Thesis (M.E.)--University of Canterbury, 2006. / Typescript (photocopy). "March 2006." Includes bibliographical references (p. [83]-84). Also available via the World Wide Web.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The versatility of power electronic converters has made them a dominant force in the current electrical and electronic engineering industry. So too industry presents a wider range of applications, forever demanding operation at higher power levels. To meet this need a variety of multilevel converters have evolved. The challenge often lies in the selection of the appropriate topology for a specific application. This thesis presents a practical comparison between the Series-Stacked and Neutral Point Clamped multilevel converter topologies as candidates for Medium Voltage Direct Current and Traction applications. Their configurations, characteristics, switching techniques and practical performances are compared, in order to aid the topology selection process. / AFRIKAANSE OPSOMMING: As gevolg van die veelsydigheid van drywings elektroniese omsetters word dit geimplementeer in n toenemende hoeveelheid toepassings met toenemende drywings vlakke in die elektriese en elektroniese industrie. Om aan hierdie behoefte te voorsien het n reeks veelvlak omsetters ontstaan. Die uitdaging hiermee is die keuse van die toepaslike topologie vir n spesifieke doelwit. Hierdie proefskrif vergelyk die Serie Gekoppelde en die Geklemde Neutrale Punt omsetters ten opsigte van konfigirasie, karakteristieke, skakel tegnieke en praktiese werksverrigting om die toepaslikheid te bepaal vir Medium Spanning Gelykstroom en Traksie toepassings.

High performance ac-to-dc converters are required to meet the regulation standards to suit wide variety of applications. This thesis presents the steady state analysis, design and operation of high frequency (HF) transformer isolated resonant converters on the single phase utility line as a low harmonic controlled rectifier. Two resonant converter configurations of third order have been studied namely the LCC-type parallel resonant converter also popularly known as series-parallel resonant converter (SPRC) and the hybrid parallel-series resonant converter bridge (HPSRCB). These converters are operated at HF using variable frequency as well as fixed frequency control and they operate in different modes depending on the choice of switching frequency and load. The variable frequency SPRC is operated in discontinuous current mode (DCM), to obtain low line current total harmonic distortion (T.H.D.) and high power factor (pf), without using active control. State space analysis has been presented for one of the predominant circuit modes encountered during its operation in DCM. The various design constraints for operating the resonant converter on the utility line for high pf operation have been stated for different control schemes. In addition, steady state analysis, design optimization carried out for dc-dc converter have been presented. The effect of resonant capacitor ratio on the converter performance characteristics have been studied. SPICE3 simulations and experimental results obtained from a 150 W converter are presented to verify the theory. Continuous current mode (CCM) operation of the SPRC, and its effect on the line current T.H.D. and pf are studied. Both fixed and variable frequency control schemes have been used to control the SPRC. Complex ac circuit analysis method has been considered as the design tool to get the design curves and design of the SPRC operating on the utility line. SPICE3 simulation results for open loop operation and experimental results for both open as well as closed loop operations (active control), for two capacitance ratio's have been presented to verify the converter performance. It is shown that nearly sinusoidal line current operation at unity pf can be obtained with closed loop operation. A HPSRCB has been proposed and operated at very high pf on the utility line as a controlled rectifier. Some of the predominant operating modes of the fixed and variable frequency HPSRCB have been identified. The steady state analysis using state space modeling presented for a dc-to-dc converter has been extended to analyze the ac-to-dc converter. Using the large signal discrete time domain model, the time variation of line current and line pf have been predicted using PROMATLAB for both fixed and variable frequency operations of HPSRCB on the utility line. SPICE3 simulation results without active control and experimental results obtained from the bread board model for both open as well as closed loop fixed and variable frequency operations have been presented to verify the theory and design performance. / Graduate

Thesis (MTech (Electrical Engineering)))--Cape Peninsula University of Technology, 2011. / This thesis presents an investigation into the generic tools, hardware and firmware, involved in power electronic converter control and feedback. The aim was to determine the optimal controller architecture through research of existing controllers. As soon as the architecture was established, design of the controller commenced. Explanations for the various components selected were provided. The design considerations when designing a printed circuit board (PCB) with mixed signals was also presented. The theory behind the control of a multicell converter as well the practical implementation of the control scheme in firmware was presented.

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

M.Ing. / The use of electronically controlled electrical power equipment, specifically power converters, has rapidly increased in recent years. It has subsequently been found that different electrical equipment, placed or working in close proximity, can negatively influences each other's performance. The degradation in performance could be attributed to mutual electromagnetic interference (EMI). Traditional methods of testing conducted EMI usually follow a black box approach with additional filter elements being added to the converter input to bring it within specification. This study focuses on the conducted electromagnetic interference of a specially built experimental boost converter that would typically be used as a preregulator to improve the power factor. The converter circuit was constructed in a number of functional circuit sections in order to assess an individual section's contribution to the emission and propagation of conducted EMI throughout the converter. The operational behaviour of the converter can thus be systematically studied and improved before additional filter components are added. The measurement standards require that conducted EMI measurements are made at the power source input of the equipment under test. These measurement techniques do not allow a systematic tracing of the propagation of conducted EMI throughout a converter circuit. Since no frequency spectrum measurement is available at any other measurement point in the converter. Part of this thesis was thus devoted to the development of an enhancement to current measurement techniques that enables EMI frequency measurements throughout a converter. A special EMI probe was developed for this purpose. Using this EMI probe conducted EMI propagation can be traced from its source throughout a converter to the power input. An analytical analysis of the boost converter's behaviour, with emphasis placed on its switching transients, was initially undertaken. This was continued with PSPICE® circuit simulation. Various aspects of the converters operational behaviour were considered. The simulation results suggested modifications to the converter switch circuit, which would improve the boost converter's conducted EMI characteristics. These were then evaluated with corresponding practical measurements carried out on the boost converter. The practical results confirm that the converters switching behaviour can be directly related to the parasitic and other components. Improvement of the converter switching behaviour lead to an improvement of the conducted EMI emissions of the boost converter.

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.