1,720,989 research outputs found
Laser Powder Bed Fusion of AlSi10Mg+4Cu and AlSi10Mg alloys
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Effect of State Feedback Coupling on the Design of Voltage Source Inverters for Standalone Applications
Full text linkThis Ph.D. thesis aims at investigating the effect of state feedback cross‐coupling decoupling of the capacitor voltage on the dynamics performance of Voltage Source Inverters for standalone microgrids/Uninterruptible Power Supply systems. Computation and PWM delays are the main factors which limit the achievable bandwidth of current regulators in digital implementations. In particular, the performance of state feedback decoupling is degraded because of these delays. Two decoupling techniques aimed at improving the transient response of voltage and current regulators are investigated, named nonideal and ideal capacitor voltage decoupling respectively. In particular, the latter solution consists in leading the capacitor voltage on the state feedback decoupling path in order to compensate for system delays. Practical implementation issues are discussed with reference to both the decoupling techniques. Moreover, different resonant regulators structures for the inner current loop are analysed and compared to investigate which is the most suitable for standalone microgrid applications. A design methodology for the voltage loop, which considers the closed loop transfer functions developed for the inner current loop, is also provided. Proportional resonant voltage controllers tuned at specific harmonic frequencies are designed according to the Nyquist criterion taking into account application requirements. For this purpose, a mathematical expression based on root locus analysis is proposed to find the minimum value of the resonant gain at the fundamental frequency. The exact model of the output LC filter of a three‐phase inverter is derived in the z‐domain. The devised formulation allows the comparison of two techniques based on a lead compensator and Smith predictor structure. These solutions permit the bandwidth of the current regulator to be widened while still achieving good dynamic performance. As a consequence, the voltage regulator can be designed for a wide bandwidth and even mitigates odd harmonics arising with unbalance loads supply. Discrete‐time domain implementation issues of an anti‐wind up scheme are discussed as well, highlighting the limitations of some discretization methods. Experimental tests performed in accordance to Uninterruptible Power Supply standards verify the theoretical analysis
Thermoeconomic analysis of a Compressed Air Energy Storage (CAES) system integrated with a wind power plant in the framework of the IPEX Market
No full textEnergy storage is regarded as a key factor to allow significant increase in the percentage of electricity generation from renewables. One of the most critical aspects related with energy storage is its economic feasibility, which intrinsically involves the analysis of the off-design conditions and the evaluation of the operating strategies using proper methodologies. This paper considers a promising system for mechanical energy storage constituted by a Compressed Air Energy Storage (CAES) integrated with a Hybrid Power Plant (HPP) and coupled with a wind farm. This system is modeled considering the South of Italy as the possible location. The HPP-CAES is simulated to operate on the Italian Power Exchange market, for one year, implementing suitable selling strategies. Cost analysis is performed using a thermoeconomic approach. Results show that reduced operating hours and large variations in the electricity production of the wind farm make the HPP-CAES cost-effective only when it is operated with the goal of solving local imbalances of the grid
Sistemi di accumulo: tipologie e applicazioni
No full textNell'articolo vengono descritti e confrontati diversi sistemi di accumulo dell'energia elettrica per applicazioni stazionarie. Essi sono in grado di fornire molteplici servizi di rete con lo scopo di garantire i livelli di adeguatezza, sicurezza e affidabilità antecedenti l'elevata penetrazione della generazione distribuit
A model for the evaluation of thermal and electric energy consumptions in residential buildings: The case study in Torino (Italy)
No full textThis work analyzes the thermal and electrical consumptions of residential buildings located in the town of Turin (northwest Italy). The aim is to create mathematical models to evaluate monthly behavior of energy consumption as a function of two predictable variables. In the evaluation of the different variables, two climatic data were chosen: the monthly average temperature and the monthly average daily solar irradiation. Two multiple linear regression models have been determined, one using standardized variables to evaluate how climatic data influence thermal and electric energy consumptions in residential buildings. The fields of application of these models can be: the evaluation of monthly energy-use data knowing the annual value with the construction of seasonal trends, the prediction of monthly energy-use data knowing the weather forecast, the management of the buildings' energy consumptions to optimize the heating or electric networks for more future expansion in urban contests. After an initial state of the art review, the case study of Torino is presented, with more than 2700 users for the electric consumptions and 130 residential condominiums. A selection of the users was made to consider an homogeneous set of users and finally the models were developed with about 1200 electric users and 100 condominiums. The results show good correlations between energy consumption and climatic data, especially with the air temperature. For electrical consumption the monthly variation is limited compared with thermal energy-use, for both the seasonal patterns obtained have a deviation of less than 5% between calculated and real consumptions
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
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