bus and simplified European systems are used to demonstrate the validity and merit of the proposed approach. Our simulation on the 6-bus system shows that when compared with the initial zonal market (ZM), the SW of the optimized ZM increased by 18 %, while the re-dispatch surrogate cost decreased to 0. Also, the penetration of RESs improved by 12 %, which guarantees the development of RESs
Optimal aggregation of a virtual power plant based on a distribution-level market with the participation of bounded rational agents
No full textVirtual power plants (VPPs) offer system flexibility by aggregating various distributed energy resources (DERs) and simultaneously create profit opportunities for these DERs. A fair and scientific operational model serves as a crucial guarantee for promoting the economically efficient operation of VPPs. Given that DERs are typically managed by various agents, this study introduces a multi‑leader single-follower Nash-Stackelberg game model. This model is designed to facilitate the optimal aggregation of DER agents in a competitive distribution-level market involving multiple players. In the optimization modeling, the DER agents function as leaders, formulating their bidding strategies to maximize profits. Conversely, the VPP acts as a follower, responsible for performing market clearing. The distributed locational marginal price derived from this process serves as the settlement basis for DERs. Furthermore, a level-k reasoning approach is used to simulate the strategic bidding behavior of agents. Case studies demonstrate the effectiveness of the proposed aggregation model in simulating the competitive dynamics among agents. This model offers an expanded set of Nash equilibrium solutions for VPPs, enabling the selection of suitable aggregation schemes tailored to practical requirements. Additionally, the proposed bounded rationality model mitigats the strategic bidding behavior of agents, which consequently leads to a reduction in the system cost.This work was supported by the National Natural Science Foundation of China under Grant U1966204
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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