Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 118-123). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 118-123). Also available on the Internet.

Power consumption of smart cameras varies significantly between sleep mode and active mode, and a smart camera operates in sleep mode for 80 — 90% of time for typical use. To prolong the battery life of smart cameras, it is essential to increase the power converter efficiency for light load, while being able to manage heavy load. The power stage of traditional buck converter is optimized for maximum load, at the cost of light-load efficiency. Wei proposed a multiphase buck converter incorporating the baby-buck concept and optimum number of phases (ONP) control. This thesis research investigated Wei's multiphase buck converter to improve the light-load efficiency for smart cameras as the target application. The proposed two-phase buck converter aims to provide power for microprocessors of smart cameras. The input voltage of the converter is 5 V DC, and the output voltage is 1.2 V DC with power dissipation range of 25 mA (30 mW) for light load and 833 mA (1 W) for heavy load. Three methods are considered to improve light-load efficiency: adopting baby-buck concept, adapting ONP control for low-power range, and implementing a pulse frequency modulation (PFM) control scheme with discontinuous conduction mode (DCM) to lower switching frequency. The first method is to adopt the baby-buck concept through power stage design of each phase to optimize efficiency for a specific load range. The baby-buck phase is optimized for light load and the heavy-load phase is designed to handle the processors maximum power consumption. The second method performs phase selection from sensed load current information. Rather than have all phases active for heavy-load as in ONP control, optimum phase selection (OPS) control is introduced to adaptively select between phases based on load current. Due to low-power constraints, OPS is more efficient for the medium to heavy-load range. The transition between phases due to load change is also investigated. The third and final method implements PFM control with DCM to lower switching frequency and reduce switching and driving losses under light load. PFM is accomplished with a constant on-time (COT) valley current mode controller, which uses the inductor current information and output voltage to generate switching signals for both the top and bottom switches. The baby-buck phase enters DCM to lower switching frequency under very light load, while the heavy-load phase remains in continuous conduction mode (CCM) throughout its load range. The proposed two-phase buck converter is designed and prototyped using discrete components. Efficiency of the two-phase converter and a power loss breakdown for each block in the control scheme were measured. The efficiency ranges from 64% to 81% for light load ranging of 30 mW to 200 mW, and the efficiency ranges from 81% to 88% for heavy load ranging from 200 mW to 1 W. The majority loss is due to controllers, which are responsible for 37 % (8.6 mW) for light load of 60 mW and for 10.9 % (9 mW) for heavy load of 600 mW. The gate driver loss is considerable for heavy load of 600 mW, consuming 11.9% (9.8mW). The converter has a 10 mV overshoot voltage for a load step-down from 225 mA to 25 mA, and it has 65 mV overshoot voltage for a load step-up from 25 mA to 225 mA. Although, a fair comparison is difficult due to use of discrete parts for OPS control, the proposed converter shows reasonably good efficiency and performance. / Master of Science

Renewable energy source plays an important role in energy co-generation and distribution. A traditional solar-based inverter system has two stages cascaded, which has simpler controller but low efficiency. A new solar-based single-stage grid-connected inverter system can achieve higher efficiency by reducing the power semiconductor switching loss and output stable and synchronizing sinusoid current into the utility grid. In Chapter 1, the characteristic I-V and P-V curve of PV array has been illustrated. Based on prediction of the PV power capacity installed on the grid-connected and off-grid, the trends of grid-tied inverter for DG system have been analyzed. In Chapter 2, the topologies of single-phase grid-connect inverter system have been listed and compared. The key parameters of all these topologies are listed in a table in terms of topology, power decoupling, isolation, bi-directional/uni-directional, power rating, switching frequency, efficiency and input voltage. In Chapter 3, to reduce the capacitance of input filter, an active filter has been proposed, which will eliminate the 120/100Hz low frequency ripple from the PV array's output voltage completely. A feedforward controller is proposed to optimize the step response of PV array output voltage. A sample and hold also is used to provide the 120/100Hz low frequency decoupling between the controller of active filter and inverter stage. In Chapter 4, the single-stage inverter is proposed. Compared with conventional two-stage inverter, which has two high frequency switching stages cascaded, the single-stage inverter system increases the system efficiency by utilizing DC/DC converter to generate rectified sinusoid voltage. A transformer analysis is conducted for the single-stage inverter system, which proves the transformer has no low-frequency magnetic flux bias. To apply peak current mode control on single-stage inverter and get unified loop gain, adaptive slope compensation is also proposed for single-stage inverter. In Chapter 5, a digital controller for single-stage inverter is designed and optimized by the Matlab Control Toolbox. A Psim simulation verified the performance of the digital controller design. In Chapter 6, three bi-directional single-stage inverter topologies are proposed and compared. A conventional single-stage bi-directional inverter has certain shortcoming that cannot be overcome. A modular grid-connect micro-inverter system with dedicated reactive energy processing unit can overcome certain shortcoming and increase the system efficiency and reliability. A unique controller design is also proposed. In Chapter 7, a PFM ZCS flyback inverter system is invented. By using half-wave quasi-resonant ZCS flyback resonant converter and PFM control, this topology completely eliminates switching loss. A detailed mathematical analysis provides all the key parameters for the inverter design. As the inductance of transformer secondary side get smaller, the power stage transfer function of PFM ZCS flyback inverter system demonstrates nonlinearity. An optimized PFM ZCS flyback DC/DC converter design resolves this issue by introducing a MOSFET on the secondary side of transformer. In Chapter 8, experimental results of uni-direcitonal single-stage inverter with grid-connection, bi-directional single-stage inverter and single-stage PFM ZCS flyback inverter have been provided. Conclusions are given in Chapter 9.

Smart cameras operate mostly in sleep mode, which is light load for power supplies. Typical buck converter applications have low efficiency under the light load condition, primarily from their power stage and control being optimized for heavy load. The battery life of a smart camera can be extended through improvement of the light load efficiency of the buck converter. This thesis research investigated the first stage converter of a car black box to provide power to a microprocessor, camera, and several other peripherals. The input voltage of the converter is 12 V, and the output voltage is 5 V with the load range being 20 mA (100 mW) to 1000 mA (5000 mW). The primary design objective of the converter is to improve light load efficiency. A 3-level buck converter and its control scheme proposed by Reusch were adopted for the converter in this thesis. A 3-level buck converter has two more MOSFETs and one more capacitor than a synchronous buck converter. Q1 and Q2 are considered the top MOSFETs, while Q3 and Q4 are the synchronous ones. The extra capacitor is used as a second power source to supply the load, which is connected between the source of Q1 and the drain of Q2 and the source of Q3 and the drain of Q4. The methods considered to improve light load efficiency are: PFM (pulse frequency modulation) control scheme with DCM (discontinuous conduction mode) and use of Schottky diodes in lieu of the synchronous MOSFETs, Q3 and Q4. The 3-level buck converter operates in CCM for heavy load above 330 mA and DCM for light load below 330 mA. The first method uses a COT (constant on-time) valley current mode controller that has a built in inductor current zero-crossing detector. COT is used to implement PFM, while the zero-crossing detector allows for DCM. The increase in efficiency comes from reducing the switching frequency as the load decreases by minimizing switching and gate driving loss. The second method uses an external current sense amplifier and a comparator to detect when to shut down the gate drivers for Q3 and Q4. Schottky diodes in parallel with Q3 and Q4 carry the load current when the MOSFETs are off. This increases the efficiency through a reduction in switching loss, gate driving loss, and gate driver power consumption. The proposed converter is prototyped using discrete components. LTC3833 is used as the COT valley current mode controller, which is the center of the control scheme. The efficiency of the 3-level buck converter was measured and ranges from 82% to 95% at 100 mW and 5000 mW, respectively. The transient response of the converter shows no overshoot due to a 500 mA load step up or down, and the output voltage ripple is 30 mV. The majority of the loss comes from the external components, which include a D FF (D flip-flop), AND gate, OR gate, current sense chip, comparator, and four gate drivers. The proposed converter was compared to two off-the-shelf synchronous buck converters. The proposed converter has good efficiency and performance when compared to the other converters, despite the fact that the converter is realized using discrete components. / Master of Science

No description available.

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.

Submitted by Caio Santos (c.dehly@gmail.com) on 2017-10-26T20:56:53Z No. of bitstreams: 2 Dissertação_Caio.pdf: 6450967 bytes, checksum: 9c0ad5f1b63e4ef97562046030ba0696 (MD5) Carta_Comprovante.pdf: 679811 bytes, checksum: b230eed541e4ff4ea1205d79507474d1 (MD5) / Approved for entry into archive by Milena Rubi ( ri.bso@ufscar.br) on 2017-11-10T12:12:33Z (GMT) No. of bitstreams: 2 Dissertação_Caio.pdf: 6450967 bytes, checksum: 9c0ad5f1b63e4ef97562046030ba0696 (MD5) Carta_Comprovante.pdf: 679811 bytes, checksum: b230eed541e4ff4ea1205d79507474d1 (MD5) / Approved for entry into archive by Milena Rubi ( ri.bso@ufscar.br) on 2017-11-10T12:12:54Z (GMT) No. of bitstreams: 2 Dissertação_Caio.pdf: 6450967 bytes, checksum: 9c0ad5f1b63e4ef97562046030ba0696 (MD5) Carta_Comprovante.pdf: 679811 bytes, checksum: b230eed541e4ff4ea1205d79507474d1 (MD5) / Made available in DSpace on 2017-11-10T12:13:12Z (GMT). No. of bitstreams: 2 Dissertação_Caio.pdf: 6450967 bytes, checksum: 9c0ad5f1b63e4ef97562046030ba0696 (MD5) Carta_Comprovante.pdf: 679811 bytes, checksum: b230eed541e4ff4ea1205d79507474d1 (MD5) Previous issue date: 2017-04-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Porous anodic alumina can be obtained, in addition to conventional methods such as potentiostatic and galvanostatic, or by pulsed method. Among these are the methods of discontinuous pulse, hybrid pulse and polarized pulse methods. The structures formed by these methods can be applied to sensors and photonic materials. In this work the influences of the pulse parameters for the porous anodic alumina were investigated by polarized pulse potentiostatic anodization. Data analysis was presented from the duty cycle seen in the literature, which provides important information about the structure formed for the applied conditions and, in addition, new ways of analyzing the data related to the pulse, such as the analysis of the potential difference and the pulse frequency, this latter complementing the analysis of the duty cycle. As a result it was possible to observe that the porous anodic alumina thickness obtained is proportional to the duty cycle applied, where the higher duty cycle, the greater the thickness obtained. From the potential difference, the differences in the morphological and optical parameters could be analyzed by the influence of the negative minimum voltage applied during the pulsed anodization. The pulse frequency, also discussed in this work, was used to analyze different pulse periods for the same duty cycle, demonstrating that can be obtained structures with different values by varying the value of the pulse frequency. For the porosity calculation, an application was developed that helped to obtain the pore distance, which is one of the variables used to calculate the porosity. With the porosity values, the effective refractive index of each sample was calculated to find the effective optical thickness (EOT) and, finally, the thickness of the obtained anodic alumina film. / A alumina anódica porosa pode ser obtida, além dos métodos convencionais como potenciostático e galvanostático, ou por métodos pulsados. Dentre estes destacam-se os métodos de pulso descontínuo, pulso híbrido e pulso polarizado. As estruturas formadas por estes métodos podem ser aplicadas em sensores e materiais fotônicos. Neste trabalho foram investigadas as influências dos parâmetros de pulso para a obtenção da alumina anódica porosa pelo método de anodização potenciostática com pulso polarizado. Foram apresentadas análises de dados a partir do ciclo de trabalho visto na literatura, onde traz importantes informações sobre a estrutura formada para as condições aplicadas e, além disto, novas formas de analisar os dados referentes aos pulsos, como a análise a partir da diferença de potencial e a frequência de pulso, este último complementando a análise do ciclo de trabalho. Como resultado foi possível observar que a espessura de alumina anódica porosa obtida é proporcional ao ciclo de trabalho aplicado, onde quanto maior o ciclo de trabalho, maior será a espessura obtida. A partir da diferença de potencial pôde-se analisar as diferenças nos parâmetros morfológicos e ópticos pela influência da tensão mínima negativa aplicada durante a anodização pulsada. A frequência de pulso, também abordada neste trabalho, foi utilizada para analisar diferentes períodos de pulsos para o mesmo ciclo de trabalho, demonstrando que variando o valor da frequência de pulso pode-se obter estruturas com valores distintos. Para o cálculo da porosidade foi desenvolvido um aplicativo que auxiliou na obtenção da distância entre poros, que é uma das variáveis utilizadas para o cálculo da porosidade. E com os valores de porosidade foi calculado o índice de refração efetivo de cada amostra para encontrar a sua espessura óptico efetivo (EOT, do inglês Effective Optical Thickness) e, por fim, a espessura do filme de alumina anódica obtido.

This thesis deals with the design of Hybrid Energy Storage System (HESS) for Light Electric Vehicles (LEV) and EVs. More specifically, a tri-mode high-efficiency non-isolated half-bridge converter is developed for the LEV based HESS applications. A 2 kW, 100 V interleaved two-phase converter prototype was implemented. The peak efficiency of 97.5% and a minimum efficiency of 88% over the full load range are achieved. Furthermore, a power-mix optimizer utilizing the real-time Global Positioning System (GPS) data for the EV based HESS is proposed. For a specific design, it is shown that at the cost of less than 1.5% of the overall energy savings, the proposed scheme reduces the peak battery charge and discharge rates by 76% and 47%, respectively. A 30 kW bi-directional dc-dc converter is also designed and implemented for future deployment of the designed HESS into a prototype EV, known as A2B.