D.Ing. (Electrical & Electronic Engineering) / 'Ihis thesis considers the application of non-linear, voltage dependent, saturating capacitors as turn-off snubbers for power electronic switches. The concept of using a non-linear turn-off snuJ::ber for the relieving of semiconductor switching devices is shown theoretically and experimentally. As proven by the results, the most outstanding advantage of non-linear snubbers is the much smaller quantity of energy which is being stored, during and after snubbing, in such a non-linear snubber device, compared to normal linear snubber elements. Depending on the saturation level of such a non-linear capacitor, the stored energy can (for existing ceramic capacitors) be an order of magnitude lower than the energy in a comparable linear capacitor. After the profitability of using non-linear saturating capacitors has been demonstrated, the non-linear capacitive snubber is analyzed by means of a computer simulation which uses the exact capacitancevoltage curve, as stored on data file. The circuit is, however, also analyzed analytically by approximating the non-linear capacitor characteristics in two different ways: (L) by an exponential approximation, and (ii) by a two-step piecewise linearization. Most of the results are within about 20 %of those obtained by the exact analysis, and the approximate analyses can therefore be regarded as very useful. Using the analysis of the non-linear snubber, an optimization in terms of minimum energy losses is carried out on a general turn-off snubber circuit which consists of a non-linear saturable capacitor in a regenerative snubber configuration. The equations and results are awlicable to most snubber cases. From the results it is evident that the same performance as obtained with complex linear regenerative snubber circuits can be obtained by a simple non-linear dissipative snubber...

M.Ing. (Electrical and Electronic Engineering) / The South African Railways covers a total distance of some 24 000 km, making use of a signalling network of 1000 interlocking systems. This comprises of the order of 1000 signalling houses each with its own unlnterruptible power supply system of which a DC·AC converter Is one of the components. Due to the requirements by Spoomet, high frequency (ultrasonic) chopper technology had to be used. This treatise describes the design and development of a 3 kVA composite DC·AC converter with an ultrasonic AC link for this application. In the primary converter (centre tapped topology) ZVS Is achieved by good circuit layout and controlled transformer capacitance. As a result the performance of the converter was improved with regard to efficiency and switching transients compared to the conventional hard switched converter. The four pulse topology with an output LC·filter was used for the secondary converter. Due to the modulation technique being used, the load perceived the switching frequency as 20kHz while the actual switching frequency was only 10kHz. In this way switching losses were kept within reasonable limns as well as satisfying the low audible noise requirement. The stability of the LC·filter was achieved with a current feedback loop. The literature describes the capacitor current being used in the feedback loop. In this case the Inductor current was used with the advantage of output short circuit protection without an additional current measurement. Apart from the advantages of small weight and volume from a maintenance point of view, the composite DC·AC converter also achieved high efficiency (> 85%) over a wide load range (10%-100% of full load).

M.Ing. (Electrical and Electronic Engineering) / Recent world events such as the fall of Communism. attempts at the unification of Europe and the reaching of the most extensive international trade agreement yet (GATT ::: General Agreement on Trade and Tariffs). have all contributed to the expansion of world markets as well as a marked intensification in the competition in those markets. Rivalry in the market for power electronic equipment is as relentless as in any other. Strict regulations with regard to Electromagnetic Interference (EMf) and Electromagnetic Compatibility (EMC) apply in Europe and compliance with these standards is legally enforced. In South Africa, compliance with such standards is merely recommended, hence local manufacturers have not yet considered these phenomena seriously enough to pose a threat to their European opposition. The two main causes of EMI are switching action, which is such an integral part of power electronics, and the excitation of parasitic circuit elements. This thesis describes the investigation carried out to determine the effect of certain layout and construction parameters on the generation of EMf. Parasitic loop inductances, self-capacitances of coils and the ground connection of heat sinks were examined in the process. A test convener containing a full-bridge converter perfonning DC·DC conversion, was built. These converters are important building blocks for equipment such as uninterruptible power supplies. One configuration of this converter was designated as the reference configuration. For every modification of a layout or construction parameter its effect on the interference spectrum was determined through a comparison with the measured interference spectrum of the reference configuration. The use of snubbers and the minimisation of the self-capacitances of inductors in an output filter effected a marked decrease in the measured interference spectrum (approximately 10 dB or a third less). Certain loop inductances have to be minimised in the design stages through proper layout of conveners, and heat sinks should preferably be grounded through high resistances. Paying due attention to these aspects in the design of power electronic converters can aid in decreasing the size and cost of bulky, expensive EMf filters required to meet the standards. It could give local manufacturers a considerable advantage over their overseas competitors.

M.Ing. (Electrical & Electronic Engineering) / The gate turn-off thyristor is discussed as a power switch. A gate-firing circuit for gate turn-off thyristors in the range 10 A - 300 A was developed. The resonant dc-link as snubber for voltage fed inverters is discussed. On considering various factors, the gate turn-off thyristor was chosen as switching component in the inverter. The problems that deve16ped with the use of gate turn-off thyristors in resonant dc-link inverters w,re discussed. Which lead to the development of a storage time compensator for gate turn-off thyristors. Attention was given to the various possible control methods for the resonant dc-link. A study of the possible control strategies results in the development and manufacturing of both a single-phase and a three-phase controller. The operation of the resonant inverter and inverter/load system were evaluated in terms of wave shapes in the time domain.

No description available.

The nonlinear dynamics of PWM DC-DC switching regulators operating in the continuous conduction mode are investigated. A quick review of the existing analysis techniques and their limitations is first presented. A discrete nonlinear time-domain model is derived for open-loop DC-DC converters. This model is then extended for closed-loop regulator systems implementing any type of compensation scheme. The equilibrium solutions of the closed-loop system are calculated and their stability is determined. The methods developed are used to study the dynamic behavior of a DC-DC buck regulator implementing different types of compensation design: proportional, integral, proportional-integral, and proportional-integral-derivative feedback control. A detailed bifurcation analysis of the dynamic solutions as a design or a control parameter is changed is presented. A period-doubling route to chaos is shown to exist in voltage-mode regulators, depending on the values of the parameters of the compensator and the input voltage. An investigation of the behavior of the converter in the instability regions has been carried out to shed light on its bifurcations. The interactions of input filters with DC-DC switching-mode regulators are investigated as well. It is shown that the small-signal averaged model widely used in the design of DC-DC regulators does not provide a complete understanding of the stability of the filter-regulator system. It can only provide the local borders of small-signal stable operation. The large-signal time-domain nonlinear averaged model is used to further understand the interaction on the slow scale using nonlinear analysis techniques. No fast scale interactions, however, can be predicted using this model. A complete nonlinear switching model is thus used to investigate the interaction of the filter and the regulator on all scales: fast and slow. / Master of Science

Power electronic systems and components that can operate in environments with ambient temperatures exceeding 250 °C are needed for innovation in automotive, aerospace, and down-hole applications. With the imminent mass electrification of transportation and industry, the high-temperature electronics market value is anticipated to grow to $15 billion by the end of 2023. Conventionally, silicon (Si)-based converters are used in these applications; however, as operating temperatures continue to increase, the inherent limits of these systems are being met. The primary limitations for the high-temperature operation of semiconductor devices is the intrinsic carrier concentration, dictated primarily by the bandgap of the material, which increases with temperature. Wide-bandgap (WBG) power semiconductors, primarily silicon carbide (SiC) and gallium nitride (GaN), have been adopted for use in these applications, but exhibit a degradation in performance at elevated temperatures. As such, gallium oxide (Ga2O3), an ultrawide-bandgap (UWBG) material with controllable doping and the potential for inexpensive substrates, has presented itself as a potential contender for use in high-temperature power electronics applications. The UWBG of Ga2O3, 4.8 eV compared to 1.1 eV for Si, 3.2 eV for SiC, and 3.4 eV for GaN, allows it to achieve nearly 1033 lower intrinsic carrier concentration than Si, permitting Ga2O3 power devices to theoretically operate at significantly higher temperatures. In addition, unipolar Ga2O3 devices have a better theoretical limit with respect to the relationship between on-resistance and breakdown voltage, which could enable higher power density and power conversion efficiency. While Ga2O3 exhibits potential in these regards, its low thermal conductivity (11–27.0 W/m·K compared to 148 W/m·K for Si, 350 W/m·K for SiC, and 130 W/m·K) means that standard packaging and cooling techniques are not suitable or effective. Furthermore, conventional polymeric and organic encapsulant materials are typically limited to operating temperatures of 200 °C and novel materials must be evaluated. This work outlines and evaluates an electro-thermal device-package co-design modeling platform that can be utilized for the efficient and accurate modeling of Ga2O3 devices and their associated packaging, with the goal of overcoming the challenges of the low thermal conductivity of Ga2O3. This permits for the electrical and thermal performance of the devices and the package to be designed in tandem for an effective design. Next, six high-temperature encapsulation materials are evaluated and conclusions are drawn about each material's feasibility for use as a dielectric encapsulation material for a power module operating at temperatures exceeding 250 °C. This simulation platform and material analysis was then used to design and fabricate a 300 °C, 1.2 kV half-bridge power module utilizing Ga2O3 diodes to assess thermal and electrical performance. / Master of Science / Power electronic systems and components that can operate in environments with ambient temperatures exceeding 250 °C are needed for innovation in automotive, aerospace, and down-hole applications. With the imminent mass electrification of transportation and industry, the high-temperature electronics market value is anticipated to grow to $15 billion by the end of 2023. Conventionally, silicon (Si)-based converters are used in these applications; however, as operating temperatures continue to increase, the inherent limits of these systems are being met. The primary limitations for of the high-temperature operation of semiconductor devices is the intrinsic carrier concentration, dictated primarily by the bandgap of the material, which increases with temperature. Wide-bandgap (WBG) power semiconductors, primarily silicon carbide (SiC) and gallium nitride (GaN), have been adopted for use in these applications, but exhibit a degradation in performance at elevated temperatures. As such, gallium oxide (Ga2O3), an ultrawide-bandgap (UWBG) material with controllable doping and the potential for inexpensive substrates, has presented itself as a potential contender for use in high-temperature power electronics applications. This work outlines and evaluates an electro-thermal device-package co-design modeling platform that can be utilized for the efficient and accurate modeling of Ga2O3 devices and their associated packaging, with the goal of overcoming the challenges of the low thermal conductivity of Ga2O3. This permits for the electrical and thermal performance of the devices and the package to be designed in tandem for an effective design. Next, six high-temperature encapsulation materials are evaluated and conclusions are drawn about each material's feasibility for use as a dielectric encapsulation material for a power module operating at temperatures exceeding 250 °C. This simulation platform and material analysis was then used to design and fabricate a 300 °C, 1.2 kV half-bridge power module utilizing Ga2O3 diodes to assess thermal and electrical performance.

The need for high-density power electronics converters becomes more critical by the day as energy consumption continues to grow across the world. Specifically, the need for medium-voltage (MV) high-density converters in power distribution systems, electric ships, and airplanes become more critical as weight and space becomes more a premium. The limited space and footprint require new packaging technologies and methods to develop an integrated power converter. The advancement of wide-bandgap (WBG) devices like silicon carbide (SiC) allows converters to have higher power and faster switching... To benefit from these devices, the packaging of the converter needs to be carefully considered. This thesis presents the design of a 250 kW integrated power electronics building block (iPEBB) for future electric system applications. This work explores the common substrate concept that would serve as the electrical, thermal, and mechanical foundation for the converter. State-of-the-art organic direct-bonded copper (ODBC) is explored to serve as the material foundation for the common substrate. Multi-domain simulations are used to design the integrated SiC bridges to achieve a power loop inductance of 3.5 nH, a maximum temperature of 175 °C, and a weight of 16 kg. ODBC and silicon nitride switching cells are packaged and analyzed in order to see the benefits on a multi-layer design as well as determining electrical and thermal trade-offs. The insights gained from hardware testing will help in the redesign and refinement of the iPEBB. / M.S. / This thesis presents the design of an integrated power electronics building block (iPEBB) for high-density systems. The PEBB concept allows for modular converters that can perform various power conversions. The design begins with exploring state-of-the-art substrates that will serve as the foundation for the iPEBB. Due to the integrated design, the substrate plays a vital role in the thermal, electrical, and mechanical performance, and contributes to the weight and reliability of the iPEBB. State-of-the-art organic direct-bonded copper (ODBC) substrates and multi-layer silicon nitride substrates are explored in this work. The ODBC is used to develop a common substrate for the converter, which allows for a high level of integration between different SiC half-bridges. Switching-cell prototypes based on the ODBC and multi-layer silicon nitride are fabricated to provide insight into the electrical and thermal performance of different substrates. This information will aid in the further redesign and refinement of the iPEBB concept.

M.Ing. (Electrical and Electronic Engineering) / In order to increase the overall performance and reduce the cost of power electronic converters, a new technology for the manufacturing of such converters is needed. The aim of this work is to investigate the possibility of the application of planar integrated manufacturing technology, to power electronic converters. A proposal of the definitions, terminology and graphical representation of the integrated structure is discussed together with some examples. A zero-voltage-switching PWM DC-DC converter is used as a case study. A conventionally constructed converter, using conventional component technology is designed and constructed, after a complete mathematical analysis of the converter topology. A similar converter is designed and constructed using the planar integrated manufacturing technology. Full design details and procedures are given for both converters. The two manufacturing technologies are then compared from the point of view of electrical performance, as well as some other aspects.

Yuen Chi Lap. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 88-94). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Motivation --- p.1 / Chapter 1.2 --- Aims --- p.2 / Chapter 1.3 --- Contributions --- p.3 / Chapter 1.4 --- Thesis Organization --- p.4 / Chapter 2 --- Background and Literature Review --- p.5 / Chapter 2.1 --- Introduction --- p.5 / Chapter 2.2 --- Vibration-to-Electrical Transducer --- p.6 / Chapter 2.2.1 --- Electromagnetic (Inductive) Power Conversion --- p.6 / Chapter 2.2.2 --- Electrostatic(Capacitive) Power Conversion --- p.8 / Chapter 2.2.3 --- Piezoelectric Power Conversion --- p.9 / Chapter 2.3 --- Wireless Sensor Platform Examples --- p.11 / Chapter 2.3.1 --- MICA[13] from UC Berkeley[49] --- p.11 / Chapter 2.3.2 --- WINS[48] from UCLA[51] --- p.13 / Chapter 2.3.3 --- Wong's Infrared System[5] --- p.13 / Chapter 2.4 --- Summary --- p.14 / Chapter 3 --- Micro Power Generator --- p.16 / Chapter 3.1 --- Introduction --- p.16 / Chapter 3.2 --- MEMS Resonator --- p.18 / Chapter 3.2.1 --- Laser-machinery --- p.18 / Chapter 3.2.2 --- Electroplating Fabrication --- p.18 / Chapter 3.3 --- Voltage Multiplier --- p.19 / Chapter 3.4 --- "Modeling, Simulations and Measurements" --- p.21 / Chapter 3.5 --- Summary --- p.30 / Chapter 4 --- Low Power Wireless Sensor Platform --- p.37 / Chapter 4.1 --- Introduction --- p.37 / Chapter 4.2 --- Generic Platform --- p.37 / Chapter 4.2.1 --- Startup Module and Power Management --- p.38 / Chapter 4.2.2 --- Control Unit --- p.43 / Chapter 4.2.3 --- Input Units (Sensor Peripherals) --- p.46 / Chapter 4.2.4 --- Output Units (Wireless Transmitters) --- p.48 / Chapter 4.3 --- Summary --- p.57 / Chapter 5 --- Application I - Wireless RF Thermometer --- p.59 / Chapter 5.1 --- Overview --- p.59 / Chapter 5.2 --- Implementation --- p.60 / Chapter 5.2.1 --- Prototype 1 --- p.60 / Chapter 5.2.2 --- Prototype 2 --- p.60 / Chapter 5.2.3 --- Prototype 3 --- p.62 / Chapter 5.2.4 --- Prototype 4 --- p.63 / Chapter 5.3 --- Results --- p.65 / Chapter 5.4 --- Summary --- p.67 / Chapter 6 --- Application II - 2D Input Ring --- p.70 / Chapter 6.1 --- Overview --- p.70 / Chapter 6.2 --- Architecture --- p.70 / Chapter 6.3 --- Software Implementation --- p.72 / Chapter 6.3.1 --- Methodology --- p.72 / Chapter 6.3.2 --- Error Control Code --- p.73 / Chapter 6.3.3 --- Peripheral Control Protocol --- p.75 / Chapter 6.4 --- Results --- p.77 / Chapter 6.5 --- Summary --- p.83 / Chapter 7 --- Conclusion --- p.84 / Chapter 7.1 --- Micro power generator --- p.84 / Chapter 7.2 --- Low power wireless sensor applications --- p.85 / Chapter 7.2.1 --- Wireless thermometer --- p.85 / Chapter 7.2.2 --- 2D input ring --- p.86 / Chapter 7.3 --- Further development --- p.86 / Bibliography --- p.88 / Chapter A --- Schematics --- p.97