Converter-flux-based current control of voltage source PWM rectifiers - analysis and implementation

Pulsewidth-modulated (PWM) rectifier technology is increasingly used in industrial applications like variable-speed motor drives, since it offers several desired features such as sinusoidal input currents, controllable power factor, bidirectional power flow and high quality DC output voltage. To achieve these features,however, an effective control system with fast and accurate current and DC voltage responses is required. From various control strategies proposed to meet these control objectives, in most cases the commonly known principle of the synchronous-frame current vector control along with some space-vector PWM scheme have been applied. Recently, however, new control approaches analogous to the well-established direct torque control (DTC) method for electrical machines have also emerged to implement a high-performance PWM rectifier. In this thesis the concepts of classical synchronous-frame current control and DTC-based PWM rectifier control are combined and a new converter-flux-based current control (CFCC) scheme is introduced. To achieve sufficient dynamic performance and to ensure a stable operation, the proposed control system is thoroughly analysed and simple rules for the controller design are suggested. Special attention is paid to the estimationof the converter flux, which is the key element of converter-flux-based control. Discrete-time implementation is also discussed. Line-voltage-sensorless reactive reactive power control methods for the L- and LCL-type line filters are presented. For the L-filter an open-loop control law for the d-axis current referenceis proposed. In the case of the LCL-filter the combined open-loop control and feedback control is proposed. The influence of the erroneous filter parameter estimates on the accuracy of the developed control schemes is also discussed. A newzero vector selection rule for suppressing the zero-sequence current in parallel-connected PWM rectifiers is proposed. With this method a truly standalone and independent control of the converter units is allowed and traditional transformer isolation and synchronised-control-based solutions are avoided. The implementation requires only one additional current sensor. The proposed schemes are evaluated by the simulations and laboratory experiments. A satisfactory performance and good agreement between the theory and practice are demonstrated.

Theoretical and numerical study of thermomagnetic convection in magnetic fluids

In this thesis, the magnetic field control of convection instabilities and heat and mass transfer processesin magnetic fluids have been investigated by numerical simulations and theoretical considerations. Simulation models based on finite element and finite volume methods have been developed. In addition to standard conservation equations, themagnetic field inside the simulation domain is calculated from Maxwell equations and the necessary terms to take into account for the magnetic body force and magnetic dissipation have been added to the equations governing the fluid motion.Numerical simulations of magnetic fluid convection near the threshold supportedexperimental observations qualitatively. Near the onset of convection the competitive action of thermal and concentration density gradients leads to mostly spatiotemporally chaotic convection with oscillatory and travelling wave regimes, previously observed in binary mixtures and nematic liquid crystals. In many applications of magnetic fluids, the heat and mass transfer processes including the effects of external magnetic fields are of great importance. In addition to magnetic fluids, the concepts and the simulation models used in this study may be applied also to the studies of convective instabilities in ordinary fluids as well as in other binary mixtures and complex fluids.

Supremacía del derecho federal sobre el Common Law en materia de requisitos de seguridad y eficacia terapéutica de productos sanitarios. Comentario a Riegel v. Medtronic, Inc. [552 U.S.__ (2008); February 20, 2008]

En Riegel v. Medtronic Inc. (552 U.S.__2008; February 20, 2008), el Sr. Riegel tuvo que ser sometido a un by-pass como consecuencia de la rotura del catéter, fabricado por Medtronic, con el que su médico le practicaba una angioplastia. A pesar de que el catéter había obtenido la autorización de comercialización de la FDA y cumplía los requisitos de seguridad previstos por el sistema regulatorio federal, el Sr. Riegel y su mujer interpusieron una acción de daños contra Medtronic –y no contra el médico- conforme a las reglas de responsabilidad civil objetiva y por negligencia del Common Law neoyorquino. Sin embargo, el Tribunal Supremo federal de los EE.UU., en ponencia del Magistrado Antonin Gregory Scalia, votó, por mayoría de ocho magistrados, rechazar el recurso de la Sra. Riegel y confirmar la sentencia de segunda instancia, desestimatoria de la demanda, porque consideró que la regla de primacía del derecho regulatorio federal sobre seguridad de productos sanitarios [Medical Device Amendments de 1976, 21 U.S.C. Artículo 360k(a)] excluye la aplicabilidad no sólo del derecho regulatorio estatal sobre seguridad de productos sanitarios, sino también del Common Law sobre responsabilidad civil del fabricante.

A web ontologies framework for digital rights management

In order to improve the management of copyright in the Internet, known as Digital Rights Management, there is the need for a shared language for copyright representation. Current approaches are based on purely syntactic solutions, i.e. a grammar that defines a rights expression language. These languages are difficult to put into practise due to the lack of explicit semantics that facilitate its implementation. Moreover, they are simple from the legal point of view because they are intended just to model the usage licenses granted by content providers to end-users. Thus, they ignore the copyright framework that lies behind and the whole value chain from creators to end-users. Our proposal is to use a semantic approach based on semantic web ontologies. We detail the development of a copyright ontology in order to put this approach into practice. It models the copyright core concepts for creation, rights and the basic kinds of actions that operate on content. Altogether, it allows building a copyright framework for the complete value chain. The set of actions operating on content are our smaller building blocks in order to cope with the complexity of copyright value chains and statements and, at the same time, guarantee a high level of interoperability and evolvability. The resulting copyright modelling framework is flexible and complete enough to model many copyright scenarios, not just those related to the economic exploitation of content. The ontology also includes moral rights, so it is possible to model this kind of situations as it is shown in the included example model for a withdrawal scenario. Finally, the ontology design and the selection of tools result in a straightforward implementation. Description Logic reasoners are used for license checking and retrieval. Rights are modelled as classes of actions, action patterns are modelled also as classes and the same is done for concrete actions. Then, to check if some right or license grants an action is reduced to check for class subsumption, which is a direct functionality of these reasoners.

Steady-state global optimization of metabolic non-linear dynamic models through recasting into power-law canonical models

Background: Design of newly engineered microbial strains for biotechnological purposes would greatly benefit from the development of realistic mathematical models for the processes to be optimized. Such models can then be analyzed and, with the development and application of appropriate optimization techniques, one could identify the modifications that need to be made to the organism in order to achieve the desired biotechnological goal. As appropriate models to perform such an analysis are necessarily non-linear and typically non-convex, finding their global optimum is a challenging task. Canonical modeling techniques, such as Generalized Mass Action (GMA) models based on the power-law formalism, offer a possible solution to this problem because they have a mathematical structure that enables the development of specific algorithms for global optimization. Results: Based on the GMA canonical representation, we have developed in previous works a highly efficient optimization algorithm and a set of related strategies for understanding the evolution of adaptive responses in cellular metabolism. Here, we explore the possibility of recasting kinetic non-linear models into an equivalent GMA model, so that global optimization on the recast GMA model can be performed. With this technique, optimization is greatly facilitated and the results are transposable to the original non-linear problem. This procedure is straightforward for a particular class of non-linear models known as Saturable and Cooperative (SC) models that extend the power-law formalism to deal with saturation and cooperativity. Conclusions: Our results show that recasting non-linear kinetic models into GMA models is indeed an appropriate strategy that helps overcoming some of the numerical difficulties that arise during the global optimization task.

Assessing chronic disease management in European health systems : concepts and approaches

This book comprises two volumes and builds on the findings of the DISMEVAL project (Developing and validating DISease Management EVALuation methods for European health care systems), funded under the European Union's (EU) Seventh Framework Programme (FP7) (Agreement no. 223277). DISMEVAL was a three-year European collaborative project conducted between 2009 and 2011. It contributed to developing new research methods and generating the evidence base to inform decision-making in the field of chronic disease management evaluation (www.dismeval.eu). In this book, we report on the findings of the project's first phase, capturing the diverse range of contexts in which new approaches to chronic care are being implemented and evaluating the outcomes of these initiatives using an explicit comparative approach and a unified assessment framework. In this first volume, we describe the range of approaches to chronic care adopted in 12 European countries. By reflecting on the facilitators and barriers to implementation, we aim to provide policy-makers and practitioners with a portfolio of options to advance chronic care approaches in a given policy context.

BUSINESS CONCEPTS OF MOBILE VALUE-ADDED SERVICES FROM OPERATOR’S POINT OF VIEW

Tämä diplomityö on tehty Lappeenrannassa Telecom Business Research Centerin 5T-projektiin liittyen. Työssä tutkitaan matkaviestinnän lisäarvopalveluiden liiketoimintakonsepteja operaattoreiden näkökulmasta. Lisäarvopalvelut laajentavat operaattoreiden palveluvalikoimaa. Niiden osuuden telekommunikaatioalan yritysten ja erityisesti operaattoreiden tuotoista on ennustettu kasvavan huomattavasti. Työn tärkeimpänä tavoitteena on tuoda uusia näkökulmia ja lisätä ymmärrystä lisäarvopalveluiden liiketoimintakonseptin rakentamisprosessista. Tätä tietämystä käytetään edesauttamaan työn empiirisessä osuudessa tutkitun Content Gateway -tuotteen liiketoimintaa. Tarjoamalla nopean liitynnän ja laskutuskanavan ulkopuolisten palveluntarjoajien ja operaattorin välille tämä tuote mahdollistaa operaattorille ja palveluntarjoajille lisäarvopalveluiden liiketoiminnan käynnistämisen. Lisäarvopalveluiden arvonluontiprosessi vaatii lukuisia yhteistyötä tekeviä osapuolia, joiden yhteistoiminta on dynaamista ja tiedonvälitys avointa, interaktiivista ja nopeaa. Arvonluontiin liittyy myös monia konvergoituvia kehityssuuntia. Perinteinen arvoketjuajattelu on riittämätön uuteen, verkottuneeseen toimintaympäristöön ja sen tilalle on tullut modernimpi arvoverkostomalli. Arvoverkosto luo kilpailuetunsa muita verkostoja vastaan jakamalla resurssit ja kompetenssit optimaalisesti ja liittämällä strategisen ja operationaalisen johtamisen kulttuurit toisiinsa. Tässä työssä verrataan arvoverkoston teoreettisia tavoitteita kahteen lisäarvopalveluiden liiketoimintakonseptiin. Näistä ensimmäinen, i-mode –niminen konsepti on valittu vertailuun edistyksellisyytensä ja tulevaa kehitystä ennakoivien ominaispiirteidensä vuoksi. Toinen esimerkkikonsepti on rakennettu edellä mainitun Content Gateway -tuotteen ympärille. Tutkimus sisältää mm. liikekumppaneiden hankinnan, ansaintalogiikoiden ja verkostojen johtamisen analysoinnin. Työn tuloksena on saatu ohjeita siihen, miten operaattori voi rakentaa tällaista konseptia ja mitä seikkoja tulee ottaa huomioon erityisesti sanomapalveluihin liittyvässä liiketoiminnassa.

Percolation of spatially constrained Erdos-R enyi networks with degree correlations

Motivated by experiments on activity in neuronal cultures [J. Soriano, M. Rodr ́ıguez Mart́ınez, T. Tlusty, and E. Moses, Proc. Natl. Acad. Sci. 105, 13758 (2008)], we investigate the percolation transition and critical exponents of spatially embedded Erd̋os-Ŕenyi networks with degree correlations. In our model networks, nodes are randomly distributed in a two-dimensional spatial domain, and the connection probability depends on Euclidian link length by a power law as well as on the degrees of linked nodes. Generally, spatial constraints lead to higher percolation thresholds in the sense that more links are needed to achieve global connectivity. However, degree correlations favor or do not favor percolation depending on the connectivity rules. We employ two construction methods to introduce degree correlations. In the first one, nodes stay homogeneously distributed and are connected via a distance- and degree-dependent probability. We observe that assortativity in the resulting network leads to a decrease of the percolation threshold. In the second construction methods, nodes are first spatially segregated depending on their degree and afterwards connected with a distance-dependent probability. In this segregated model, we find a threshold increase that accompanies the rising assortativity. Additionally, when the network is constructed in a disassortative way, we observe that this property has little effect on the percolation transition.

Diffusion-weighted MR imaging in musculoskeletal diseases: Current concepts.

MR imaging is currently regarded as a pivotal technique for the assessment of a variety of musculoskeletal conditions. Diffusion-weighted MR imaging (DWI) is a relatively recent sequence that provides information on the degree of cellularity of lesions. Apparent diffusion coefficient (ADC) value provides information on the movement of water molecules outside the cells. The literature contains many studies that have evaluated the role of DWI in musculoskeletal diseases. However, to date they yielded conflicting results on the use and the diagnostic capabilities of DWI in the area of musculoskeletal diseases. However, many of them have showed that DWI is a useful technique for the evaluation of the extent of the disease in a subset of musculoskeletal cancers. In terms of tissue characterization, DWI may be an adjunct to the more conventional MR imaging techniques but should be interpreted along with the signal of the lesion as observed on conventional sequences, especially in musculoskeletal cancers. Regarding the monitoring of response to therapy in cancer or inflammatory disease, the use of ADC value may represent a more reliable additional tool but must be compared to the initial ADC value of the lesions along with the knowledge of the actual therapy.