Moore's Law has been used to describe and predict the blossom of IC industries, so increasing the data density is clearly the ultimate goal of all technological development. If the power density of power electronics converters can be analogized to the data density of IC's, then power density is a critical indicator and inherent driving force to the development of power electronics. Increasing the power density while reducing or keeping the cost would allow power electronics to be used in more applications. One of the design challenges of the high-density power converter design is to have high-density magnetic components which are usually the most bulky parts in a converter. Increasing the switching frequency to shrink the passive component size is the biggest contribution towards increasing power density. However, two factors, losses and parasitics, loom and compromise the effect. Losses of high-frequency magnetic components are complicated due to the eddy current effect in magnetic cores and copper windings. Parasitics of magnetic components, including leakage inductances and winding capacitances, can significantly change converter behavior. Therefore, modeling loss and parasitic mechanism and control them for certain design are major challenges and need to be explored extensively. In this dissertation, the abovementioned issues of high-frequency transformers are explored, particularly in regards to high-power converter applications. Loss calculations accommodating resonant operating waveform and Litz wire windings are explored. Leakage inductance modeling for large-number-of-stand Litz wire windings is proposed. The optimal design procedure based on the models is developed. / Ph. D.

This work presents the design and analysis of two Litz wire transformers for a 500 kHz, 18 kW input­parallel output­series partial power processing converter (IPOS PPP). Because the two power paths in the IPOS PPP operate as “dc transformers” (DCX), both transformers are designed with the goal of leakage inductance minimization in order to reduce gain variation around the resonant frequency. The selected winding topology with the lowest leakage inductance results in an impedance mismatch among parallel secondaries used in the majority power path transformer, resulting in poor current sharing. In order to balance the goals of leakage inductance minimization and even current sharing, a new winding technique called “intra­leaving” is presented which reduces current sharing error from 50%, to 5%. A design rule for “intra­leaving” is also established which extends the winding method to different winding configurations and higher numbers of parallel winding. A novel cooling duct designed with computational fluid dynamics is used for transformer thermal management. The cooling duct uses two 30 mm 7.7 CFM fans to cool the transformer winding and achieves a small height of 43 mm and only 6.8 W power consumption. Using the cooling duct, 106 °C peak winding temperature and 76 °C peak core temperature is achieved at 15 kW load, an ∼ 8% reduction compared to using a conventional 120 mm fan 41 CFM fan. The two transformers with the cooling system achieve 635 W/in3 power density, 1U height compliance, and 99.4% peak efficiency. / M.S. / As society moves towards the electric grid of the future, there have been increased calls for the research and development of resonant power converters due to their high efficiency, high power density, and low electromagnetic interference. The high frequency transformer is one of the main components of the resonant converter system as it contributes substantially to the converters volume, power loss, and thermal management risks. This work seeks to address the trade­offs between leakage inductance minimization and transformer current sharing and proposes a winding method called “intra­leaving” which achieves both. Using “intra­leaving” current sharing error was reduced from 50%, to 5%. Operating transformers at high frequency reduces their volume in accordance with Faraday’s law but also increases thermal risks due to decreased core surface area, higher winding fill factor, and higher loss per unit volume. A novel cooling duct designed using computational fluid dynamics is presented using two 30 mm 7.7 CFM fans and achieves a small height of 43 mm and only 6.8 W power consumption. Using the cooling duct, 106 °C peak winding temperature and 76 °C peak core temperature is achieved at 15 kW load, an ∼ 8% reduction compared to using a conventional 120 mm fan 41 CFM fan. The transformers with the cooling system designed in this work achieve 635 W/in³ power density, 1U height compliance, and 99.4% peak efficiency.

Made available in DSpace on 2014-12-17T14:56:08Z (GMT). No. of bitstreams: 1 GiancarlosCB_DISSERT.pdf: 5458787 bytes, checksum: 8900cf5f95194fd230853ddd24b869cd (MD5) Previous issue date: 2012-08-13 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work discusses the design of a transformer used in a plant plasma. This plant, which is being developed in UFRN, will be used in the treatment of waste. It consists basically of a radio frequency power supply and a inductive plasma torch. The transformer operates at the nominal frequency of 400 kHz, with 50 kW, allowing the adaptation of impedance between the power supply and torch. To develop the project, a study was done on the fabrication technologies and physical effects on the frequency of operation. This was followed by the modeling of this transformer. Finally, simulations and tests were conducted to validate the design / Este trabalho aborda o projeto de um transformador utilizado em uma planta de plasma. Esta planta, que est? sendo desenvolvida na UFRN, ser? utilizada no tratamento de res?duos. Ela ? composta, basicamente, por uma fonte de alimenta??o de radiofrequ?ncia e uma tocha indutiva de plasma. O transformador opera na frequ?ncia nominal de 400 kHz, com pot?ncia de 50 kW, permitindo a adapta??o de imped?ncias entre a fonte de alimenta??o e a tocha. Para o desenvolvimento do projeto, foi feito um estudo sobre as tecnologias de fabrica??o e efeitos f?sicos na frequ?ncia de opera??o. Posteriormente, foi realizada a modelagem deste transformador. Por fim, foram realizados simula??es e testes de forma a validar o projeto

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To achieve higher power density, converters and components must be able to handle higher voltage and current ratings at higher percentages of efficiency while also maintaining low cost and a compact footprint. To meet such demands, medium-voltage resonant converters have been favored by researchers for their ability to operate at higher switching frequencies. High frequency (HF) operation enables soft switching which, when achieved, reduces switching losses via either zero voltage switching (ZVS) or zero current switching (ZCS) depending on the converter topology. In addition to lower switching losses, the converter operates with low harmonic waveforms which produce less EMI compared to their hard switching counterparts. Finally, these resonant converters can be more compact because higher switching frequencies imply decreased volume of passive components. The passive component which benefits the most from this increased switching frequency is the transformer. The objective of this work is to design a >400 kHz, 100 kW transformer which will provide galvanic isolation in a Solid-State Transformer (SST) based PEBBs while maintaining high efficiency, high power density, and reduced size. This work aims to present a simplified design process for high frequency transformers, highlighting the trade-offs between co-dependent resonant converter and transformer parameters and how to balance them during the design process. This work will also demonstrate a novel high frequency transformer insulation design to achieve a partial discharge inception voltage (PDIV) of >10 kV. / Master of Science / As the world's population expands and countries progress, the demand for electricity that is high-powered, highly efficient, and dependable has increased exponentially. Further, it is integral to the longevity of global life that this development occurs in a fashion that mitigates environmental consequences. The power and technology sectors have been challenged to address the state of global environmental affairs, specifically regarding climate change, carbon dioxide emissions, and resource depletion. To move away from carbon emitting, non-renewable energy sources and processes, renewable energy sources and electric power systems must be integrated into the power grid. However, the challenge lies in the fact that there is not an easy way to interface between these renewable sources and the existing power grid. Such challenges have undermined the widespread adoption of renewable energy systems that are needed to address environmental issues in a timely manner. Recent developments in power electronics have enabled the practical application of the solid-state transformer (SST). The SST aims to replace the current, widespread form of power transformation: the line frequency transformer (50/60 Hz). This transformer is bulky, expensive, and requires a significant amount of additional circuitry to interface with renewable energy sources and electric power systems. The SST overcomes these drawbacks through high frequency operation (>200 kHz) which enables higher power at a reduced size by capitalizing on the indirect proportionality between the two parameters. The realization of the SST and its implementation has the ability to greatly advance the electrification of the transportation industry which is a top contributor to carbon emissions. This work aims to demonstrate a >400 kHz, 100 kW SST with a novel magnetic design and insulation structure suited for electric ship applications.

In this thesis, the possibility of detection of fault location in the cable distribution systems by using traveling waves due to fault and circuit breaker operations is investigated. Waveforms originated from both actions and fault steady state are separately analyzed. During such switching actions, high frequency variations which are absent in the steady state conditions, take place. In order to simulate high frequency changes properly, system elements are modeled accordingly. In other words, frequency dependent models are introduced, and they are used in Electro-Magnetic Transients Program (EMTP). Since the characteristics of waveforms are different for separately analyzed portions, different fault locating algorithms with their limitations are introduced.

It is anticipated that massive amounts of energy will be transferred long distances via High-Voltage Direct Current (HVDC) links in the future and the prospect of having meshed HVDC grids is envisioned, for example the European super grid. Such a power system would benefit greatly if HVDC circuit breakers could reliably clear faults within the HVDC network. Different ways to break large direct currents have been proposed throughout the years and one distinguished concept is based on generating an artificial zero-crossing of the current and pass it through a mechanical interrupter as it opens. This concept is implemented in the Voltage-Source Converter Assisted Resonant Current (VARC) circuit breakers developed at Scibreak which require auxiliary power from an off-line supply unit to energize their electronic equipment. This thesis continuous and builds on research previously carried out at Scibreak on a special Auxiliary Power Supply (APS) concept for 525 kV HVDC applications. In essence, it is a unique modularized high-frequency transformer whose power transfer and voltage withstand capabilities are the cornerstones of its design. The APS must supply an adequate amount of power to drive the VARC circuit breakers with preferably high efficiency while also fulfilling the considerable insulation demands of HVDC grids. A feasibility study of this APS concept was carried out by building a parametric 3D model in the Finite Element Analysis (FEA) software Ansys Maxwell which includes all parts that affect both its magnetic and electrical properties. The initial model reproduced experimental results from a magnetic APS prototype and was then used to explore a plethora of different geometries and materials with regards to its magnetic and dielectric designs. Specific design candidates were selected for more in-depth analysis and experimental work. All obtained results together with knowledge of commercially available materials show that the APS holds great promise to meet the necessary design criteria for its HVDC applications. Its dielectric design is well suited to continuously handle an operating voltage of 525 kV DC, meet the required impulse voltage levels of the grid and properly shield the magnetic structure. It is expected to have a long life time where the design criterion was always 30 years in this work. Moreover, its magnetic design is anticipated to supply a few kW of active power with efficiencies between 80 to 95 percent and manage a continuous operating time of 5 min. Both design aspects are interchangeable to a decent extent in order to cope with one another and produce a compromised design. / Det förväntas att enorma mängder energi kommer överföras långa sträckor med Högspänd Likström (HVDC) i framtiden och blivande HVDC-nät håller på att föreställas, till exempel det europeiska superelnätet. Ett sådant kraftsystem skulle ha stor nytta av HVDC-brytare som tillförlitligt kan bryta felströmmar inom HVDC-nätet. Olika sätt att bryta stora likströmmar har föreslagits med åren och ett distinkt koncept bygger på att generera en artificiell nollgenomgång av strömmen och föra den genom en mekanisk brytarkammare när den öppnas. Detta koncept är implementerat i de så kallade VARC-strömbrytarna som utvecklas hos Scibreak, vilka kräver hjälpmatning av effekt från en extern försörjningsenhet för att driva deras elektroniska utrustning. Denna avhandling fortsätter och bygger vidare på forskning som tidigare utförts hos Scibreak på ett speciellt Hjälpmatningskoncept (APS) för 525 kV HVDC-tillämpningar. I huvudsak är det en unik modulariserad högfrekvenstransformator vars kraftöverföring och spänningståligheter är huvudfokusen i dess design. Hjälpmatningen måste kunna leverera en tillräcklig mängd effekt för att driva VARC-brytarna med företrädesvis hög verkningsgrad, samtidigt som den ska uppfylla de betydande isolationskraven för HVDC-nät. En genomförbarhetsstudie av detta APS-koncept gjordes genom att bygga en parametrisk 3D modell i Finita Elementmetodsprogramvaran (FEM) Ansys Maxwell som inkluderar alla delar som påverkar både dess magnetiska och elektriska egenskaper. Den initiala modellen reproducerade experimentella resultat från en magnetisk APS-prototyp och användes sedan för att utforska en uppsjö av olika geometrier och material med avseende på dess magnetiska och dielektriska konstruktioner. Specifika designkandidater valdes ut för mer djupgående analys och experimentiellt arbete. Alla erhållna resultat tillsammans med kunskap om kommersiellt tillgängliga material visar att APS:n har stora möjligheter att uppfylla alla nödvändiga kriterier för sina HVDC-tillämpningar. Dess dielektriska design är väl lämpad för att kontinuerligt hantera en driftspänning på 525 kV DC, möta de erforderliga stötspänningståligheterna i nätet och ordentligt skydda den magnetiska strukturen. Den förväntas ha en lång livstid där designkriteriet alltid var 30 år i detta arbete. Dessutom förväntas dess magnetiska design leverera några kW aktiv effekt med verkningsgrader mellan 80 till 95 procent och klara en kontinuerlig drifttid på 5 min. Båda designaspekterna kan justeras i en någorlunda utsträckning för möta de krav som ställs från varandra och producera en kompromissad design.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Master Thesis presents a new analysis, modeling and design guideline for an Insulated Power Factor Corrected Single-Stage Converter. First, the operating principle is presented which provides a better understanding of the converter. So, based on this new analysis, the two operation modes description and the new steady-state gain of the converter are provided. A new control strategy for the input current control-loop is also proposed which provides an improvement of the total harmonic distortion (THD). The conditions to reset the magnetic flux for the high frequency transformer (HFT) into a switching period and the mitigation of the reactive energy are provided. At the sequence, the transfer functions that describe the dynamic behavior of the output voltage and the input current due to perturbations on duty-cycle and input voltage are derived. These dynamic models are derived based on the averaged equivalent circuit (AEC) obtained by modeling an equivalent DC-DC converter. Finally, the design guideline and experimental results for validation of the mathematical analysis and numerical simulation confirmation are provided. / Esta Dissertação de Mestrado apresenta uma nova análise, modelagem e metodologia de projeto de um conversor CA-CC isolado com um único estágio e correção do fator de potência. Inicialmente, é apresentado o princípio de operação do conversor em estudo propiciando um melhor entendimento do funcionamento do mesmo. Assim, baseada na nova análise, são apresentados os dois modos de operação do conversor e o novo ganho estático resultante. Também é proposta uma nova estratégia de controle para a corrente de entrada do conversor proporcionando uma redução na distorção harmônica total (DHT). Também serão estabelecidas as condições necessárias para a desmagnetização do núcleo do transformador de alta freqüência (TAF) em um período de chaveamento e a minimização de reativos circulantes. Posteriormente, são obtidas as funções de transferências que descrevem o comportamento dinâmico da tensão de saída e da corrente de entrada para perturbações na variável de controle ou na tensão de entrada. Esses modelos dinâmicos serão derivados do circuito médio equivalente (CME) obtido através da modelagem do conversor em estudo operando como um conversor CC-CC equivalente. Por fim, são apresentadas uma metodologia de projeto e os resultados experimentais para a validação da análise matemática e confirmação dos resultados obtidos através de simulações numéricas.

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