The purpose of this study was to investigate the conveyancing process in South Africa with a view to identify how the process might be improved in terms of its efficiency and effectiveness. Land is an asset and still remains a valuable factor in production, even in the modern knowledge economy. In many parts of the world, land is a limited resource, therefore, in most countries, custodianship and ownership of land and landed properties generally tend to be guarded through the meticulous capturing, recording and storage of appropriate data and information. Legislative provisions for the transfer of custodianship and/or ownership require the involvement of a variety of role players in the conveyancing processes that culminate in the registration of land and associated immovable property. In some countries, the conveyancing processes tend to be complex and cumbersome. The study provides a conceptual framework for conveyancing processes based on a content-based review of land and immovable property registration systems in five countries, namely, Barbados, the Netherlands, Australia, Taiwan and South Africa. The study further investigates the South African conveyancing processes. Quantitative questionnaires were completed by six respondent groups from the conveyancing service chain, and qualitative interviews were conducted with two of the four major banks in South Africa. Descriptive statistics was used to analyse the quantitative data, and content analysis was used to analyse the qualitative data. The findings were used to develop a de-bottlenecking framework for South African conveyancing. / Business Management / M. Com. (Business Management)

Les vibrations aléatoires sont les sollicitations les plus représentatives à celles qui se trouvent dans l'environnement réel. Elles sont souvent rencontrées dans l'environnement de fonctionnement automobile, aéronautique, spatial, ferroviaire et d'autres. La particularité des vibrations aléatoires est l'utilisation de son analyse par fatigue. Grâce aux propriétés statistiques des signaux aléatoires que les méthodes spectrales permettent d'estimer la moyenne du dommage d'une façon efficace et économique mais avec certaines limitations. Une étude numérique sur un système électronique embarqué accompagnée des essais expérimentaux ont été mis en place dans cette thèse pour présenter une démarche complète d'une analyse spectrale des vibrations aléatoires. Une modélisation par éléments finis a été réalisée ainsi qu'une technique du 'zoom structural' en analyse spectrale des vibrations aléatoires a été proposée dans ce travail avec la présentation des équations de cette technique. Une application numérique a montré la validité de la technique proposée en appliquant une étude de l'endommagement par fatigue par l'approche temporelle et par l'approche spectrale. Les résultats numériques de cette application mènent à une estimation d'un temps à l'initiation de la fissure très proche du temps de défaillance observé dans les résultats des essais expérimentaux. Cette technique montre la performance et l'efficacité des méthodes spectrales dans l'estimation du dommage par fatigue aléatoire. Une étude de l'optimisation d'un système soumis aux sollicitations aléatoires a été développée. L'objectif de cette étude est de rechercher la conception optimale du système soumis aux vibrations aléatoires en posant des limitations sur le dommage qui en résulte. Ce dommage estimé par les méthodes spectrales de Dirlik et de Single Moment ne doit pas dépasser un dommage cible pour assurer la fiabilité du système étudié. / Random vibrations are the most representative excitations that can be found in the real environment. They are often encountered in the automotive, aeronautical, space, railway and other operating environments. The special feature of the random vibrations is their important role in damage fatigue analysis. The spectral methods allow to estimate efficiently and economically the mean of the damage using the statistical properties of the random signals. A numerical study on an embedded electronic system with experimental tests was set up in this thesis to present a complete spectral analysis of random vibrations methodology. A finite element model was performed as well as submodelling technique in spectral analysis of random vibrations with associated equations was proposed in this work. A numerical application has shown the validity of the proposed technique by applying the fatigue damage study using the time-domain approach and the spectral approach. The numerical results of this application lead to the estimation of a crack initiation time very close to the failure time observed in the experimental tests. This technique shows the performance and efficiency of spectral methods in the estimation of random fatigue damage. The optimization of a system subjected to random excitations has been developed in this work. The objective of this study is to retrieve the optimal design of the system subjected to random vibrations with limitations on the resulting damage. This damage estimated by Dirlik and Single Moment spectral methods must not exceed defined target damage in order to insure the reliability of the studied system.

La récupération d'énergie par élément piézoélectrique est une technique prometteuse pour les futurs systèmes électroniques nomades autoalimentés. L'objet de ce travail est d’analyser des approches simples et agiles d’optimisation de la puissance produite par un générateur piézoélectrique. D'abord le problème de l’optimisation de l’impédance de charge d’un générateur piézoélectrique sismique est posé. Une analyse du schéma équivalent global de ce générateur a été menée sur la base du schéma de Mason. Il est démontré que la puissance extraite avec une charge complexe adaptée puisse être constante quelle que soit la fréquence et que de plus elle est égale à la puissance extraite avec la charge résistive adaptée du même système sans pertes. Il est montré toutefois que la sensibilité de cette adaptation à la valeur de la réactance de la charge la rend difficilement réaliste pour une application pratique. Une autre solution pour améliorer l’énergie extraite est de considérer un réseau de générateurs positionnés en différents endroits d’une structure. Des simulations sont proposées dans une configuration de récupération d’énergie de type directe sur une plaque encastrée. Les générateurs piézoélectriques, associés à la technique SSHI, ont été reliés selon différentes configurations. Les résultats attestent que l’énergie produite ne dépend pas de façon critique de la manière dont sont connectés les éléments. Toutefois l’utilisation d’un seul circuit SSHI pour l’ensemble du réseau dégrade l’énergie extraite du fait des interactions entre les trop nombreuses commutations. Enfin une nouvelle approche non-linéaire est étudiée qui permet l’optimisation de l’énergie extraite tout en gardant une grande simplicité et des possibilités d’auto alimentation. Cette technique appelée S3H pour « Synchronized Serial Switch Harvesting » n’utilise pas d’inductance et consiste en un simple interrupteur en série avec l’élément piézoélectrique. La puissance récupérée est le double de celle extraite par les méthodes conventionnelles et reste totalement invariante sur une large gamme de résistances de charge. / Piezoelectric energy harvesting is a promising technique for battery-less miniature electronic devices. The object of this work is to evaluate simple and robust approaches to optimize the extracted power. First, a lightweight equivalent circuit derived from the Mason equivalent circuit is proposed. It’s a comprehensive circuit, which is suitable for piezoelectric seismic energy harvester investigation and power optimization. The optimal charge impedance for both the resistive load and complex load are given and analyzed. When complex load type can be implemented, the power output is constant at any excitation frequency with constant acceleration excitation. This power output is exactly the maximum power that can be extracted with matched resistive load without losses. However, this wide bandwidth optimization is not practical due to the high sensitivity the reactive component mismatch. Another approach to improve power extraction is the capability to implement a network of piezoelectric generators harvesting on various frequency nodes and different locations on a host structure. Simulations are conducted in the case of direct harvesting on a planar structure excited by a force pulse. These distributed harvesters, equipped with nonlinear technique SSHI (Synchronized Switching Harvesting on Inductor) devices, were connected in parallel, series, independently and other complex forms. The comparison results showed that the energy output didn’t depend on the storage capacitor connection method. However, only one set of SSHI circuit for a whole distributed harvesters system degrades the energy scavenging capability due to switching conflict. Finally a novel non-linear approach is proposed to allow optimization of the extracted energy while keeping simplicity and standalone capability. This circuit named S3H for “ Synchronized Serial Switch Harvesting” does not rely on any inductor and is constructed with a simple switch. The power harvested is more than twice the conventional technique one on a wide band of resistive load.

Actuellement, les systèmes permettant de transférer de l’énergie dans le but de recharger les accumulateurs d’appareils électroniques sans l’emploi de câble se démocratisent davantage chaque jour. On comprend donc bien l’intérêt de tels systèmes dans des environnements embarqués et confinés tels que l’habitacle d’un véhicule. Le principe de l’induction magnétique réside dans un transfert de flux magnétique entre deux antennes inductives. Le champ magnétique servira de vecteur au transport d’une puissance électrique, puisque c’est au travers de cette création de flux magnétique que sera échangée ou transférée la puissance d’un émetteur vers un récepteur. Un tel système d’émission-réception de puissance utilisant le principe d’induction magnétique contient un émetteur, des antennes (bobines) inductives couplées et un récepteur. Un premier chapitre sera donc consacré à l’étude des antennes d’un point de vue théorique et technologique. Des modèles électromagnétiques d’antennes inductives seront développés, et après validation par corrélation avec des mesures électriques et électromagnétiques, ils seront employés au travers d’intenses simulations électromagnétiques. Ceci afin de montrer l’impact des paramètres définissant ces antennes inductives sur leurs comportements électrique et électromagnétique. Une fois les antennes inductives optimisées et leurs paramètres clés identifiés, on étudiera dans un deuxième temps les effets de l’induction magnétique lorsque qu’une antenne d’émission et une autre de réception sont présentées ensembles et mises en condition de transfert d’énergie. On mettra donc en évidence le principe de couplage magnétique entre les antennes ainsi que la notion de rendement de puissance appelé aussi efficacité de liaison. Les différents paramètres des antennes seront là aussi caractérisés afin d‘étudier leur influence sur le transfert d’énergie inductif. Le tout illustré de la même manière que précédemment, en s’appuyant sur d’intenses simulations électromagnétiques et des modèles validés par rapport à différentes méthodes de mesure. Ceci dans le but de comprendre les mécanismes de fonctionnement et d’optimisation d’un système de transfert d’énergie par induction magnétique ainsi que de proposer des règles générales de conception d’antennes inductives. Dans un troisième temps, on présentera les différents étages électroniques composant les systèmes de transfert d’énergie inductif. Une partie sera dédiée à la définition du point de vue système des éléments constituant la chaine complète d’émission et de réception. La conception, l’optimisation et la mesure des amplificateurs de puissance utilisés au niveau de l’émetteur seront également présentés. En effet, ces systèmes doivent être suffisamment performants afin de transférer des puissances capables d’alimenter des appareils électroniques de type téléphones tout en ayant un bilan de puissance efficace avec des pertes limitées. A partir de modèles de circuits émetteur et récepteur et en s’appuyant sur des simulations circuits, nous estimerons les bilans de puissances afin d’évaluer les performances et les limites des différents systèmes. Ces simulations une fois validées par mesures permettront de quantifier l’efficacité du transfert de puissance et proposer des voies d’optimisation. Ces systèmes et technologies sont de plus en plus utilisés pour l’électronique grand public et il existe actuellement plusieurs standards régissant le transfert d’énergie inductif. Les différentes études présentées dans cette thèse seront donc orientées vers ces différentes normes, et des analogies seront réalisées tout le long du mémoire afin de mettre en exergue leurs différents principes de fonctionnement. / Nowadays there is a strong demand of systems allowing to transfer energy in a wirelessly way to small electronic devices. So we can well understand the interest of such systems in embedded environments such as vehicle cockpit. The principle of magnetic induction comes from a magnetic flux exchange between two inductive antennas. The magnetic field will be used to transport an electrical power from an emitter to a receiver. These systems using the magnetic induction to transfer energy contain an emitter, inductive antennas (coils) and a receiver. A first chapter will be dedicated to the antennas employed in inductive wireless power transfer systems on theoretical and technological points of views. An electromagnetic modeling of these inductive antennas will be realized and validated through correlation with measurements. Once the modeling process defined and the validations done, it will be used through intensive electromagnetic simulations in order to show the impact of antennas parameters on their electrical and electromagnetic performances. After the inductive antennas characterization and their key parameters identification done, we will study in a second time the magnetic induction effects when emission and reception antennas are placed together in order to realize an inductive power transfer. Notions of magnetic coupling which appears between inductive antennas and magnetic efficiency which characterizes how much quantities of power are transferred will be highlighted. In the same conditions as before, the impact of antennas parameters on the power transfer and magnetic coupling will be investigated through electromagnetic modeling of inductive antennas and the use of intensive electromagnetic simulations. Thus, we will have the opportunity to precisely understand the meaning of the inductive power transfer and the different ways of optimizations. By this way, we will also propose some general design guidelines for antennas employed in inductive wireless power transfer systems. A third chapter will be dedicated to the presentation of the different electronic stages used in inductive wireless power transfer systems. A part of it will be employed on the definitions of the different elements allowing the wireless power transfer on a system approach. The design, optimization and measurement of power amplifiers used on the emission stage will be presented too.. Indeed, it is necessary to have efficient power amplification in order to transfer the required power to different receivers such as phones at the same time to limit the power losses. From circuit modeling of different emitter and receiver and with circuit simulations, we will develop power budgets in order to evaluate the performances and limits of these systems. Once the simulation validated by measurement, we will be able to quantify the total power transfer efficiency and propose optimization ways. Because of the current existence of different inductive wireless power standards on the industrial market for electronic consumer, analogies with them will be done all along the different steps of this thesis in order to highlighted their different functioning principles.

Les convertisseurs électroniques font actuellement l'objet d'intensives recherches en raison de l'intérêt grandissant pour l'électronique de puissance. Ceci est principalement dû au grand nombre d'applications dans lesquelles ils apparaissent, comme, par exemple, dans les ordinateurs et téléphones portables, les véhicules, les équipements électroniques industriels, les grands systèmes de communication et bien plus encore. Ces investigations portent particulièrement deux points. Le premier concerne la recherche de topologies de convertisseurs dédiées à chaque application. Le second point traite de la conception de mécanismes de contrôle assurant que les objectifs de conversion sont satisfaits. Ma thèse se concentre sur l'élaboration des solutions de contrôle pour deux types de convertisseurs, qui ont des propriétés et des applications intéressantes. Les convertisseurs considérés sont, premièrement, un inverseur type « boost », et ensuite, un convertisseur « DC-DC VddHopping » pour les applications de faible puissance. Dans le premier cas, l'inverseur type boost, l'objectif de contrôle peut être vu comme la génération d'un cycle limite stable. Ce cycle limite est défini par une amplitude et une fréquence données. Les tensions de sortie des deux parties du système présentent, pour cette fréquence, un comportement sinusoïdal avec un changement de phase pré-spécifié. De plus, la loi de commande doit inclure des propriétés de robustesse par rapport à un certain nombre de contraintes. Par exemple, nous considérerons le cas de charges connues mais aussi inconnues. Un autre objectif important est de déterminer un ensemble de valeurs initiales de voltage et de courants, pour lesquelles les variables du système tendent vers leurs équilibres lorsque la loi de commande est appliquée à l'investisseur « boost». La deuxième partie de la thèse met l'accent sur le contrôle du convertisseur Vdd-Hopping DC-DC, consacré à des technologies de faible puissance. Ce travail se situe dans le cadre du projet national français appelé ARAVIS, parrainé par le pôle de compétitivité international Minalogic. Bien que ce soit aussi un convertisseur, la structure et la dynamique de ce système ainsi que les objectifs de contrôle sont radicalement différents du précédent. Ici il s'agit d'un système non linéaire du premier ordre. La sortie doit atteindre une valeur constante désirée et certaines requêtes exigées pour des systèmes de faible puissance doivent être satisfaites, telles qu'une haute efficacité, la stabilité de l'équilibre, la robustesse de l'équilibre incluant des retards et des incertitudes sur les paramètres, des phases transitoires rapides, la fiabilité, etc...

This thesis addresses the problem of building a Cognitive Radio that has the ability to interact with human users in a better way by making use of Quality of Experience (QoE) as its basis and marshalling its resources optimally around the user. Salient activities of this thesis include: Analysis of CR leads to the definition of its basic functional blocks such as cognition, learning and adaptation of radio behaviour in a multi-disciplinary manner. CR tracts signal processing for radio and sensors, cognitive and behavioural psychology for user intelligence, machine learning and AI for decision systems and optimization etc. Therefore it provides a rich, fertile area to make lateral connections across diverse helds. This thesis proposes a broad definition for CR (called as Unifed Cognitive Radio) inspired by key foundation works described in literature. Besides, it also describes its functionality and its ecosystem. Taking cue from the definition of UCR, this thesis proposes architectural frame-works for various sub-systems. Also their design and implementation is achieved with the aid of a comprehensive tested setup and is tested using realistic scenarios. Builds a set of intelligent decision systems that help to achieve the set goal. This involves various design decisions with a set of diverse algorithms from the world of signal processing, machine learning and articial intelligence. Transitioning disparate small functional entities (mostly built around experiments) into an integrated system that works in real-world environment is the key aspect of this thesis. It is definitely a challenging task. Therefore, starting from deterring the architectural reference frameworks for realizing various sub-systems of UCR to an evaluation based on integrated scenario, this being an important final step constitutes a sign cant amount of work. Analysis and implementation of the integrated system to meet the desired end functionality - QoE centricity of the CR system to satisfy the needs of the end user better is the contribution of this thesis

Compact Models are the physically based accurate mathematical description of the cir-cuit elements, which are computationally efficient enough to be incorporated in circuit simulators so that the outcome becomes useful for the circuit designers. As the multi-gate MOSFETs have appeared as replacements for bulk-MOSFETs in sub-32nm technology nodes, efficient compact models for these new transistors are required for their successful utilization in integrated circuits. Existing compact models for common double-gate (CDG) MOSFETs are based on the fundamental assumption of having symmetric gate oxide thickness. In this work we explore the possibility of developing models without this approximation, while preserving the computational efficiency at the same level. Such effort aims to generalize the compact model and also to capture the oxide thickness asymmetry effect, which might prevail in practical devices due to process uncertainties and thus affects the device performance significantly. However solution to this modeling problem is nontrivial due to the bias-dependent asym-metric nature of the electrostatic. Using the single implicit equation based Poisson so-lution and the unique quasi-linear relationship between the surface potentials, previous researchers of our laboratory have reported the core model for such asymmetric CDG MOSFET. In this work effort has been put to include Non-Quasistatic (NQS) effects, different small-geometry effects, and noise model to this core, so that the model becomes suitable for practical applications. It is demonstrated that the quasi-linear relationship between the surface potentials remains preserved under NQS condition, in the presence of all small geometry effects. This property of the device along with some other new techniques are used to develop the model while keeping the mathematical complexity at the same level of the models reported for the symmetric devices. Proposed model is verified against TCAD simulation for various device geometries and successfully imple-mented in professional circuit simulator. The model passes the source/drain symmetry test and good convergence is observed during standard circuit simulations.

Wheeled systems are energy efficient on prepared surfaces like roads and tracks. Legged systems are capable of traversing different terrains but can be lossy. At low speeds and on off-road surfaces, legged systems using dynamic walking can be energy efficient. Towards this objective, the dynamics of the walker needs to be modelled and controlled. In addition, the braking and ground impact losses need to be minimized. This thesis presents analysis and experiments on the dynamics and control of a rimless-spoked-wheel based mobile robot (Chatur ∗) that belongs to a category between wheeled and legged systems. This rolling rimless wheel is effectively a 2D dynamic walker that serves as a platform for investigating the dynamics and energetics of inverted pendulum walking with constant step angle. A pulsed actuation torque is proposed for the system resulting in four torque regimes defined by the ratio of energy losses to available actuator torque. Five physical constraints that impose fundamental limits on the choice of operating points of a generic inverted pendulum walker are expounded and a method for locating optimal operating points is discussed. Chatur’s hardware design is elaborated and a control topology is proposed for pulsed actuation of the dual brushless dc (BLDC) motor driven platform with wheel synchronization. Various actuator torque profiles can be used to achieve dynamic ‘walking’ in a hub-actuated rimless wheel. The proposed pulsed actuation torque gives rise to four torque regimes that achieve sustained walking and a fifth regime where the walker keeps slowing down with each step. The regimes can be identified based on the fraction of stance phase for which the actuator is energized. Theoretical analysis and experimental results are presented. A simple closed-form analytical solution, using hyperbolic functions, is proposed for the stance phase inverted pendulum dynamics considering planar motion. Ground impacts are assumed to cause abrupt drop in velocity. A constant braking torque that lumps together the effect of several loss phenomena is also considered. Based on whether the CoM is rising or falling and whether or not there is an actuating torque, a stance phase can have four types of sub-phases — actuated rise, unactuated rise, actuated fall, unactuated fall. These are concatenated in four different ways to form repeating cycles yielding the four regimes. The experimental set-up is a fixed step-angle walker constructed using two synchronized adjacent rimless wheels independently actuated at the hub. Varying the magnitude and duty ratio of the torque pulse, the four proposed regimes are experimentally shown. The mechanical power consumption and cost of transport are computed from measured motor currents for different average forward speeds. Videos of the walks are also taken. The space of operating points for an inverted pendulum based bipedal dynamic walker in terms of constraints and optimality is investigated. The operating point of the walker can be specified by the combination of initial mid-stance velocity (v0) and step angle (φm) chosen for a given walk. Not all operating points lead to a realizable steady-state gait. Using basic mechanics, a framework of physical constraints that limit the choice of operating points is proposed. The constraint lines thus obtained delimit the valid region of operation of the walker in the v0–φm plane. Within this allowable region, sub-regions that result in various regimes of walking are identified. A given average forward velocity vx,avg can be achieved by several combinations of v0 and φm. Only one of these combinations results in the minimum mechanical power consumption and can be considered the opti-mum operating point for the given vx,avg. A method is proposed for obtaining this optimal operating point based on tangency of the power and velocity contours. Putting together all such operating points for various vx,avg, a family of optimum operating points, called the optimal locus, is obtained. For the energy loss and internal energy models chosen, the optimal locus obtained has a largely constant step angle with increasing speed but tapers off at non-dimensional speeds close to unity. Thus, choosing the right step angle and keeping it fixed over a broad range of speeds could lead to an inverted pendulum walker that is close to optimal from a mechanical energy perspective. The complete hardware design for Chatur and the caveats associated with reliable performance of the mechanical and electrical subsystems are elaborated. In order to en-sure lateral stability, the system uses two contralateral wheels each driven by a separate BLDC hub motor. From a motor drive perspective, the mechanical load belongs to a unique class of dynamic loads whose reflected torque has a characteristic cyclic varia-tion that repeats several times within a mechanical revolution. The proposed control topology has two hierarchical levels, an inner loop for torque control of BLDC motor implemented using a standard proportional-integral controller, and an outer loop for torque reference generation that uses the information on the ground impact instants and the motor position feedback. Ground impacts of the spokes are detected by an accelerometer to initiate the application of torque. The torque pulse magnitude can be set internally or by a manual operator via radio control. The pulse duration is programmable and enables attainment of various torque regimes at different steady state speeds. The wheels are synchronized so that corresponding spokes on both wheels move in unison. This is achieved by including a wheel synchronization loop that compensates for any lag between the wheels. Lag is detected based on number of sector changes in the hall-effect position sensor data received from both motors. An improved BLDC motor drive is developed wherein non-commutating current feedback is used to reduce current spikes during sector transitions. Experimental waveforms for controller validation are shown.

Multilevel inverters play a major role in the modern day medium and high power energy conversion processes. The classic two level voltage source inverter generates PWM pole voltage output having two levels with strong fundamental component and harmonics centered around the switching frequency and its multiples. With higher switching frequency, its components can be easily filtered and results in better Total harmonic distortion (THD) output voltage and current. But with higher switching frequency, switching loss of power devices increases and electromagnetic interferences also increases. Also in two level inverter, pole voltage switches between zero and DC bus volt-age Vdc. This switching results in high dv=dt and causes EMI and increased stress on the motor winding insulation. The attractive features of multilevel inverters compared to a two level inverter are reduced switching frequency, reduced switching loss, improved volt-age and current THD, reduced dv=dt, etc. Because of these reasons, multilevel invertersultilevelinvertersplayamajorroleinthemoderndaymediumandhighpower find application in electric motor drives, transmission and distribution of power, transportation, traction, distributed generation, renewable energy systems like photo voltaic, hydel power, energy management, power quality, electric vehicle applications, etc. AC motor driven applications are consuming the significant part of the generated electrical energy (more than 60%) around the world. The multilevel inverters are ideal for such applications, since the switching frequency of the devices can be kept low with lower out-put voltage dv=dt. Also by using multilevel inverters, the common mode voltage (CMV) switching can be made zero and associated motor bearing failure can be mitigated. For multilevel inverter topologies, as the number of level increases, the power circuit becomes more complex by the increase in the number of DC power supplies, capacitors, switching devices and associated control circuitry. The main focus of development in multilevel inverter for medium and high power applications is to obtain an optimized number of voltage levels with reduced number of switching devices, capacitors and DC power sources. In this thesis, a new hybrid seven level inverter topology with a single DC supply is proposed with reduced switch count. The inverter is realized by cascading two three level flying capacitor inverters with a half bridge module. Compared to the conventional seven level inverter topologies, the proposed inverter topology uses lesser number of semiconductor devices, capacitors and DC power supplies for its operation. For this topology, capacitor voltage balancing is possible for entire modulation range irrespective of the load power factor. Also capacitor voltage can be controlled over a switching cycle and this result in lowering the capacitor sizing for the proposed topology. A simple hysteresis band based capacitor voltage balancing scheme is implemented for the inverter topology. For a voltage source inverter fed induction motor drive system, the inverter pole voltage is the sum of motor phase voltage and common mode voltage. In induction motors, there exists a parasitic capacitance between stator winding and stator iron, and between stator winding and rotor iron. Common mode voltage with significant magnitude and high frequency switching causes leakage current through these parasitic capacitances and motor bearings. This leakage current can cause ash over of bearing lubricant and corrosion of ball bearings, resulting in an early mechanical failure of the drive system. In this thesis, analysis of extending the linear modulation range of a general n-level inverter by allowing reduced magnitude of common mode voltage (CMV) switching (only Vdc/18) is presented. A new hybrid seven level inverter topology, with a single DC supply and with reduced common mode voltage (CMV) switching is presented in this thesis for the first time. Inverter is operated with zero CMV for modulation index less than 86% and is operated with a CMV magnitude of Vdc/18 to extend the linear modulation range up to 96%. Experimental results are presented for zero CMV operation and for reduced common voltage operation to extend the linear modulation range. A capacitor voltage balancing algorithm is designed utilizing the pole voltage redundancies of the inverter, which works for every sampling instant to correct the capacitor voltage irrespective of load power factor and modulation index. The capacitor voltage balancing algorithm is tested for different modulation indices and for various transient conditions, to validate the proposed topology. In recent years, model predictive control (MPC) using the system model has proved to be a good choice for the control of power converter and motor drive applications. MPC predicts system behavior using a system model and current system state. For cascaded multilevel inverter topologies with a single DC supply, closed loop capacitor voltage control is necessary for proper operation. This thesis presents zero and reduced common mode voltage (CMV) operation of a hybrid cascaded multilevel inverter with predictive capacitor voltage control. For the presented inverter topology, there are redundant switching states for each inverter voltage levels. By using these switching state redundancies, for every sampling instant, a cost function is evaluated based on the predicted capacitor voltages for each phase. The switching state which minimizes cost function is treated as the best and is switched for that sampling instant. The inverter operates with zero CMV for a modulation index upto 86%. For modulation indices from 86% to 96% the inverter can operate with reduced CMV magnitude ( Vdc/18) and reduced CMV switching frequency using the new space-vector PWM (SVPWM) presented herein. As a result, the linear modulation range is increased to 96% as compared to 86% for zero CMV operation. Simulation and experimental results are presented for the inverter topology for various steady state and transient operating conditions by running an induction motor drive with open loop V/f control scheme. The operation of a two level inverter in the over-modulation region (maximum peak phase fundamental output of inverter is greater than 0:577Vdc) results in lower order harmonics in the inverter output voltage. This lower order harmonics (mainly 5th, 7th, 11th, and 13th) causes electromagnetic torque ripple in motor drive applications. Also these harmonics causes extra losses and adversely affects the efficiency of the drive system. Also inverter control becomes non linear and special control algorithms are required for inverter operation in the over modulation region. In conventional schemes, maximum fundamental output voltage possible is 0:637Vdc. In that case inverter is operated in a square wave mode, also called six-step mode. This operation results in high dv=dt for the inverter output voltage. With multilevel inverters also, the inverter operation with peak phase fundamental output voltage above 0:577Vdc results in lower order harmonics in the inverter output voltage and results in electromagnetic torque pulsation. In this thesis, a new space vector PWM (SVPWM) method to extend the linear modulation range of a cascaded five level inverter topology with a single DC supply is presented. Using this method, the inverter can be controlled linearly and the peak phase fundamental output voltage of the inverter can be increased from 0:577Vdc to 0:637Vdc without increasing the DC bus voltage and without exceeding the induction motor voltage rating. This new technique makes use of cascaded inverter pole voltage redundancy and property of the space vector structure for its operation. Using this, the induction motor drive can be operated till the full speed range (0 Hz to 50 Hz) with the elimination of lower order harmonics in the phase voltage and phase current. The ve level topology presented in this thesis is realized by cascading a two level inverter and two full bridge modules with floating capacitors. The inverter topology and its operation for extending the modulation range is analyzed extensively. Simulation and experimental results for both steady state and dynamic operating conditions are presented. Zero common mode voltage (CMV) operation of multilevel inverters results in reduced DC bus utilization and reduced linear modulation range. In this thesis two reduced CMV SVPWM schemes are presented to extend the linear modulation range by allowing reduced CMV switching. But using these SVPWM schemes the peak phase fundamental output voltage possible is only 0:55Vdc in the linear region. In this thesis, a method to extend the linear modulation range of a CMV eliminated hybrid cascaded multilevel inverter with a single DC supply is presented. Using this method peak fundamental voltage can be increased from 0 to 0:637Vdc with zero CMV switching inside the linear modulation range. Also inverter can be controlled linearly for the entire modulation range. Also, various PWM switching sequences are analyzed in this thesis and the PWM sequence which gives minimum current ripple is used for the zero CMV operation of the inverter. The inverter topology with single DC supply is realized by cascading a two level inverter with two floating capacitor fed full bridge modules. Simulation and experimental results for steady state and dynamic operating conditions are presented to validate the proposed method. A three phase, 400 V, 3.7 kW, 50 Hz, two-pole induction motor drive with the open-loop V/f control scheme is implemented in the hardware for testing proposed inverter topology and proposed SVPWM algorithms experimentally. The semiconductor switches that were used to realize the power circuit for the experiment were 75 A, 1200 V IGBT half-bridge modules (SKM-75GB-12T4). Optoisolated gate drivers with de-saturation protection (M57962L) were used to drive the IGBTs. For the speed control and PWM timing computation, TMS320F28335 DSP is used as the main controller and Xilinx SPARTAN-3 XC3S200 FPGA as the PWM signal generator with dead time of 2.5 s. Level shifted carrier-based PWM algorithm is implemented for the normal inverter operation and zero CMV operation. From the PWM algorithm, information about the pole voltage levels to be switched can be obtained for each phase. In the sampling period, for capacitor voltage balancing of each phase, the DSP selects a switching state using the capacitor voltage information, current direction and pole voltage data for each phase. This switching state information along with the PWM timing data is sent to an FPGA module. The FPGA module generates the gating signals with a dead time of 2.5 s for the gate driver module for all the three phases by processing the switching state information and PWM signals for the given sampling period. For fundamental frequencies above 10Hz, synchronous PWM technique was used for testing the inverter topology. For modulation frequencies 10Hz and below, a constant switching frequency of 900 Hz was used. Various steady state and transient operation results are provided to validate the proposed inverter topology and the zero and reduced CMV operation schemes and extending the linear modulation scheme presented in this thesis. With the advantages like reduced switch count, single DC supply requirement, zero and reduced CMV operation, extension of linear modulation range, linear control of induction motor over the entire modulation range with zero CMV, lesser dv=dt stresses on devices and motor phase windings, lower switching frequency, inherent capacitor balancing, the proposed inverter power circuit topologies, and the SVPWM methods can be considered as good choice for medium voltage, high power motor drive applications.

The purpose of this study was to investigate the conveyancing process in South Africa with a view to identify how the process might be improved in terms of its efficiency and effectiveness. Land is an asset and still remains a valuable factor in production, even in the modern knowledge economy. In many parts of the world, land is a limited resource, therefore, in most countries, custodianship and ownership of land and landed properties generally tend to be guarded through the meticulous capturing, recording and storage of appropriate data and information. Legislative provisions for the transfer of custodianship and/or ownership require the involvement of a variety of role players in the conveyancing processes that culminate in the registration of land and associated immovable property. In some countries, the conveyancing processes tend to be complex and cumbersome. The study provides a conceptual framework for conveyancing processes based on a content-based review of land and immovable property registration systems in five countries, namely, Barbados, the Netherlands, Australia, Taiwan and South Africa. The study further investigates the South African conveyancing processes. Quantitative questionnaires were completed by six respondent groups from the conveyancing service chain, and qualitative interviews were conducted with two of the four major banks in South Africa. Descriptive statistics was used to analyse the quantitative data, and content analysis was used to analyse the qualitative data. The findings were used to develop a de-bottlenecking framework for South African conveyancing. / Business Management / M. Com. (Business Management)