D.Ing. (Electrical and Electronic Engineering) / increased dramatically during the past few years. This progress can mainly be attributed to recent developments in power electronic switching devices. Switching times are reduced, resulting in lower switching power loss, on-state voltage is reduced leading to lower conduction power losses, and higher voltage and current capabilities are possible. These advances are mainly responsible for a reduction in physical size of the converters, especially of the reactive components; an increase in dynamic response; and also, to a lesser extent, have an influence on the converter behaviour. Different applications of DC-DC converters require different characteristic behaviour, and the trend to obtain these different characteristics is usually accomplished by adding additional components to existing DC-DC converters. The disadvantage of such an approach is that it adds to the complexity of the converter topology and controller, and consequently increases the manufacturing cost, and reduces reliability. In this thesis, the objective is to identify a galvanic isolated DC-DC converter having inherent short circuit protection, sinusoidal transformer current, a low number of components and a simple controller. Hard switched DC-DC converters are approached from a fundamental point of view, weighing simplicity against characteristics, and a systematical classification is addressed. In order to address the issue of sinusoidal transformer current and inherent short circuit protection, a systematic classification of simple resonant converters is also addressed. The partial series resonant converter, which is a new converter topology, is identified and analysed. It does not follow the trend of increased converter and controller complexity with different characteristics, and meets all the objectives mentioned above. In addition to these objectives, it has the following characteristics: Output current can be controlled without any current measurement, while obtaining inherent short circuit protection. Switching losses are ultra low due to zero voltage switching at reduced turn-off current, enabling the use of insulated gate bipolar transistors at switching frequencies in excess of 50 kHz, which, among others, benefits dynamic response. The output load line resembles a natural constant output power load line at constant switchingfrequency. The combination of these characteristics is shown to provide major advances in low inductance load applications, such as arc welding and battery charging. Furthermore, all the magnetic components are integrated into one physical structure, which benefits, among others, manufacturability and cooling. The analysis and feasibility of the partial series resonant converter is verified by the construction of multi kilowatt prototypes for both battery charging and arc welding.

M.Ing. / In power electronics most applications are custom designed. Even though similar topologies are used, each application is designed to fit specific requirements. Presently there is a move towards standard modules that can be connected together to perform the desired power conversion, in much the same way as IC’s have been used for a few decades now. It is important to ensure that the modules can work together without performance degradation. The close proximity of active, passive and logic devices in high power applications dramatically increases the risk of EMI between the various components. This document describes the design and characterisation of a planar conducted RF-EMI power line filter to be used between modules and between modules and power supplies. The filter consists of two sets of transmission lines in parallel. The first is a high permittivity material with nickel conductors, referred to as the attenuator. The second is a set of copper conductors that are placed on the outside of the attenuator. The filter must be able to remove conducted differential mode noise from power line to the module and from the module tot the power line. The filter dimensions are comparable to the wavelengths that have to be attenuated. This allows for a possible combination of RF filtering techniques and power line filtering techniques. The design of the filter and the electromagnetic effects that govern its behaviour is explained. The transfer characteristic of the filter is made possible by the choice of materials and their relation to each other. Each material is discussed and evaluated. Characterisation methods are described and results presented. The influence the materials have on the performance of the filter and the methods and problems of construction of the filter are discussed. The construction of the filter and the commercial processes available are discussed. A prototype filter was built to demonstrate the feasibility of the construction processes. The performance of the prototype filter was then measured. The various test set-ups for different applications are explained. Small signal tests in 50 W systems were used to allow for comparisons with other filter types. The prototype has minimal insertion loss in the pass band and an average slope of attenuation of 40 dB/decade beyond the corner frequency. The corner frequency is at 1 MHz. Transmission line theory is used to develop a distributed element model for the filter using the ABCD-matrix representation of transmission lines. From this matrix an equivalent P-model can be calculated. Applicable assumptions are made to simplify the equations and values for a lumped element P-model is calculated. Both models indicate the importance that the material parameters have on the performance of the simulation results. Good correlation between the measured performance and simulated performance is established. The material parameters are sensitive to temperature. A one-dimensional thermal model is presented to estimate the operating temperature of the filter. It is determined that the attenuation of the filter is primarily determined by the attenuator. Based on the findings, new attenuator designs are made in an attempt to improve the performance of the filter. The small signal measurements of the various designs and the test results under load conditions are compared. A power test is performed. The filter performance varies as the voltage rating is increased. Finally, a temperature characterisation is done. The filter is absorptive and heat is dissipated in both the conductors and the dielectric material. The filter performance is sensitive to the operating temperature. A summary of the technology and the evaluation of this type of filter are presented in the conclusion.

M.Ing. / In this thesis, a new isolated DC-DC converter topology is designed which implements a high frequency primary tap changing transformer. This converter is designed to be implemented into renewable energy applications. Renewable or alternative energy resources are becoming more popular by necessity. The voltage generated by renewable energy resources is dependent on the weather conditions, thus the voltage may vary. This novel topology can maintain a regulated DC output voltage for a wide input voltage range by implementing a high frequency primary tap changing transformer. This converter is thus designed to accommodate the voltage changing conditions of renewable energy resources. This converter only requires output bus capacitance for DC bus stiffening. The overall required bus capacitance is therefore effectively reduced compared to other converter topologies. This isolated topology also improves the fundamental power quality. Other power quality components of this new converter are also analysed.

D.Ing. / In this thesis, contactless power transmission with sliding transformers to mobile loads is investigated. The sliding transformer comprises an extended primary winding - placed along the path of travel - which is fed through a core containing a secondary winding and which is attached to a mobile load. In the first chapter problems with existing power supply systems are discussed whereafter several possible applications of such a system are identified. In this chapter different methods of obtaining contactless power transmission are also discussed and a brief discussion of a practical, cost effective system is given. In chapter two the application of different resonant topologies to compensate the large structural inductance of the sliding transformer is investigated. A Series Resonant, Series Loaded topology is identified as the most practical and efficient topology for this application and a more detailed analysis of this topology - as applied to this case - is given. Formulas to calculate the sliding transformer parameters are given in the third chapter and two quantities relating the optimization of sliding transformers to the parameters thereof, are defined. Methods to optimize sliding transformers in terms of these two quantities, and also with respect to EMI, are also discussed in this chapter. The design of a five meter long experimental system which delivers 15 kVA to a mobile load is given in chapter four and experimental results of this system are presented. In chapter five a detailed investigation into different output power control methods is conducted. The effect of these control methods on EMI is investigated by means of numerical simulation of a Series Resonant, Series Loaded system under these different control methods. The most complex control method which generates the most EMI, namely frequency and pulse burst control, is implemented into the experimental system to investigate the limitations thereof. Experimental results of this controlled system are presented. It is found that this control method increases the control range obtainable with classical frequency control but introduces many limitations due to discontinuous primary current. It is concluded in the last chapter that it is possible to optimize sliding transformers within achievable cost constraints to such an extent that such systems have acceptable efficiencies and that reasonable system lengths are obtainable.

This thesis describes the design and development of a sampling-type function generator and a four-quadrant analog multiplier. The project is divided into two parts, the general arrangement and circuitry of the function generator and multiplier, and the timing circuits which actuate them. This thesis is concerned with the general circuitry. The functions to be generated are photographed on 35 mm. film and mounted in standard frames which are then fastened to the rim of a rotating disk. An optical system is used to scan the functions in a time-sequential manner. A timing system selects the required abscissa and actuates a combination of electronic gates and clamping circuits which stores the voltage, Eք, representing the ordinate, and the voltage, Eм, representing the maximum of the function. These two stored voltages, Eք and Eм, are applied to separate sweep circuits which produce sweep outputs of EքN(t) and EмN(t) respectively. A system of comparator circuits and gates samples the EքN(t) at the instant a reference voltage, E, equals the sweep EмN(t). Since the sweeps, N(t) are identical, the value of EքN(t) at the instant of sampling is (formula not included). This sequence of operations occurs for each function as it is scanned. Each successive multiplication is stored in its own storage unit. All the circuits are designed to be self-calibrating to minimize error due to drift. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

M.Ing. / This thesis investigates how genetic algorithms may be applied to solving for flyback converter design optimization. The genetic algorithm finds the combinations of components and switching frequency required for a capable, efficient and small fly-back solution. Ways of effectively evaluating the proposed solutions are discussed in light of the circuit theories of power electronics, and specifically, fly-back converters. Applying component data effectively to the evaluation process is addressed, especially in the light of the optimization goals. A solution evolved by a genetic algorithm is tested and compared against a prototype designed through conventional methods.

D.Ing. / This thesis treats aspects of electromagnetic integration in planar structures. These structures are for use in power electronic converters. The electromagnetically integrated structures fulfil the same electromagnetic function as conventional component structures, but have manufacturing advantages. In order to reduce the cost of power electronic systems, a new cost effective manufacturing technology is needed. In this work a planar manufacturing approach is considered. This manufacturing approach lends itself well to the concept of integrated electromagnetics, where one physical structure fulfils more than one electromagnetic function. As not all the electromagnetic functions of a given converter may be integrated into a single structure, the approach is one of hybridisation. Some aspects remain conventional and some aspects are totally electromagnetically integrated. A proposal for a new schematic representation of converter topologies is put forward. These new schematics bridge the gap between conventional circuit diagrams and full three dimensional figures of the physical structures. These schematics form the basis of the design and analysis procedure and are necessary in order to convey information on the structures in a concise manner. A complex electromagnetic function, that of a resonant circuit with transformer coupling, is described and analysed in detail. The design equations governing the structure are derived and their implications on the volume of the structure is discussed. In the analysis only first order effects are considered. Two case studies are carried out. The two converters are described in detail with respect to their construction. Several aspects of general planar construction are identified and discussed.

M.Ing. (Electrical And Electronic Engineering) / An AC/DC force commutated controlled converter, designed for use in a pulsed laser power supply, is presented here. The converter is controlled with a digital signal processor (DSP). The converter has to supply a stable DC voltage to the load, while drawing sinusoidal currents at unity power factor from the supply grid. The design of such a converter is discussed here, as well as the experimental evaluation of a prototype converter able to supply 30kW to a load.

This thesis presents the development of a Hybrid Multilevel Switching Converter (HMSC) for Ring-Magnet Power Supplies (RMPS). The thesis includes the analysis, design and control of the proposed converter. It introduces multilevel switching converters to the field of ring-magnet power supplies. RMPS feed the electromagnets that produce the magnetic field required to energize and guide subatomic particles in a synchrotron. The accuracy and extreme precision of this magnetic field imposes stringent restrictions on the design and performance of the RMPS used. Study of conventional power supplies highlights the need for modern power supply solutions which can meet the specifications of RMPS. The complete frequency-domain analysis of the conventional resonant-type RMPS along with the Energy Make-up Unit (EMU) is presented. The resonant frequency drift is identified as the main factor in the design of the EMU. The analysis of the input filter network is presented for development of design criteria for input filter components. The principle advantages and disadvantages of the resonant-type RMPS are summarized before identifying multilevel converters as a viable option among switching converters for a non-resonant type of RMPS. The Hybrid Multilevel Switching Converter (HMSC) is proposed as a non-resonant type RMPS to overcome the disadvantages of the resonant-type RMPS. The operational features of the HMSC are explained and the simplification of the general HMSC configuration for positive output currents is identified. The steady-state analysis of the HMSC develops comprehensive design criteria for the device ratings and component stresses, including the methods for reducing the switching losses in the HMSC. Multilevel converters encounter voltage balancing problem among the DC-link capacitors. It is shown that the HMSC configuration is versatile in minimizing this problem. Harmonic spectrum of the output voltage of the HMSC is derived and the effect of number of output voltage levels in reducing the harmonic contents is established. A detailed survey of different current control techniques is presented to form the background for developing an effective current control algorithm for multilevel converters. A dead-beat current control strategy is chosen as an appropriate control technique to suit the needs of RMPS. The control scheme is extended to the control of multilevel converters in general. The control algorithm is developed to track a given arbitrary current reference signal for both single-variable and multi-variable systems. It is also shown that the output dead-beat control is a special case of the pole placement technique. The transient behaviour of the system has been studied and stability considerations of the system are examined. Extensive computer simulation studies have been performed using SABER to study the reference tracking nature of the proposed control scheme. The output current of the HMSC using the modified dead-beat control scheme is shown to follow a given arbitrary-reference with very small tracking error. The reference tracking nature has been simulated for a simple RL magnet load and a magnet load with LCR filter. Experimental results obtained from a laboratory prototype of the HMSC with an RL load, have been presented to substantiate the analytical results. Criteria for improvement in the reference tracking properties of the proposed system have been identified. / Graduate

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