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Switch-mode power supplies (SMPS's) not only convert energy, they also consume it. Typical operational efficiencies are approximately 25 to 60% for linear power supplies, and approximately 50-90% for switching power supplies. This means that products whose end-use electronics are dc, such as televisions and DVD players, could consume 50% less power when operating if the power supply were upgraded from 40% efficiency to 80% efficiency. Savings can occur not only from using SMPS's instead of linear power supplies, but also from specifying highly efficient switching power supplies. In many cases, efficiencies are still lagging to keep costs down, since the power consumption is considered to be relatively low (40W-700W range). Over time, however, efficiency improvement strategies will pay back based on the cost of energy. Therefore three common flyback converter topologies have been studied through this thesis in the Low (15W), Medium (40W), and High (150W) Power levels. Efficiency analysis on the three power level topologies showed that the greatest opportunity for efficiency improvement existed in the 40W (medium power) topology. Efficiency improvement and measurement approaches are investigated and an optimized medium-power flyback converter is proposed and implemented resulting in an efficiency improvement from 57.8% to 83.6%. / Graduation date: 2004

The advancement of Very Large Scale Integration (VLSI) technology has reduced the size and increased the speed of information processing circuits. Consequently, power supplies for such circuits have had to meet increasing demands for power, yet simultaneously decrease in size. This need for higher power density in the supplies can be met with higher circuit operating frequencies and by using high-density circuit fabrication techniques. Generally, when the conversion frequency of conventional Pulse-Width-Modulated (PWM) supplies approaches 1 MHz, the switching loss becomes very large. This sharply reduces the efficiency of the supply. A quasi-resonant topology reduces much of this loss. For a Zero-Current-Switched (ZCS) Quasi-Resonant Converter (QRC) the turn-off loss is nearly eliminated. It was the objective of the research reported here to combine the quasi-resonant technology with thick-film hybrid microelectronics technology to produce a high density dc-dc converter. For this research endeavor an off-line, half-bridge ZCS-QRC was used. The circuit processed 300V and up to 20A with switching frequencies in the 1MHz to 2MHz range. The voltage and current levels exemplify the high electric field and current densities that must be considered in the design of most QRC circuits that process power up to 100W. Only available materials for thick-film hybrid processing were used although some characteristics were modified. No special magnetic or capacitive components, or semiconductors were developed. To combine technologies the following were performed: 1. identification of critical power electronic circuit and hybrid component parameters such as maximum voltages and currents, thermal and electrical component impedances; 2. assessment of thick-film hybrid microelectronic materials and their compatibility in circuits having high voltage and current levels; 3. development of a complete thick-film power hybrid process; and 4. design, fabrication and evaluation of a power hybrid QRC that has high power-processing density. / Ph. D.

M.Ing. / Please refer to full text to view abstract

This dissertation looks closely at deployment of thin-film integrated inductors within power electronics, including details on the state-of-the-art technology for such inductors and related packaging techniques. Design challenges for systems using these inductors are discussed in detail, including the current outlook on magnetics development and the impact of these non-linearities on system design. In particular, this work looks closely at effects often left behind in modern discrete-component-based power module design, such as soft core saturation and significant high-frequency losses. In conjunction with the magnetics, a well-known non-linear controller for buck converters is analyzed in-depth for the first time, using frameworks from variable structure and sliding-mode control. This allows for development of a more profound rationale for the heuristic design guidelines that have been heretofore provided for this class of controllers. To verify the theoretical development, a testbench integrated CMOS front-end for a switched-inductor step-down, or buck converter is used to investigate departures of system behavior from the general wisdom around buck converter performance. Two packaging methodologies are explored for integration, and their impact on the design cycle and module lifetimes are discussed in some detail.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis proposes a family of non-isolated bidirectional converter in order to interface dc and ac variables. Such power electronics solutions guarantee: (i) bidirectional power flow between dc and ac converter sides, (ii) independent control in both converter sides, (iii) high level of integration with a reduction of one power switch and its drive circuits, (iv) implementation of two functions by using a unique power conversion stage and (v) reduction of the capacitor losses. Despite proposing new power converter solutions, this thesis presents an analysis of the converters in terms of pulse-width-modulation (PWM) strategy, dc-link capacitor variables, and suitable a control approach. Solutions for single-phase, three-phase and three-phase four-wire systems are proposed by employing a converter leg with three switches. A possible application of this converter is in Vehicle-to-Grid (V2G) systems and interfacing dc microgrid with a utility grid. In addition to the new power electronics converters proposed in this thesis, an experimental setup has been developed for validation of the simulated outcomes. The proof-of-concept experimental setup is constituted by: DSP, Drivers & Integrating Board, Power Supply and, Power Converter & Heat-Sink .

Indiana University-Purdue University Indianapolis (IUPUI) / The existing topologies of solar micro inverter use a number of stages before the DC input voltage can be converted to AC output voltage. These stages may contain one or more power converters. It may also contain a diode rectifier, transformer and filter. The number of active and passive components is very high. In this thesis, the design of a new solar micro inverter is proposed. This new micro inverter consists of a new single switch inverter which is obtained by modifying the already existing single ended primary inductor (SEPIC) DC-DC converter. This new inverter is capable of generating pure sinusoidal waveform from DC input voltage. The design and operation of the new inverter are studied in detail. This new inverter works with a controller to produce any kind of output waveform. The inverter is found to have four different modes of operation. The new inverter is modeled using state space averaging. The system is a fourth order system which is non-linear due to the inherent switching involved in the circuit. The system is linearized around an operating point to study the system as a linear system. The control to output transfer function of the inverter is found to be non-minimum phase. The transfer functions are studied using root locus. From the control perspective, the presence of right half zero makes the design of the controller structure complicated. The PV cell is modeled using the cell equations in MATLAB. A maximum power point tracking (MPPT) technique is implemented to make sure the output power of the PV cell is always maximum which allows full utilization of the power from the PV cell. The perturb and observe (P&O) algorithm is the simplest and is used here. The use of this new inverter eliminates the various stages involved in the conventional solar micro inverter. Simulation and experimental results carried out on the setup validate the proposed structure of inverter.