Thesis (MScEng (Electrical and Electronic Engineering))-- University of Stellenbosch, 2006. / This thesis presents the design and implementation of a high voltage DC-DC converter using a series stacked topology. The converter’s specifications were set by Spoornet and the converter forms part of a DC-AC inverter to be installed in Spoornet substations. Different converter topologies will be considered. A high frequency, high power coaxially wound transformer will be analysed, designed and manufactured for this specific converter application. A thermal analysis of the transformer will be carried out. The merits of different control schemes, leading to the choice of an average current mode controller, will be discussed. This controller will be designed and implemented to control the converter. The converter is then simulated to test and verify the controller functionality. A two-level series stacked converter is built and tested to verify the converter design and to test the functionality of the coaxially wound transformer. Finally, the results obtained will be discussed.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / A WSN (wireless sensor network) consists of a collection of small, low power electronic devices that can sense their environment and communicate with each other in order to send data to a base station for logging and monitoring. Research done on WSNs has increased rapidly over the past few years, as the necessary RF hardware has become cheaper and smaller. The wealth of information and hardware available in this field has made it possible to design and deploy networks for a multitude of monitoring purposes, on almost any terrain, without an existing telecommunication infrastructure. This thesis presents research into some major aspects of WSNs and the implementation of a test system with wireless sensor motes, that can be used for environmental monitoring, conservation purposes, impact studies, early warning systems for floods, fires etc. The system also has a wide range of possible uses in agriculture, as more data and better control over crops can increase yield. The power constraint of sensor nodes is one of the biggest concerns, as batteries can be depleted quickly and render a system useless. For this reason, work was focused on reducing power consumption of the hardware by means of various methods. Power use was also simulated very successfully, giving a accurate way of predicting node lifetime with a variety of battery types. The system was implemented on the Tmote Sky hardware platform using the open source sensor network operating system, TinyOS.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / The purpose of this study was to investigate multi-spectral tracking. Various algorithms were investigated and developed to enhance the contrast between target and non-target classes. Different tracking algorithms were implemented on the resulting grayscale input. A physical tracking system consisting of a video input processor and DSP was designed and built to implement algorithms and investigate the viability of realtime multi-spectral tracking. It is illustrated that conventional intensity tracking clouds the available information and that by studying various spectral inputs information is extracted more efficiently from the available data.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / In this thesis, the maneuvering and orientation of an inspection/service satellite is investigated. This thesis will demonstrate a simplified satellite maneuver around another satellite (for docking purposes). This is illustrated with a cart on an air bearing table (frictionless environment) which simplifies the problem to two dimensions. A mathematical model of the system was designed and simulated (Matlab) for this maneuver. With the simulation, different strategies were considered to maneuver the cart in a circle around another object. The conclusion was made that approximating the circle with segments would conserve propellant. This strategy was implemented on the air bearing table.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / Power system stability simulations are of growing importance for studying the operational integrity of modern power systems, especially in developing economies where generating and transmission capacity lead the demand by relatively small margins. The relevant model topologies, i.e. for synchronous generators, automatic voltage regulators (AVR) and governor control systems, and the simulation software tools are well established. The MATLAB® Power System Blockset provides engineers with a versatile power system stability simulation environment, particularly where the focus is on individual units or small systems. In comparison with dedicated power system simulation tools such as DIgSILENT®, the MATLAB® environment features a superior set of advanced data processing and data analysis features. This includes features such as optimisation and parameter estimation functions. The main aim of this project is to make use of the MATLAB® package in a bid to test an alternative platform with which to estimate the synchronous machine parameters. Conditioning of field data can delay the process considerably, thus the secondary task of this thesis is to solve this issue by ensuring that only one platform is needed for the entire process starting in the field and ending in the modelling and parameter estimation environment within MATLAB®. In closing, the following points summarise the essential aims of this project: • An application using MATLAB® Script must be created that is responsible for importing and processing the data, so it is suitable for analysis purposes. The processing could include cropping, scaling and filtering of data. • Once the data has been imported it must be used with appropriate models to estimate for machine parameters. This will require the use of the Power Systems Blockset. The actual estimation process also requires the creation of an effective cost function, thus a number of different scenarios will have to be investigated before a solution can be found.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / A great demand exits for higher data rates and increased reliability of future consumer based mobile communication systems while being more bandwidth and power efficient. Orthogonal frequency division multiplexing (OFDM) in combination with multiple-input multiple-output (MIMO) schemes has become a promising candidate for fulfilling the demand of next generation communication systems. The sensitivity of MIMO OFDM systems to physical impairments is of great interest and particularly the Alamouti space-time block code is under investigation in this thesis. Generic and comprehensive simulation models of an OFDM communication system incorporating the spacetime block code are developed in a modular fashion and used in a performance evaluation with non-ideal component and channel behaviour.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2008. / Horizon sensing is an effective way to determine the pitch and roll of a LEO satellite and Earth horizon sensors that operate in the visible range of the electromagnetic spectrum are commonly used. These sensors have the disadvantage that they cannot operate when the satellite is in eclipse. Earth horizon sensors that operate in the infrared spectral range are a solution to take attitude measurements when the satellite is in eclipse. Until recently infrared detectors could only operate at very low temperatures and needed to be cryogenically cooled. The result was that their power consumption and physical characteristics (like dimensions and mass) were such that they were not suitable for use in small and medium LEO satellites. As a result of technology expansion in the field of infrared imagers the past few years, infrared imagers were developed which do not require cooling. The scope of this project was to develop and implement an Earth horizon sensor by using a low-cost, uncooled infrared imager. The performance and physical characteristics of various imager were evaluated and it was decided to select a low resolution thermopile imager mainly as a result of the cost limitations of the project. Software algorithms were then evaluated and selected for horizon detection and attitude determination. The Earth horizon sensor that was developed did not comply with the accuracy requirement (3s < 0.1o) that was set for the project because of the low resolution of the sensor. Methods to improve the accuracy were investigated and finally a sub-pixel edge estimation algorithm was developed and implemented which resulted in an improvement of 69% in the pitch accuracy and 49% in roll accuracy. With the sub-pixel edge estimation algorithm implemented the horizon sensor almost met the accuracy requirements (s < 0.0811o for pitch and s < 0.2944o for roll). This project confirms that, with further improvement to the design and test facilities, developing a low-cost, uncooled infrared Earth horizon sensor that meets the accuracy requirements is feasible.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / Statistical speech recognition systems typically utilise a set of statistical models of subword units based on the set of phonemes in a target language. However, in continuous speech it is important to consider co-articulation e ects and the interactions between neighbouring sounds, as over-generalisation of the phonetic models can negatively a ect system accuracy. Traditionally co-articulation in continuous speech is handled by incorporating contextual information into the subword model by means of context-dependent models, which exponentially increase the number of subword models. In contrast, transitional models aim to handle co-articulation by modelling the interphone dynamics found in the transitions between phonemes. This research aimed to perform an objective analysis of diphones as subword units for use in hidden Markov model-based continuous-speech recognition systems, with special emphasis on a direct comparison to a context-dependent biphone-based system in terms of complexity, accuracy and computational e ciency in similar parametric conditions. To simulate practical conditions, the experiments were designed to evaluate these systems in a low resource environment { limited supply of training data, computing power and system memory { while still attempting fast, accurate phoneme recognition. Adaptation techniques designed to exploit characteristics inherent in diphones, as well as techniques used for e ective parameter estimation and state-level tying were used to reduce resource requirements while simultaneously increasing parameter reliability. These techniques include diphthong splitting, utilisation of a basic diphone grammar, diphone set completion, maximum a posteriori estimation and decision-tree based state clustering algorithms. The experiments were designed to evaluate the contribution of each adaptation technique individually and subsequently compare the optimised diphone-based recognition system to a biphone-based recognition system that received similar treatment. Results showed that diphone-based recognition systems perform better than both traditional phoneme-based systems and context-dependent biphone-based systems when evaluated in similar parametric conditions. Therefore, diphones are e ective subword units, which carry suprasegmental knowledge of speech signals and provide an excellent compromise between detailed co-articulation modelling and acceptable system performance

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / In order to rapidly detect, monitor and predict changes in milk as it ferments, sensors would need to be designed specifically for milk. To this end, invasive surgical stainless steel probes were investigated and the probe impedances were characterised according to measurements made in various saline concentrations. Based on these findings, specific probes were designed that were robust and easy to use in milk. To measure multiple probe sensors continuously and accurately, an automatic measurement device was designed and manufactured. The device was self-sustaining, portable and calculated and stored all probe impedance data internally, allowing experimental runs to take place in controlled laboratory environments. The probes designed in this thesis were consequently tested in various milk fermentation experiments and it was found that surgical stainless steel probes were effective at detecting and monitoring fermentation changes. The probe impedance changes also lead the pH changes in milk, giving it a predictive element. The probe sensor studies provided enough data so that studies could be done into potential non-invasive sensors. Therefore, capacitive sensors were investigated and a fringe field capacitor was presented as a potential non-invasive milk fermentation sensor.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis is about the dynamic control of a permanent magnet assisted reluctance synchronous machine (PMA RSM). The PMA RSM in this thesis is a 110 kW traction machine and is ideal for the use in electrical rail vehicles. An application of the dynamic control of the PMA RSM in electrical rail vehicles is to reduce wheel slip. The mathematical model of the PMA RSM is derived and explained in physical terms. Two methods of current control for the PMA RSM are investigated, namely constant field current control (CFCC) and constant current angle control (CCAC). It is shown that CCAC is more appropriate for the PMA RSM. A current controller for the PMA RSM that guarantees stability is derived and given as an analytic formula. This current controller can be used for any method of current control, i.e. CFCC or CCAC. An accurate simulation model for the PMA RSM is obtained using results from finite element analysis (FEA). The accurate model is used in a simulation to verify CCAC. A normal proportional integral speed controller for the PMA RSM is designed and the design is also verified by simulation. Practical implementation of the current and speed controllers is considered along with a general description of the entire drive system. The operation of the resolver (for position measurement) is given in detail. Important safety measures and the design of the electronic circuitry to give protection are shown. Practical results concerning current and speed control are then shown. To improve the dynamic performance of the PMA RSM, a load torque observer with compensation current feedback is investigated. Two observer structures are considered, namely the reduced state observer and the full state observer. The derivation of the full state observer and the detail designs of the observer elements are given. The accurate simulation model of the PMA RSM is used to verify the operation of the observer structures and to evaluate the dynamic performance. Both observer structures are implemented practically and practical results are shown. One method of position sensorless control, namely the high frequency voltage injection method, is discussed in terms of the PMA RSM. This work is additional to the thesis but it is shown, because it raises some interesting questions regarding the dynamic control of the PMA RSM.