published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

With superior longevity, approximately 5 times that of compact fluorescents (CFLs), and high efficacy, around 1.5 times that of CFLs, LEDs are now attracting vast attention from both academic and industrial sectors. Unfortunately, current power supply drivers for LEDs have the following drawbacks: (1) for a two-stage configuration, the power factor correction (PFC) circuit can help LEDs achieve good operating performance but contain too many components and are large in size, have low efficiency and relatively high cost; (2) a single-stage configuration can perform well in PFC and efficiency, however reliability issues occur due to the use of the electrolytic capacitor. In this thesis, the theoretical analysis and implementation of two high power factor, soft-switched, electrolytic-capacitor-less LED drivers are presented. The two drivers solve the aforementioned issues while minimizing its size and cost. The detailed theoretical analysis illustrates the advantages of the presented circuits and provides insight into their design and operation. The simulated and experimental implementations verified the performance of both circuits, which achieve a high power factor, indicating that the drivers have good operating performance. Elimination of the electrolytic capacitors improves the LED drivers’ reliability. In addition, with the help of soft-switching capability, high efficiency is achieved. Simulation and experimental results are presented to support all merits of the two circuits. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2013-04-30 13:22:28.471

Thesis advisor: Zhifeng Ren / Thermoelectrics, as one promising approach for solid-state energy conversion between heat and electricity, is becoming increasingly important within the last a couple of decades as the availability and negative environmental impact of fossil fuels draw increasing attention. Therefore, various thermoelectric materials in a wide working temperature range from room temperature to 1000 degrees Celsius for power generation or below zero for cooling applications have been intensively studied. In general, the efficiency of thermoelectric devices relies on the dimensionless figure-of-merit (ZT) of the material, defined as ZT=(S<super>2</sup>&sigma;)T/&kappa;, where S is the Seebeck coefficient, [sigma] the electrical conductivity, [kappa] the thermal conductivity (sum of the electronic part, the lattice part, and the bipolar contribution at high temperature region), and T the absolute temperature during operation. Techniques to measure those individual parameters will be discussed in the 2nd chapter while the 1st chapter mainly covers the fundamental theory of thermoelectrics. Recently, the idea of using various nanostructured materials to further improve the ZT of conventional thermoelectric materials has led to a renewed interest. Among these types of nanostructured materials, nanocomposites which mainly denote for the nano-grained bulk materials or materials with nano-sized inclusions are the major focus of our study. For nanocomposites, the enhancement in ZT mainly comes from the low lattice thermal conductivity due to the suppressed phonon transport by those interfaces or structure features in the nanometer scale without deteriorating the electron transport. In the last few years, we have successfully demonstrated in several materials systems (Bismuth Telluride, Skutterudites, Silicon Germanium) that ball milling followed by hot pressing is an effective way for preparing large quantities of those nanocomposite thermoelectric materials with high ZT values in the bulk form. Therefore, in the 3rd part of this thesis, I will talk about how I applied the same technique to the Thalllium (Tl) doped Lead Telluride (PbTe) which was reported for an improved Seebeck coefficient due to the creation of resonant states near the Fermi level, leading to a high ZT of about 1.5 at around 500 degrees Celsius. I showed that comparing with conventional tedious, energy consuming melting method, our fabrication process could produce such material with competing thermoelectric performance, but much simpler and more energy effective. Potential problems and perspectives for the future study are also discussed. The 4th chapter of my thesis deals with the challenge that in addition to those nanostructuring routes that mainly reduce the thermal conductivity to improve the performance, strategies to enhance the power factor (enhancing [sigma] or S or both) are also essential for the next generation of thermoelectric materials. In this part, modulation-doping which has been widely used in thin film semiconductor industry was studied in 3-D bulk thermoelectric nanocomposites to enhance the carrier mobility and therefore the electrical conductivity [sigma]. We proved in our study that by proper materials design, an improved power factor and a reduced thermal conductivity could be simultaneously obtained in the n-type SiGe nanocomposite material, which in turn gives an about 30% enhancement in the final ZT value. In order to further improve the materials performance or even apply this strategy to other materials systems, I also provided discussions at the end of chapter. In the last chapter, the structural and transport properties of a new thermoelectric compound Cu₂Se was studied which was originally regarded as a superionic conductor. The [beta]-phase of such material possesses a natural superlattice-like structure, therefore resulting in a low lattice thermal conductivity of 0.4-0.5 Wm^-1K^-1 and a high peak ZT value of ~1.6 at around 700 degrees Celsius. I also studied the phase transition behavior between the cubic [beta]-phase and the tetragonal [alpha]-phase of such material from the discontinuity of transport property curves and the change in crystal structure. In addition, I also talk about the abnormal decrease in specific heat with increasing temperature that I observed in the as-prepared Cu₂Se samples. I suggest this material is of general interest to a broad range of researchers in Physics, Chemistry, and Materials Science. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Orientador: Fernando Pinhabel Marafão / Coorientador: Marcelo Gradella Villalva / Banca: José Antenor Pomílio / Banca: Marcelo Godoy Simões / Resumo: O objetivo deste trabalho foi desenvolver um sistema de geração fotovoltaico híbrido, ou seja, capaz de funcionar tanto interligado à rede elétrica como desconectado (ilhado) desta. Quanto ilhado, este sistema fornece potência e uma tensão senoidal para a carga, desde que haja energia solar nos módulos fotovoltaicos e/ou energia armazenada no banco de baterias. Quando conectado, o sistema de geração fotovoltaico é capaz de fornecer potência ativa para a carga e/ou rede elétrica e, simultaneamente, funcionar com um Stalic Synchrnous Compensator (STATCOM), auxiliando no suporte de tensão no ponto de acoplamento comum ou, como um compensador ativo seletivo, atenuando os distúrbios elétricos causados pela carga. Para atingir o objetivo deste trabalho, o sistema de geração fotovoltaico foi estudado, projetado e analisado. O estudo passou por definições de geração distribuida e de microrede; modelagem do dispositivo fotovoltaico; escolha da técnica de rastreamento do ponto de máxima potência (MPPT); modelagem do banho de baterias; projeto, modelagem e controle dos conversores eletrônicos; projeto das malhas de controle de potência, responsáveis pelo gerenciamento do balanço de potência. Também foi realizada uma análise de três diferentes controladores aplicados ao sistema de geração fotovoltaico isolado e, análises do funcionamento do sistema híbrido com algumas multifuncionalidades agregadas, tais como: funcionamento híbrido, STATCOM e compensador ativo seletivo. Os estudos relacionados à modelagem do dispositivo fotovoltaico, escolha da técnica de MPPT, modelagem do banco de baterias e, projeto, modelagem e controle dos conversores CC-CC foram realizados por meio de simulação. Enquanto que o projeto, modelagem e controle do conversor CC-CA, os estudos do sistema fotovoltaico isolado e híbrido, assim como suas multifuncionalidades... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The goal of this work is to develop a hybrid photovoltaic generated system, which means, able to run both connected to the grid as disconnected (islanded). When it operates in the islanted mode, the system provides power and a sinusoidal voltage to the local loads, since there exist solar energy at the photovoltaic modules and/or storage energy in the battery bank. When the photovoltaic system operates in the connected mode, it is able to supply active power to the load and/or grid and, simultaneously, works as a static synchronous compensator (STATCOM), assisting in the voltage support at the point of common coupling or, as a selective active compensator, mitigating disturbance caused by the load. To reach the goal of this work, the photovoltaic system was studied designed and analyzed. The studies addressed to definition of distributed generation and microgrids; modeling of the photovoltaic device; choose of the maximum power point tracking (MPPT) technique; modeling of the battery bank; design, modeling and control of the electronic converters; design of the power control loops responsible for the power balance manager. It was also perfomed an analyze of three different controllers applied in an isolated photovoltaic generated system and analyzed a hybrid system with multifunctionalities, such as: hybrid operation, STATCOM function and selective active compensator function. The studied related to the modeling of the photovoltaic device, choose of the MPPT technique, modeling of the battery bank and, design, modeling and control of the DC-DC converters have been performed by simulation results. Whereas the design, modeling and control of the DC-AC converter, the studies the isolated and hybrid photovoltaic system, such as multifunctionalities, have been analyzed by simulation results and validated by experimental results... (Complete abstract click electronic access below) / Mestre

In the thesis, LED driver circuits which are applied in low power lighting LED with constant output current and Power Factor Correction are presented. The non-isolated Buck converter are used for the LED drivers. According to different operating mode of inductance current, Power Factor Correction are realized with both the method of Voltage Follower Approach Control under Discontinuous Conduction Mode and the method of Nonlinear Carrier Control under Continuous Conduction Mode. NLC doesn¡¦t need the multiplier which is used in traditional power factor correction, therefore NLC can reduce the system cost. The designed circuits are verified by simulation of IsSpice software and practical experiments. From simulation and experimental results, it shows the proposed approaches achieve the goal with high power factor and constant output current.

To fulfill the requirements of the operation in a wide power range, a parallel configuration with modular power factor correctors (PFCs) is proposed. Each PFC module is composed of a bridge-rectifier, a fly-back converter and associated passive filters. The fly-back converter is independently operated at a fixed frequency with a discontinuous inductor current. This allows the modules to achieve a high power factor and to regulate the output power with simple control. With the same duty-ratio and frequency, the total current will be distributed equally to each operating module without complex current sharing control. The operating modules are equally phase-shifted to take the advantages of the continuous current mode when operated at a higher power. Experiments were conducted to achieve a power rating of 1 kVA by operating 10 PFC modules in parallel. The duty-ratio of the operating modules is controlled by a micro-controller to regulate the output power in accordance with the load requirement. A complex programmable logic device (CPLD) is used for phase-shifting. All modules are operated in turn to share the operating cycles in a more equal manner. Experimental results demonstrate the parallel configuration can achieve the expected performances.

This thesis presents the design and implementation of a single-stage with high power factor asymmetrical half-bridge converter. The main structure combines a boost converter with an asymmetrical half-bridge. An Asymmetrical half-bridge converter has many advantages such as soft-switching properties and fewer components. Therefore it is suitable for DC/DC cell. The boost converter is used in a PFC cell that operating in discontinuous condition mode have innate ability of power factor correction without additional controller. In this thesis, the complete analysis of operation principle and design of controller for the equivalent circuits of a single-stage AC/DC converter in every operating stage have been described in detail. Finally, we construct the single-stage circuit and experimental result show that it can reach the expected goal for power-factor correction.

The thesis aims to the research of active power factor correction (PFC) circuit and develop a DSP-based digital controller. In the thesis, PI controller is the control core for the voltage loop¡Band current loop, and then achieve the function of the power factor correction of boost converter. Finally, we develop a boost converter and connect it to a DSP-based controller to measure the waveforms and verify the power factor correction. Furthermore, the research can be extended to a simulating platform which we can verify the power factor correction by just changing the control law on DSP .

Fluorescent lamps are nowadays the most important light sources in industrial, commercial, and domestic applications. To drive fluorescent lamps, electronic ballasts with high-frequency resonant inverter, instead of the electromagnetic ones, are increasingly used due to the benefits of lightweight, small size, high luminous efficiency, and long lamp life. Recently, efforts are concentrated on how to reduce the product cost as well as to improve the circuit performances. To further curtail the product cost, the power-factor-correction circuit is integrated into the ballast circuit as single-stage high-power-factor electronic ballast. On the other hand, the unit cost per lamp can be substantially reduced by developing a ballast circuit which is capable of driving multiple lamps. For convenient use, the user may turn on the desired number of the lamps in accordance with the expected luminosity. A starting-aid circuit is added to eliminate the glow current during preheating. In addition, a protection circuit will be included in the multi-lamp electronic ballast. In case of operating partial lamps, a high power factor at the line input will be always retained. In this thesis, the feasible circuit configuration is developed and design equations are derived. Accordingly, design guidelines for determining circuit parameters are provided. The laboratory circuits are built and tested to verify the computer simulations and analytical predictions.

In this thesis, a high voltage discharging testing circuit is proposed for cold cathode fluorescent lamps(CCFLs). The testing circuit uses only a single active power switch operating at a high frequency incorporating with reactive components to accumulate a relatively high voltage on the capacitor. This voltage is then stepped up by a transformer to provide the required high voltage for discharging the CCFLs. The circuit has the advantages of simple configuration, less component count, and low cost. In addition, a high power factor at the ac line source can be achieved. The proposed circuit is analyzed based on the mode operation. Accordingly, the design equations are derived to determine the circuit parameters. A prototype is designed and built for testing the 19 inch CCFLs. The discharging tests are made to recognize the malfunctions during the manufacturing process. Moreover, the distributions on the spectral power and chromaticity of lamps can be examined to ensure the product quality.