1,720,995 research outputs found
Node Type Distribution and Its Impacts on Performance of Power Grids
Full text linkThe theory of complex networks has been studied extensively since its inception. However, until now, the impact of the node-type distributions is related to network topology and cannot be evaluated independently. In this paper, a network structure is modeled via an adjacency matrix (network topology) and a set of node type distribution vectors. Three specific issues that need to be considered for node type distributions in smart grid testing and planning are summarized in this paper. First, a set of metrics are proposed and defined to evaluate the impact of node-type distributions on network performance independently. Second, another metric named the generation distribution factor is proposed to evaluate the distribution of generation buses resulting from the specific function and purpose of power grids and by considering the distribution of load buses as given conditions. Third, another metric, i.e., the power supply redundancy metric based on entropy, is proposed to evaluate the inequality of load in power supply. Finally, a discrimination factor is defined to ensure the overall evaluation and comparison of different networks is made for this inequality. All proposed metrics can be applied to the IEEE-30, IEEE-118, IEEE-300 bus systems, as well as Italian power grid components. The simulation results indicate that the IEEE-118 system has the best node type distribution and minimum discrimination; the Italian system has the worst node-type distribution and most serious discrimination of load power supply
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
Electric Vehicle Energy Management Considering Stakeholders' Interest in Smart Grids
Full text linkWith the electrification in transportation systems, Electric Vehicles (EVs) have developed
rapidly in recent years. At the same time, with large-scale EV integration to power
grids, the charging behaviours of EVs bring both challenges and opportunities to power
grids operation. This thesis focuses on the EV energy management in smart grids, and
the EV energy management problem is studied considering three stakeholders' interests,
i.e. EV owner, aggregator and grid, respectively.
First, the economic relationship between EV owners and the aggregator is studied
(EV owners' and aggregator's interest). Two multi-objective optimisation methods are
applied to investigate the economic relationship between these two stakeholders and the
aggregator{owner economic inconsistency issue is presented. To mediate this issue, a
rebate factor is proposed in the model. The results show that a signi cant reduction in
the EV owners' charging fee from self-scheduling can be achieved while the aggregator
pro t is maximised.
Second, the EV aggregator bidding strategy in the electricity market is studied
(aggregator's interest). By jointly considering the reserve capacity in the day-ahead
market and the uncertainty of reserve deployment requirements in the real-time market,
a scenario-based stochastic programming method is used to maximise the expected
aggregator pro t. The risk of the deployed reserve shortage is addressed by introducing
a penalty factor in the model. In addition, an owner{aggregator contract is designed to
mitigate the economic inconsistency issue between EV owners and the aggregator. The
results show that the expected aggregator pro t is guaranteed by maximising reserve deployment payments and mitigating the penalties and thus the uncertainty of the
reserve market is well managed.
Third, the EV integration in a transmission system is studied (grid's interest) to
achieve the coordination between generators and EVs. To tackle the challenge of
large-scale EV integration problem, a bi-level scheduling strategy is proposed. The
bi-level strategy clearly de nes the responsibility of transmission system operator and
the aggregator. An EV information grouping method is designed, which could e ciently
tackle the optimisation complexity problem. In addition, a detailed EV battery charging
model is built. The results show that the total cost of the systems is minimised and
EVs could shave the peak and ll the valley loads.
This thesis discusses the EV energy management problem considering three stakeholders'
interests, respectively. The proposed strategies in this thesis clearly evaluate
and de ne the economic relationships and responsibility among EV owners, aggregator
and the grid in managing EV charging and discharging behaviours. Based on three case
studies conducted in this thesis, EV energy management could bene t the stakeholders
as follows: (1) the EV owner charging fee is minimised while their driving requirements
are satis ed; (2) the aggregator pro t is maximised by participation in the electricity
market; (3) the cost of the system is minimised by achieving the coordination between
EVs and generators
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
Integrated network partitioning and DERs allocation for planning of Virtual Microgrids
Full text linkThe Virtual Microgrid (VM) method is a solution for addressing challenges in Conventional Distribution Network (CDN), such as power fluctuations or load mismatches, by actively partitioning the CDN into interconnected Microgrid-style VMs. Previous studies have fewer discussions about the mutual interaction between the grid's partition performance and Distributed Energy Resources (DERs) allocation. This paper proposes a new approach for dividing a large power grid into clusters by using the complex network theorem. The approach integrates power flow dynamic, line impedance, generator-load relations and power generator cost-efficiency into a single static weighted adjacency matrix. Meanwhile, a multi-objective Genetic Algorithm (GA) planning structure is also denoted for transforming a CDN to VMs with mutual interaction between partition and DER allocation. The proposed metric is tested in both transmission and distribution networks. The IEEE 118-bus system test shows that even with a higher value of the proposed indicator, there are fewer power exchanges between sub-networks. Meanwhile, in the 69-bus radial system tests, the GA-based co-planning method outperforms previous methods in forming more self-sufficient and more efficient interconnected VMs. An intermediate solution is suggested by implementing a trade-off between inter-VM power exchange and the operation cost
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
Interrelation of structure and operational states in cascading failure of overloading lines in power grids
No full textAs the modern power system is expected to develop to a more intelligent and efficient version, i.e. the smart grid, or to be the central backbone of energy internet for free energy interactions, security concerns related to cascading failures have been raised with consideration of catastrophic results. The researches of topological analysis based on complex networks have made great contributions in revealing structural vulnerabilities of power grids including cascading failure analysis. However, existing literature with inappropriate assumptions in modeling still cannot distinguish the effects between the structure and operational state to give meaningful guidance for system operation. This paper is to reveal the interrelation between network structure and operational states in cascading failure and give quantitative evaluation by integrating both perspectives. For structure analysis, cascading paths will be identified by extended betweenness and quantitatively described by cascading drop and cascading gradient. Furthermore, the operational state for cascading paths will be described by loading level. Then, the risk of cascading failure along a specific cascading path can be quantitatively evaluated considering these two factors. The maximum cascading gradient of all possible cascading paths can be used as an overall metric to evaluate the entire power grid for its features related to cascading failure. The proposed method is tested and verified on IEEE30-bus system and IEEE118-bus system, simulation evidences presented in this paper suggests that the proposed model can identify the structural causes for cascading failure and is promising to give meaningful guidance for the protection of system operation in the future
Structural Evaluation for Distribution Networks with Distributed Generation Based on Complex Network
Full text linkStructural analysis based on complex network theory has been considered promising for security issues of power grids. At the same time, modern power distribution networks with more Distributed Generations (DGs) and Energy Storage Systems (ESS) have taken on more challenges in operation and security issues. This paper proposed a dedicated metric named as Power-Supply-Ability for power distribution networks based on net-ability. Special features of DGs, such as relations of capacities, identification of effective supply area, and limitation in continuous power supply, have been considered in definition. Furthermore, a novel opinion is proposed that the extent of improvement for operation and security by adding DGs also depends on the original structure of the distribution networks. This is an inherent ability of the original networks and could be quantitatively analyzed. Through case studies, this method has been proved to be effective in identifying potential structural vulnerabilities of distribution networks; particularly the impact of DGs on security has been studied. Furthermore, it can help in site selection for DGs by providing different priorities of locations compared with results of other works. This can help to complement other methods to construct a more comprehensive methodology by considering aspects of security, economy, and quality
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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