A Full Order Sensorless Control Adaptive Observer for Doubly-Fed Induction Generator

This paper presents a sensorless control for a Doubly Fed Induction Generator (DFIG) in the context of grid-connected turbine-based wind generation systems. The paper proposes a full order adaptive observer able to track with excellent accuracy the DFIG rotor position even in presence of significant parameters deviations. The developed adaptive observer is coupled with a traditional stator flux based Field Oriented Control (FOC). The novel approach has been validated by an extensive numerical analysis

Doubly-Fed Induction Generator (DFIG) in Connected or Weak Grids for Turbine-Based Wind Energy Conversion System

In the last thirty years the quantity of wind electricity generation has grown significantly due to its high-power density. Advances in wind energy technology have significantly decreased the cost of producing electricity from this renewable source. Nowadays, the generation of energy from wind sources plays a crucial role to increasing the green energy. In this context, wind energy conversion systems (WEC) must guarantee, in connected or weak grid operation, good stability in balanced or unbalanced conditions, high efficiency, high reliability and maximum power tracking in order to achieve the best performance when operating conditions vary

Tecniche di controllo ottimizzate, monitoraggio parametrico e diagnostica per azionamenti PM brushless mono e plurimotore

Nel presente elaborato si affronta il problema del controllo di azionamenti utilizzanti motori brushless a magneti permanenti, sia in configurazione classica che pluri-motore, e con particolare riguardo ai sistemi di monitoraggio parametrico e di diagnostica. A seguito di una prima parte descrittiva si andrà a caratterizzare il modello matematico della macchina PM brushless, presentando le strategie di controllo tradizionali ad orientamento di campo, gli schemi di alimentazione e di modulazione delle tensioni. Si descriveranno in seguito le procedure atte e definire per via sperimentale il set di parametri caratteristico della macchina, consentendo di proporre una soluzione di controllo innovativa basata sul concetto della predizione dello stato del sistema, in sostituzione della metodologia tradizionale con regolatori standard sulla retroazione di corrente. Mettendo poi in discussione la validità delle approssimazioni che si è soliti fare nell’imbastire il sistema di controllo, si procederà alla definizione di nuovi algoritmi che prescindono dalla trascurabilità dei parametri resistivi. In ambito di azionamenti in configurazione multi-motore, si affronterà il problema della stabilità e si proporranno diverse tecniche di controllo con confronti incrociati dei risultati ottenuti a mezzo di analisi numerica. Si introdurrà poi un nuovo approccio analitico, definendo il modello matematico dei sistemi dual motor, e introducendo una tecnica di controllo con ottimizzazione dal punto di vista prestazionale a regime e/o dinamico; i risultati ottenuti con queste ultime due tecniche saranno messi a confronto con quelli precedenti. Si analizzerà in dettaglio il fenomeno della variabilità parametrica in relazione alla condizione di funzionamento, rimuovendo alcune ipotesi semplificative che attengono all’idealità dei materiali e alla linearità. L’introduzione del fenomeno di saturazione e della non idealità dei materiali costituenti la macchina consentirà la definizione di un nuovo modello matematico del motore PM brushless. Sulla base di tale modello si affronterà il problema del monitoraggio parametrico a mezzo di algoritmi di stima ricorsivi in grado di operare on-line, durante il normale funzionamento della macchina, e proponendo un metodo di eliminazione delle sovraelongazioni. Con riferimento ad un motore PMSM di 52 kW progettato e realizzato dal Dipartimento di Azionamenti Elettrici, Istituto per le Tecnologie Energetiche e di Automazione dell’Università Tecnica di Berlino, l’analisi numerica in ambiente Matlab-Simulink verrà messa a confronto con i risultati ottenuti per via sperimentale su banco prova. Si proporrà in fine un metodo diagnostico atto ad individuare l’insorgenza di condizioni di funzionamento anomalo e/o di guasto, utilizzando i profili dei parametri ottenuti dallo stesso estimatore parametrico

Spectroscopic binaries in the Solar Twin Planet Search program: from substellar-mass to M dwarf companions

Previous studies on the rotation of Sun-like stars revealed that the rotational rates of young stars converge towards a well-defined evolution that follows a power-law decay. It seems, however, that some binary stars do not obey this relation, often by displaying enhanced rotational rates and activity. In the Solar Twin Planet Search program we observed several solar twin binaries, and found a multiplicity fraction of $42\% \pm 6\%$ in the whole sample; moreover, at least three of these binaries (HIP 19911, HIP 67620 and HIP 103983) clearly exhibit the aforementioned anomalies. We investigated the configuration of the binaries in the program, and discovered new companions for HIP 6407, HIP 54582, HIP 62039 and HIP 30037, of which the latter is orbited by a $0.06$ M$_\odot$ brown dwarf in a 1-month long orbit. We report the orbital parameters of the systems with well-sampled orbits and, in addition, the lower limits of parameters for the companions that only display a curvature in their radial velocities. For the linear trend binaries, we report an estimate of the masses of their companions when their observed separation is available, and a minimum mass otherwise. We conclude that solar twin binaries with low-mass stellar companions at moderate orbital periods do not display signs of a distinct rotational evolution when compared to single stars. We confirm that the three peculiar stars are double-lined binaries, and that their companions are polluting their spectra, which explains the observed anomalies.Comment: 13 pages, 7 figures, accepted for publication in MNRA

The temporal evolution of neutron-capture elements in the Galactic discs

Important insights into the formation and evolution of the Galactic disc(s) are contained in the chemical compositions of stars. We analysed high-resolution and high signal to noise HARPS spectra of 79 solar twin stars in order to obtain precise determinations of their atmospheric parameters, ages ($\sigma$$\sim$0.4 Gyr) and chemical abundances ($\sigma$$<$0.01~dex) of 12 neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy). This valuable dataset allows us to study the [X/Fe]-age relations over a time interval of $\sim$10 Gyr and among stars belonging to the thin and thick discs. These relations show that i) the $s$-process has been the main channel of nucleosynthesis of $n$-capture elements during the evolution of the thin disc; ii) the thick disc is rich in $r$-process elements which suggests that its formation has been rapid and intensive. %; iii) a chemical continuity between the thin and thick discs is evident in the abundances of Ba. In addition, the heavy (Ba, La, Ce) and light (Sr, Y, Zr) $s$-process elements revealed details on the dependence between the yields of AGB stars and the stellar mass or metallicity. Finally, we confirmed that both [Y/Mg] and [Y/Al] ratios can be employed as stellar clocks, allowing ages of solar twin stars to be estimated with an average precision of $\sim$0.5~Gyr

Integrated BMS-MMC Balancing Technique Highlighted by a Novel Space-Vector Based Approach for BEVs Application

This paper proposes a new mathematical model of modular multilevel converters for battery electric vehicles with space-vectors enabling a critical analysis of cell balancing for the battery management system. In particular, the requirements for power balancing and the actual number of degrees of freedom of the control are investigated. The paper shows that the traditional approach of cell balancing is a special case of the proposed control methodology. Numerical analyses with Matlab/Simulink™ highlight the reasons of the slow response of the standard balancing technique for specific operating conditions of the battery electric vehicle. The paper suggests potential improvements that could be introduced through the proposed generalised approach

The Chemical Homogeneity of Sun-like Stars in the Solar Neighborhood

The compositions of stars are a critical diagnostic tool for many topics in astronomy such as the evolution of our Galaxy, the formation of planets, and the uniqueness of the Sun. Previous spectroscopic measurements indicate a large intrinsic variation in the elemental abundance patterns of stars with similar overall metal content. However, systematic errors arising from inaccuracies in stellar models are known to be a limiting factor in such studies, and thus it is uncertain to what extent the observed diversity of stellar abundance patterns is real. Here we report the abundances of 30 elements with precisions of 2% for 79 Sun-like stars within 100 parsecs. Systematic errors are minimized in this study by focusing on solar twin stars and performing a line-by-line differential analysis using high-resolution, high-signal-to-noise spectra. We resolve [X/Fe] abundance trends in galactic chemical evolution at precisions of $10^{-3}$ dex Gyr$^{-1}$ and reveal that stars with similar ages and metallicities have nearly identical abundance patterns. Contrary to previous results, we find that the ratios of carbon-to-oxygen and magnesium-to-silicon in solar metallicity stars are homogeneous to within 10% throughout the solar neighborhood, implying that exoplanets may exhibit much less compositional diversity than previously thought. Finally, we demonstrate that the Sun has a subtle deficiency in refractory material relative to >80% of solar twins (at 2$\sigma$ confidence), suggesting a possible signpost for planetary systems like our own.Comment: ApJ accepted versio

The outcome of peripheral t-cell lymphoma patients failing first-line therapy: A report from the prospective, international t-cell project

This analysis explored factors influencing survival of patients with primary refractory and relapsed peripheral T-cell lymphomas enrolled in the prospective International T-cell Project. We analyzed data from 1020 patients with newly diagnosed disease, enrolled between September 2006 and December 2015. Out of 937 patients who received first-line treatment, 436 (47%) were identified as refractory and 197 (21%) as relapsed. Median time from the end of treatment to relapse was 8 months (range 2-73). Overall, 75 patients (8%) were consolidated with bone marrow transplantation, including 12 refractory and 22 relapsed patients. After a median follow up of 38 months (range 1-96 months) from documentation of refractory/relapsed disease, 440 patients had died. The median overall survival (OS) was 5.8 months; 3-year overall survival rates were 21% and 28% for refractory and relapsed patients, respectively (P12 months, HR 0.57, P=0.001) and salvage therapy with transplantation (HR=0.36, P<0.001) were associated with a better OS. No difference was found in OS with respect to histology. This study accurately reflects outcomes for patients treated according to standards of care worldwide. Results confirm that peripheral T-cell lymphomas patients had dismal outcome after relapse or progression. Patients with chemotherapy sensitive disease who relapsed after more than 12 months might benefit from consolidation bone marrow transplantation. (Registered at clinicaltrials.gov identifier: 01142674)

The Li-age correlation: The Sun is unusually Li deficient for its age

This work aims to examine in detail the depletion of lithium in solar twins to better constrain stellar evolution models and investigate its possible connection with exoplanets. We employ spectral synthesis in the region of the asymmetric 6707.75 Å Li I line for a sample of 77 stars plus the Sun. As in previous works based on a smaller sample of solar twins, we find a strong correlation between Li depletion and stellar age. In addition, for the first time we show that the Sun has the lowest Li abundance in comparison with solar twins at similar age (4.6 ± 0.5 Gyr). We compare the lithium content with the condensation temperature slope for a subsample of the best solar twins and determine that the most lithium-depleted stars also have fewer refractory elements. We speculate whether the low lithium content in the Sun might be related to the particular configuration of our Solar system.This study was financed in part by the Coordenac¸ao de ˜ Aperfeic¸oamento de Pessoal de N´ıvel Superior – Brasil (CAPES) – Finance Code 001. JM is thankful for the support of Fundac¸ao de ˜ Amparo a Pesquisa do Estado de S ` ao Paulo (FAPESP, 2014/18100- ˜ 4, 2018/04055-8) and Conselho Nacional de Desenvolvimento Cient´ıfico e Tecnologico (CNPq, Bolsa de Produtividade). LAdS ´ acknowledges the financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (project FOUR ACES; grant agreement No. 724427)

Innate Sex Differences in the Timing of Spring Migration in a Songbird

In migrating animals protandry is the phenomenon whereby males of a species arrive at the breeding grounds earlier than females. In the present study we investigated the proximate causes of protandry in a migratory songbird, the northern wheatear Oenanthe oenanthe. Previous experiments with caged birds revealed that males and females show differentiated photoperiod-induced migratory habits. However, it remained open whether protandry would still occur without photoperiodic cues. In this study we kept captive first-year birds under constant photoperiod and environmental conditions in a “common garden” experiment. Male northern wheatears started their spring migratory activity earlier than females, even in the absence of environmental cues. This indicates that protandry in the northern wheatear has an endogenous basis with an innate earlier spring departure of males than females