Thesis (M.E.)--University of Canterbury, 2009. / Typescript (photocopy). "November 2009." Includes bibliographical references (p. [120]-123). Also available via the World Wide Web.

This thesis presents the operation, analysis, simulation and experimental results of a single-phase single-stage soft-switched high frequency (HF) transformer isolated ac-to-dc bridge converter with low total harmonic distortion (THD) and its extension to ac-to-dc multiphase converter. A single-phase single-stage soft-switched ac-to-dc bridge converter cell has been proposed based on a new gating scheme. Due to the discontinuous current mode (DCM) operation of the boost inductor, natural power factor correction and low THD are ensured. The single-stage ac-to-dc multiphase converter is realized based on this bridge converter cell to reduce HF harmonic components in the line current. The steady-state operation of the single-stage bridge converter is explained for all operating modes. Intervals of operation in these modes are identified and analyzed. The steady-state solutions are presented. Based on these solutions, design curves are obtained. Design example of a 1.7 kW converter is presented to illustrate the design procedure. Operational characteristics are obtained for different line and load conditions. PSPICE simulation results for the designed converter are presented. An experimental prototype is built to verify the operation and performance of the converter. All four switches in the fixed frequency bridge converter undergo soft switching (common switch requires an auxiliary circuit) for a wide line and load range. A single-stage HF transformer isolated ac-to-dc multiphase converter is proposed. The analyses of the single-stage bridge converter cell are extended to the multiphase converter. It is shown that N = 3 is near the optimum number of cells to reduce the input current HF harmonic components. A design example of a 166 to 260 V (rms) input, 420 V output, 5 kW converter switching at 50 kHz is presented. PSPICE simulation results are obtained for the designed converter to study its performance for varying load and line conditions. A 3-cell 1.5 kW experimental prototype is built and experimental results are obtained. All the results show that HF harmonics in the line current are reduced and output voltage ripple frequency is increased. Each cell handles equal power and all bridge-switches are soft switched. As a result, uniform thermal distribution is obtained. Small-signal analysis of the single-stage ac-to-dc bridge converter cell is presented for all operating modes using state-space averaging technique. Based on this analysis, small signal transfer functions are obtained. Frequency response of the transfer functions are plotted using MATLAB program and verified by PSPICE simulation results. A closed loop control system is designed and frequency response of the overall loop gain is presented. Large-signal transient behavior of the converter cell is studied with open loop using PSPICE simulation program for step change in line and load conditions. The simulation results show that the closed loop system is required to improve the converter performance during step increase in line voltage. / Graduate

Orientador: José Carlos Rossi / Banca: Fabio Toshiaki Wakabayashi / Banca: Kleiber David Rodrigues / Resumo: Este trabalho está direcionado à implementação de uma modelagem que venha possibilitar a realização dos cálculos das perdas técnicas no cobre do transformador trifásico de distribuição operando em condições não-senoidais, através da utilização do valor médio de Distorção Harmônica Total de Corrente drenada por suas cargas. Essa implementação visa facilitar a obtenção dos valores das perdas técnicas para múltiplas unidades transformadoras. Para atingir o objetivo mencionado, realizou-se um ensaio em curto-circuito através de ensaios experimentais aplicadas em uma unidade transformadora trifásica de distribuição com 15 kVA de capacidade. A fonte trifásica de alimentação utilizada na atividade proporciona o ajuste de tensão e da freqüência, possibilitando obter os valores de resistências CA dos enrolamentos do transformador para diferentes ordens harmônicas. Com o propósito de validar esta nova proposta, foi realizada uma análise confrontando-se os dados obtidos através da modelagem proposta neste trabalho e de uma outra bastante difundida pela literatura atual. Os cálculos foram efetuados utilizando-se dados de distorções harmônicas de correntes oriundas de medições de ramais de distribuição. Através da comparação dos resultados obtidos é possível verificar a validade da modelagem proposta. / Abstract: This work is addressed to the implementation of a modeiling that comes to make possible the calculations of the technical losses in the copper of three-phase distribution transformers operating under non-sinusoidal conditions, using the médium value of Total Current Harmónio Distortion. This implementation seeks to provide easiness in the obtaining of the values of the technical losses for multiple transformer units in non-sinusoidal environment. Aiming to reach the mentioned objective, it was carried out a test in short circuit through appiied experimental activities in a three-phase distribution transformer unit with 15 k VA capacity. The three-phase source used in the activity provides the voltage and the frequency adjustment, making possible to obtain the values ofca resistances ofthe windings ofthe transformer for some harmónio orders. With the purpose ofvalidating this new proposal, an analysis was accomplished being confronted the data obtained through the modeiling proposed in this work with another one quite spread in the current literature. The calculations were carried out using current harmónio distortion data of measurements in distribution branch lines. Through the comparison of the obtained results it is possible to verify the validity ofthe proposed modeiling. / Mestre

This thesis presents new configurations for three-phase AC-to-DC single-stage, softswitched, high frequency (HF) transformer isolated converters with power factor correction (PFC) and low harmonic distortion. Four different configurations are presented. Topology of all these four configurations is based on integration of a front-end DCM boost with a soft switching HF transformer isolated DC-to-DC PWM converter with fixed frequency. DCM operation of the front-end boost provides natural PFC with low total harmonic distortion (THD) and the DC-to-DC HF transformer isolated soft switching PWM converter with an appropriate gating scheme provides output voltage regulation. A double switch AC-to-DC converter is presented in Chapter 2. Due to unsymmetrical gating scheme, DC blocking capacitors are required to avoid transformer saturation. To reduce this problem, a new gating scheme is proposed in Chapter 3, which can be used in full bridge converters providing ZVS. This gating scheme is first used in a DC-to-DC bridge converter. In the next three chapters, this new gating scheme is applied to three different types of single-stage AC-to-DC boost integrated fixed-frequency bridge converters. These configurations are: (i) boost integrated single inductor linear current DC-to-DC PWM bridge converter, (ii) boost integrated series resonant DC-to-DC bridge converter and (iii) boost integrated parallel resonant DC-to-DC bridge converter. The steady state operation of each converter and modes of operation are explained with equivalent circuits for each interval of HF cycle. The general solutions for all the intervals are derived and design curves are obtained based on steady state relations. The design procedure is illustrated with a design example. Detailed PSPICE simulation results and experimental results obtained from a laboratory prototype model are given for all the converters to verify the theory and analysis. THD of the line current without any complex control circuit remains in a reasonable range of 8% to 13% for the total range of operation. Input line current waveforms for all suggested converters shows a low harmonic distortion similar to a single 3-Φ DCM boost. The difference would be in increase or decrease of DC bus voltage in each case, which can affect THD of the boost converter. Three switches in the full bridge converter operate with zero-voltage switching (ZVS) while the main switch operates with ZVS at full load, minimum line voltage and with ZVT at lower loads conditions. Soft switching of all the switches helps in lower loss. Chapter 6 presents the contributions of this thesis, summarizes the advantages and disadvantages of each configuration and gives some suggestions for future work. / Graduate

M.Ing. (Electrical and Electronic Engineering) / Please refer to full text to view abstract

Partial discharges (p.d.'s) are a major source of the progressive deterioration of insulation in / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.

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Thesis (Ph.D.)-- University of Adelaide, Dept. of Mechanical Engineering, 2000. / Bibliography: leaves 182-190. Also available electronically.