This dissertation presents the derivation, analysis and application issues of advanced topologies with coupled inductors. The proposed innovative solutions can achieve significant performance improvement compared to the state-of-the-art technology. New applications call for high-efficiency high step-up DC-DC converters. The basic topologies suffer from extreme duty ratios and severe rectifier reverse recovery. Utilizing coupled inductor is a simple solution to avoid extreme duty ratios, but the leakage inductance associated with the coupled inductor induces severe voltage stress and loss. An innovative solution is proposed featuring with efficient leakage energy recovery and alleviated rectifier reverse recovery. Impressive efficiency improvement is achieved with a simple topology structure. The coupled inductor switching cell is identified. Topology variations and evaluations are also addressed. The concept that utilizes coupled inductors to alleviate rectifier reverse recovery is then extended, and new topologies suitable for other applications are generated. The proposed concept is demonstrated to solve the severe rectifier reverse recovery that occurs in continuous current mode (CCM) boost converters. Significant profile reduction and power density improvement can be achieved in front-end CCM power factor correction (PFC) boost converters, which are the overwhelmingly choice for use in telecommunications and server applications. This dissertation also proposes topologies to realize the single-stage parallel PFC by utilizing coupled inductors. Compared to the state-of-the-art single-stage PFC converters, the proposed topologies introduce a new power flow pattern that minimizes the bulk-capacitor voltage stress and the switch current stress. / Ph. D.

The proliferation of distributed energy resources (DER)s has prompted interest in the expansion of DC power systems. The technological limitations that hinder the expansion of DC power systems are the absence of DC circuit breakers and high step-up/high step-down DC converters for interconnecting DC systems. This thesis presents a transformerless high step-up DC-DC converter intended for use as an interconnect between DC systems. The converter is required to operate at medium to high voltage (>1kV) and provide high voltage gain (>5). This work details the steady state operation and dynamic model of the proposed converter. The component ratings are identified and converter design limitations are investigated. A 100V:1kV/4kW prototype is produced to verify the analytic steady state model and measure efficiency. An experimental efficiency of 90% was achieved at a step-up ratio of 1:10, however efficiency at low power is limited due to the need to circulate power.

The proliferation of distributed energy resources (DER)s has prompted interest in the expansion of DC power systems. The technological limitations that hinder the expansion of DC power systems are the absence of DC circuit breakers and high step-up/high step-down DC converters for interconnecting DC systems. This thesis presents a transformerless high step-up DC-DC converter intended for use as an interconnect between DC systems. The converter is required to operate at medium to high voltage (>1kV) and provide high voltage gain (>5). This work details the steady state operation and dynamic model of the proposed converter. The component ratings are identified and converter design limitations are investigated. A 100V:1kV/4kW prototype is produced to verify the analytic steady state model and measure efficiency. An experimental efficiency of 90% was achieved at a step-up ratio of 1:10, however efficiency at low power is limited due to the need to circulate power.

Important considerations of a photovoltaic (PV) source are achieving a high voltage and drawing currents with very little ripple component from it. Furthermore, the output from such a source is variable depending on irradiation and temperature. In this research, literature review of prior methods employed to boost the output voltage of a PV source is examined and their limitations identified. This research then proposes a multi-phase tapped-coupled inductor boost DC-DC converter that can achieve high voltage boost ratios, without adversely compromising performance, to be used as an interface to a PV source. The proposed converter achieves minimal current and voltage ripple both at the input and output. The suitability of the proposed converter topology for variable input voltage and variable power operation is demonstrated in this dissertation. The proposed converter is also shown to have good performance at high power levels, making it very suitable for high power applications. Detailed analysis of the proposed converter is done. Advantages of the proposed converter are explained analytically and confirmed through simulations and experimentally. Regulation of the converter output voltage is also explained and implemented using a digital controller. The simulation and experimental results confirm that the proposed converter is suitable for high power as well as variable power, variable voltage applications where high voltage boost ratios are required. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Electrical, Electronic and Computer Engineering / Unrestricted

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O presente trabalho apresenta o estudo de um conversor CC/CC com dois estÃgios para aplicaÃÃo no desenvolvimento de sistemas autÃnomos de energia elÃtrica. O conversor sob estudo consiste basicamente da associaÃÃo de dois conversores CC/CC, em que entre eles à inserido um banco de baterias para dar continuidade ao fornecimento de energia em perÃodos em que nÃo hà radiaÃÃo solar. Todos os conversores utilizados para a composiÃÃo do sistema sÃo do tipo boost utilizando a cÃlula de comutaÃÃo de trÃs estados (CCTE). O primeiro conversor tem a funÃÃo enviar energia desde os painÃis fotovoltaicos a um banco de baterias de 48 V e permitir a operaÃÃo dos painÃis fotovoltaicos no ponto de mÃxima potÃncia (MPP- Maximum Power Point). O segundo estÃgio à constituÃdo por um conversor de alto ganho de tensÃo, cujo papel à elevar a tensÃo do banco de baterias de 48 V para uma tensÃo de 400 Vcc, formando assim o barramento de saÃda do sistema em tensÃo contÃnua. Para garantir a regulaÃÃo da tensÃo em 400 Vcc, foi implementada a tÃcnica de controle LQR (Linear Quadratic Regulator). Para o projeto do controle LQR à utilizado uma metodologia simplificada para a obtenÃÃo de um modelo reduzido do conversor de alto ganho de tensÃo. Para cada estÃgio à apresentado seu estudo teÃrico, anÃlise de perdas e dimensionamento dos componentes para o atendimento das especificaÃÃes de projeto. Para verificar a anÃlise teÃrica foi montado um protÃtipo para cada estÃgio e os resultados experimentais sÃo apresentados neste trabalho. / This work presents a study of a DC/DC converter with two stages for implementation of a stand-alone photovoltaic power system. The converter under study consists of two DC/DC converters, in which between them is inserted a battery bank to give continuity to the energy supply in periods when there isnât solar radiation. All converters used for the composition of the system are of type boost based on the three-state switching cell (TSSC). The first converter has function of to send energy from photovoltaic panels to a battery bank of 48 V formed by four batteries of 12V connected in series, and its function is to allow the photovoltaic panels operation at the maximum power point (MPP). The second stage consists of a converter of high voltage gain, whose role is to raise the 48 V battery bank voltage to 400V DC output bus voltage. To ensure the regulation of voltage at 400 V DC, was implemented the control LQR (Linear Quadratic Regulator). To design the controller LQR, a simplified methodology to obtain a model of the high-gain voltage converter is used. For each stage is presented its theoretical study, analysis and the components were designed and specified. To verify the theoretical analysis, was developed a prototype for each stage and the experimental results are presented in this work.

In sustainable energy systems those using fuel cells, high step-up gain converters are widely used to increase the output voltage to levels that can be used by other converters, such as inverters for grid connection or powering other AC loads. In order to obtain a higher voltage gain, in comparison to a traditional boost converter, often different topologies techniques are involved. In this project a new topology is studied, cascading to half bridges, each working similar to a boost converter but with magnetic coupled inductors in-between.    The converter design is modeled in PLECS Blockset and MATLAB Simulink to simulate and evaluate the performance with proper design procedure. The results showed that a high step-up gain was achieved, and the gain could easily be adjusted by changing the duty cycle and/or the coupling factor. The converter design showed similarities and differences to a traditional boost converter. The coupled inductor has its advantage reducing the fuel cell current ripple with the effect of the duty cycle.

This thesis introduces a new photovoltaic (PV) system architecture employing low voltage parallel-connected PV panels interfaced to a high voltage regulated DC bus of a three-phase grid-tied inverter. The concept provides several improvements over existing technologies in terms of cost, safety, reliability, and modularity. A novel resonant mode DC-DC boost converter topology is proposed to enable the PV modules to deliver power to the fixed DC bus. The topology offers high step-up capabilities and a nearly constant efficiency over a wide operating range. A reduced sensor maximum power point tracking (MPPT) controller is developed for the converter to maximize energy harvesting of the PV panels. The reduced sensor algorithm can be generally applied to the class of converters employing pulse frequency modulation control. A ZigBee wireless communication system is implemented to provide advanced control, monitoring and protection features. A testbench for a low cost 500 $W$ smart microconverter is designed and implemented, demonstrating the viability of the system architecture.

This thesis introduces a new photovoltaic (PV) system architecture employing low voltage parallel-connected PV panels interfaced to a high voltage regulated DC bus of a three-phase grid-tied inverter. The concept provides several improvements over existing technologies in terms of cost, safety, reliability, and modularity. A novel resonant mode DC-DC boost converter topology is proposed to enable the PV modules to deliver power to the fixed DC bus. The topology offers high step-up capabilities and a nearly constant efficiency over a wide operating range. A reduced sensor maximum power point tracking (MPPT) controller is developed for the converter to maximize energy harvesting of the PV panels. The reduced sensor algorithm can be generally applied to the class of converters employing pulse frequency modulation control. A ZigBee wireless communication system is implemented to provide advanced control, monitoring and protection features. A testbench for a low cost 500 $W$ smart microconverter is designed and implemented, demonstrating the viability of the system architecture.