M.Ing. / The purpose of this study is to introduce a new three-phase AC-DC-DC converter topology with low electromagnetic interference (EMI) and unity power factor. This converter topology is obtained by merging the three-phase boost-rectifier and the full-bridge resonant-transition converter into a single, unique converter topology. This converter's boost-stage is completely soft-switched, in contrast with conventional topologies. Thus, each switch in the converter is soft-switched, and therefore the converter --is named the three-phase All Soft-Switching Unity Power Factor Converter (ASSUP). Due to the zerovoltage switching of each switch, this converter has lower switching losses as well as EMI-levels than the conventional design. In the conventional design, the boost-stage, used for power factor correction, and the actual power converter, i.e. the full-bridge DC-DC converter, are realized in two seperate stages with two separate controllers. In contrast, the converter proposed here consists of one stage only, with one controller. The first topic discussed is a theoretical background on both low-frequency power quality (power factor and THD), and high-frequency power quality (EMI). This background is necessary for comparing the proposed converter with the conventional converter. Secondly, an in-depth analysis of both the three-phase boost-rectifier and the full-bridge resonanttransition converter is done. This analysis is crucial in the analysis of the three-phase ASSUP, which is discussed thirdly. For each of the converters, a typical switching waveform is divided into unique intervals, for which the appropriate expressions are derived. The design of the practical component values is also discussed, as well as the control method for each of the converters. The three-phase ASSUP, introduced here, is lastly experimentally compared with the cascade-connection of the three-phase boost-rectifier and the full-bridge resonant-transition converter.

D.Ing. (Electrical and Electronic Engineering) / Solid state converters are showing considerable progress in all applications for power electronics, mainly because of the advances made in the field of power semiconductor devices. Higher frequencies and power ratings of converters are therefore possible, leading to more and more applications for these solid state converters in induction heating. The available knowledge in this fast evolving field is however limited, leading to numerous research possibilities. It is none the less important to learn to crawl before attempting to run and a systematic line is therefore followed in this research. The combination of the heating-coil and work-piece is a challenging electromagnetic problem, resembling a transformer with a short circuited secondary. The heating of the work-piece to above the Curie temperature causes considerable variations in the parameters of the load. A study of the influence of temperature on the physical properties of the heated material is therefore made to obtain an understanding of these variations and is aided by Finite Element Simulations. Numerous circuit topologies and switching strategies are possible candidates for induction heating, and a collection of more than thirty converters is presented. Each of these has its own advantages and disadvantages, of which a good understanding is necessary to obtain the most suitable converter for a certain application in this field. The behaviour of some of the most popular converters under typical load variations is investigated to facilitate the final decision. This knowledge is then applied to some every day applications. A converter is chosen both for an induction cooker and a surface heater, after the specific requirements for each have been identified. A detailed design procedure and experimental results are presented...

M.Ing. / The focus of the project is on the design of a variable output current source applied in the testing of circuit breakers. The possibility of the use of high-frequency, switch mode converters for the application, will be investigated. The expectation is the improvement of the system currently in use, with the help of a power electronic converter. For the application, a 1 to 200A adjustable current source must be developed, which will be powered from the 220V, 50Hz network. A number of possible solutions to the problem will be investigated. One of the challenges of the project is that the output of the converter must be a current and not a voltage, which is normally the case. Based on mathematical calculations and practical results, the best possible solution to the problem is obtained. An optimum system is presented, which meets the desired specifications.

D.Ing. / In this dissertation a pulsed DC voltage bus comprising a full wave rectified sinusoidal voltage will be investigated for use as a link voltage. A background study into existing converter topologies for single phase uninterruptable power supplies and three phase front end converters, applicable to the study, is discussed. The definition of the bus voltage will be given as well as the power handling limitations. An experimental 3.3kW single phase UPS and a 3.3kW three phase front end converter using the bus was designed, built, tested and the results presented. The design and modelling of the two systems are discussed so as to clarify the advantages, disadvantages and limits of using such a bus. The appropriate standards pertaining the two converter systems have been looked up and the impact on the design discussed. The discussion will be concluded with a summarisation and possible future work is discussed.

D.Ing. / This study describes the technology of the Nonlinear Resonant Pole Converter. The NLRP is a soft switching topology that has different advantages.over other power electronic converters. This study describes the evolution, analysis, application and design of the NLRP. An introduction and background section with operating principles are provided. Detail analysis with operational limits is given ...

A rectifier is an electrical device, comprising one or more semiconductor devices arranged for converting alternating current to direct current by blocking the negative or positive portion of the waveform. The purpose of this study would be to evaluate dynamic and static electrical characteristics of rectifier chips fabricated with (a) DY8 process and (b) YI8 process and compare them with the existing DI8 process rectifiers. These new rectifiers were tested to compare their performance to meet or exceed requirements of lower forward voltages, leakage currents, reverse recovery time, and greater sustainability at higher temperatures compared to diodes manufactured using boron as base (DI8 process diodes) for similar input variables.

The proposed hybrid system generates AC power by combining solar and wind energy converted by a doubly-fed induction generator (DFIG). The DFIG, driven by a wind turbine, needs rotor excitation so the stator can supply a load or the grid. In a variable-speed wind energy system, the stator voltage and its frequency vary with wind speed, and in order to keep them constant, variable-voltage and variable-frequency rotor excitation is to be provided. A power conversion unit supplies the rotor, drawing power either from AC mains or from a PV panel depending on their availability. It consists of a multilevel inverter which gives lower harmonic distortion in the stator voltage. Maximum power point tracking techniques have been implemented for both wind and solar power. The complete hybrid renewable energy system is implemented in a PSIM-Simulink interface and the wind energy conversion portion is realized in hardware using dSPACE controller board.

The Light-emitting diodes (LEDs) are rapidly emerging as the dominant light source given their high luminous efficacy, long lift span, and thanks to the newly enacted efficiency standards in favor of the more environmentally-friendly LED technology. The LED lighting market is expected to reach USD 105.66 billion by 2025. As such, the lighting industry requires LED drivers, which essentially are power converters, with high efficiency, wide input/output range, low cost, small form factor, and great performance in power factor, and luminance flicker. These requirements raise new challenges beyond the traditional power converter topologies. On the other hand, the development and improvement of new device technologies such as printed thin-film capacitors and integrated high voltage/power devices opens up many new opportunities for mitigating such challenges using innovative circuit design techniques and solutions. Almost all electric products needs certain power delivery, regulation or conversion circuits to meet the optimized operation conditions. Designing a high performance power converter is a real challenge given the market’s increasing requirements on energy efficiency, size, cost, form factor, EMI performance, human health impact, and so on. The design of a LED driver system covers from high voltage AC/DC and DC/DC power converters, to high frequency low voltage digital controllers, to power factor correction (PFC) and EMI filtering techniques, and to safety solutions such as galvanic isolation. In this thesis, we study design challenges and present corresponding solutions to realize highly integrated and high performance LED drivers combining switched-capacitor and resonant converters, applying re-configurable multi-level circuit topology, utilizing sigma delta modulation, and exploring capacitive galvanic isolation. A hybrid switched-capacitor-resonant (HSCR) LED driver based on a stackable switched-capacitor (SC) converter IC rated for 15 to 20 W applications. Bulky transformers have been replaced with a SC ladder to perform high-efficiency voltage step-down conversion; an L-C resonant output network provides almost lossless current regulation and demonstrates the potential of capacitive galvanic isolation. The integrated SC modules can be stacked in the voltage domain to handle a large range of input voltage ranges that largely exceed the voltage limitation of the medium-voltage-rated 120 V silicon technology. The LED driver demonstrates > 91% efficiency over a rectified input DC voltage range from 160 VDC to 180 VDC with two stacked ICs; using a stack of four ICs > 89.6% efficiency is demonstrated over an input range from 320 VDC to 360 VDC . The LED driver can dim its output power to around 10% of the rated power while maintaining >70% efficiency with a PWM controlled clock gating circuit. Next, the design of AC main rectifier and inverter front end with sigma delta modulation is described. The proposed circuits features a pair of sigma delta controlled multilevel converters. The first is a multilevel rectifier responsible for PFC and dimming. The second is a bidirectional multilevel inverter used to cancel AC power ripple from the DC bus. The system also contains an output stage that powers the LEDs with DC and provides for galvanic isolation. Its functional performance indicates that integrated multilevel converters are a viable topology for lighting and other similar applications.

The oxyfuel cutting method is still widely used nowadays, even though it is not a fully autonomous process. Thisthesis presents a computational model to study ion and electron transport and current-voltage characteristics inside a methane-oxygen flame. By finding the relationship between current-voltage characteristics and critical parameters,such as standoff, fuel oxygen ratio, and flow rate, a control algorithm could be implemented into the system and make it autonomous. Star CCM+ software is used to develop preheat phase computational models by splitting the simulations into the combustion and electrochemical transport parts. Both the laminar and turbulent flows are considered. Several laboratory experiments are used to compare test data with the numerical results generated using this model. The initial and boundary conditions used in the simulation were to the extent possible similar to the experimental conditions in the laboratory experiment. In the combustion part, the general GRI3.0 mechanism plus three additional ionization reactions are applied, and the combustion part results are then used as input into the electrochemical transport part. A particular inspection line inside the domain is created to analyze the results of the electrochemical transport part. Ions, electrons number density, and current density are studied in the interval from -40V to 40V electric potential. The ions are heavier and more challenging to move than electrons. The results show that at both the torch and work surfaces, charged sheaths are formed, which cause three different regions of current-voltage relations to form in a similar manner as observed in the tests. / Master of Science / Oxyfuel cutting is essential to numerous industries, such as shipbuilding, rail, earth moving equipment, commercial building construction, etc. Tuning the process parameters and diagnosing problems with the oxyfuel process still relies on experienced operators. The main obstacles to the automation of the oxyfuel process come from the limitations of the sensing suites currently in use. Since typical sensors are highly unreliable in the harsh environment near the high-temperature flame, an alternate method is proposed to find the co-dependence between the flame's electrical characteristics and critical parameters of the oxyfuel cutting system (standoff, flow rate, F/O ratio, etc.). The relevant electrical characteristics are the electrical potential and distribution of ions and electrons. Two-dimensional models are created to analyze the combustion of methane-oxygen flame and transport of ions and electrons. The models allow the derivation of the current-voltage characteristic between the torch and work surface. Also, the way sheath phenomena of ions and electrons on the surface affect the current-voltage relationship can be analyzed from ions and electrons distribution. The electric field is added to the model by applying a constant voltage to the torch tip surface. To validate the models, a laboratory experiment with a similar geometry arrangement is used as a comparison. The models' results reveal three different regimes in the current-voltage relationship.

The problems associated with IGT/COMFET devices in PWM converters, such as turn off current tailing and latching are largely avoided in a resonant converter. Dynamic saturation loss is identified as the predominant power loss in IGT/COMFET devices for very high frequency resonant operation. Device design change is suggested for very high frequency resonant operation applications. / M.S.