Tecnologias HVDC que utilizam conversores do tipo fonte de tensão, o VSC-HVDC, ainda não são completamente difundidas e aplicadas no Brasil, em contraste com outros países que começaram a estudar e empregar este tipo de transmissão. Comparado com o HVDC tradicional, o VSC-HVDC é uma tecnologia de transmissão mais eficiente e pode superar deficiências encontradas na transmissão em corrente contínua convencional. O VSC-HVDC pode ser utilizado de maneira mais eficiente nas novas redes de energia, para alimentar ilhas, integração de geração eólica, renovação das linhas em centros urbanos, aplicações multiterminais e conexão com sistemas fracos. Por se tratar de uma tecnologia recente, o VSC-HVDC ainda não é amplamente adotado e uma das principais limitações da utilização destes sistemas é a sua fragilidade diante faltas na linha de corrente contínua. Neste contexto, limitadores de corrente de falta (LCF) podem ser utilizados para minimizar o impacto das faltas. A ação dos limitadores é benéfica ao sistema durante condições de falta, contudo, ainda assim é necessária a atuação do sistema de proteção para extinguir a condição faltosa. Portanto, este trabalho visa propor e avaliar um novo esquema de proteção que opere de maneira seletiva e confiável para sistemas VSC-HVDC na presença de LCF baseados em materiais supercondutores ou LCF indutivos. Para tanto, foram implementadas quatro funções de proteção tradicionais das linhas em CC, a saber: direcional de corrente, diferencial, sobrecorrente com restrição de tensão e ondas viajantes, e ainda, foi proposta uma nova função de proteção, a de condutância, a qual apresentou o menor tempo de identificação de falta, considerando as faltas mais severas. Adicionalmente, foi avaliado o comportamento destas funções quando o sistema apresenta os LCF em série com a linha. Foi demonstrado que é possível extrair os benefícios dos LCF sem deteriorar a qualidade dos resultados das funções de proteção, o que aumenta a segurança e confiabilidade dos sistemas VSC-HVDC, uma vez que os impactos das faltas são minimizados e as mesmas são identificadas em um curto intervalo de tempo. / HVDC technology based on voltage source converters, VSC-HVDC, are not yet fully disseminated and applied in Brazil, in contrast to other countries that have begun to study and widely employ this type of transmission technology. When compared with traditional HVDC systems, VSC-HVDC systems are more efficient and can overcome the challenges encountered in the conventional direct current transmission. The VSC-HVDC can be used more efficiently in the new energy networks to feed islands, integration of wind generation, renewal of lines in urban centers, multiterminal applications and connection with weak systems. Because it is a recent technology, VSC-HVDC is not yet widely adopted and a major limitation of using these systems is their weakness against faults in the DC line. In this context, fault current limiters (FCL) can be used to minimize the impact of faults. The action of the limiters is beneficial to the system during fault conditions, however, the use of protection schemes to detect the fault and extinguish the faulty condition is still required. Therefore, this work aims to propose and evaluate a new protection scheme operating in selective and reliable way for VSC-HVDC systems in the presence of FCL based in superconductor materials or inductive FCL. To reach such a goal, in this work it has been implemented four traditional DC lines protection functions, namely: directional current, differential, overcurrent with voltage restraint and traveling waves, and also proposed a new protection function, which is based on the conductance. This last protection function has presented the lowest detection time, when considering the most severe faults. In addition, it was evaluated the behavior of these functions when the system presents the FCL in series with the DC line. It has been shown that it is possible to extract the benefits of FCL without deteriorating the quality of the results of the protection functions, which increases the safety and reliability of the VSC-HVDC systems, since the impact of faults is minimized and they are identified in a short time.

The following is a thesis project involving investigation of applicability of trench type IGBTs in present and future VSC based HVDC convertors. The work involves three major sections – theoretical loss evaluation of adoption of Trench technology (both IGBT and BIGT) for HVDC Light® applications, testing the Trench IGBT prototype with existing gate units and finalizing with a hypothesis and a practical solution for unexplained turn-on phenomenon observed during testing. The thesis concludes with the suggestion of suitable driving mechanisms (e.g. reduced number of current sources and removal of active gate snubbers) which shall result in both simpler and more cost effective driving compared to the present employed methods. / Följande avhandling är en studie om tillämpligheten av trench type IGBTer i nuvarande och framtida VSC baserade HVDC konverterare. Arbetet omfattar tre övergripande delar – teoretisk förlustberäkning vid tillämpning av trench teknologi (både IGBT och BIGT) till HVDC Light applikationer, prov av Trench IGBT prototyp med befintliga gate enheter och slutligen en hypotes och praktisk lösning till oförklarliga turn-on fenomen som observerats under prövning. Avhandlingen avslutas med en sammanfattning över lämpliga drivningsmekansimer (t.ex om antal strömkällor och borttagning av aktiv snubber vid gate enheten) som torde resultera både i enklare och kostnadseffektivare drivning jämfört metoder som tillämpas idag

Dans le domaine du transport de l'électricité, les qualités intrinsèques des réseaux alternatifs s'estompent devant la difficulté imposée par le transport de la puissance réactive lorsque les lignes aériennes ou, plus particulièrement, les câbles souterrains ou sous-marins atteignent des longueurs critiques. Dans le cadre des réflexions visant à exploiter au mieux les énergies renouvelables d'origine éolienne off-shore ou hydrolienne, l'hypothèse de la création d'un réseau électrique à haute tension continue pour acheminer ces énergies jusqu'aux centres de consommation est considérée. Ce travail de thèse est en lien avec le projet européen TWENTIES (Transmission system operation with large penetration of Wind and other renewable Electricity sources in Networks by means of innovative Tools and Integrated Energy Solutions, ref 249812), financé dans le cadre du programme FP7 de la Commission Européenne. Ces travaux traitent de la protection des réseaux à courant continu contre les défauts d'isolement dans les câbles et au niveau des jeux de barre. L'étude se concentre sur des réseaux multi-terminaux bouclés et/ou maillés, et propose d'étudier la faisabilité d'un plan de protection comportant un algorithme principal et un secours en cas de défaillance d'un disjoncteur. / In the area of power transmission grids, the inherent qualities of alternative current networks fade behind the difficulty imposed by the transmission of the reactive power when overhead lines or, particularly, underground or undersea cables reach critical lengths. As part of thought aimed for operate at best renewable energy resources, namely wind or marine resources, the assumption of the creation of a high voltage direct current power grid to dispatch those energies to the consumption centers is considered. This Ph.D work is linked to the European project TWENTIES (Transmission system operation with large penetration of Wind and other renewable Electricity sources in Networks by means of innovative Tools and Integrated Energy Solutions, ref 249812), funded as a part of the 7th framework program of the European Commission. This work deal with the protection of DC grids against insulation faults occurring in the cables or at a busbar. The study focusses on meshed and/or looped multi-terminal grids, and proposes to study the feasibility of a protection plan including a main protection algorithm and a backup in case of breaker failure.

Titel: Kostnadskalkylering för lean-företag – En systematisk litteraturstudie Författare: Max Börjesson Handledare: Helena Forslund Examinator: Elin Funck Lärosäte: Ekonomihögskolan vid Linnéuniversitetet i Växjö Kurs: Examensarbete i controller för Civilekonomprogrammet Nyckelord: lean, kostnadskalkylering, standardkostnader, activity based costing, ABC, value stream costing, VSC. Bakgrund och problemformulering: lean är en filosofi som fått stort genomslag. Samtidigt kräver användandet av filosofin anpassningar, bland annat i företags kostnadskalkylering. I den befintliga forskningen är det inte tydligt vilken forskning som faktiskt passar bäst för företag som använder lean. Syfte: Syftet med studien är att kartlägga forskningen om kostnadskalkylering tillsammans med lean, samt utreda vilket av verktygen för kostnadskalkylering som passar bäst för företag som använder lean. De verktygen som undersöks är standardkostnader, ABC och VSC. Metod: metoden är baserad på en systematisk litteraturstudie, kompletterat med ett teorikapitel. Slutsats: studien visar att kostnadskalkylering för lean-företag är ett område som fått ett ökat intresse sedan år 2002. Den identifierade litteraturen kommer framförallt från Europa och Nordamerika. Standardkostnader används ofta som en jämförelse till andra verktyg, medan activity based costing och value stream costing ofta har en mer central roll i studier. I studien har få fördelar med standardkostnader identifierats. Både activity based costing och value stream costing framstår som lämpliga, utifrån den litteraturen som finns idag. / Title: Lean Cost Accounting – A Systematic Literature Review Author: Max Börjesson Tutor: Helena Forslund Examiner: Elin Funck Institution: School of Business and Economics, Linnaeus University, Växjö Course: Degree Project in Controlling, The Business Administration and Economics Programme, 4FE18E. Keywords: lean, cost accounting, standard costing, activity based costing, ABC, value stream costing, VSC. Background and problem discussion: the interest for lean has been great. Implementation of lean requires companies to make adoptions. One of the adoptions that needs to made is in the cost accounting. The current literature has not identified what the best method for lean companies is. Purpose: the purpose of this study is to identify the existing research about cost accounting for lean companies, and to examine the method that fits lean companies the best. The tools used are standard costing, activity based costing and value stream costing. Method: A systematic literature review is used in this study. Conclusion: This study shows that the interest for cost accounting for lean companies has developed since 2002. The identified literature is primarily from Europe and North America. Standard costing is often used for comparisons with other tools. Activity based costing and value stream costing have a more central role in studies when they are used. This study has not identified any benefits of using standard costing, while both activity based costing and value stream costing seem to be useful.

The thesis describes the development of a model of the three-phase Voltage Source Converter (VSC) in the Harmonic State Space (HSS) domain, a Linear Time Periodic (LTP) extension to the Linear Time Invariant (LTI) state space. The HSS model of the VSC directly captures harmonic coupling effects using harmonic domain modelling concepts, generalised to dynami- cally varying signals. Constructing the model using a reduced-order three-phase harmonic signal representation achieves conceptual simplification, reduced computational load, and direct inte- gration with a synchronous frame vector control scheme. The numerical switching model of the VSC is linearised to gain a small-signal controlled model, which is validated against time-domain PSCAD/EMTDC simulations. The controlled model is evaluated as a STATCOM-type system, exercising closed-loop control over the reactive power flow and dc-side capacitor voltage using a simple linear control scheme. The resulting state- space model is analysed using conventional LTI techniques, giving pole-zero and root-locus analyses which predict the dynamic behaviour of the converter system. Through the ability to independently vary the highest simulated harmonic order, the dependence on the closed-loop response to dynamic harmonic coupling is demonstrated, distinguishing the HSS model from fundamental-only Dynamic Phasor models by its ability to accurately model these dynamics.

In this master thesis control systems for a voltage-source converter HVDC connected to weak ac networks are investigated. HVDC stands for high voltage direct current and is a way to transfer power in the electrical power system. A HVDC uses direct current (dc) instead of alternate current (ac) to transfer power, which requires transformation between ac and dc since most power grids are ac networks. The HVDC uses converters to transform ac to dc and dc to ac and the converter requires a control system. A complete control system of a voltage source converter HVDC contains many different parts. The part investigated in this thesis is the active power control. Different structures containing PID controllers have been tested and evaluated with respect to stability and performance using control theory. The impact of weak ac networks has been evaluated in regards to the different control structures. The investigations have been conducted using mainly steady-state simulations. Based on the simulation and analyzes of the simulation results a promising control structure has been obtained and suggested for further investigation.

L’IRM apporte des informations morphologiques concernant la tumeur, mais également des informations concernant sa micro-vascularisation. En TEP/TDM, l’accumulation de la 18F-FDopa dans les cellules tumorales résulte de l’activité métabolique plus importante que celle des tissus sains. Nous avons étudié 28 gliomes pour lesquels nous avons analysé les données provenant d’IRM et de TEP/TDM. Une méthode de recalage a été développée afin de combiner les informations issues des deux modalités TEP et IRM et d’extraire des volumes d’intérêt sur la base des données conjointes TEP et IRM. L’analyse du contenu de ces volumes d’intérêt par un modèle de mélange gaussien a permis de différencier, dans ces volumes, les tissus tumoraux et les tissus sains, et d’obtenir ainsi des volumes tumoraux et de référence communs pour les modalités TEP et IRM. Des paramètres issus de la TEP ou de l’IRM ont ensuite été calculés dans ces volumes communs aux deux modalités, pour caractériser les tumeurs et les tissus sains. L’analyse discriminante linéaire (ADL) des données TEP/TDM et d’IRM combinées permet de discriminer les différentes classes tissulaires. Les courbes Receiver Operating Characteristic ROC combinées à l’ADL permettent d’évaluer les critères multiples [SUVmax , rCBV] et [rk1 , rCBV] et conduisent à des AUC respectives de 0,88 et 0,92. En considérant les informations combinées [SUVmax , rCBV], nous avons obtenu une sensibilité de détection des tumeurs de haut grade de 95% pour une spécificité correspondante de 60% ainsi qu’une valeur prédictive négative de 52% pour une valeur prédictive positive de 95%. De même, avec le critère [rk1 , rCBV], nous avons obtenu une spécificité de 60% pour 95% de sensibilité de détection des tumeurs de haut grade ainsi qu’une valeur prédictive négative de 60% pour une valeur prédictive positive de 95%. Nos travaux montrent que la fusion des informations microvasculaires et métaboliques est possible. Dans le cas du diagnostic différentiel des gliomes, l’information microvasculaire n’apporte cependant pas d’information plus discriminante que l’information métabolique seule. / MRI provides morphological information about tumour, but also provides information regarding the micro-vascularization of the tumour. In PET/CT, the accumulation of 18F-FDopa in tumour cells results from the metabolic activity greater than that of healthy tissues. We studied 28 gliomas for which we analysed data from MRI and PET/CT. A registration method has been developed to combine information from both PET and MRI and to extract volumes of interest consistent with the information included in the two modalities. In these volumes, the tumour compartment and normal tissue compartment were identified using a Gaussian mixture model. Parameters from PET or MRI data were then calculated in these compartments. ROC analyses combined with linear discriminant analyses were used to assess whether joint observation of standardized uptake value (SUVmax ) and relative Cerebral Blood Volume (rCBV) or of relative rk1 and rCBV could distinguish between low grade and high grade tumours. We found that using this joint analysis, 82.4% of high-grade tumors and 70.0% of low-grade tumors were correctly classified (AUC of 0.88 for [SUVmax , rCBV] and of 0.92 for [rk1 , rCBV]). Considering the [SUVmax , rCBV] combined information, the sensitivity for detecting high-grade tumors was 95% with a specificity of 60%. The negative predictive value was 52% for a positive predictive value of 95%. Similarly, considering the [rk1 , rCBV] combined information, we also a specificity of 60% associated with a 95% sensitivity for detecting high-grade tumors, with a negative predictive value of 60% and positive predictive value of 95%. Our work shows that joint analysis of microvascular and metabolic information is possible by combining PET and MR imaging data. However, we found that, in our patient population, the microvascular information given by MR did not bring information more discriminating than the metabolic information derived from PET only.

The deterioration in power quality due to the increase in non linear loads has sparked a new interest in the filtering techniques used in transmission and distribution systems. Unlike passive filters, active filters are adaptable to rapidly changing source impedance and provide the necessary harmonic compensation for varying non-linear loads. This thesis models a Voltage Source Converter (VSC) based shunt active filter (SAF) to filter harmonics due to large non linear loads. SAF compensates the harmonics by injecting a compensating current which is equal in magnitude but opposite in phase to the disturbance in the system. The power circuit of this SAF consists of a three-phase VSC and the switching signals for this converter is generated by hysteresis based current modulation method. The controller uses the sinusoidal current control strategy of the generalized instantaneous p-q control theory to calculate the reference compensating current. Proposed SAF is simulated using EMTP-RV simulation package under steady state and dynamic conditions and its effectiveness in mitigating harmonics is tested. The stability and response of the SAF is also tested satisfactorily under transient load and severe AC / DC fault conditions. / UOIT

The interest in the utilization of offshore wind power is increasing significantly. Due to the shortage of in-land locations for wind farm and the wind speed offshore is potentially higher than that of onshore, which leads to a much higher power production. In this thesis a large offshore wind farm is modeled using Matlab simulation package. In the simulations active stall regulated wind turbines driving fixed speed asynchronous generators are used. Two different types of interconnections are modeled and compared, one is the Voltage Source Converter (VSC) based HVDC link and the other one uses high voltage AC (HVAC) cable interconnection. Transmission faults are simulated in each system and the transient response are examined. Three phase fault and single line to ground fault are used to compare the performance of the VSC based HVDC interconnection system and HVAC interconnection. It is found that compared to the traditional HVAC transmission, the VSC based HVDC transmission would have better performance under various system disturbances.

Presently power systems are being operated under high stress level conditions unforeseen at the moment they were designed. These operating conditions have negatively impacted reliability, controllability and security margins. FACTS devices and HVDC transmissions have emerged as solutions to help power systems to increase the stability margins. VSC-HVDC transmissions are of particular interest since the principal characteristic of this type of transmission is its ability to independently control active power and reactive power. This thesis presents various control strategies to improve damping of electromechanical oscillations, and also enhance transient and voltage stability by using VSC-HVDC transmissions. These control strategies are based of different theory frames, namely, modal analysis, nonlinear control (Lyapunov theory) and model predictive control. In the derivation of the control strategies two models of VSC-HVDC transmissions were also derived. They are Injection Model and Simple Model. Simulations done in the HVDC Light Open Model showed the validity of the derived models of VSC-HVDC transmissions and the effectiveness of the control strategies. Furthermore the thesis presents an analysis of local and remote information used as inputs signals in the control strategies. It also describes an approach to relate modal analysis and the SIME method. This approach allowed the application of SIME method with a reduced number of generators, which were selected based on modal analysis. As a general conclusion it was shown that VSC-HVDC transmissions with an appropriate input signal and control strategy was an effective means to improve the system stability. / QC 20110412