1,721,011 research outputs found
Designing Inverters’ Current Controllers with Resonance Frequencies Cancellation
No full textThis paper presents an innovative and effec-tive linear current regulator for grid-connected convertersinterfaced by an LCL filter. The proposed scheme entailsthe use of voltages measured at the terminals of the out-put filter capacitors as feedforward signals to be includedin a classical structure of proportional–resonant (PR) con-troller. Processing these signals by an opportune filterK(s), the resonance effects characterizing the LCL filter areneutralized and the impact of the grid impedance’s varia-tions on the converter’s performances is greatly reduced.The proposed solution simplifies the controller’s design,whose gains are obtained by a straightforward mathemat-ical formula which prevents complex root locus analyses.Moreover, for a given phase margin, the proposed tech-nique ensures the achievement of maximum possible band-width of closed-loop system, sidestepping the guessworktypical of the conventional methods used for selectingthe crossover frequency. Conclusions are supported by adetailed mathematical analysis and validated by laboratoryresults obtained with a 7.5-kW three-phase inverter proto-type connected t
Extensive assessment of virtual synchronous generators in intentional island mode
No full textVirtual Synchronous Generators (VSGs) are considered one of the most effective cutting-edge technologies for seamlessly integrating Renewable Energy Systems (RESs) into power grids. While various VSG control schemes have been proposed and analysed for different technical aspects, not many experimental demonstrations have been published about VSGs operating in Intentional Island Mode (IIM). Inversely, the IIM has become increasingly attractive, nowadays, to energize those remote areas of the world where entire districts are served by a small number of RESs operating off-grid. In this scenario, the main objective of this paper is to present an extensive performance assessment of the VSG operating in IIM. Different working conditions are considered, with special focus on: black start capability, grid-connected-to-IIM transition, grid reconnection, feeding of non-linear and asymmetric local loads, load sharing between multiple VSGs operating in parallel. In order to achieve this objective, an improved structure of VSG is implemented on 8kVA three-phase converters and significant experimental results are presented. Algorithms for black start capability and grid synchronization are illustrated in detail as well. Meaningful information is provided for engineers involved in activity of designing and testing islanded VSGs
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Smart Operation of Wind Turbines and Diesel Generators According to Economic Criteria
No full textThis paper proposes an innovative system for Smart Grid (SG) management aiming at minimizing the total costs supported for carrying out the delivery of energy to consumers. These costs include the production costs of distributed generators, the cost of the power provided by the primary substation, and the cost associated with grid power losses. After a brief overview on the main SG aspects, this paper describes the proposed approach that makes use of an optimal power flow algorithm and the active management schemes. The efficiency of the method is verified on a distribution system comprising wind turbines and diesel generators, considering the time-varying characteristics of the load demand and wind power generation
Smart Grids Operation with Distributed generation and Demand Side Management
No full textThe integration of Distributed Generation (DG) based on renewable
sources in the Smart Grids (SGs) is considered a challenging task because of the
problems arising for the intermittent nature of the sources (e.g. wind or sun), only
partly predictable. Another important issue concerning the design of SGs is how to
support the consumers’ participation in the electricity market minimizing the costs
of the global energy consumption. This chapter proposes an Energy Management
System for SGs using Optimal Power Flow and integrating the demand side man-
agement mechanism and the active management schemes for the optimization of a
SG in a competitive power market. The idea is that they can achieve a better inte-
gration of different types of DG improving flexibility while reducing the costs of
energy for customers. The efficiency of the proposed technique is verified on a 19-
bus 11 kV distribution network
Experimental evaluation of virtual synchronous generators with high regulation performance to enhance AC–DC grid interconnections
No full textIn the recent years there has been a significant increase in the interest surrounding the interconnection of AC and DC networks due to its potential to improve the power systems reliability. Despite the potential advantages, however, the AC and DC grid coexistence can pose challenges if not appropriately managed. In this scenario, this paper presents an enhanced control scheme enabling the use of Virtual Synchronous Generators (VSGs) as elements of interconnection between AC and DC networks. The proposed solution enables VSG operation with both fast dynamics for DC voltage regulation and slow dynamics for AC inertia emulation. This approach accommodates the contrasting requirements arising from the distinct mechanisms of DC voltage regulation and AC frequency regulation. Simulation and experimental results obtained with a 8 kVA three-phase converter prototype are provided to validate the effectiveness of the proposed technique and prove its better performances with respect to the solutions currently presented in literature
COMBINED OPERATION OF RENEWABLE ENERGY SYSTEMS AND RESPONSIVE DEMAND IN A SMART GRID
No full textThe integration of renewable energy systems (RESs) in smart grids (SGs) is a challenging task, mainly due to the in-
termittent and unpredictable nature of the sources, typically wind or sun. Another issue concerns the way to support the consumers’
participation in the electricity market aiming at minimizing the costs of the global energy consumption. This paper proposes an energy management system (EMS) aiming at optimizing the SG’s operation. The EMS behaves as a sort of aggregator of distributed energy resources allowing the SG to participate in the open market.
By integrating demand side management (DSM) and active man-agement schemes (AMS), it allows a better exploitation of renewable energy sources and a reduction of the customers’ energy con-
sumption costs with both economic and environmental benefits. It can also improve the grid resilience and flexibility through the active participation of distribution system operators (DSOs) and electricity supply/demand that, according to their preferences and
costs, respond to real-time price signals using market processes.
The efficiency of the proposed EMS is verified on a 23-bus 11-kV
distribution network
Variations on the Author
Get PDF“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
Get PDFWe 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
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