Dissertations / Theses on the topic 'Snubber'

Made available in DSpace on 2016-12-12T20:27:39Z (GMT). No. of bitstreams: 1 Luiz Ricardo Lima.pdf: 7933900 bytes, checksum: 225fa96a5d447127d12b2a23f0483893 (MD5) Previous issue date: 2011-08-12<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>This work presents a study about the NPC (Neutral Point Clamped) three-level inverter with a modified Undeland snubber and using a Buck-Boost converter to regenerate the energy processed by the snubber. Initially, qualitative and quantitative analysis of this inverter with the presence of the snubber are presented and a project methodology is proposed. The same analysis and project are presented for the Buck-Boost converter and it is shown that this converter can operate under ZVS (Zero Voltage Switching). Next, mathematical models of all circuitry necessary for the realization of the digital control of the inverter are presented and a controller is projected. Using data of the projected NPC inverter, Buck-Boost converter and digital controller, simulation results are presented. These simulations were done using software s Orcad Pspice and Simulink. Finally, implementation details and experimental results of a 1.5 kW, 800 V input voltage, 127 V output voltage and 200 kHz switching frequency prototype are presented.<br>Este trabalho apresenta um estudo do inversor NPC (Neutral Point Clamped) a três níveis com snubber de Undeland modificado, utilizando um conversor Buck-Boost para regeneração da energia processada pelo snubber. Inicialmente são feitas analises qualitativa e quantitativa desse inversor com a presença do snubber e é apresentada uma metodologia de projeto. As mesmas analises e projeto são feitos para o conversor Buck-Boost e é mostrado como ele pode operar com comutação ZVS (Zero Voltage Switching). A seguir são mostrados os modelos matemáticos de todos os circuitos necessários para se realizar o controle digital do inversor e é apresentado um projeto de controlador digital. Utilizando os dados de projeto do inversor NPC, do conversor Buck-Boost e do controle são apresentados os resultados de simulações feitas nos programas Orcad Pspice e Simulink. Por ultimo, são apresentados detalhes de implementação e resultados experimentais de um protótipo de 1,5 kW, 800 V de tensão de barramento, 127 V de tensão de saída e 200 kHz de freqüência de comutação.

In the application of power inverters, power density has become a key design specification where it has stringent requirements on system size and weight. Achieving high power density need to combine lasted wide bandgap (WBG) device technology and high switching frequency to reduce passive filter size thus further shrink overall space. While still maintaining decent power conversion efficiency and low electromagnetic interference (EMI) with higher switching frequency, soft-switching needs to be implemented. A novel auxiliary resonant snubber is introduced. The design and operation are carried out, in which this snubber circuitry enables main Gallium Nitride (GaN) switches operating under zero voltage switching (ZVS) condition, and auxiliary Silicon Carbide (SiC) diodes switching under zero current switching (ZCS) condition. Besides, the auxiliary snubber circuitry gating algorithm is also optimized which allows reduction of the switching and conduction loss in auxiliary GaN switches to obtain higher system efficiency and better thermal performance. Here, this novel auxiliary resonant snubber circuitry is applied to a traditional full bridge inverter with flexible modulation suitability. This proposed inverter can be applied to a wide range of potential applications, such as string solar inverter, renewable energy combined distributed generation, dc-ac part of bi-directional electrical vehicle (EV) on-board charger, and uninterruptible power supply (UPS), etc.<br>Master of Science

With the rise in demand for renewable energy sources, photovoltaics have become increasingly popular as a means of reducing household dependence on the utility grid for power. But solar panels generate dc electricity, a dc to ac inverter is required to allow the energy to be used by the existing ac electrical distribution. Traditional full bridge inverters are able to accomplish this, but they suffer from many problems such as low efficiency, large size, high cost, and generation of electrical noise, especially common mode noise. Efforts to solve these issues have resulted in improved solutions, but they do not eliminate all of the problems and even exaggerate some of them. Soft switching inverters are able to achieve high efficiency by eliminating the switching losses of the power stage switches. Since this action requires additional components that are large and have additional losses associated with them, these topologies have traditionally been limited to higher power levels. The resonant snubber inverter is a soft switching topology that eliminates many of these problems by taking advantage of the bipolar switching action of the power stage switches. This allows for a significant size reduction in the additional parts and elimination of common mode noise, making it an ideal candidate for lower power levels. Previous attempts to implement the resonant snubber inverter have been hampered by low efficiency due to parasitics of the silicon devices used, but, with recent developments in new semiconductor technologies such as silicon carbide and gallium nitride, these problems can be minimized and possibly eliminated. The goal of this thesis is to design and experimentally verify a design of a resonant snubber inverter that takes advantage of new semiconductor materials to improve efficiency while maintaining minimal additional, parts, simple control, and elimination of common mode noise. A 600 W prototype is built. The performance improvements over previous designs are verified and compared to alternative high efficiency solutions along with a novel control technique for the auxiliary resonant snubber. A standalone and grid tie controller are developed to verify that the auxiliary resonant snubber and new auxiliary control technique does not complicate the closed loop control.<br>Master of Science

This thesis presents an analytical approach using Root-Loci method for designing optimum passive series RC snubbers for continuous-current synchronous buck switch mode power supply (SMPS). Synchronous buck SMPS is the most popular power converter topology found in modern consumer electronics. It offers relatively good efficiency to target the high-current and low-voltage requirements while it is also relatively inexpensive to implement. Passive series RC snubbers are simple, efficient and cost-effective open-loop equalizer circuit for synchronous buck SMPS. Its purpose is to control and to balance between the rate of rise and the overshoots of transient switching waveform in order to optimize efficiency and reliability Existing methods of RC snubber design are solely based on second-order approximation. It is investigated in this research that this approximation is highly inaccurate in SMPS applications because higher order equivalent models are required for the load path of the SMPS. The results using the RC snubbers obtained from existing method are shown to be unsatisfactory without correlation to the calculations and simulations based on second-order approximation. Optimum RC values obtained using Root-Loci approach presented in this thesis are shown to correlate to both Spice simulation and lab measurements.

Electromagnetic interference (EMI) is a major concern in inverter motor drive systems. The sources of EMI have been commonly identified as high switching dv/dt and di/dt rates interacting with inverter parasitic components. The reduction of parasitic components relies on highly integrated circuit layout and packaging. This is the way to deal with noise path. On the other hand, switching dv/dt and di/dt can be potentially reduced by soft-switching techniques; thus the intensity of noise source is reduced. <p> In this paper, the relation between the dv/dt di/dt and the EMI generation are discussed. The EMI sources of a hard-switching single-phase PWM inverter are identified and measured with separation of common-mode and differential-mode noises. The noise reduction in an auxiliary resonant snubber inverter (RSI) is presented. The observation of voltage ringing and current ringing and the methods to suppress these ringing in the implementation of RSI are also discussed. The test condition and circuit layout are described as the basis of the study. And the experimental EMI spectra of both hard- and soft-switching inverter are compared. The effectiveness and limitation of the EMI reduction of the ZVT-RSI are also discussed and concluded. <p> The control interface circuit and gate driver design are described in the appendix. The implementation of variable charging time control of the resonant inductor current is also explained in the appendix.<br>Master of Science

Thesis (MScEng)--University of Stellenbosch, 2001.<br>ENGLISH ABSTRACT: This thesis describes the study of two soft-switching inverter topologies that are well suited to high-power applications. For the first topology, namely an active resonant turn-off snubber, the existing theory is expanded with a detailed study into operation strategies and topology protection. This is followed by an investigation into the second topology, which is a combined snubber that reduces both turn-off and turn-on losses. The investigation involves a detailed analysis of the losses in the snubber components and main devices, as well as a study into the effects of parasitic components and diode reverse recovery on the operation of the snubber. Based on this theory a snubber optimisation procedure is also developed. Possible operation strategies and protection techniques were also evaluated for this topology. Single-phase experimental inverters were used to verify the basic operation theory and switching loss prediction for both topologies. The thesis is concluded by the design and construction of a practical soft-switching threephase inverter. After implementation the experimental inverter is used for theory verification.<br>AFRIKAANSE OPSOMMING: Hierdie proefskrif beskryf die ondersoek na twee saggeskakelde omsetter topologieë wat veral geskik is vir hoë-drywing toepassings. Die bestaande teorie aangaande die eerste topologie, naamlik 'n aktiewe, resonante, afskakel gapser, word uitgebrei met 'n deeglike-studie oor bedryfstegnieke en beskermingsmetodes. Vervolgens word 'n gekombineerde gapser topologie, wat beide aanskakel- en afskakelverliese verminder, ondersoek. Die studie behels 'n volledige analise van die verliese in die omsetter en gapser komponente en die invloed van parasitêre komponente en diode tru-herstel. Hierdie teorie word ook gebruik om 'n optimale gapser ontwerp prosedure te ontwikkel. Die moontlikke bedryfstegnieke en beskermingsmetodes word ook vir hierdie topologie evalueer. In albei gevalle is eksperimentele, enkelfase omsetters gebruik om die teorie oor basiese werking en skakelverlies vermindering te verifieer. Die ondersoek word afgesluit deur die ontwerp en konstruksie van 'n praktiese, saggeskakelde, drie-fase omsetter te beskryf. Na implimentering van die omsetter word volledige eksperimentele verifikasie uitgevoer.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.<br>Made available in DSpace on 2012-10-18T00:59:22Z (GMT). No. of bitstreams: 0Bitstream added on 2014-09-25T18:45:10Z : No. of bitstreams: 1 182239.pdf: 4426878 bytes, checksum: 85f08d8cd86db634a6d92cbdfba27250 (MD5)<br>Este trabalho apresenta o estudo do inversor Três Níveis, também conhecido como inversor com ponto neutro grampeado, da sigla inglesa N.P.C. Inicialmente, são explicados os princípios de funcionamento do inversor, através da utilização da estratégia de modulação por largura de pulso único. A seguir, são apresentadas e comparadas qualitativamente as demais técnicas de modulação existentes na literatura, para aplicação ao inversor Três Níveis. É apresentada a análise teórica, primeiramente demonstrando o equacionamento dos esforços de corrente nos interruptores do inversor, desconsiderando as comutações. Em seguida, a aplicação da técnica passiva de comutação suave, conhecida como Snubber de Undeland (modificado), é explorada detalhadamente. Ao final, tem-se os resultados da experimentação de um inversor de 10 kVA, comutando a uma freqüência de 20 kHz. Diante dos resultados apresentados, são mencionados os efeitos causados pelos componentes parasitas existentes em um circuito real. São, também, comentados os aspectos positivos e negativos da utilização do snubber ao inversor.

Thesis (Ph. D.) -- University of Maryland, College Park, 2009.<br>Thesis research directed by: Dept. of Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Made available in DSpace on 2016-12-12T17:38:35Z (GMT). No. of bitstreams: 1 Jonathan Domini Sperb.pdf: 5918080 bytes, checksum: ca2651157f2d17c4c98cd0a08aeee98c (MD5) Previous issue date: 2007-08-03<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>This work deals with the design and implementation of the digital instantaneous averaged values control for output voltages of the three-phase inverter with Underland s snubber, using the Buck-Boost converter for regeneration of the snubber s energy. The qualitative and quantitative analysis of the inverter power structure, snubber and auxiliary converter, as well as the project for a set of presented specifications is presented. All needed block models for the design of the control are shown, as well as the project methodology of frequency response control. Results of simulation complement the work and prove the presented methodology. For experimental validation, it s developed a three-phase inverter with snubber and auxiliary converter, with output power of 4.5kVA, switching frequency of 50kHz, and with capacity to operate with full power for output voltage from 127V up to 220V. Experimental results of the power circuits and control performance complement the study.<br>Este estudo trata do projeto e implementação do controle digital por valores médios instantâneos das tensões de saída do inversor trifásico com Snubber de Undeland, utilizando conversor auxiliar Buck-Boost para regeneração da energia processada pelo snubber. São apresentados os estudos qualitativo e quantitativo das estruturas do inversor, snubber e conversor auxiliar, bem como o projeto final para um conjunto de especificações apresentadas. Para a realização do controle são mostrados os modelos matemáticos de todos os blocos necessários para o projeto do controlador, assim como é apresentada uma metodologia de projeto de controle baseado na resposta em freqüência. Resultados de simulação complementam o estudo e comprovam a metodologia apresentada. Para validação experimental, é desenvolvido um protótipo do inversor com snubber e conversor auxiliar, com potência de saída de 4,5kVA, freqüência de operação de 50kHz, e com capacidade de operar com potência nominal para a faixa de tensão de saída de 127V a 220V. Resultados experimentais dos circuitos de potência e controle complementam a validação deste estudo.

<p>This master thesis aim to design and evaluate a high power 3-phase DC/AC and AC/AC converter. The purpose is to use it for an electric motor in an aircraft possibly driving electric actuators, a propeller in an UAV or a small vehicle. Factors such as power loss and weight are of importance and will be estimated using known models supplied by various manufacturers of components. Different topologies of semiconductors suitable for this purpose are examined and presented. Extensive resources have been put to properly select the most suitable switching device according to their power loss and weight.</p><p>The need for filters and protective circuits will be estimated according to regulations of common military avionic standards and will be included in the resulting estimation along with simulations to evaluate their need and importance. Snubber circuits will be presented and their specific ability to reduce voltage transients and switching losses will be examined along with some simulations to illustrate their performance. In the final part an estimation of efficiency and weight of higher and lower power models of the same inverter has been made using the same procedure as presented in this paper. Engineering rules have been formed from these estimations to simply be able to calculate the proportions of a future converter of arbitrary rated power.</p>

CAPES<br>Este trabalho apresenta um sistema eletrônico com entrada universal utilizando um retificador SEPIC não isolado para fornecer e controlar a corrente de LEDs de potência. Um Snubber regenerativo que reduz as perdas de comutação e melhora a eficiência do sistema é proposto. Para realizar a dimerização, bem como reduzir a ondulação da corrente nos LEDs, um regulador linear de corrente é conectado na saída do conversor SEPIC. A utilização do regulador linear também permite que o conversor opere com entrada universal sem a utilização de circuitos adicionais. Para evitar perdas excessivas, o regulador é configurado para operar na região limiar da regulação. O ponto de perda mínimo do regulador é ajustado através de um circuito detector de mínimo com o sistema operando em malha fechada. As etapas de operação, as formas de onda e as principais equações do snubber regenerativo aplicado ao SEPIC são descritas no trabalho. Para verificar e validar a análise teórica são apresentados dois protótipos com potências de saída de 42 W e 145 W, variando de 15% a 100%, para o conversor operando com tensão de entrada de 90 a 240 V e alimentado 35 LEDs conectados em série.<br>This paper presents a universal-input AC electronic lighting system using a non-isolated SEPIC PFC rectifier to drive and control power LEDs currents. One energy regenerative snubber for reducing the converter switching losses and improve the system efficiency is proposed. The dimmable flicker-free current in the LEDs array is obtained through a linear current regulator placed in the SEPIC’s output terminals. In order to reduce the efficiency impairment, the conditions for achieving minimum energy loss in the current regulator are also detailed. Point of minimum energy loss in the linear regulator is adjusted through valley detector circuit in closed loop system operation. The operation stages as well as the theoretical waveforms and main equations at steady state of the proposed SEPIC rectifier using the regenerative snubber are described. To verify the theoretical analysis carried out, experimental results of two prototypes (42 W and 145 W) operating from 90 to 240 V and output power from 15 to 100% for 35 LEDs are also presented.

Práce se zabývá popisem jednotlivých typů zdrojů s důrazem na izolované topologie. Poté je rozebírána nejvhodnější volba pro zdroj na anodické bondování, kde jsou kladeny požadavky na vysoké výstupní napětí s malým proudem. Další část rozebírá problematická místa návrhu a na co je třeba dávat pozor. Poté je proveden vlastní návrh zdroje s popisem optimalizačních kroků. Tento zdroj je odsimulován. Dva rozdílné přístupy k realizaci takového zdroje jsou poté porovnány a nejlepší je vybrán. Je ukázána možnost, jak realizovat bipolární výstup. V poslední části je tento zroj sestaven a proměřeny jeho parametry.

The design of series-loaded resonant converters using the state of the art SiC power transistorsis investigated in the thesis. SiC devices are chosen as they offer lower switching losses comparedto conventional Si based devices A very detailed study about the working and differentmodes of operation of the resonant converter is carried out. The thesis further explains how thehigh speed switching capabilities of the SiC devices remain untapped owing to the presence ofstray inductances in the switch-snubber layout. A comparison of all the commercially availableSiC devices are carried out to find the most suitable switch for the resonant converter. Thethesis also carries out a very detailed step by step design of the circuit and the PCB layout forthe resonant converter. Two different layouts are proposed and then compared for their strayinductance and power losses. Finally, based on the experiments the thesis validates the suitabilityof using discrete SiC power transistors in place of power modules.<br>Utformningen av serie-belastade resonansomvandlare med hjälp av toppmoderna SiC högeffekttransistorernaundersöks i denna avhandlingen. SiC-enheter väljs eftersom de erbjuderlägre switch-förluster jämfört med konventionella Si-baserade enheter.En mycket detaljeradstudie om funktionen och de olika operationella tillstånden hos resonansomvandlare utförs.Avhandlingen förklarar vidare hur förmågan till högfrekvent switchning hos SiC-enheterförblir ofullständigt utnyttjad på grund av förekomsten av ströinduktanser i switch-snubberlayouten.En jämförelse av alla kommersiellt tillgängliga SiC-enheter genomförs för att hittaden mest lämpliga switchen för resonansomvandlaren. Avhandlingen utförs också en mycketdetaljerad steg-för-steg-utformning av resonansomvandlaren kretsschema och kretskortlayout.Två olika layouter föreslås och jämförs därefter utifrån deras ströinduktanser ocheffektförluster. Slutligen, baserat på experimentella resultat bekräftar avhandlingen.Lämpligheten att använda diskreta SiC-effekttransistorer istället för effektmoduler medintegrerade drivarsteg för styrelektroderna.

The necessity of new and clean technologies for energy production from one hand and the carbon dioxide emission regulations on the other are inducing nuclear fusion research to speed towards a possible future energy source. So the next experiment, which is being built in France, called ITER (acronym for International Thermonuclear Experimental Reactor, an international collaboration between European Union, Japan, Russian Federation, India, China, South Korea and United States of America) has to give an answer on the real feasibility to achieve nuclear fusion, and in particular on the possibility to control the plasma stability for long time at high temperature, to maintain the stationary phase and to reach fusion temperature. One of the components necessary to heat the plasma is the Neutral Beam Injector; the concept has been developed for many years up to the present experiments. The principle is basic: the plasma is hit by a neutral atoms beam (not affected by the high magnetic field of the system) at high kinetic energy so that this energy is transferred by collisions to the ions of the plasma. Meanwhile the beam helps to drive the plasma current, necessary for the plasma confinement inside the vessel in a “tokamak” configuration. The engineering requirements for the ITER NBI are very demanding, as it is subjected by severe mechanical, thermic and electrical stress. In particular, the neutral beam power requested is 16.5 MW while the energy of the deuterium or hydrogen negative ions, accelerated before neutralization, is in the order of 1 MeV. This involves a total accelerating voltage equal to 1 MV. So one of the most critical topic for the whole system is the operation very close to the breakdown limits for the accelerating grids, so that breakdown is not considered as a fault but a common working condition for the system. The activity reported in this doctoral thesis, mainly carried out at Consorzio RFX, deals on this matter. In particular the effects of arc between the grids are analyzed, both in terms of arc energy deposition on the grids and in terms of the current and voltage transient propagation on different locations of the system. Arc energy has to be limited below a certain threshold value in order to avoid an irreversible grids damage; this would cause the de-conditioning and the loss of high voltage holding with a breakdown occurrence at lower voltage level. Instead the fast voltage transients are dangerous because they can induce overvoltages on some tricky points and therefore lead to unexpected insulation losses; in addition they are source of electromagnetic noise (EMI) due to high frequencies in the order of MHz, a problem if we consider the large number of diagnostic devices. In this thesis some design solutions to limit these effects are explained; they are supported by proper circuital simulations or experimental validation. The devices presented are alternative to the present adopted solutions, as they form a comprehensive protection strategy. Then, they are passive protections because we need an instantaneous intervention after breakdown to be effective, contrary to active protections which need some delay due to the signal acquisition demonstrating the arc occurrence. The thesis is organized as follows. In the chapter 1 the ITER neutral beam injector is presented, in the framework of the nuclear fusion research; the operation principles and the main components are basically described. Finally the test facility being built in Padua is shown; it is constituted by two experiments, a ITER full-scale negative ion sources, with a single -100 kV accelerating stage, and a full-scale injector, identical to that which will be installed in ITER. The chapter 2 shows at first the operating conditions, from the electrical point of view, foreseen for the neutral beam injector. In particular high voltage holding issues are presented, together with the conditioning process in vacuum; then a tentative vacuum arc modeling for long gap is described, considering arc energy dissipation due mainly to radiation phenomenon. At last present countermeasures against breakdown effects are shown, namely a concentrated core snubber at the injector transmission line ends and the active protections. In the chapter 3 two new concepts for passive protections are introduced. The first is a damping resistor connecting the last accelerating grid (the so called grounded grid) with the vacuum vessel (grounded) of the injector with the aim to damp the arc current involving this grid and the return conductor of the transmission line. Then the design and the assembly of a prototype are described; this is installed at the French laboratory of CEA (Commissariat à l’Énergie Atomique) in Cadarache, where it will be tested. The detailed circuital modeling of this test bed is reported; the model is useful to compare and understand experimental results. The second device is a distributed core snubber along the whole transmission line to damp the breakdown with a less cumbersome element and a simpler, more effective structure. The results on a small-scale example are presented to support this proposal. The chapter 4 outlines an integration of a comprehensive design for passive protections on a whole system. In particular, for the experimental negative ion source the positive effects of some devices are proposed, studied and optimized, i.e. a damper resistor, a distributed core snubber and a L–R parallel input impedance between the power supply and the transmission line. Finally the core snubber design is described, constituted by a series of magnetic cores evenly distributed on the transmission line and polarized by a proper biasing circuit.<br>L’esigenza di nuove tecnologie per la produzione di energia, compatibili con l’ambiente, e le normative sulle emissioni di anidride carbonica stanno spingendo la ricerca sulla fusione nucleare come possibile alternativa futura. Da questo punto di vista il prossimo esperimento in via di costruzione in Francia, ITER (acronimo di International Thermonuclear Experimental Reactor, frutto di una collaborazione internazionale tra Unione Europea, Giappone, Russia, India, Cina, Corea del Sud e Stati Uniti d’America), dovrà dare delle risposte sull’effettiva fattibilità della fusione nucleare, e in particolare sul controllo della stabilità di plasma per lunghi tempi e ad alte temperature, sulla possibilità di funzionamento in regime stazionario e sull’effettivo raggiungimento della temperatura di fusione. Uno dei dispositivi necessari per il riscaldamento del plasma è l’iniettore di neutri, concetto sviluppato già in diverse macchine operanti fino ad oggi. Il principio è semplice: si tratta di “bombardare” il plasma con un fascio di atomi neutri (quindi insensibili ai forti campi magnetici presenti) ad alta energia cinetica in modo da trasferire mediante collisioni l’energia agli ioni del plasma stesso. Nel contempo il fascio aiuta anche il ostenimento della corrente di plasma, necessaria per il confinamento nella camera di scarica in configurazione “tokamak”. Le prestazioni ingegneristiche richieste all’iniettore di neutri di ITER sono molto gravose, sia dal punto di vista delle sollecitazioni meccaniche e termiche che da quelle elettriche. In particolare, la potenza del fascio di atomi neutri richiesto è di 16.5 MW mentre l’energia di accelerazione del fascio di ioni negativi di deuterio o idrogeno, a monte della neutralizzazione, è di 1 MeV. La tensione di accelerazione corrispondente è perciò di 1 MV. Uno dei punti più critici dell’intero sistema è dato dalle condizioni operative molto vicine ai limiti di scarica per le griglie di accelerazione, tanto che la scarica stessa non è considerata un fenomeno di guasto bensì una normale condizione di funzionamento del sistema. Il lavoro esposto in questa tesi di dottorato, svolto principalmente presso il Consorzio RFX, si inserisce in questo contesto. In particolare vengono analizzati gli effetti dell’arco tra le griglie sia in termini di energia d’arco depositata sulle griglie stesse che dei transitori di tensione e corrente che si propagano nei vari punti del sistema. Riguardo all’energia d’arco, essa dev’essere limitata al di sotto di un certo valore per evitare il danneggiamento irreversibile delle griglie stesse con conseguente decondizionamento del sistema, perdita delle proprietà di tenuta della tensione e quindi il verificarsi della scarica a tensioni più basse. I transitori di tensione invece possono essere dannosi, sia perché possono indurre sovratensioni in punti delicati del sistema con conseguente perdita dell’isolamento, sia perché sono fonte di disturbi elettromagnetici (EMI) per le varie apparecchiature diagnostiche presenti, legati alle alte frequenze in gioco dell’ordine dei MHz. Vengono in questa sede proposte alcune soluzioni progettuali per limitare tali effetti, corroborate da opportune simulazioni circuitali o da validazione sperimentale. I dispositivi esposti sono alternativi a quelli fino ad oggi impiegati, presentando una strategia d’insieme per la protezione. In più, sono di tipo passivo in quanto devono intervenire istantaneamente al verificarsi della scarica per poter essere efficaci, contrariamente alle protezioni attive che necessitano di un certo tempo di intervento legato all’acquisizione di un segnale comprovante la scarica. La tesi è articolata nel modo seguente. Nel capitolo 1 viene introdotto l’iniettore di neutri di ITER nell’ambito delle ricerche sulla fusione nucleare; ne vengono descritti schematicamente i principi di funzionamento e i componenti principali. Infine viene presentata l’installazione sperimentale in via di costruzione a Padova, costituita da due esperimenti, ovvero una sorgente di ioni negativi in scala 1:1 rispetto a quella di ITER, con un unico stadio di accelerazione del fascio a -100 kV, e un iniettore vero e proprio, identico a quello che verrà installato su ITER. Il capitolo 2 presenta dapprima le condizioni operative previste per l’iniettore di neutri dal punto di vista elettrico. In particolare vengono introdotte le problematiche della tenuta alla tensione e del processo di condizionamento in vuoto; quindi viene descritta una possibile modellazione circuitale per l’arco elettrico su lunghe distanze, considerando il fenomeno dell’irraggiamento come preponderante per la dissipazione dell’energia d’arco. Infine vengono presentate le attuali soluzioni contro gli effetti della scarica, ovvero uno snubber magnetico concentrato alle estremità della linea di trasmissione dell’iniettore e le protezioni di tipo attivo. Nel capitolo 3 vengono introdotti due nuovi concetti di protezioni passive. Il primo è un resistore di smorzamento che collega l’ultima griglia di accelerazione del fascio di ioni (la griglia di terra) con la cassa esterna dell’iniettore (messa a terra) in modo da smorzare la corrente d’arco che interessa tale griglia e si richiude sul conduttore di ritorno della linea di trasmissione. Vengono descritti il progetto e la costruzione di un prototipo installato presso il laboratorio francese del CEA (Commissariat à l’Énergie Atomique) di Cadarache, dove dovrà essere testato. L’impianto di prova di tale laboratorio viene poi modellato nel dettaglio per poter confrontare i risultati sperimentali e poterli interpretare. Il secondo dispositivo è uno snubber magnetico distribuito lungo tutto lo sviluppo della linea di trasmissione, in modo da smorzare al meglio ogni possibile guasto con un minor ingombro sul sistema e una struttura più semplice ed efficace. I risultati di una prova sperimentale su un modello in scala ridotta sono presentati a supporto della proposta. Il capitolo 4 delinea un esempio di progetto integrato di protezioni passive su un intero sistema. In particolare, per l’esperimento della sorgente di ioni negativi, vengono proposti, studiati e ottimizzati su un opportuno circuito equivalente gli effetti positivi del resistore di smorzamento, dello snubber magnetico distribuito e di un’impedenza L–R parallelo interposta tra alimentatore e linea di trasmissione. Infine viene descritto il progetto dello snubber, costituito da una serie di nuclei magnetici equispaziati lungo la linea e polarizzati da un opportuno circuito.

Photovoltaic (PV) system is one of the most prominent energy sources, producing electricity directly from sunlight. In additionally, it is easy to install and is supported financially by many governments as part of their strategy to reduce CO2 gas emissions, and to achieve their agreed set of reduction targets by 2020. In the meantime, researchers have been working on the PV system to make it more efficient, easy to maintain, reliable to use and cost effective. In the stand-alone PV system, a battery is required. This is due to the fluctuating nature of the output energy delivered by the PV arrays owing to the weather conditions and the unpredictable behaviour of uses with regard to the consumption of energy. During the hours of sunshine, the PV system is directly feeding the load and any surplus electrical energy is stored in the battery at a constant current. During the night, or during a period of low solar irradiation, the energy is supplied to the load from the battery. However, the stand-alone PV system is designed to provide an acceptable balance between reliability and cost, which is a major challenge to the designer owing to the approaches used to size the PV arrays and the battery bank. As a result, the unpredictable, quick daily changes on the PV output is not dependable. Moreover, battery performance, length of life and energy efficiency depends on the rate at which it is discharged. Therefore, it is essential to use other methods to deal with any quick variation in energy. In this thesis, a super capacitor is used to solve this problem, as it can deal with the fast-changing weather, or a rapid variation in the energy requirements of the customer. A critical evaluation with in-depth analysis of the placement and the implementation for the super-capacitor in the PV standalone system has been carried out. The results show, super-capacitor capacitance and the converter efficiency affect the delivered load energy. However, the bi-directional topology performs better than uni-directional under the same conditions. Finally, a further improvement of the system at component level, has been developed through an energy recovery snubber for the switching transition and achieved a recovery of energy for the resistive load, 94.44% for the turn on transition and 92.86% for the turn off transition. Moreover, for the inductive load, 78.33% and 97.33% of energy has been recovered for the turn on and for the turn off transition respectively.

This master thesis describes the design of a DC/DC converter for one photovoltaic panel with a 250 W peak power. The master thesis is divided into parts dealing with detailed design of power electronics, analog circuit design, description of control MPPT algorithms and software for control circuit. The chapter with the mathematical modeling of the converter created in the Matlab Simulink was added beyond the assignment.

This thesis deals with DC motor control. Main goal was design and realization of DC motor controler module with feedback. The first part dwells on methods for DC motor control and HW design of control module. The second part describes development of software for the module, testing and sums up results.

The trend of electrification in transportation applications has led to the fast development of high-power-density power electronics converters. High-switching-frequency and high-temperature operations are the two key factors towards this target. Both requirements, however, are challenging the fundamental limit of silicon (Si) based devices. The emerging wide-bandgap, silicon carbide (SiC) power devices have become the promising solution to meet these requirements. With these advanced devices, the technology barrier has now moved to the compatible integration technology that can make the best of device capabilities in high-power-density converters. Many challenges are present, and some of the most important issues are explored in this dissertation. First of all, the high-temperature performances of the commercial SiC MOSFET are evaluated extensively up to 200 degree C. The static and switching characterizations show that the device has superior electrical performances under elevated temperatures. Meanwhile, the gate oxide stability of the device - a known issue to SiC MOSFETs in general - is also evaluated through both high-temperature gate biasing and gate switching tests. Device degradations are observed from these tests, and a design trade-off between the performance and reliability of the SiC MOSFET is concluded. To understand the interactions between devices and circuit parasitics, an experimental parametric study is performed to investigate the influences of stray inductances on the MOSFETs switching waveforms. A small-signal model is then developed to explain the parasitic ringing in the frequency domain. From this angle, the ringing mechanism can be understood more easily and deeply. With the use of this model, the effects of DC decoupling capacitors in suppressing the ringing can be further explained in a more straightforward way than the traditional time-domain analysis. A rule of thumb regarding the capacitance selection is also derived. A Power Electronics Building Block (PEBB) module is then developed with discrete SiC MOSFETs. Integrating the power stage together with the peripheral functions such as gate drive and protection, the PEBB concept allows the converter to be built quickly and reliably by simply connecting several PEBB modules. The high-speed gate drive and power stage layout designs are presented to enable fast and safe switching of the SiC MOSFET. Based on the PEBB platform, the state-of-the-art Si and SiC power MOSFETs are also compared in the device characteristics, temperature influences, and loss distributions in a high-frequency converter, so that special design considerations can be concluded for the SiC MOSFET. Towards high-temperature, high-frequency and high-power operations, integrated wire-bond phase-leg modules are also developed with SiC MOSFET bare dice. High-temperature packaging materials are carefully selected based on an extensive literature survey. The design considerations of improved substrate layout, laminated bus bars, and embedded decoupling capacitors are all discussed in detail, and are verified through a modeling and simulation approach in the design stage. The 200 degree C, 100 kHz continuous operation is demonstrated on the fabricated module. Through the comparison with a commercial SiC phase-leg module designed in the traditional way, it is also shown that the design considerations proposed in this work allow the SiC devices in the wire-bond structure to be switched twice as fast with only one-third of the parasitic ringing. To further push the performance of SiC power modules, a novel hybrid packaging technology is developed which combines the small parasitics and footprint of a planar module with the easy fabrication of a wire-bond module. The original concept is demonstrated on a high-temperature rectifier module with SiC JFET. A modified structure is then proposed to further improve design flexibility and simplify module fabrication. The SiC MOSFET phase-leg module built in this structure successfully reaches the switching speed limit of the device almost without any parasitic ringing. Finally, a new switching loop snubber circuit is proposed to damp the parasitic ringing through magnetic coupling without affecting either conduction or switching losses of the device. The concept is analyzed theoretically and verified experimentally. The initial integration of such a circuit into the power module is presented, and possible improvements are proposed.<br>Ph. D.

This thesis examines converter topologies suitable for Module Integrated Converters (MICs) in grid interactive photovoltaic (PV) systems, and makes a contribution to the development of the MIC topologies based on the two-inductor boost converter, which has received less research interest than other well known converters. The thesis provides a detailed analysis of the resonant two-inductor boost converter in the MIC implementations with intermediate constant DC links. Under variable frequency control, this converter is able to operate with a variable DC gain while maintaining the resonant condition. A similar study is also provided for the resonant two-inductor boost converter with the voltage clamp, which aims to increase the output voltage range while reducing the switch voltage stress. An operating point with minimized power loss can be also established under the fixed load condition. Both the hard-switched and the soft-switched current fed two-inductor boost converters are developed for the MIC implementations with unfolding stages. Nondissipative snubbers and a resonant transition gate drive circuit are respectively employed in the two converters to minimize the power loss. The simulation study of a frequency-changer-based two-inductor boost converter is also provided. This converter features a small non-polarised capacitor in a second phase output to provide the power balance in single phase inverter applications. Four magnetic integration solutions for the two-inductor boost converter have also been presented and they are promising in reducing the converter size and power loss.

My study contains a semiotic analysis of two photos posted by the Instagram account Snubbarinreder, an account that posts photos of homes allegedly belonging to men. There are clear tendencies on the account to portray men as heavy consumers of alcohol and video games alongside a general inability or disinterest in caring for a home. My study is based mainly on studies by Beverly Skeggs and Göran Eriksson on how the working class are commonly portrayed in the media. The purpose of the study is to investigate aspects of class in the portrayal of men in the posted photos. Eriksson and Skeggs explains that it is common to portray the working class as exaggerated, tasteless and out of control, which my study shows are also recurring themes in the portrayal of men on Snubbarinreder. Thus, the results of the study shows that there are similarities between the portrayal of the working class in, for example Reality-TV, and the portrayal of men on the Instagram account Snubbarinreder.

Syftet med studien är att beskriva hur involverad skolpersonal och samverkande socialsekreterare arbetar för att kartlägga och motverka elevers ogiltiga frånvaro. Genom att undersöka personalens upplevelse av orsaker till ogiltig frånvaro, hur de upplever att de arbetar med ogiltig frånvaro och hur de tillsammans arbetar för att motverka ogiltig frånvaro. Den aktuella publicerade forskning som använts är både internationell och nationell. Styrdokument, lagtext, allmänna råd samt forskning av Skolverket och Socialstyrelsen har även beaktats. Det teorietiska perspektiv som ligger till grund för analys är inklusion och exklusion. Utifrån kvalitativa halvstrukturerade livsvärldsintervjuer med fem informanter som tillfrågats med utgångspunkt av dessas yrkesroll i skolan. De professioner som tillfrågats är rektor, kurator, socialpedagog, lärare samt samverkande socialsekreterare. Intervjuer med informanterna har spelats in med diktafon, transkriberats för att sedan analyseras. Analysen gjordes utifrån teman: orsaker, arbete med och arbete tillsammans med ogiltig frånvaro. Tolkningen av materialet har skett utifrån samstämmighet och olikheter i svaren. I studiens diskussion tas det upp att den främsta orsaken till ogiltig frånvaro är hemsituationen. I de fall eleven har en svår hemsituation visar forskningen att skolan kan vara en skyddsfaktor för att förhindra elevens exklusion. Där den ogiltiga frånvaron ändå är skolrelaterade beror det främst på andra elevers inflytande, grupptryck. Alla informanter upplever att de i sitt arbete har en medvetenhet om var eleverna med stor ogiltig frånvaro befinner sig utifrån skolans arbetsmodell. Studiens resultat är att de orsaker som ligger bakom ogiltig frånvaro huvudsakligen är relaterade till hemsituationen. Involverad personal upplever en förbättring utifrån arbetsrutinen i skoltrappan. Att arbeta tillsammans är en framgångsfaktor för att minska ogiltig frånvaro.<br>The aim of the study is to describe how school staff and social workers identify and prevent truancy in the Swedish compulsory school. The study explores the school workers professional experiances of the underlying causes of truancy and what measures are taken in collaboration with social authorities to prevent pupils´ absence from school. The study is based on current international and national research and takes into account policy documents, legal texts and general advice issued by the Swedish National Agency for Education and the National board of Health and Welfare. The theoretical perspective used in of the analyses are the terms inclusion and exclusion. Qualitative semi-structured lifeworld interviews with five professional categories (a school head master, a councelor, a  teacher and two social workers) working in school were performed. The interviews focused on causes of truancy and collaborative work involving both school professionals and social workers. The interviews were recorded and subsequently transcribed and analysed. The analysis was performed thematically, causes of truancy and collaborative work to prevent truancy. The interpretation of the data was based on consensus and differences in the responses. As can be seen from the discussion, the primary cause of truancy is related to the pupil´s home situation. Research shows that school can be a protective factor to prevent exclusion. In cases where truancy is related to the school situation it is principally a result of group pressure from other pupils. All respondents in the interviews stated that they have an awareness of where pupils with extensive absenteeism are in relation to the school´s work model to prevent truancy. Collaborative work is a success factor to reduce truancy.

Modeling of switched-mode DC-DC converters has been receiving significant interest due to their widespread applications. Averaged modeling is the most common approach (and tool) that has been used to analyze dynamic performance of converter circuits. Specifically, state-space averaged models are widely used because of their simplicity and generality. However, as has been shown in the literature, the challenges of directly applying this approach to predict the discontinuous variables (states) and include the parasitics and losses have limited application of this approach to a wider range of converter circuits. The recently introduced parametric average value models (PAVM) has a potential to overcome this problem. In this Thesis, first of all a second-order flyback converter has been investigated. An analytical solution of state-apace averaging and small-signal analysis of the flyback converter in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) is given without and with parasitics. The PAVM methodology has been applied to the second-order model to overcome the problem of discontinuous state during the DCM. The snubber circuits in flyback converter have also been investigated. Appearance of snubbers in the model introduces a problem on the output voltage besides improving the efficiency prediction. It is shown that with the snubbers the conventional state-space averaging cannot predict the output voltage correctly in CCM and DCM. To solve this problem the model is partitioned into two different sub-circuits: i) switching sub-circuit circuit; and ii) non-switching sub-circuit. Thereafter it becomes possible apply the averaging on the switching sub-circuit only. Finally, a full-order flyback converter with two RC snubber circuits and all the basic parasitics is considered. The PAVM methodology has been extended to this class of switching converter for the first time. It is shown that including the snubbers and parasitics significantly improves the model accuracy in terms of predicting converter efficiency, which represents an appreciable improvement over all previously existing average models. The proposed model has been verified with detailed simulations and hardware measurements.

Modeling and analysis of basic DC-DC converters is essential for enabling power-electronic solutions for the future energy systems and applications. Average-value modeling (AVM) provides a time-efficient tool for studying power electronic systems, including DC/DC converters. Many AVM techniques including the analytical and numerical state-space averaging and circuit averaging have been developed over the years and available in the literature. Average-value modeling of ideal PWM converters neglects parasitics (losses) to simplify the derivations and modeling procedures, and the resulting models may not be sufficiently accurate for practical converters. In this work, first we consider a second-order Flyback converter, which has transformer isolation and additional parasitics such as conduction losses that have not been accurately included in the prior literature. We propose three new AVMs using the analytical state-space averaging, circuit averaging, and parametric AVM approaches, respectively. By taking into account conduction losses, the accuracy of the proposed average-value models is significantly improved. The derived (corrected) models show noticeable improvement over the traditional (un-corrected) models. Next, we consider the Flyback converter including the snubbers and leakage inductances in the full-order model. Snubbers reduce electromagnetic interfaces (EMI) during transients and protect switching devices from high voltage, and therefore are necessary in many practical converter circuits. Including snubbers into the model improves accuracy in predicting the circuit variables during the time-domain transients as well as predicting the converter efficiency. It is shown that conventional analytical/numerical methods of averaging do not result in accurate AVM for the full-order Flyback converter. A new formulation for the state-space averaging methodology is proposed that is functional for higher-order converters with parasitics and result in highly accurate AVM. The new approach is justified mathematically and verified experimentally using hardware prototype and measurements. The new model is demonstrated to achieve accurate results in large signal time-domain transients, and small-signal frequency-domain analysis in continuous conduction mode (CCM) and discontinuous conduction mode (DCM), which represents advancement to the state-of-the-art in this field.

Smartphones have changed the way people interact with each other in modern society. However, while they are becoming more omnipresent in human life, there is increasing concern that they are often used at inappropriate times during social interactions, and that people often ignore others in favour of their phones. In this thesis, we explore the phenomenon of "phubbing" - the act of snubbing someone in a social setting by concentrating on one's mobile phone. In a series of ten empirical studies, we demonstrate that Internet addiction, fear of missing out, and self-control predict smartphone addiction, which in turn predicts the extent to which people phub. This path also predicts the extent to which people feel that phubbing is normative, both via (a) the extent to which people are phubbed themselves, and (b) independently. Phubbing also significantly dampens perceived communication quality and relationship satisfaction in dyadic conversation. These effects are mediated by reduced feelings of belonging and both positive and negative affect. In addition, the results indicate that the degree to which someone is affected by phubbing is not determined by the relationship status between phubber and phubbee. We also develop and validate the Generic Scale of Phubbing (GSP) to assess phubbing behaviour, and the Generic Scale of Being Phubbed (GSBP) to assess the experience of being phubbed. Both scales reveal good psychometric properties. In conclusion, the results of the current research allow us to better understand how phubbing permeates and affects human social life.

Questa tesi si propone di analizzare e comprendere il funzionamento del convertitore flyback, un circuito elettronico appartenente alla categoria dei convertitori DC/DC operanti in commutazione, avvalendosi anche dell’ausilio del software per la simulazione circuitale LTSPICE. Vengono dettagliatamente analizzati gli effetti delle disperse del trasformatore, valutato l'inserimento di snubber dissipativi, analizzato il comportamento dinamico del convertitore retroazionato, presa in considerazione la possibilità di inserire ulteriori uscite.

Syftet med denna studie är att belysa verksamma förskollärares upplevelser av arbetet med attstötta, stimulera och utmana barn i grovmotoriska svårigheter. Denna studie är således enkvalitativ studie med semistrukturerade intervjuer med sex förskollärare på sex olikaförskolor. Studiens forskningsfrågor har behandlat verksamma förskollärares upplevelser avderas arbetssätt, erfarenheter och orsaker till att barn befinner sig i grovmotoriska svårighetersamt förutsättningar för att stötta, stimulera och utmana dessa barn i förskolan. Denna studiehar sin utgångspunkt i ett relationellt perspektiv där barn beskrivs som att de befinner sig isvårigheter. Det framgår i vår studie att samtliga informanter beskriver att de arbetar med attstötta, stimulera och utmana barn i svårigheter i deras grovmotorik i både vardagssituationeroch i lärarledda aktiviteter, vilket lyfts av tidigare forskning som angeläget. Informanterna harvarierande erfarenheter av barn i grovmotoriska svårigheter. Orsaker till att barn befinner sig isvårigheter i grovmotoriken framgår i denna studie som komplext och beroende av arv, miljö,omgivning samt möjligheter till att öva, vilket sociokulturell teori betonar. Viktiga slutsatserfrån denna studie är att miljön och förskollärarens roll är central för barns grovmotoriskautveckling samt att förskolans förutsättningar för att stötta, stimulera och utmana barn i derasgrovmotoriska utveckling har försämrats exempelvis genom större barngrupper.

Solar Bora AB is a Linköping based company that provides end to end solution for clean and reliable energy. System developed by them generates high power 230V AC to run electrical appliances. The system consist of string of batteries which are charged by rooftop solar cells and the energy stored in the batteries is converted to AC to provide a grid voltage like experience even though the system is not connected to a grid. Energy stored in the batteries need to be converted from DC to AC efficiently. Inverter used for conversion should be efficient enough to reduce losses. This master thesis deals with optimization and Up-gradation of Half-Bridge inverter board so that switching loss can be minimized to increase efficiency. Initial part of the thesis involves investigation of different parameters which contribute to losses in inverter. Based on that some improvements were suggested in existing design of half-bridge board. Another task involved in the thesis was complete re-design of half-bridge. More efficient and robust components were selected for complete re-design. Based on new components and its specifications a new circuit and PCB was designed in Altium Designer. Lab testing was performed to verify the functionality of new Half-bridge.

碩士<br>國立臺灣海洋大學<br>電機工程學系<br>96<br>With the ongoing development of power electronics technology, the inverter of IGBT are widely applied to power converting applications. It is well known that output over-voltage and energy loss during switching of inverter are the main causes for the damage of power electronic devices. To solve this problem, we first characterize the general behavior of IGBT with research, then energy loss of IGBT in both hard switching and soft switching is empirically studied. Based on these simulation results, this thesis proposes a new kind of snubber using passive lossless IGBT half-bridge inverter. Extensive simulations are carried out, and results of which verify that the snubber can suppress over-voltage and the switching loss can be effectively reduced.

碩士<br>國立臺灣科技大學<br>電子工程系<br>94<br>This thesis aims at the analysis of an active-clamping flyback converter. The comparisons between the active-clamping flyback converter and the conventional flyback converters adopting passive snubbers are made. The resonant tank of the active-clamping flyback converter consists of the leakage inductance of the transformer and the parasitic capacitance of the switch. The zero-voltage swtiching can be achieved by adequately design the circuit parameters. The conversion efficiency can thus be raised and the voltage spike on the switch can be reduced. Also the loss distribution is derived. An active-clamping flyback converter with an output rating of 24V/8A/200W is implemented in the lab. The experimental results are closely conformed to the theoretical analysis and the simulations.

碩士<br>國立臺北科技大學<br>車輛工程系所<br>101<br>This thesis proposes a pulse-width-modulation (PWM) inverter with the soft switching for the brushless DC motor (BLDCM) of the electric scooter. This motor drive could reduce switching losses, increase driving and regenerative efficiency. Moreover, this system could obtain some advantages, such as low cost and high efficiency which the capacitance is easily designed in the switched capacitor snubber. In the switching control method of this motor driver, a bidirectional conduction of inverter is used to match the relationship of the three-phase voltage of BLDCM, besides, the each internal winding of the BLDCM could be operated in a inductor. Thus a boost circuit is made up of the inductors, the MOSFET power switches, the motor electromotive force (EMF) and the input DC source. By this switching control approach, a reverse torque could be resulted in the electric brake that transfers the braking kinetic into the electric energy to the battery, thus the driving range of EV could be increased by this approach. Finally, this thesis uses a hub motor with 48V/750W to build an experimental system and some experimental results are provided to verify the correctness and feasibility of the proposed schemes.

碩士<br>義守大學<br>電機工程學系<br>91<br>An efficient active LC snubber for multi-output converters is proposed in this paper. The proposed active LC snubber can be used to reset transformer and suppress switching surges. Besides, by storing surge energy in the proposed active LC snubber and then releasing it to the flyback auxiliary output, the converter can achieve high efficiency. For a forward converter with flyback auxiliary output,91.02%,the maximum output efficiency, can be achieved. For the SR forward converter with active LC snubber, 93.72%, the maximum output efficiency, can be achieved. Experimental results also show that the output efficiency of this converter with the proposed active LC snubber is higher than that of converters with an active clamp snubber.

碩士<br>國立海洋大學<br>電機工程學系<br>91<br>It has been known that normal switching power supply utilize one or more switches to transform DC from one level to another. When the switch of circuit is turned on or turned off, it has switching power losses. In order to lower volume and weight of converter its frequency needs to be raised for power density. It makes switching power loss of circuit larger than before. The efficiency of system is also reduced when the switching frequency is increased. There is a method to solve this problem. It is a soft switching technique. The paper uses soft switching technique that improves performance of the boost converter by reducing switching power loss. The theoretical results of paper is proved by simulation. The loss is reduced by an active snubber which consists of a rectifier, an inductor, a capacitor, a main switch and an auxiliary switch. The reverse recovery related of the rectifier loss is also reduced by the active snubber.

碩士<br>崑山科技大學<br>電機工程研究所<br>98<br>The circuit design, simulation, and implementation of a forward converter with LCD snubber are presented in this thesis. The LCD snubber is composed of an inductor, a capacitor and a diode, known as passive and non-dissipative flux reset mechanism for single-ended forward converter. The capacitor of the snubber also resets the energy stored in the leakage inductor and hence, minimizes the spike voltage and reduces the EMI/RFI during the OFF period. The operational principles of the LCD snubber are analyzed in detail during steady state. According to the energy balance at resting resonant mode, a set of non-linear equation is derived and solved using the Newton-Raphson method. The magnetizing current in each breaking point is evaluated and the transformer core excited in the first and the third quadrants of the B-H plane is confirmed. The IsSpice simulation is also applied to verify the accuracy of theoretical analysis. Finally, the prototypes of a forward converter with an input of 48 V, output of 5 V/ 6 A, and switching frequency of 100 kHz has been implemented in the laboratory. In general, good agreement is observed between the theoretical and experimental results.

碩士<br>國立高雄第一科技大學<br>系統資訊與控制研究所<br>100<br>In this paper, we propose that Multi-objective algorithm and the Taguchi method be employed in the optimal design of a DC-DC converter with an RCD snubber. The RCD snubber is usually used in flyback converter to limit the voltage spikes which are caused by leakage inductance of the transformer. The design considerations of RCD snubber are commonly two objectives: (1) minimize power loss in the snubber ; (2) minimize the voltage spikes across the transistor. But the RCD design consideration for voltage spikes suppression is usually in contradiction with power loss. So we implement the circuit by using optimal trade-off parameters, which results from comparison of pareto solution set of Multi-objective Differential Evolution (MODE), Non-Dominated sort genetic algorithm-II (NSGA-II) and Multi-objective particle swarm optimization (MOPSO) methods. Finally, the comparison of the spike voltage and power loss showed the advantages of the optimal circuit design over a non-optimal design .

碩士<br>輔仁大學<br>電機工程學系碩士在職專班<br>106<br>The thesis presents a method to achieve a high voltage gain by voltage stacking technology and increasing the number of secondary winding of the coupled inductor. Then, the active snubber circuit is added to absorb the spike energy of the transformer leakage inductance for reducing the surge in the source system. Experiments and simulation results are used to verify the performance of the proposed converter operated in continuous conduction mode (CCM), discontinuous conduction mode (DCM) and boundary condition mode (BCM).

博士<br>國立成功大學<br>電機工程學系碩博士班<br>90<br>In this dissertation, various integrated AC/DC converters with power factor correction and nondissipative snubber are discussed. A novel integrated AC/DC converter with power factor correction and line-frequency ripple suppression is proposed. And a novel nondissipative snubber integrated with AC/DC converters is also proposed. 　　The proposed topology combines an integrated flyback and forward circuits with a post regulator. The integrated flyback and forward circuits function as two sub-converters that share the total output power. To maintain a high power factor, the flyback circuit delivers the major output power. The post-regulator with fast response to suppress line-frequency ripple controls the output voltage in constant. Therefore the proposed circuit can result in a good performance with fast dynamic response. Without the use of high voltage bulk capacitor or current sensor, the circuit features high power factor and low output line-frequency ripple in discontinuous conduction mode. The input voltage can be varied over the standard testing range (0.8-1.2 p.u.), it is suitable for home or industrial applications. 　　To improve the efficiency of AC/DC converters, especially operating in discontinuous conduction mode, an integrated nondissipative snubber is proposed. By the use of a multi-winding transformer, the novel nondissipative snubber can be integrated with flyback or proposed AC/DC converters. No additional magnetic core, active switching and driver are needed for the proposed integrated nondissipative snubber. Therefore the proposed topology improves the efficiency without over-dimensioning of parts and with very low cost. The theoretical analysis and experimental results are presented.

碩士<br>東海大學<br>電機工程學系<br>101<br>The power components in the transient state of switching will cause voltage overshoot on the circuit that is particularly serious to the system safty. In this thesis, we use the C++ language to design flyback circuits. It will be easier to design, make compareisons between different designs, and analyze flyback circuits with different specifications by using a computer program. In the analysis of snubber circuit, we simplify the complicated circuit to a equivalent circuit. Then, we use four work steps to derive the equations. Finally, we use Matlab language to perform numerical analyses on the snubber circuit, more understanding about how to control V_d (MAX) was obtained. At the last, we propose the idea of snubber built-in Power IC, and using T-suprem to simulate the device process. Then use Medice to load the devices for circuit simulation, and finally we get the results as expected.

碩士<br>國立成功大學<br>電機工程學系碩博士班<br>98<br>This thesis presents a proposed forward-flyback converter with the snubber-feedback network for the contactless power supply applications. In order to reduce the component count and volume, the output inductor and transformer are integrated with the proposed magnetic integration technology. Since the contactless power supply has the low conversion efficiency and low load regulation, the snubber-feedback network is applied to overcome these drawbacks. In the snubber-feedback network, an auxiliary winding of the integrated transformer is utilized as both the magnetic-loop voltage feedback and the lossless snubber inductor. A prototype circuit of the 15W forward-flyback power converter is built to verify the performances, such as load regulation, voltage stress on the power switch and efficiency, comparing with conventional one. Keyword:contactless power supply,lossless snubber,integrated transformer,output-voltage sensing circuit,forward-flyback converter

碩士<br>國立成功大學<br>電機工程學系碩博士班<br>99<br>This thesis presents a proposed universal-input single-stage PFC flyback LED driver with the lossless snubber circuit. In order to provide high power factor and low total harmonic distortion, the single-stage PFC flyback converter is employed. Moreover, in order to reduce the voltage stress on the power switch, increase the power-conversion efficiency, regulate the output voltage, the concepts of the lossless-snubber network and the isolated output-voltage-sensing network are adopted. The two windings of the lossless-snubber network and the output-voltage-sensing network are integrated as one common winding to reduce the component count Finally, a prototype circuit of the 24W universal-input single-stage PFC flyback LED driver with the lossless snubber circuit is built to verify the performances, such as voltage stress on the power switch, power conversion efficiency, power factor, total harmonic distortion, and input current harmonics.

碩士<br>國立臺灣科技大學<br>電子工程系<br>95<br>In this thesis, three kinds of representative snubbers are discussed, including R-C, R-C-D and L-C-D snubbers, respectively. R-C snubber, a dissipative snubber, associating with circuit leakage inductance is to form a R-L-C circuit to eliminate overvoltage and ring wave around the power device so as to suppress ring wave EMI. R-C-D snubber, a dissipative and polarized snubber, acts as a capacitor to prolong the rise time of voltage waveform around the power switch so as to suppress EMI resulted from rise time changed by voltage variation in power regulation. The last L-C-D snubber, a lossless snubber, uses inductor and resonant circuit to prolong rise time of current waveform around the power device, in which the capacitor is used to prolong rise time of the voltage waveform. It is appropriate for suppressing EMI resulted from rise time changed by voltage and current variations in power regulation. The investigation for R-C snubber is appropriate for all kinds of converters about ring wave suppression. R-C-D snubber is appropriate for all kinds of converters about voltage rise time change. L-C-D snubber is appropriate for buck and boost converters about rise time changes of current and voltage. Three kinds of snubbers are respectively applied in PFC, forward and flyback converter topologies by way of mathematics analysis and simulation for achieving a unified relationship between the mentioned snubbers, including waveform comparison and spectrum distribution. In this thesis, experiments for the three kinds of snubber circuits applied in PFC, forward and flyback converters are examined. Their performances are quite close to the theoretical predictions.

碩士<br>國立雲林科技大學<br>電機工程系碩士班<br>100<br>A bridgeless isolated SEPIC converter with active-clamp snubber is presented. This converter uses the bridgeless topology to reduce the rectifier diodes and improve the efficiency. The proposed converter is operated on the fixed frequency, and its input current consists of CCM and DCM parts simultaneously. During some parts of the line frequency, the converter is operated in the DCM so it can achieve the high power factor and confirm to the requirement of IEC 61000-3-2 class D. Although the converter is partly operated in the CCM will decrease the power factor, the efficiency can be improved. In addition, the active-clamp topology can achieve the characteristic of zero voltage turn-on for all switches when the converter is in the CCM operation. The main switches in the DCM operation can also achieve the function of zero current turn-on. The proposed converter is verified to be functionally worked by the experimental and simulation results based on the 150W prototype circuit and it also conforms to the requirement of IEC 61000-3-2 class D. Finally, the improved efficiency for the proposed converter can be further verified once the input current consists of the part of the CCM operation.

碩士<br>國立臺灣科技大學<br>電子工程系<br>107<br>In the applications of full bridge, phase shift is a most popular architecture. It has an excellent performance on efficiency thanks to soft-switching, especially in high power high voltage applications. However, whether the secondary side uses synchronous rectification or non-synchronous rectification, it will produce the voltage spike on secondary rectifier switches. The voltage spike increases the voltage stress of rectifier switches. This thesis proposes a new type of buck snubber circuit not only to clamp the voltage spike but also to replace the of clamping diode on the primary side because its temperature will be high in light load and increase the power loss. The buck snubber stores the energy of voltage spike into the capacitor and transfers the energy to output which makes the spike energy recovery. By the way, the voltage stress on rectifier switches was reduced, the rectifier switches can be changed as lower voltage stress with lower turn-on resistance. The efficiency of the system will also be increased. In addition, the thesis will compare the difference of clamping point between the rectifier switch and secondary transformer. Finally, the simulation waveform and measure waveform will be used to prove the feasibility of buck snubber and its improvement of efficiency.

碩士<br>國立臺灣科技大學<br>電子工程系<br>105<br>Full-bridge phase-shift converter has the merit of zero-voltage switching (ZVS) which can reduce the switching loss and the high frequency noise interference. However, there will be voltage spike induced on the secondary side synchronous rectification MOSEFTs. This thesis presents the study upon an active snubber circuit which is designed to reduce the spike. This active snubber is compared with the well-known RC and RCD passive snubbers. The stray energy on the secondary-side is restored to the snubber capacitors, then the snubber transfers the stored energy back to the primary-side. Due to the energy retrieval, the active snubber circuit surpasses the passive counterpart on energy efficiency. Besides, the voltage stress on the synchronous rectification MOSFETs is lowered benefited from the spike reduction; the MOSFET conduction resistance i.e. the conduction loss can also be reduced. That is, the power efficiency is further improved by the application of the active snubber.

碩士<br>逢甲大學<br>電機工程所<br>94<br>This thesis presents a design of the poultry electric stunner. An interleaving forward converter with a single-capacitor snubber to smooth out switch turn-off transient the drain-source voltage of metal-oxide-semiconductor field effect transistor(MOSFET) switch to reduce turn-off loss is proposed to improve the conversion efficiency. In addition, the converters are operated on the boundary of continuous and discontinuous conduction modes to reduce output current ripple, as compared with the counterparts of conventional converter under full load condition, about 3% higher. As compared with the counterparts of conventional converter topologies, the proposed converters have the merits of less components count, smaller size, and they are easier to implement. The outputs of converter are direct-voltage, and alternating voltage is necessary for the poultry electrical stunner, one full-bridge inverter is added to convert dc to ac. The converters have auto-stunning mechanism, which include over-voltage, over-current and over-temperature protection circuits.