Η παρούσα διπλωματική εργασία πραγματεύεται την μελέτη και το σχεδιασμό μιας τριφασικής ανορθωτικής διάταξης με την οποία επιτυγχάνεται διόρθωση του συντελεστή ισχύος. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Κύριος σκοπός αυτής της διπλωματικής εργασίας είναι η κατασκευή ενός μετατροπέα ανόρθωσης ανύψωσης ο οποίος λειτουργεί σε ασυνεχή αγωγή και μπορεί να τοποθετηθεί στην έξοδο μιας ανεμογεννήτριας σαν πρώτο στάδιο σύνδεσης με το δίκτυο. Απώτερος σκοπός είναι η πειραματική επιβεβαίωση της θεωρίας καθώς και του μηχανισμού με τον οποίο επιτυγχάνεται η διόρθωση του συντελεστή ισχύος. Αρχικά γίνεται μια γενική αναφορά στην έννοια της ποιότητας ισχύος, τα χαρακτηριστικά της μεγέθη, το συντελεστή ισχύος και τις ανώτερες αρμονικές. Επίσης αναφέρονται βασικές τριφασικές ανορθωτικές διατάξεις με διορθωμένο συντελεστή ισχύος ενώ γίνεται και μια γενική αναφορά στα αιολικά συστήματα, τον τρόπο λειτουργίας τους και την σύνδεση τους με το δίκτυο. Στη συνέχεια, αναλύεται η λειτουργία του μετατροπέα που κατασκευάστηκε κατά την διάρκεια αυτής της διπλωματικής εργασίας, δηλαδή τριφασικής διάταξης ανόρθωσης-ανύψωσης με ένα διακοπτικό στοιχείο, που λειτουργεί στην περιοχή ασυνεχούς αγωγής (DCM). Ο μετατροπέας αυτός θα δέχεται πολική τάση στην είσοδο του 40-100V, ανυψώνοντας την στα 350V στην έξοδο. Παράλληλα το ρεύμα εισόδου έχει μικρό αρμονικό περιεχόμενο επιτυγχάνοντας έναν υψηλό συντελεστή ισχύος. Το επόμενο βήμα είναι η μοντελοποίηση και η προσομοίωση του μετατροπέα σε περιβάλλον Matlab/Simulink έτσι ώστε να εξακριβωθεί η ορθή λειτουργία του σύμφωνα με τη θεωρητική ανάλυση. Τέλος, μελετάται και κατασκευάζεται στο εργαστήριο η πειραματική διάταξη με την οποία διεξάγονται μετρήσεις για την επιβεβαίωση και αξιολόγηση της θεωρητικής μελέτης. / In this diploma thesis the analysis and design of a three phase rectifier achieving high power factor are presented. This work was developed in the Laboratory of Electromechanical Energy Conversion at the Department of Electrical Engineering and Computer Technology of the Polytechnic School, University of Patras, Greece. The main purpose of this diploma thesis is the implementation of a Power Factor Correction Three Phase Rectifier operated in Discontinuous Current Mode (DCM) which can be used as a first stage for the connection of a small wind turbine to the grid. Through this work, the theoretical analysis and the mechanism that achieves the high power factor are verified through the implementation of a laboratory prototype. Initially, the concepts of power quality, power factor and high order harmonics are explained. Furthermore, some common power factor correction rectifier topologies are reported as well as a reference on wind turbines, their operation and their connection to the grid. Secondly, the working principle of the Single Switch Power Factor Correction DCM Boost Rectifier is presented. This converter is designed to rectify and boost the voltage of a small wind turbine, varying between 40 and 100V line to line rms, to 350Vdc. In addition the converter’s input current presents low harmonic distortion which results in a high power factor. The following step is to model and simulate the converter in Matlab/Simulink in order to verify its operation based on the theoretical analysis. Finally, a laboratory prototype is designed and implemented, on which experiments are conducted, in order to verify and evaluate the theoretical study.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 6, 2009). Thesis advisor: Dr. Naz E. Islam. Includes bibliographical references.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Cash can be seen as a fast moving consumer good. Approaching cash as inventory within the ATM cash management environment of a South African retail bank, provided the opportunity to apply well known industrial engineering techniques to the financial industry. This led to the application of forecasting, inventory management, operational research and simulation methods. A forecasting model is designed to address the multiple seasonalities and calendar day effects that is prevalent in the demand for cash. Special days, e.g. paydays, lead to an increase in demand for cash. The weekday on which the special day falls will also influence the demand. The multiplicative Holt-Winters method is combined with an improvised distribution method to determine the demand for cash for the region and per ATM. Reordering points are calculated and simulated to form an understanding of the effect this will have on the ATM network. Direct replenishment and the traveling salesman problem is applied and simulated to determine the difference in using one or the other. Various simulation models are build to test the operational and financial impact when certain variables are amended. It is evident that more work is required to determine the optimal combination of variable values, i.e. forecasting frequency, aggregate forecasting or individual forecasting, reorder levels, loading levels, lead times, cash swap or cash add, and the type of transportation method. Each one of these are a science in itself and cannot be seen (calculated) in isolation from the other as a change in one can affect the overall operational efficiency and costs of the ATM network. The thesis proves that significant cost savings is possible, compared to the current set-up, when applying industrial engineering techniques to a geographical ATM network within South Africa. / AFRIKAANSE OPSOMMING: Kontant kan gesien word as vinnig bewegende verbruikersgoedere. Deur kontant te benader as voorraad binne die ATM kontant bestuur omgewing van ’n Suid Afrikaanse kleinhandelsbank, het dit die geleentheid geskep om bekende bedryfsingenieurstegnieke toe te pas in die finansiële industrie. Dit het gelei tot die toepassing van vooruitskatting, voorraadbestuur, operasionele navorsing en simulasie metodes. ’n Vooruitskattingsmodel is ontwerp om die verskeie seisoenaliteite en kalenderdae effekte wat deel uitmaak van die vraag na kontant aan te spreek. Spesiale dae, bv. betaaldae, lei tot ’n toename in die vraag na kontant. Die weeksdag waarop die spesiale dag voorkom sal ook ’n invloed hê op die vraag. Die multiplikatiewe Holt-Winters metode is gekombineer met ’n geïmproviseerde verspreidingsmetode om die vraag na kontant vir die streek en per ATM the bepaal. Bestellingsvlakke is bereken en gesimuleer om ’n prentjie te skep van die invloed wat dit op die ATM netwerk sal hê. Direkte hervulling en die handelsreisigerprobleem is toegepas en gesimuleer om die verskille te bepaal tussen die gebruik van of die een of die ander. Veskeie simulasie modelle is gebou om die operasionele en finansiële impak te toets, wanneer sekere veranderlikes aangepas word. Dit is duidelik dat meer werk nodig is om die optimale kombinasie van veranderlike waardes te bepaal, bv. vooruitskatting frekwensie, totale vooruiskatting of individuele vooruitskatting, bestellingsvlakke, leitye, kontant omruiling of kontant byvoeging, en die tipe vervoermetode. Elkeen van hierdie is ’n wetenskap op sy eie en kan nie in isolasie gesien en bereken word nie, want ’n verandering van een se waarde kan die hele operasionele doeltreffendheid en kostes van die ATM netwerk beïnvloed.

Orientador: Ennio Peres da Silva / Dissertação ( mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-17T04:55:49Z (GMT). No. of bitstreams: 1 Gambetta_Francielle_M.pdf: 4780185 bytes, checksum: f2071d96fca67109088a5766792577eb (MD5) Previous issue date: 2010 / Resumo: Para países com disponibilidade de energia elétrica relativamente barata, como o Brasil, o custo de instalação é o fator mais importante para a produção de hidrogênio eletrolítico, representando mais de 50% do custo total. O retificador de corrente é um dos principais equipamentos que compõem um sistema de eletrólise da água e é objeto de estudo desta dissertação. A partir de uma análise técnica, concluiu-se que, atualmente, o sistema de retificação mais adequado ao processo de produção de hidrogênio eletrolítico é o sistema a tiristor, principalmente por apresentar maior eficiência e confiabilidade operacional. Por meio de uma análise de mercado, concluiu-se que o mercado nacional, em sua maioria, está apto a fornecer retificadores industriais apenas para aplicação em eletrolisadores unipolares, já o mercado internacional possui uma vasta gama de retificadores com diversos níveis de tensão e corrente de saída, sendo capaz de fornecer estes equipamentos tanto para alimentar eletrolisadores industriais unipolares quanto bipolares. O custo do hidrogênio foi calculado tomando como base estudos anteriores e utilizando a Energia Vertida Turbinável (EVT) da UHE de Itaipu, o que resultou em US$ 2,66/kg para uma planta com capacidade de produzir 4.365 m3/h de hidrogênio. A influência do custo do retificador sobre o custo de produção é de 10,8% e, assim, uma diminuição de 50% no custo deste equipamento promoveria uma redução de 5,4% no custo do hidrogênio eletrolítico. Apesar de pequena, esta redução pode ser determinante em muitos casos. Assim, a introdução de uma linha de pesquisa em um pólo tecnológico para o desenvolvimento destes equipamentos é interessante, pois além de contribuir com a redução do custo do hidrogênio eletrolítico, representa uma oportunidade de crescimento econômico que pode colocar o Brasil em destaque de forma positiva dentro dos cenários energético e econômico mundiais / Abstract: For countries with relatively cheap electricity availability, such as Brazil, the cost of installation is the most important factor for the production of electrolytic hydrogen, representing more than 50% of the total. The power rectifier is one of the main devices comprising the water electrolysis system and it is the object of study in this dissertation. From a technical analysis, it was concluded that currently the most suitable system for electrolytic hydrogen production is the thyristor system, mainly due to its higher efficiency and operational reliability. Through market analysis, it was concluded that most of rectifiers available in the domestic market are designed only for use in industrial unipolar electrolysers. On the other hand, the international market has a wide range of rectifiers with different levels of voltage and current output, being capable of providing such equipment for both industrial unipolar and bipolar electrolysers. The cost of hydrogen was calculated using previous studies of the Spilled Turbinable Energy (STE) of Itaipu Hydroelectric Energy Plant, and resulted in US$ 2.66/kg for a plant with capacity to produce 4,365 m3/h of hydrogen. The influence of the rectifier cost on the gas production cost is 10.8%, and thus a decrease of 50% in the cost of such equipment would promote a reduction of 5.4% in the cost of the electrolytic hydrogen. Although small, this reduction can be decisive in many cases. Thus the introduction of a research line at a technological center for the development of this equipment is interesting, which also contributes to lowering the cost of electrolytic hydrogen and is an opportunity for economic growth to highlight Brazil in the worldwide energy and economic scenery / Mestrado / Mestre em Planejamento de Sistemas Energéticos

Σκοπός της συγκεκριμένης διπλωματικής εργασίας είναι η εξομοίωση ενός φωτοβολταϊκού συστήματος διασυνδεδεμένου στο τριφασικό δίκτυο με σκοπό τη μελέτη της λειτουργίας του και του καλύτερου σχεδιασμού του. Το σύστημα περιλαμβάνει τη φωτοβολταϊκή γεννήτρια, ένα φίλτρο διασύνδεσης της γεννήτριας με τον αντιστροφέα και ένα απλοποιημένο μοντέλο του τριφασικού συστήματος. Για την εξομοίωση του κυκλώματος το οποίο είναι χρονικά μεταβαλλόμενο λόγω της διακοπτικής λειτουργίας του μετατροπέα αναπτύσσεται μια συστηματική και αποτελεσματική μέθοδος για την ανάλυση κυκλωμάτων που περιέχουν e-R-L, C κλάδους και ιδανικούς διακόπτες. Χρησιμοποιώντας την τοπολογία του κυκλώματος και κατάλληλες μήτρες μετασχηματισμού οι εξισώσεις που περιγράφουν το αγώγιμο και μη αγώγιμο τμήμα του κυκλώματος προκύπτουν αυτόματα. Οι χρησιμοποιούμενες μήτρες μετασχηματισμού προκύπτουν με απλό και συστηματικό τρόπο από τις θεμελιώδης μήτρες του κυκλώματος. Σε κάθε βήμα προκύπτουν τα ρεύματα όλων των κλάδων του κυκλώματος από την επίλυση του αγώγιμου τμήματος αυτού και οι τάσεις των βαλβίδων που δεν άγουν από την επίλυση του μη αγώγιμου τμήματός του. Η μέθοδος είναι γενική και μπορεί να εφαρμοστεί για την μελέτη τυχόντων σφαλμάτων σε οποιοδήποτε τμήμα του κυκλώματος. Παρουσιάζονται τα αποτελέσματα της εξομοίωσης για λειτουργία του μετατροπέα ως ανορθωτή, ως αντιστροφέα, ως αντιστροφέα με φωτοβολταϊκή γεννήτρια και ως αντιστροφέα με φωτοβολταϊκή γεννήτρια και με ανιχνευτή σημείου μέγιστης ισχύος. Το χρησιμοποιηθέν μοντέλο θα μπορούσε να βελτιωθεί αν στην θέση του τριφασικού συστήματος χρησιμοποιηθεί ακριβέστερη αναπαράσταση του τριφασικού δικτύου στην οποία να περιλαμβάνεται και ο τριφασικός μετασχηματιστής ισχύος που διασυνδέει το φωτοβολταϊκό σύστημα με το AC δίκτυο. / The objective of this “Diploma Thesis” is the simulation of a grid connected photovoltaic (PV) system and the study of its operation. The system consists of a PV generator, a DC filter and a simplified model of the three-phase system. The method which was used for the simulation of the circuit (which is a varying topology circuit due to the switching operation of the converter) is a systematic, efficient and conceptually simple method for the analysis of circuits consisting of linear e, R, L, C elements and ideal switches. On the basis of well known network topological concepts a suitable transformation tensor is constructed at every step. This tensor constitutes a flexible and powerful tool to assemble automatically the necessary on-switch current and off-switch voltage equations required for any conduction pattern. The method is general and can be applied for the study of any random faults in any part of the circuit. Results of the simulation for operation of the converter as rectifier, as inverter with battery, as inverter with PV generator and as inverter with PV generator and with MPPT are presented. The used model could be improved if the three-phase system is more precisely represented by a power three-phase transformer which connects the PV system with the AC network.

Este trabalho apresentou a análise e a implementação prática do conversor CC-CC trifásico série ressonante operando no modo ZCS. A estrutura deste conversor foi modificada a fim de gerar um barramento CC isolado em alta frequência com tensões simetricamente divididas. Com base na teoria de retificadores multipulsos, a ponte de Graetz do estágio de saída do conversor CC-CC foi substituída por dois retificadores trifásicos, em ponte completa, conectados em série. O transformador isolador também necessitou de alterações, no sentido de alimentar isoladamente esses retificadores, conferindo independência ao funcionamento dos mesmos. Com isso, conseguiu-se grampear cada uma das saídas dos retificadores em uma tensão proporcional a tensão de alimentação do conversor, sem o uso de controladores. Nesse aspecto, o objetivo de gerar um barramento simétrico, propício à alimentação de inversores multiníveis do tipo NPC foi plenamente satisfeito. Demonstrou-se que a estratégia de geração de um barramento com tensões simetricamente divididas pode ser estendida a inversores com mais do que três níveis, caso do NPC. Todos os resultados teóricos foram confirmados através da implementação de um protótipo de 2 kW que atingiu um rendimento superior a 95%. / This work presents the analysis and practical implementation of the three-phase resonant series CC-CC converter operating in ZCS mode. The structure of this converter has been modified in order to generate a DC bus insulated at high frequency with symmetrically divided voltages. Based on the theory of multipulse rectifiers, the Graetz bridge of the output stage of the DC-DC converter has been replaced by two full-bridge three-phase rectifiers connected in series. The isolating transformer also needed changes, in the sense of feeding these rectifiers in isolation, giving independence to the operation of the same. As a result, each of the rectifier outputs was stapled to a voltage proportional to the drive voltage, without the use of controllers. In this respect, the objective of generating a symmetrical bus, suitable for feeding NPC multilevel inverters, was fully satisfied. It has been shown that the strategy of generating a bus with symmetrically divided voltages can be extended to inverters with more than three levels, in the case of the NPC. All theoretical results were confirmed by the implementation of a 2 kW prototype that achieved an efficiency of over 95%.

A presente dissertação tem como objetivo principal propor um conversor bridgeless SEPIC trifásico com elevado fator de potência, baseado em um conversor monofásico apresentado em Costa (2015). Como objetivo secundário e a fim de assimilar o funcionamento do conversor, é estudado o conversor monofásico e então é proposta uma modulação alternativa para comando dos transistores. Outro objetivo secundário é a aplicação do retificador proposto em um sistema de aerogerador de pequeno porte (AGPP), a fim de que este conversor possa processar a energia elétrica gerada sendo proposta também uma metodologia de controle de maximização da potência gerada (MPPT). No desenvolvimento do retificador monofásico é apresentada a análise teórica com cada modulação e posterior equacionamento. Posteriormente, são mostrados os resultados de simulação e experimentais para as duas modulações, podendo-se comparar rendimento, THD e fator de potência. As condições nominais para o conversor monofásico são: tensão eficaz de entrada de 220 V, tensão de saída de 200 V, frequência de comutação de 50 kHz e potência de saída de 500 W. Contextualizando a aplicação do retificador trifásico, é apresentado o funcionamento de um sistema de geração eólica, onde primeiramente tem-se uma introdução dos principais conceitos de energia eólica, seguido de um panorama do aproveitamento da energia eólica no mundo e no Brasil. Em seguida pode-se ver o funcionamento dos sistemas eólicos, apresentando as turbinas e geradores utilizados. Então, propõe-se um modelo, baseado em um retificador trifásico bridgeless SEPIC PFC em MCD processando a energia proveniente do aerogerador. O conversor proposto é então simulado e implementado, utilizando o método MPPT para controlá-lo, a fim de comprovar o modelo e a teoria proposta. As especificações para o conversor trifásico são: tensão eficaz de entrada de 90 V, tensão de saída de 250 V, frequência de comutação de 25 kHz e potência de saída de 1500 W. / The main objective of this dissertation is to propose a three-phase bridgeless SEPIC PFC rectifier, based on a single-phase converter presented in Costa (2015). As a secondary objective and in order to assimilate the operation of the converter, the single-phase converter is studied, and an alternative modulation is proposed for controlling the transistors compared with a traditional PWM modulation, in order to obtain results that justify or not its use in the converter proposed. Another secondary objective is the application of the proposed rectifier in a small-scale wind turbine system, in order that this converter can process the electric energy generated; also is proposed a methodology of control of maximization (MPPT) of generated power. To develop this study, is presented the theoretical analysis with each modulation, followed by design equations. Subsequently are shown the results of numerical simulation and experimental for the two modulations, being able to compare efficiency, THD and power factor. The nominal conditions for the single-phase converter are: rms input voltage of 220 V, output voltage of 200 V, switching frequency of 50 kHz and output power of 500 W. Contextualizing the application of the three-phase rectifier: has an introduction of the main wind power concepts, followed by an overview of wind energy in the world and in Brazil. Then one can see the operation of wind turbines and electrical generators. Next, is propose a system based on a three-phase bridgeless PFC SEPIC rectifier in DCM processing the energy from the wind turbine. This proposed model is then simulated and implemented using the MPPT method to control it, to prove the model and the proposed theory. The specifications for the three-phase converter are: rms input voltage of 90 V, output voltage of 250 V, switching frequency of 25 kHz and output power of 1500 W.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Many control techniques applied to converters with power factor correction (PFC) use cascaded control to compensate the output voltage and the input current. These techniques usually employ linear time-invariant (LTI) models and ignore the periodic output voltage oscillation by using compensator with low-pass characteristic. To ensure correlation between the rectifier and its LTI model, as well as power factor correction, these techniques reduce the crossing frequency, which result in a closed-loop voltage with poor dynamic response. Aiming to reduce the time-response designers have associated notch filters into the controller to increase the bandwidth. These filters increase the attenuation in ripple frequencies making possible to enlarge system bandwidth without compromising power factor correction. However, increasing the crossing frequency enhances the interaction between ac output components and the feedback system. In these cases, linear time-invariant (LTI) approach can not adequately represent the closed loop dynamics. As a result, LTI stability analysis based on LTI approach is no longer valid. On the other hand, a better dynamic representation can be achieved by using linear time-periodic models (LTP). These models include the modulation effects inherent in the output voltage dynamics. This work presents an alternative systematic methodology to perform the stability analysis for continuous-time closed-loop control systems using linear time-periodic (LTP) models. This methodology use an LTP representation in frequency domain called harmonic transfer function (HTF). This method extends the multi-variable LTI techniques for LTP approach. Finally is detailed the stability analysis of full-bridge and half-bridge single-phase PFC rectifiers. Theoretical, simulation and experimental results are presented to validate the proposed technique. / Muitas técnicas de controle aplicadas a retificadores monofásicos com correção do fator de potência (PFC) utilizam controladores em cascata para compensação da tensão de saída e da corrente de entrada. Essas técnicas, em geral, empregam modelos lineares e invariantes no tempo (LTI) e desconsideram as oscilações periódicas presentes nas tensões de saída, fazendo uso de leis de controle com características passa-baixa. Para garantir a correlação entre o modelo LTI e o retificador, bem como a correção do fator de potência, estas estratégias utilizam banda-passante reduzida, o que limita consideravelmente a resposta dinâmica da compensação da tensão. No intuito de reduzir o tempo de resposta da malha de tensão, sem comprometer a correção do fator de potência, projetistas têm associado filtros rejeita-banda à malha de controle. Esses filtros acentuam a atenuação nas frequências de interesse e, assim, possibilitam elevar a banda-passante sem comprometer a correção do fator de potência na entrada. Porém, a elevação da banda-passante aumenta a interação das componentes alternadas da tensão do lado cc com o sistema de compensação. Nestes casos, a abordagem LTI pode não representar adequadamente as dinâmicas de malha fechada e, consequentemente, não é válida para a análise da estabilidade. Por outro lado, uma melhor representação dinâmica da malha de compensação da tensão de retificadores PFC monofásicos pode ser obtida com a utilização de modelos lineares periódicos no tempo (LTP). Esses modelos dinâmicos incluem os efeitos de modulação inerentes da dinâmica da tensão de saída. Este trabalho apresenta uma metodologia sistemática alternativa para a análise da estabilidade de malha fechada de retificadores PFC monofásicos empregando-se modelos LTP em tempo contínuo. A metodologia de análise da estabilidade utiliza uma representação dos modelos LTP no domínio da frequência, denominado função de transferência harmônica (HTF). Esta representação estende as técnicas clássicas de análise da estabilidade de sistemas LTI multivariáveis para a abordagem LTP. Por fim, são detalhadas as análise de estabilidade dos retificadores monofásicos em ponte completa e meia ponte, considerando-se a operação com correção do fator de potência de entrada. Resultados teóricos, de simulação e experimentais são apresentados para validar a técnica de análise da estabilidade.

O aquecimento indutivo e uma técnica utilizada na indústria para obter resultados de fundição, brasagem, forjaria e também tratamento térmico, aplicação foco deste trabalho. O aquecimento indutivo dá-se através de campos eletromagnéticos induzidos a uma peca metálica, a qual se deseja aquecer. Isso faz com que haja um aumento de temperatura sobre a peca devido ao efeito joule, corrente de foucault e histerese, entre outros efeitos. Para gerar os efeitos acima relatados, são necessários conversores de alta potência e frequência. Tais conversores são compostos em muitos casos de: um retificador, um capacitor filtro de barramento, um inversor e um circuito ressonante. Neste trabalho e proposto a topologia de um circuito ressonante LLC sendo chaveado por um inversor ponte completa. Como todo circuito ressonante, em operação a frequências próximas da ressonância, as correntes são elevadas e consegue-se operar com chaveamento em comutação suave. Entre algumas vantagens da topologia LLC frente a topologias como a série-ressonante, por exemplo, podem-se citar: proteção contra curto-circuito e fácil casamento de impedância entre o circuito ressonante e o inversor. No entanto, conversores com retificadores comuns possuem baixo fator de potência, FP=0,5. Para resolver este problema, propõe-se a utilização de um retificador de alto fator de potência integrado ao conversor através do inversor, formando um sistema de aquecimento indutivo integrado a um retificador com alto fator de potência. Através de um dos braços de comutação do inversor, dá-se o controle do retificador e do conversor ao mesmo tempo. A técnica apresentada resulta em um projeto de custo reduzido e baixo nível de complexidade de implantação. Para controlar a potência do sistema e utilizada uma modulação PWM assimétrica com razão cíclica variável que controla os dois conversores simultaneamente. / Induction heating is a technique used in industry to get results like casting, brazing, forging and heat treatment also, application focus of this work. Induction heating occurs through electromagnetic fields induced in a metal part, which it wants to warm up. This means that there is an increase in temperature on the piece it wants to heat up due to the Joule effect, eddy current and hysteresis, among other effects. To generate the effects reported above, high power converters and frequency are required. These converters are composed in many cases by: a rectifier, filter capacitor DC Link, an inverter and a resonant circuit. This paper proposes the topology of LLC resonant circuit being switched by a full bridge inverter. Like any resonant circuit operating at near of the resonance frequencies, the currents are high and it is possible to operate with soft switching. Among some advantages of the LLC topology against other topologies such as series resonant, for example, can be mention: protection against short-circuit and easy impedance matching between the resonant circuit and the inverter. However, converters with common rectifiers have low power factor. To solve this problem, the use of a rectifier high power factor built into the converter is proposed. This rectifier is integrated into the converter through the inverter, forming a single stage high power factor induction heating system. Through an arm of the inverter is given the control of the rectifier and the converter at the same time. The technique presented results in low cost and low complexity implementation. An asymmetric PWM modulation is used with variable duty cycle to control the power system, which controls both converters at the same time.

A presente dissertação apresenta uma análise comparativa entre os resultados experimentais de dois retificadores monofásicos. Também apresenta o estudo e projeto de um retificador trifásico, o qual é destinado ao processamento de energia elétrica proveniente de aerogeradores de pequeno porte. Ambos retificadores possuem elevado fator de potência, são modulados por largura de pulso e são baseados no conversor CC-CC SEPIC operando no modo de condução descontínuo. Com a finalidade de validar os estudos teóricos, são apresentados os resultados obtidos via simulação numérica e os resultados experimentais obtidos de cada um dos três retificadores. As especificações dos retificadores monofásicos são: potência processada de 500W; tensão de entrada de 220V; tensão de saída de 200V; frequência de comutação de 50kHz. As especificações do retificador trifásico são as mesmas que a dos monofásicos, exceto, pela potência processada que é de 1,5kW. / The present master thesis presents a comparative analysis between the experimental results of two single-phase rectifiers. Also presents the study and design of a three-phase rectifier, which is intended for processing power from small wind turbines. Both rectifiers have high power factor, is modulated by pulse width and are based on DC-DC SEPIC converter operating in discontinuous conduction mode. In order to validate the theoretical studies, presents the results obtained by numerical simulation and experimental results for each of the three rectifiers. The specifications of the single-phase rectifiers are: processed power of 500W; input voltage of 220V; output voltage of 200V; 50kHz switching frequency. The specifications of the three-phase rectifier is the same as that of single phase, except that it is processed by the power of 1.5kW.