1,721,370 research outputs found
A novel ramp-rate control of grid-tied PV-Battery systems to reduce required battery capacity
Full text linkThis paper proposes a novel ramp-rate control of PV-battery systems in microgrids, including the coordination and control of time-varying loads. The power consumed by the loads is part of regulation strategy and participates in mitigating the overall ramp-rate of the controlled PV system and the loads. The control strategy is grid-friendly as the power fluctuation of the loads is also considered besides that of the PV system. Furthermore, this control strategy economizes on the number and size of auxiliary batteries that tipically are considered combined with PV system, since a part of the required active power is now borrowed from the loads. Combined to the load control a ramp-rate control, based on the virtual synchronous generator technology, is originally proposed to further reduce the use of the batteries and to provide innovative ancillary service. Finally numerical simulations on a test microgrid indicate the effectiveness of the proposed ramp-rate control. The test cases also demonstrate that this control strategy succeeds in reducing the battery capacity and the number of (dis)charge cycles as well as in offering frequency support to the microgrid
Ancillary service with grid connected PV: A real-time hardware-in-the-loop approach for evaluation of performances
Full text linkThe integration of photovoltaic (PV) systems with the grid is undoubtedly an issue of great interest both in terms of energy production, but also as a support to the grid as an ancillary service, but to evaluate the performance of the use of PV in an unconventional way, it is necessary to have reference models to be applied to evaluate the characteristics and integration requirements. In this work, an ancillary service provided by a grid-connected PV is shown and a hardware in the loop simulation environment is created to simulate performances and integration issues
Modelling of Photovoltaic Systems for Real-Time Hardware Simulation
Full text linkThe real-time simulation is a valid help to test electrical systems when a physical device is not available. This is significantly evident when used in hardware and software co-simulation environment, where it is possible to connect the emulator to a real subsystem to test or validate it. In this paper, a model of the photovoltaic system is presented that can be implemented within a hardware simulator to be able to interface it with a real circuit, the hardware simulator used is the National Instruments RIO system
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
Reactive power injection to mitigate frequency transients using grid connected PV systems
Full text linkThe increasing integration of renewable energies reduces the inertia of power systems and thus adds stiffness to grid dynamics. For this reason, methods to obtain virtual inertia have been proposed to imitate mechanical behavior of rotating generators, but, usually, these methods rely on extra power reserves. In this paper, a novel ancillary service is proposed to alleviate frequency transients by smoothing the electromagnetic torque of synchronous generators due to change of active power consumed by loads. Being implemented by grid-tied inverters of renewables, the ancillary service regulates the reactive power flow in response to frequency transients, thereby demanding no additional power reserves and having little impact on renewables' active power generation. Differently from the active power compensation by virtual inertia methods, it aims to low-pass filter the transients of the active power required to synchronous generators. The proposed ancillary service is firstly verified in simulation in comparison with the virtual inertia method, and afterwards tested on processor by controller-hardware-in-the-loop simulation, analysing practical issues and providing indications for making the algorithm suitable in real implementation. The ancillary service proves effective in damping frequency transients and appropriate to be used in grid with distributed power 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
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
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