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.

The advent of the integration of discrete passive components is a direct result of the drive towards the minimisation of power electronic converters and filters. To this end Integrated Power Passive Modules (IPPMs) have been utilised in the past. The IPPMs discussed in this dissertation refer to structures consisting of dielectric layers sandwiched between layers of conductive material. The use of these types of structures in various applications has been well documented. However, the applications have been single-phase in nature and the exact configuration of the IPPMs has been largely dependent on the designers’ past experience with the modules. The development of a synthesis procedure to identify the required configuration for any particular application would be of great benefit to designers. The foundation of such a synthesis procedure was laid through an exhaustive search of all possible configurations that can be realised with a three conductive layer IPPM. From this exhaustive search a number of general trends, between the configurations and their associated frequency response, were observed. Furthermore, a number of principles underlying the functionality of the configurations were highlighted during the course of the exhaustive search. The validity of some of these results was experimentally investigated through the design and implementation of an integrated EMI filter. The EMI filter considered in this study differed from integrated EMI filters, previously reported on, through the fact that the filter considered herein was to be implemented in a three-phase application. To this end a set of configurations that realise low pass filters were identified from the results of the exhaustive search. The application of these configurations was expanded from single-phase to three-phase by mapping the configurations onto a building block component used to realise the three-phase application. Simulations of these three-phase filters were used to analyse the filter performance. From this analysis a subset of configurations were identified as displaying the best performance characteristics. The configurations within this subset were further analysed using the results of the exhaustive search. In so doing two configurations were isolated for use in a practical realisation of the three-phase filters. The physical design and construction of the integrated three-phase filters, as well as the test bench, was considered. The performance of the filters was investigated through comparative measurements of common mode and differential mode currents, in the test bench, in the presence and absence of the filters. From this investigation significant reduction in the conducted EMI noise was seen through the introduction of the filters into the system. / Dr. I. W. Hofsajer

No description available.

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.

Thesis (Ph. D.)--Ohio State University, 2006. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2007 Sep 19

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed January 22, 2009) Includes bibliographical references.

M.Ing. (Electrical and Electronic Engineering) / The main purpose of the study is to propose an unique unity power factor AC-DC converter topology, with isolated output. The proposed converter is obtained by merging the unity power factor boost converter and the full bridge resonant transition converter. The converter is unique as resonant switching techniques are used to obtain a zero voltage switching boost stage, resulting in an all soft switching converter. The result is lower levels of conducted EMI, as well as lower switching losses. Conventional topologies utilize more than one converter stage to obtain the required results, whereas _ the proposed converter results in a single step solution. As the purpose of the proposed converter is power factor regulation resulting in lower levels of conducted EMI, the study is commenced with a review of the definitions and equations for both power factor and EM!. Thereafter sources and propagation of conducted EMI are discussed. To gain a better understanding of the operation of the proposed converter, the operation of the unity power factor boost converter, as well as the full bridge resonant transition converter are discussed in depth. A switching cycle of the proposed converter is divided into different intervals, and analytical equations for the relevant currents and voltages for each interval are derived seperately. Possible control schemes are introduced and where applicable, conditions for zero voltage switching are given. It is concluded that a constant frequency PWM controller is the most ideal control scheme to ensure proper operation of the converter. A simple design procedure is presented by which the size of the most important circuit parameters can be designed in terms of the desired switching frequency and permissable duty cycle variation. Finally, experimental results obtained from the practical converter, are given. Deviations from the ideal are interpreted and methods of improving the performance are suggested.

D.Ing. / The propagation of fast disturbances along power transmission structures depends on the parameters of the excitation for the disturbance, the characteristics of the power transmission structure, and eventually on the characteristics of the electrical load connected to the structure. This thesis will therefore target the determination of the parameters of transmission structures in Chapter 2, applicable transmission-line theory in Chapter 3, modelling the load in Chapter 4, and apply this knowledge to the specific problem of over-voltages on the terminals of machines fed via cables from inverters in Chapter 5. The rest of this chapter is devoted to explaining the introductory aspects of this application problem.

No description available.