This thesis presents an analytical approach using Root-Loci method for designing optimum passive series RC snubbers for continuous-current synchronous buck switch mode power supply (SMPS). Synchronous buck SMPS is the most popular power converter topology found in modern consumer electronics. It offers relatively good efficiency to target the high-current and low-voltage requirements while it is also relatively inexpensive to implement. Passive series RC snubbers are simple, efficient and cost-effective open-loop equalizer circuit for synchronous buck SMPS. Its purpose is to control and to balance between the rate of rise and the overshoots of transient switching waveform in order to optimize efficiency and reliability Existing methods of RC snubber design are solely based on second-order approximation. It is investigated in this research that this approximation is highly inaccurate in SMPS applications because higher order equivalent models are required for the load path of the SMPS. The results using the RC snubbers obtained from existing method are shown to be unsatisfactory without correlation to the calculations and simulations based on second-order approximation. Optimum RC values obtained using Root-Loci approach presented in this thesis are shown to correlate to both Spice simulation and lab measurements.

Within the existing available mix of numerical and analytical thermal analysis options, lumped parameter thermal modelling is selected as the operational backbone to develop an improved novel synchronous generator thermal modelling package. The objective is for the creation of a user friendly quick feedback tool, which can serve as a means to make quick machine design thermal calculations and answer customer queries quickly and reliably. Furthermore, thermally improved generator designs will allow for inevitable operational losses to be channelled away from the machine more efficiently. As a result, machine component temperatures will be reduced, allowing lower generator thermal ratings. The end result will be smaller, longer lasting, more efficient generators, with the ability to be adapted with greater ease to particular applications. With the contribution of selected numerical analysis techniques, mainly finite element analysis for the distribution of iron losses, the MySolver thermal modelling package is developed and presented in this thesis. It is this combination of numerical and analytical tools that improves synchronous generator thermal modelling accuracy, but ultimately it is the lumped parameter nature of the thermal models developed that makes MySolver succeed as a reliable quick feedback electrical machine thermal design tool, validated using experimental results for a wide range of operating conditions. The initial part of the thesis analyses the electrical machine thermal modelling techniques available today, indicating advantages and disadvantages associated with each one, and providing a rationale for the selection of lumped parameter modelling to be used by MySolver. The development of the synchronous generator lumped parameter thermal models is detailed, with examples on its construction presented. Subsequently, finite element analysis is utilised to predict the distribution of machine iron losses across the rotor and stator laminations, with the findings applied to MySolver. Furthermore, a study is performed into the lumped parameter discretisation level needed to effectively represent machine windings. MySolver is experimentally verified using experimental data from a fully instrumented synchronous generator and this data is also used to obtain further insight into the temperature distribution within the generator. In the final part results are evaluated and the use of MySolver for modelling and optimising electrical machines is discussed. Finally, appropriate conclusions on the work presented are drawn.

We study a discrete time, structured population dynamic model that is motivated by recent field observations concerning certain life history strategies of colonial- nesting gulls, specifically the glaucouswinged gull ( Larus glaucescens). The model focuses on mechanisms hypothesized to play key roles in a population's response to degraded environment resources, namely, increased cannibalism and adjustments in reproductive timing. We explore the dynamic consequences of these mechanics using a juvenile- adult structure model. Mathematically, the model is unusual in that it involves a high co- dimension bifurcation at R0 = 1 which, in turn, leads to a dynamic dichotomy between equilibrium states and synchronized oscillatory states. We give diagnostic criteria that determine which dynamic is stable. We also explore strong Allee effects caused by positive feedback mechanisms in the model and the possible consequence that a cannibalistic population can survive when a non- cannibalistic population cannot.

Permanent magnet synchronous motors are finding ever increasing use in hybrid and electric vehicles. This thesis develops a new control strategy for Permanent Magnet Synchronous Motors (PMSMs) to reduce the motor and inverter losses compared to conventional control techniques. The strategy utilises three common control modes for PMSMs; brushless DC with 120°E conduction, brushless DC with 180°E conduction, and brushless AC control. The torque and power output for each control mode is determined for an example motor system using a three phase axial flux YASA motor and an IGBT inverter. The loss components for the motor and inverter are also estimated using a combination of analytical and simulation techniques and results are then validated against experimental measurements. Efficiency maps for each control mode have been used to determine an optimal mode utilisation strategy, which minimises the total system losses and maximises the available motor torque output. The proposed control strategy switches between the three control modes without interruption of motor torque to maximise the system efficiency for the instantaneous operating speed and demanded torque output. The benefits of the new strategy are demonstrated using an example vehicle over a simulated drive cycle. This yields a 10% reduction in losses compared to conventional brushless AC control.

Four aspects of the dynamics of continuous-time dynamical systems are studied in this work. The relationship between the Lyapunov exponents of the original system and the Lyapunov exponents of induced Poincare maps is examined. The behavior of these Poincare maps as discriminators of chaos from noise is explored, and the possible Poissonian statistics generated at rarely visited surfaces are studied.

Master of Science / Department of Electrical and Computer Engineering / Ruth Douglas Miller / This thesis presents the design of two models for permanent-magnet direct-drive wind turbines. The models are of a 10 kW and a 5 MW wind turbine, which are representative of residential scale and commercial scale turbines respectively. The models include aerodynamic and mechanical simulations through the FAST software, as well as concurrent electrical simulations through the SimPowerSystems toolbox for MATLAB/Simulink. The aim is to provide wind turbine designers and researchers with a comprehensive simulation tool that they can use to design and test many different aspects of a wind turbine. The particular novelty of these models is their high level of detail in electromechanical simulations. For each model, a generator speed controller was designed in a reference frame attached to the generator’s rotor, and was executed with a 3-phase active rectifier using space-vector pulse-width modulation. Also for each model, active and reactive power controllers were designed in a reference frame synchronous with the grid, and were executed with a 3-phase inverter using space-vector pulse-width modulation. Additionally, a blade pitch controller was designed for the 5 MW model. Validation of the models was carried out in the MATLAB/Simulink environment with satisfactory results.

M. Tech. (Engineering: Electrical, Department Electronic Engineering, Faculty of Engineering and Technology), Vaal University of Technology, / “If we think oil is a problem now, just wait 20 years. It’ll be a nightmare.” — Jeremy Rifkin, Foundation of Economic Trends, Washington, D.C., August 2003. This statement harmonises with the reality that human civilisation faces today. As a result, humankind has been forced to look for alternatives to fossil fuels. Among possible solutions, fuel cell (FC) technology has received a lot of attention because of its potential to generate clean energy. Fuel cells have the advantage that they can be used in remote telecommunication sites with no grid connectivity as the majority of telecommunication equipment operates from a DC voltage supply. Power plants based on phosphoric acid fuel cell (PAFC) have been installed worldwide supplying urban areas, shopping centres and medical facilities with electricity, heat and hot water. Although these are facts regarding large scale power plants for on-site use, portable units have been explored as well. Like any other fuel cell, the PAFC output power is highly unregulated leading to a drastic drop in the output voltage with changing load value. Therefore, various DC–DC converter topologies with a wide range of input voltages can be used to regulate the fuel cell voltage to a required DC load. An interleaved synchronous buck converter intended for efficiently stepping down the energy generated by a PAFC was designed and developed. The design is based on the National Semiconductor LM5119 IC. A LM5119 evaluation board was redesigned to meet the requirements for the application. The measurements were performed and it was found that the converter achieved the expectations. The results showed that the converter efficiently stepped down a wide range of input voltages (22 to 46 V) to a regulated 13.8 V while achieving a 93 percent efficiency. The conclusions reached and recommendations for future research are presented. / Telkom Centre of Excellence, TFMC, M-Tech, THRIP.

M.Ing. (Electrical and Electronic Engineering) / In this study, the problem of correcting burst of adjacent deletions by adapting product codes was investigated. The first step in any digital transmission is to establish synchronization between the sending and receiving nodes. This initial synchronization ensures that the receiver samples the information bits at the correct interval. Unfortunately synchronization is not guaranteed to last for the entire duration of data transmission. Though synchronization errors rarely occur, it has disastrous effects at the receiving end of transmission. These synchronization errors are modelled as either insertions or deletions in the transmitted data. In the best case scenario, these errors are restricted to single bit errors. In the worst case scenario, these errors lead to bursts of bits being incorrect. If these synchronization errors are not detected and corrected, it can cause a shift in the transmitted sequence which in turn leads to loss of synchronization. When a signal is subjected to synchronization errors it is difficult accurately recover the original data signal. In addition to the loss of synchronization, the information transmitted over the channel is also subjected to noise. This noise in the channel causes inversion errors within the signal. The objective of this dissertation is to investigate if an error correction scheme can be designed that has the ability to detect and correct adjacent bursts of deletions and random inversion errors. This error correction scheme needed to make use of a product code matrix structure. This product matrix needed to incorporate both an error correction and synchronization technique. The chosen error correcting techniques were Hamming and Reed-Solomon codes. The chosen synchronization techniques for this project were the marker technique or an adaptation of the Hamming code technique. In order to find an effective model, combinations of these models were simulated and compared. From the research obtained and analyzed in this document it was found that, depending on the desired performance, complexity and code rate, an error correction scheme can be used in the efficient correction of bursts of adjacent deletions by adapting product codes.

Methods for detecting patterns of angler selective fishing behaviour in the long term recreational fishery statistics are presented in this Ph.D. Thesis. The motivating idea is that mainly different anglers' fishing preferences or attitudes towards particular fish species obstruct applying anglers' catches data for ongoing use in ichthyology research. Better recognising angler selectivity is therefore judged to be the key point from the viewpoint of fish and fishery sciences. Methods affecting angler behaviour can be directly applied by other specialists, e.g. social scientists. The thesis consists of five papers two of which are published (paper 1, 2), other two of which are accepted for publishing (paper 3, 4) and the last of which (paper 5) is in the status of manuscript before submitting. In the first two papers the role of common carp catches is focused. By using multivariate techniques it is studied if the increased exploitation of carp increases also the exploitation of other fish species. Time series of carp catches serve as an explanatory variable, other species catches through the same time are processed as independent variables. According to expectations the positive effect of carp catches on those of the other species was approved at the river section with the highest expected density...

Synchronous generators used for hydro power and nuclear power is a well known topology but there is a vast amount of intricate technologies and methods to making them function properly. This masters thesis covers the development, implementation and verification of a magnetisation system for a synchronous generator. The software implementation is made in the LabVIEW programming environment and uses a high performance CompactRIO with an FPGA for measurements, calculation and output control signals. Together with several peripheral devices, the CompactRIO forms an excitation system and most importantly, an automatic voltage regulator. This system keeps the output voltage of the generator stable and has a variety of safety features such as over excitation limits, under excitation limits and a V/Hz limiter. The resulting system successfully monitors and controls the generator characteristics and the controllers, based on PI controllers, have short rise times, low overshoot and no significant static error. This magnetisation system was verified on a 185 kW synchronous machine and all functions showed satisfying results with the exception of the implemented power system stabiliser which need to be re-tuned.