Nova shema za izravno upravljanje momentom asinkronih motora napajanih iz trofaznog izmjenjivača

This paper presents a novel controller based on Direct Torque Control (DTC) strategy. This controller is designed to be applied in the control of Induction Motors (IM) fed with a three-level Voltage Source Inverter (VSI). This type of inverter has several advantages over the standard two-level VSI, such as a greater number of levels in the output voltage waveforms, lower dV/dt, less harmonic distortion in voltage and current waveforms and lower switching frequencies. In the new controller, torque and stator flux errors are used together with the stator flux angular frequency to generate a reference voltage vector. Experimental results of the novel system are presented and compared with those obtained for Classical DTC system employing a two-level VSI. The new controller is shown to reduce the ripple in the torque and flux responses. Lower current distortion and switching frequency of the semiconductor devices are also obtained in the new system presented.U ovome se članku opisuje novi regulator zasnovan na strategiji izravnog upravljanja momentom i razvijen za primjenu u upravljanju asinkronim motorima napajanim iz trorazinskih izmjenjivača napona. Taj tip izmjenjivača ima nekoliko prednosti u odnosu na standardne dvorazinske izmjenjivače napona, kao što je veći broj razina u izlaznom valnom obliku napona, niži du/dt, manja distorzija harmonika u valnim oblicima napona i struje i niže frekvencije komutacije. U novom regulatoru moment i pogreške u statorskom toku koriste se zajedno s kutnom frekvencijom statora za tvorbu referentne vrijednosti vektora napona. Eksperimentalni su rezultati novog sustava prikazani i uspoređeni s rezultatima klasičnog sustava koji koristi dvorazinski pretvarač napona. Novi regulator pokazuje smanjeni šum u odzivima momenta i toka motora. U predloženom je sustavu također postignuta i manja distorzija struje i manja frekvencija komutacije poluvodičkih sklopova

Improving the interoperability between MPI and task-based programming models

In this paper we propose an API to pause and resume task execution depending on external events. We leverage this generic API to improve the interoperability between MPI synchronous communication primitives and tasks. When an MPI operation blocks, the task running is paused so that the runtime system can schedule a new task on the core that became idle. Once the MPI operation is completed, the paused task is put again on the runtime system's ready queue. We expose our proposal through a new MPI threading level which we implement through two approaches. The first approach is an MPI wrapper library that works with any MPI implementation by intercepting MPI synchronous calls, implementing them on top of their asynchronous counterparts. In this case, the task-based runtime system is also extended to periodically check for pending MPI operations and resume the corresponding tasks once MPI operations complete. The second approach consists in directly modifying the MPICH runtime system, a well-known implementation of MPI, to directly call the pause/resume API when a synchronous MPI operation blocks and completes, respectively. Our experiments reveal that this proposal not only simplifies the development of hybrid MPI+OpenMP applications that naturally overlap computation and communication phases; it also improves application performance and scalability by removing artificial dependencies across communication tasks.This work has been developed with the support of the European Union Horizon 2020 Programme through both the INTERTWinE project (agreement No. 671602) and the Marie Sk lodowska-Curie grant (agreement No. 749516); the Spanish Government through the Severo Ochoa Program (SEV-2015-0493); the Spanish Ministry of Science and Innovation (TIN2015-65316-P) and the Generalitat de Catalunya (2017-SGR-1414).Peer ReviewedPostprint (author's final draft

Strategies to reengage patients lost to follow up in HIV care in high income countries, a scoping review

Background: Despite remarkable achievements in antiretroviral therapy (ART), losses to follow-up (LTFU) might prevent the long-term success of HIV treatment and might delay the achievement of the 90-90-90 objectives. This scoping review is aimed at the description and analysis of the strategies used in high-income countries to reengage LTFU in HIV care, their implementation and impact. Methods: A scoping review was done following Arksey & O'Malley's methodological framework and recommendations from Joanna Briggs Institute. Peer reviewed articles were searched for in Pubmed, Scopus and Web of Science; and grey literature was searched for in Google and other sources of information. Documents were charted according to the information presented on LTFU, the reengagement procedures used in HIV units in high-income countries, published during the last 15 years. In addition, bibliographies of chosen articles were reviewed for additional articles. Results: Twenty-eight documents were finally included, over 80% of them published in the United States later than 2015. Database searches, phone calls and/or mail contacts were the most common strategies used to locate and track LTFU, while motivational interviews and strengths-based techniques were used most often during reengagement visits. Outcomes like tracing activities efficacy, rates of reengagement and viral load reduction were reported as outcome measures. Conclusions: This review shows a recent and growing trend in developing and implementing patient reengagement strategies in HIV care. However, most of these strategies have been implemented in the United States and little information is available for other high-income countries. The procedures used to trace and contact LTFU are similar across reviewed studies, but their impact and sustainability are widely different depending on the country studied

Disseny òptim d'amplificadors d'audio commutats DCI-NPC d'alta potència i qualitat

Class-D Amplification has been an absolute improvement in terms of electrical efficiency in audio amplification systems, but it has been during the first stabilization decade of this technology in the market when manufacturers have made public their concern about the incompatibility between distributed audio or PA (Public Address) applications and HiFi or Professional sound applications. High quality sound systems need switching frequencies (>1MHz) whose switching losses do not allow to work at high power (>250W). To the contrary, applications for high power amplification need high electrical efficiency, so the switching frequencies must be set to low values (1MHz) per les quals les pèrdues en commutació no permeten treballar a potències elevades (>250W). Per al contrari, per aplicacions d'amplificació de so de potència es necessita d'alta eficiència elèctrica, amb el que les freqüències de commutació han de quedar fixades a valors baixos (<400kHz), reduint la qualitat del senyal. Aquesta incompatibilitat d'aplicacions s'anomena Compromís Qualitat-Potència. Les topologies Multinivell de convertidors electrònics de potència DC-AC, per les seves característiques, permeten treballar a gran potència (augmentant la tensió de treball), mantenint o augmentant la qualitat del senyal de sortida mitjançant els nivells extra en el senyal PWM de sortida. L'aplicació d'aquestes topologies en el mon de l'Amplificació de So, podria suposar la resolució del compromís Qualitat-Potència, i per tant de la principal problemàtica que presenta la Classe-D. Aquesta Tesis proposa en primer lloc l'estudi de les topologies Multinivell per determinar quina és la que millors prestacions i viabilitat mostra en quant a la seva aplicació com a Amplificador d'Àudio Commutat. Un cop determinada la Topologia Òptima, es proposa estudiar, caracteritzar i modelar els fenòmens no ideals i mecanismes generadors d'errors de Temps i d'Amplitud al polsos del senyal PWM de sortida d'un Amplificador amb la Topologia seleccionada. A partir d'aquests models, s'estudia mitjançant simulació els efectes dels errors en els senyals de sortida, expressant aquests efectes mitjançant factors de mèrit no normatius. Aquests factors de mèrit, al contrari que els normatius, permeten avaluar quantitativa i qualitativament el grau d'afectació de cada una de les diferents fonts d'errors intrínseques al disseny i a la topologia. A partir d'aquests resultats es desenvolupen Models d'Estimació dels Factors de Mèrit No Normatius, que permeten calcular el valor d'Error d'Amplitud i Distorsió, local o total, generat per qualsevol font d'error de la Cadena d'Amplificació de So. Per tal d'expressar aquesta informació en valors normatius, es desenvolupen Models d'Estimació d'Eficiències Elèctriques, Distorsió (THD) i Eficiència de Senyal a partir dels valors estimats d'Error d'Amplitud i Distorsió no normatius. Aquests models d'estimació proveeixen d'una informació que, un cop ordenada i classificada per tal de ser utilitzada, com a eina en els diferents nivells del procés de disseny, producció i comercialització d'equips d'amplificació commutada, permet, de forma òptima en la fase de pre-disseny, la selecció de components i la presa de decisions per tal d'assegurar, un cop construït, la futura validació de l'amplificador commutat multinivell, sota criteris normatius de mercat. Els models d'estimació d'Errors d'Amplitud i Distorsió, així com els models d'estimació de les Eficiències Elèctriques, de Distorsió i de Senyal han estat validats mitjançant la seva comparació amb resultats experimentals obtinguts a partir d'un prototipus de laboratori i un prototipus de fabricació industrial, dissenyat per una empresa del sector a partir de l'ús de les Eines de Disseny Òptim basades en els Models d'Estimació, desenvolupades en aquesta Tesis. Els resultats experimentals confirmen que els valors normatius mesurats d'Eficiència Elèctrica, Distorsió i Eficiència de Senyal estan dintre dels valors acceptables per la comercialització de l'equip

Improving the interoperability between MPI and task-based programming models

In this paper we propose an API to pause and resume task execution depending on external events. We leverage this generic API to improve the interoperability between MPI synchronous communication primitives and tasks. When an MPI operation blocks, the task running is paused so that the runtime system can schedule a new task on the core that became idle. Once the MPI operation is completed, the paused task is put again on the runtime system's ready queue. We expose our proposal through a new MPI threading level which we implement through two approaches.The first approach is an MPI wrapper library that works with any MPI implementation by intercepting MPI synchronous calls, implementing them on top of their asynchronous counterparts. In this case, the task-based runtime system is also extended to periodically check for pending MPI operations and resume the corresponding tasks once MPI operations complete. The second approach consists in directly modifying the MPICH runtime system, a well-known implementation of MPI, to directly call the pause/resume API when a synchronous MPI operation blocks and completes, respectively.Our experiments reveal that this proposal not only simplifies the development of hybrid MPI+OpenMP applications that naturally overlap computation and communication phases; it also improves application performance and scalability by removing artificial dependencies across communication tasks.This work has been developed with the support of the European Union Horizon 2020 Programme through both the INTERTWinE project (agreement No. 671602) and the Marie Sk lodowska-Curie grant (agreement No. 749516); the Spanish Government through the Severo Ochoa Program (SEV-2015-0493); the Spanish Ministry of Science and Innovation (TIN2015-65316-P) and the Generalitat de Catalunya (2017-SGR-1414).Peer Reviewe