| 1. |
- de Jong, R. S., et al.
(författare)
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4MOST : Project overview and information for the First Call for Proposals
- 2019
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Ingår i: The Messenger. - : European Southern Observatory. - 0722-6691. ; 175, s. 3-11
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We introduce the 4-metre Multi-Object Spectroscopic Telescope (4MOST), a new high-multiplex, wide-field spectroscopic survey facility under development for the four-metre-class Visible and Infrared Survey Telescope for Astronomy (VISTA) at Paranal. Its key specifications are: a large field of view (FoV) of 4.2 square degrees and a high multiplex capability, with 1624 fibres feeding two low-resolution spectrographs (R = λ/Δλ ~ 6500), and 812 fibres transferring light to the high-resolution spectrograph (R ~ 20 000). After a description of the instrument and its expected performance, a short overview is given of its operational scheme and planned 4MOST Consortium science; these aspects are covered in more detail in other articles in this edition of The Messenger. Finally, the processes, schedules, and policies concerning the selection of ESO Community Surveys are presented, commencing with a singular opportunity to submit Letters of Intent for Public Surveys during the first five years of 4MOST operations.
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| 2. |
- Cipriani, G., et al.
(författare)
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A Procedure for the Producibility Curve Identification of a Dish-Stirling Plant, Starting from Experimental Data
- 2019
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Ingår i: Proceedings - 2019 IEEE International Conference on Environment and Electrical Engineering and 2019 IEEE Industrial and Commercial Power Systems Europe, EEEIC/I and CPS Europe 2019.
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Konferensbidrag (refereegranskat)abstract
- This article presents a procedure for the producibility curve identification of a dish-Stirling plant, starting from experimental data. The producibility data was measured, recorded, analysed, filtered and monthly aggregated. Moreover, the incidence of the ambient temperature and of the mirrors cleaning on producibility data is highlighted and a procedure to normalize the measured data in temperature and cleaning level was developed. To provide a validation of the developed procedure the producibility curves at 25 °C have been obtained and compared with the one issued by the manufacturer. The two curves are in good agreement, presenting a maximum deviation of the 7 %.
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| 3. |
- Bongiorno, Massimo, 1976, et al.
(författare)
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Inertial response of isolated power networks with wind power plants
- 2019
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Ingår i: 2019 IEEE Milan PowerTech, PowerTech 2019.
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Konferensbidrag (refereegranskat)abstract
- The constant increase of power generation provided by renewable energy source (RES) power plants is causing a progressive reduction of the overall inertia of the power systems. Especially in the case of small, isolated power networks, the replacement of conventional generation plants with RES power plants can affect significantly the frequency response of the system. The critical low-inertia conditions can be improved by the introduction of specific additional controls to the RES power converters. These control schemes are known as 'synthetic inertia' or 'virtual inertia' controls. The paper analyzes the impact of a derivative-based inertial control on a small, isolated power system, with a relevant share of power supplied by a wind power plant. The inertial response control is added to the standard IEC wind turbine active power controller of type WT4A. Simulations performed on the dynamic model of the system indicate the appearance of frequency oscillations in response to the applied power unbalance. A comprehensive analysis of the observed phenomenon is given, and a tuning of the inertial control parameters is then proposed. Simulations repeated with the proposed tuning of the controller prove the validity of the applied modifications, and show a satisfactory transient response of the system, even in the case of critical low-inertia conditions.
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| 4. |
- Favuzza, S., et al.
(författare)
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An Analysis of the Intertial Response of Small Isolated Power Systems in Presence of Generation from Renewable Energy Sources
- 2018
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Ingår i: 2018 IEEE 4th International Forum on Research and Technology for Society and Industry (RTSI). - 9781538662823
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Konferensbidrag (refereegranskat)abstract
- Renewable Energy Sources are posing critical issues related to the mining of power systems stability, essentially due to a decrement of the inertial response during system's contingencies. As a consequence, to preserve the security and the reliability of the system, it is necessary to adopt new frequency adjustments mechanisms. This issue becomes particularly critical in isolated power systems, like those of small islands not supplied by the main grid, in the case of high shares of production from unpredictable renewabies such as photovoitaic and wind sources. In this framework, the present work deals with the analysis of the variation of the inertia time constant of a small island in various scenarios characterized by a different share of renewable energy. The study represents the first step of a more extended feasibility study for the conversion of a traditional power system based on fossil fuel towards a renewable energy-based power system.
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| 5. |
- Favuzza, S., et al.
(författare)
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System Stability of a Small Island's Network with Different Levels of Wind Power Penetration
- 2018
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Ingår i: 2018 IEEE 4th International Forum on Research and Technology for Society and Industry (RTSI). - 9781538662823
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Konferensbidrag (refereegranskat)abstract
- The reduction of the inertial response of the generation system has been one of the main obstacles to the penetration of high sharing of renewable energy sources in islanded systems. This issue can be solved thanks to innovative control that makes wind turbines able to provide the so-named synthetic inertia. The paper investigates some scenarios with different levels of wind power penetration in a small island whose grid is not supplied by the main grid, by the use of the software NEPLAN 360, simulating the wind power plants accordingly to the standard IEC 61400-27. The aim of the paper is to assess the maximum level of penetration in the island of wind generation, with traditional control systems, that does not threaten the stability of the system.
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| 6. |
- Pierre, M., et al.
(författare)
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The XXL survey : First results and future
- 2017
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Ingår i: Astronomical Notes - Astronomische Nachrichten. - : Wiley-VCH Verlagsgesellschaft. - 0004-6337 .- 1521-3994. ; 338:2-3, s. 334-341
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Tidskriftsartikel (refereegranskat)abstract
- The XXL survey currently covers two 25 deg(2) patches with XMM observations of similar to 10 ks. We summarize the scientific results associated with the first release of the XXL dataset, which occurred in mid-2016. We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z < 2) cluster, (z < 4) active galactic nuclei (AGN), and cosmic background survey science will then benefit from an extraordinary data reservoir. This, combined with deep multi-lambda observations, will lead to solid standalone cosmological constraints and provide a wealth of information on the formation and evolution of AGN, clusters, and the X-ray background. In particular, it will offer a unique opportunity to pinpoint the z > 1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions.
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| 7. |
- Pierre, M., et al.
(författare)
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The XXL Survey I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Tidskriftsartikel (refereegranskat)abstract
- Context. The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum. Over the past two decades, the Chandra and XMM-Newton observatories have supported numerous studies of X-ray-selected clusters of galaxies, active galactic nuclei (AGNs), and the X-ray background. The present paper is the first in a series reporting results of the XXL-XMM survey; it comes at a time when the Planck mission results are being finalised. Aims. We present the XXL Survey, the largest XMM programme totaling some 6.9 Ms to date and involving an international consortium of roughly 100 members. The XXL Survey covers two extragalactic areas of 25 deg(2) each at a point-source sensitivity of similar to 5 x 10(-15) erg s(-1) cm(-2) in the [0.5-2] keV band (completeness limit). The survey's main goals are to provide constraints on the dark energy equation of state from the space-time distribution of clusters of galaxies and to serve as a pathfinder for future, wide-area X-ray missions. We review science objectives, including cluster studies, AGN evolution, and large-scale structure, that are being conducted with the support of approximately 30 follow-up programmes. Methods. We describe the 542 XMM observations along with the associated multi-lambda and numerical simulation programmes. We give a detailed account of the X-ray processing steps and describe innovative tools being developed for the cosmological analysis. Results. The paper provides a thorough evaluation of the X-ray data, including quality controls, photon statistics, exposure and background maps, and sky coverage. Source catalogue construction and multi-lambda associations are briefly described. This material will be the basis for the calculation of the cluster and AGN selection functions, critical elements of the cosmological and science analyses. Conclusions. The XXL multi-lambda data set will have a unique lasting legacy value for cosmological and extragalactic studies and will serve as a calibration resource for future dark energy studies with clusters and other X-ray selected sources. With the present article, we release the XMM XXL photon and smoothed images along with the corresponding exposure maps.
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| 8. |
- Romano, P., et al.
(författare)
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The Effect of the Harmonic Content Generated by AC/DC Modular Multilevel Converters on HVDC Cable Systems
- 2019
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. ; 2019-October, s. 666-669
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Konferensbidrag (refereegranskat)abstract
- With the increasing penetration of renewable and decentralized energy sources into the power grid, an extended use of DC voltages is expected on both distribution and transmission levels. Generation of DC voltages by means of voltage source converters is associated with a wide spectrum of harmonic distortions at converter terminals, both on the ac and on the dc sides. This can lead to partial discharges in power cables, which deteriorate insulation material thus weakening its performance and reducing cable life-time. In the previously published paper, the effect of harmonic distortion on appearance of partial discharges in cable insulation was evaluated. Here, the study related to the PD behavior has been made focusing on the influence of multilevel converter parameters such as the number of submodules and the switching frequency chosen to generate different voltage stresses. In addition, effects of using a function generator for producing desired waveform instead of the dSPACE board as in the previous work, are highlighted. In particular, it is shown implementation of the former made it possible utilizing the Pry-Cam synchronization and thus the realization of the PD pattern.
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| 9. |
- Chernet, Selam, 1984, et al.
(författare)
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Online variation of wind turbine controller parameter for mitigation of SSR in DFIG based wind farms
- 2017
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Ingår i: ECCE 2016 - IEEE Energy Conversion Congress and Exposition, Proceedings. - 2329-3721. - 9781509007370 ; , s. Article no 7855310-
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Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to investigate the risk for Subsynchronous Resonance (SSR) conditions in Doubly Fed Induction Generator (DFIG) based wind farms connected to series-compensated transmission lines. The well-known IEEE First Benchmark Model for SSR studies is adopted and the impact of the turbine controller parameters on the risk for unstable conditions is analyzed. In particular, it is shown through frequency domain studies that a reduction of the closed-loop bandwidth of the current controller that regulates the rotor current effectively reduces the risk for SSR. Simulation results are presented to validate the theoretical findings.
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| 10. |
- Grazian, A., et al.
(författare)
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Lyman continuum escape fraction of faint galaxies at z similar to 3.3 in the CANDELS/GOODS-North, EGS, and COSMOS fields with LBC
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 602
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Tidskriftsartikel (refereegranskat)abstract
- Context. The reionization of the Universe is one of the most important topics of present-day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the H I ionizing background at z greater than or similar to 3. Aims. We measure the Lyman continuum escape fraction, which is one of the key parameters used to compute the contribution of star-forming galaxies to the UV background. It provides the ratio between the photons produced at lambda <= 912 angstrom rest-frame and those that are able to reach the inter-galactic medium, i.e. that are not absorbed by the neutral hydrogen or by the dust of the galaxy's inter-stellar medium. Methods. We used ultra-deep U-band imaging (U = 30.2 mag at 1 sigma) from Large Binocular Camera at the Large Binocular Telescope (LBC/LBT) in the CANDELS/GOODS-North field and deep imaging in the COSMOS and EGS fields in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27 <= z <= 3.40 to faint magnitude limits (L = 0.2L*, or equivalently M-1500 similar to -19). The narrow redshift range implies that the LBC U-band filter exclusively samples the lambda <= 912 angstrom rest-frame wavelengths. Results. We measured through stacks a stringent upper limit (<1.7% at 1 sigma) for the relative escape fraction of H I ionizing photons from bright galaxies (L > L*), while for the faint population (L = 0.2L*) the limit to the escape fraction is less than or similar to 10%. We computed the contribution of star-forming galaxies to the observed UV background at z similar to 3 and find that it is not sufficient to keep the Universe ionized at these redshifts unless their escape fraction increases significantly (>= 10%) at low luminosities (M-1500 >= -19). Conclusions. We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature, and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental in order to measure the Lyman continuum escape fraction down to faint magnitudes (M-1500 similar to -16) that are inaccessible with the present instrumentation on blank fields. These results will be important in order to quantify the role of faint galaxies to the reionization budget.
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| 11. |
- Tsolaridis, G., et al.
(författare)
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Losses and cost comparison of DS-HB and SD-FB MMC based large utility grade STATCOM
- 2016
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Ingår i: 16th International Conference on Environment and Electrical Engineering, EEEIC 2016, Florence, Italy, 7-10 June 2016. - 9781509023196
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Konferensbidrag (refereegranskat)abstract
- Among the various multilevel converter topologies used in medium and high voltage grid applications, the Modular Multilevel Converter (MMC) has been the most promising since it combines good harmonic performance with low switching frequency and high reliability. A major concern however for inverter designers has been the associated cost due to the need for a large number of power devices and capacitors. This paper focuses on the application of MMC in transformer-less STATic synchronous COMpensators (STATCOMs). Initially, the double-star half bridge (DS-HB) and the single-delta full bridge (SD-FB) configurations are presented. Their specific components are designed in an analytical way followed by loss estimation. Finally, a comparison of the necessary components gives an insight of the total cost associated with each configuration.
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