A comprehensive analysis of SVPWM for a Five-phase VSI based on SiC devices applied to motor drives

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents a comprehensive analysis of SVPWM for a five-phase VSI based on SiC devices applied to motor drives. The modulation techniques analyzed use medium and large vectors to reach the reference vector. The 2L SVPWM uses two large space vectors, and the generated output signal contain low frequency harmonics. 2L+2M SVPWM uses two large and two medium space vectors. This technique provides good power loss distribution. 4L SVPWM works with the activation of four large space vectors. This modulation is able to generate low common-mode voltage. The performance and main features are analyzed using Matlab/Simulink and PLECS blockset software. Power losses, total harmonic distortion and common-mode voltage are compared and evaluated.Postprint (author's final draft

Efficiency analysis of wide band-gap semiconductors for two-level and three-level power converters

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Power devices based on wide band-gap materials are emerging as alternatives to silicon-based devices. These new devices allow designing and building converters with fewer power losses, and are thus more highly efficient than traditional power converters. Among the wide band-gap materials in use, silicon carbide (SiC) and gallium nitride (GaN) devices are the most promising because of their excellent properties and commercial availability. This paper compares the losses produced in two-level and three-level power converters that use the aforementioned technologies. In addition, we assess the impact on the converter performance caused by the modulation technique. Simulation results under various operating points are reported and compared.Peer ReviewedPostprint (author's final draft

Multiphase PMSM and PMaSynRM flux map model with space harmonics and multiple plane cross harmonic saturation

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Multiphase Synchronous Machines vary in rotor construction and winding distribution leading to non-sinusoidal inductances along the rotor periphery. Moreover, saturation and cross-saturation effects make the precise modeling a complex task. This paper proposes a general model of multi-phase magnet-excited synchronous machines considering multi-dimensional space modeling and revealing cross-harmonic saturation. The models can predict multiphase motor behavior in any transient state, including startup. They are based on flux maps obtained from static 2D Finite-Element (FE) analysis. FE validations have been performed to confirm authenticity of the dynamic models of multiphase PMaSynRMs. Very close to FE precision is guaranteed while computation time is incomparably lower.Postprint (author's final draft

Modulation strategies for the neutral-point-clamped converter and control of a wind turbine system

Els convertidors multinivell són topologies de convertidors d’electrònica de potència que poden generar tres o més nivells de voltatge en cadascuna de les fases de sortida. Com a resultat, els voltatges i corrents generats per aquestes topologies presenten una distorsió harmònica baixa. Hi ha diferents configuracions de convertidors multinivell, les quals es basen en connectar dispositius de potència o convertidors en sèrie. El resultat d’aquestes connexions permet obtenir voltatges alts, tant en la part de corrent continu com en la de corrent altern del convertidor. A més, cada dispositiu sols ha de suportar una fracció del voltatge total del bus de corrent continu. Per aquestes raons, els convertidors multinivell són generalment utilitzats en aplicacions d’alta potència. El convertidor de tres nivells amb connexió a punt neutre (neutral-point-clamped) és el més utilitzat. La recerca d’aquesta tesis doctoral està focalitzada en aquesta topologia de convertidor, i el principal objectiu és l’aportació de noves tècniques de modulació. Aquestes tenen en compte diferents aspectes: la velocitat computacional dels algorismes, l’equilibrat de les tensions dels condensadors del bus de contínua, les pèrdues de commutació i les oscil·lacions de baixa freqüència en el punt neutre del convertidor. Totes les estratègies de modulació proposades en aquesta tesis són modulacions d’amplada de polses basades en portadora. En la primera modulació que es presenta, s’injecta un senyal comú (seqüència zero) a totes les moduladores, que es basa en els patrons de la modulació vectorial que utilitza tres vectors dels més propers al de referència (nearest-three-vector modulation). S’estudien i es comparen els resultats d’aquesta modulació amb la seva homòloga, basada en perspectiva vectorial. Una segona proposta és l’anomenada modulació d’amplada de polses de doble senyal (double-signal pulse-width modulation). Aquesta modulació és capaç d’eliminar completament les oscil·lacions de voltatge en el punt neutre del convertidor. No obstant això, es produeix un increment de les pèrdues de commutació en els dispositius de potència i, a més, no hi ha un equilibrat natural de les tensions en els condensadors del bus. Una última estratègia de modulació, anomenada modulació híbrida (hybrid pulse-width modulation), es basa en la combinació de la modulació sinusoïdal (sinusoidal pulse-width modulation) i la de doble senyal. Aquesta presenta una solució de compromís entre reduir les pèrdues de commutació, en detriment d’un augment de l’amplitud de les oscil·lacions de voltatge en el punt neutre. Una segona part d’aquesta tesis es centra en les aplicacions a generació eòlica, ja que els convertidors multinivell estan començant a ser utilitzats en aquest camp. Això es produeix fonamentalment per l’augment continu de les dimensions de les turbines eòliques. En aquesta part de la recerca s’ha considerat la configuració de dos convertidors multinivell connectats a un mateix bus de contínua (back-to-back), tot i que els convertidors han estat estudiats independentment. Inicialment s’ha estudiat el convertidor que va connectat a la xarxa elèctrica i s’ha aplicat l’estratègia de control coneguda com a control orientat a tensió (voltage-oriented control). S’han utilitzat controladors estàndard (proporcional-integral), als quals s’ha afegit un control difús que supervisa i modifica els valors de les constants dels controladors. Aquest supervisor difús millora la dinàmica de la tensió del bus de contínua davant canvis de càrrega quan el convertidor treballa com a rectificador. Per una altra part, s’ha estudiat el control d’una turbina eòlica basada en un generador d’imants permanents. En aquest cas, s’ha aplicat l’estratègia de control coneguda com a control orientat a camp (field-oriented control). S’han avaluat i comparat els avantatges i inconvenients de diferents formes de sintonitzar els controladors.Multilevel converters are power electronic topologies that can generate three or more voltage levels in each output phase. As a result, the voltage and current waveforms generated have lower total harmonic distortion. Multilevel topologies are based on connecting power devices or converters in a series. Consequently, high voltages can be handled on the dc and ac sides of the converter, while each device stands only a fraction of the total dc-link voltage. For these reasons multilevel converters are generally applied to high-power applications. The three-level neutral-point-clamped converter is the most extensively used multilevel topology. This topology is the main focus of research in this dissertation. The main objective is to propose new modulation strategies that are able to meet a compromise solution while considering computational algorithm speed, voltage balance in the dc-link capacitors, switching losses and low frequency voltage oscillations at the neutral point. All the modulation strategies proposed here are based on carrier-based pulsewidth modulation. A new modulation strategy has been implemented using a proper zero-sequence signal injected into the modulation signals. The zero sequence is determined from a space-vector modulation standpoint, particularly the nearest-threevector modulation strategy. The proposed carrier-based technique is compared with its space-vector modulation counterpart. It shows some advantages, such as easier implementation and reduced switching events; however, it still produces oscillations in the neutral-point voltage for some operating conditions. A new modulation strategy able to completely remove such voltage oscillations is also presented. It is called double-signal pulse-width modulation. The main drawback of this strategy is that it increases the switching frequency of the power devices and has no natural capacitor voltage balance. Some balancing strategies are proposed in this dissertation for this specific modulation. Furthermore, a hybrid pulse-width modulation approach is presented which is able to combine sinusoidal pulse-width modulation with doublesignal pulse-width modulation; this represents a compromise solution between switching losses and neutral-point voltage oscillation amplitudes. The second part of this thesis is focused on wind generation applications. Multilevel converters are starting to be used in such a field nowadays, and are expected to be further applied in the near future as the sizes of wind turbines grow. Two back-toback-connected power converters are considered in this application, although they are analyzed independently. First of all, the control of the grid-connected converter is studied. A voltage-oriented control is used with standard proportional-integral controllers. The originality of the method is that a fuzzy supervisor is designed and included in the structure; the fuzzy supervisor is able to modify the proportionalintegral parameters online. It is shown how the control of the total dc-link voltage improves significantly under load changes when the converter is working as a rectifier. On the other hand, a control study is performed on the wind turbine side. The variable speed wind turbine is based on a permanent magnet synchronous generator. A field-oriented control strategy is applied. The controllers are evaluated and compared using different tuning strategies which highlight the advantages and drawbacks of each

A Versatile workbench simulator: Five-phase inverter and PMa-SynRM performance evaluation

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Thispaperpresents the design and structure of aversatileworkbench simulator forevaluating the performance of a five-phase inverter andPermanent Magnet assisted Synchronous Reluctance Motor(PMa-SynRM). The simulatorallows for adding variations tothe modulationtechniques, changingthe inverter structure’s semiconductordevice, and calculatingtheinverter’spower losses. Itcanalso facilitate observingthe current, voltage,andthe jointtemperature ofthe semiconductors devices. Furthermore,wecanobtain a perform that is close to anactualPMa-SynRM, dependingon the desired conditionsof speed and torque. The workbench simulator wasdevelopedby combining three software: Matlab/Simulink, PLECSand Altair Flux.Postprint (author's final draft

Hybrid sensorless permanent magnet synchronous machine four quadrant drive based on direct matrix converter

Permanent Magnet Synchronous Machines (PMSMs) have several advantages, such as high ef¿ciency and low volume and weight, which make them attractive for aerospace applications and high performance servo drives. Matrix Converters (MCs) are an all-silicon alternative, with no bulky reactive elements, to the standard voltage source inverter. The most common control technique for such PMSM MC-fed drives is the so-called Field-Oriented Control (FOC), which requires the permanent magnet ¿ux position to achieve high dynamic performance. Encoders or resolvers are the most common sensing devices used for such a purpose, which not only increases the total cost of the PMSM drive but also adds extra electronics and cabling that may cause failures. This paper investigates and proposes an all range (from zero to full) speed hybrid sensorless FOC. The novelty of this paper relies on the use of a hybrid sensorless four quadrant FOC that averages the needed angle estimation from a model based angle estimator and a voltage pulse test injection angle estimator when feeding the PMSM with an MC instead of a standard voltage source inverter. Speed reversal and load impact simulation results are included, fully supporting the claims made in this paperPeer ReviewedPostprint (published version

The role of Computational Linguistics in the search for information

Aquest article presenta una visió general de les noves aplicacions de cerca d’informació que estan emergint fent ús de la semàntica superficial. Es presenten tres exemples d’aquest tipus d’aplicacions desenvolupades per la fundació Barcelona media-Yahoo! Research Barcelona, Yahoo! correlator, TimeExplorer i Quest.This paper presents a general view of the new emerging search applications which make use of shallow semantics. Three different applications developed by fundació Barcelona media-Yahoo! Research Barcelona, Yahoo! correlator, TimeExplorer and Quest, are presented

Incremento en la prevalencia del VIH y en las conductas de riesgo asociadas en hombres que tienen sexo con hombres: 12 años de encuestas de vigilancia conductual en Cataluña

ResumenObjetivosDescribir las tendencias en la prevalencia de la infección por VIH, las conductas de riesgo asociadas a su transmisión y las actitudes respecto a los tratamientos antirretrovirales en el colectivo de hombres que tienen sexo con hombres reclutados en Cataluña entre 1995 y 2006.MétodosEstudios transversales bianuales en una muestra de conveniencia de hombres que tienen sexo con hombres reclutados en saunas, sex-shops, bares y un parque público, y por correo a los socios de la Coordinadora Gai-Lesbiana, mediante un cuestionario anónimo y autoadministrado. Se recogieron muestras de saliva para determinar la prevalencia de la infección por VIH. La significación de las tendencias lineales en las proporciones se analizó mediante el test de χ2 de tendencia lineal, estratificando por edad.ResultadosLa prevalencia global del VIH aumentó del 8,5% (1995) al 14,1% (2006) en los menores de 30 años (p=0,162), y del 18,2% (1995) al 21,2% (2006) en los de 30 años y más (p=0,07). El uso consistente del preservativo en la penetración anal con parejas ocasionales descendió del 72,9% al 58,7% en los menores de 30 años (p<0,05), y del 77,2% al 65,6% en los de 30 años y más (p<0,001). El porcentaje que afirmó que debido a los antirretrovirales «yo cada vez elijo prácticas de más riesgo» pasó del 9,2% al 19,4% en los menores de 30 años, y del 8,3% al 16,7% en los de 30 años y más (p<0,05).ConclusionesLos resultados muestran una tendencia creciente en la prevalencia del VIH y de las conductas de riesgo asociadas en el colectivo de hombres que tienen sexo con hombres de Cataluña. Por tanto, los programas de prevención dirigidos a este colectivo deberían intensificarse e incorporar nuevas estrategias de reducción de riesgos, así como otros mensajes educativos sobre los antirretrovirales.AbstractObjectivesTo describe trends in HIV prevalence, in risk behaviors associated with HIV transmission, and in knowledge and attitudes related to antiretroviral therapy (ART) among men who have sex with men (MSM) recruited in Catalonia between 1995 and 2006.MethodsBiannual cross-sectional surveys were performed. An opportunistic sample of MSM was recruited in saunas, sex shops, bars and a cruising site in a public park. In addition, an anonymous self-administered questionnaire was sent by mail to all members of a gay and lesbian association (Coordinadora Gai-Lesbiana). Oral fluid samples were collected to determine HIV prevalence. Linear trends in proportions were assessed by the χ2 test, stratified by age.ResultsThe overall prevalence of HIV infection increased from 8.5% (1995) to 14.1% (2006) among men aged less than 30 years old (p=0.162) and from 18.2% (1995) to 21.2% (2006) among those aged 30 years old or more (p=0.07). Consistent condom use in anal intercourse with occasional partners decreased from 72.9% to 58.7% in men aged less than 30 years old (p <0.05) and from 77.2% to 65.6% in those aged 30 years old or more (p<0.001). The proportion of men who reported they chose riskier behaviors because of ART increased from 9.2% to 19.4% in men aged less than 30 years old and from 8.3% to 16.7% in those aged 30 years old or more (p<0.05).ConclusionsAn increasing trend in the prevalence of HIV and associated risk behaviors was found in Catalonia among MSM. Therefore, preventive programs targeting this population should be intensified and should include new risk reduction strategies, as well as other educational messages about ART

A simple control strategy to increase the total efficiency of multi-converter systems

This paper presents a simple control strategy that is employed together with an optimization methodology to achieve optimal efficiency in systems composed by multiple parallel converters. An external loop is responsible for regulating the dc bus voltage and providing a current reference that is weighted in function of the power processed by the system, and then generating optimal current references for each converter. This enable the system to operate with optimal efficiency for all its load range. Experimental results demonstrate th e superior performance of the proposed strategy, improving the efficiency of the system in almost 10 % under light load operation in comparison with the conventional strategy of equal power sharing among convertersPeer ReviewedPostprint (author’s final draft