Thesis (PhD (Electric and Electronic Engineering))--University of Stellenbosch, 2006. / This study focuses on the drive control system of a novel direct field and torque current control applied to a six-phase induction motor. Special phase current waveforms that make it possible to have separate field and torque windings and currents in the motor are proposed. In this thesis the control of these field and torque windings to control directly the flux and torque of the motor is investigated. With the special phase current waveforms the performance of the six-phase induction motor is evaluated through theoretical and finite element analysis. In the analysis the air gap resultant field intensity and flux density produced by the stator field, stator torque and rotor currents are investigated. It is shown that with the special current waveforms a quasi-square shaped, smooth rotating air gap flux density is generated. This smooth rotating flux is important for proper induction motor operation. An equation for the electromagnetic torque is derived and used in the theoretical calculations. The ease of the torque performance calculations is conspicuous. An approximate magnetic circuit calculation method is developed to calculate the air gap flux density versus field current relationship taking magnetic saturation into account. The air gap MMF harmonics and the per phase self and mutual inductances are analysed and calculated using, amongst other things, winding functions. In the finite element analysis specific attention is given to the MMF balanced condition (zero quadrature flux condition) in the motor and the development of a per phase equivalent model. The drive system’s performance with the proposed direct control technique is verified by a developed Matlab simulation model and measurements on a small (2 kW) two-pole, six-phase induction motor drive under digital hysteresis current control. It is shown in the thesis that the calculated results from theoretical derived equations are in good agreement with finite element and measured results. This is particularly the case for the formulas of the MMF balanced constant (zero quadrature flux linkage constant) used in the control software. The results of the simulated and measured linear relationship between the torque and torque current show that MMF balance is maintained in the motor by the drive controller independent of the load condition. The direct control of the torque also explains the good measured dynamic performance found for the proposed drive.

Thesis (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The development of a tool kit for the design of superconducting programmable gate arrays (SPGAs) is discussed. A circuit optimizer using genetic algorithms is developed and evaluated. Techniques and a program are also developed for the generation of segmentized 3D models with which to calculate inductance in circuit structures through FastHenry. The ability to add random variations to the dimensions of the models is included. These tools are then used to design novel latching elements that allow the construction of reprogrammable Rapid Single Flux Quantum (RSFQ) circuits. A circular process is used, whereby layouts are converted back to circuit diagrams through element extraction, and reoptimized if necessary. Two programmable frequency dividers are then designed; one for testing the routing and switch structures and programming architecture of an SPGA, and another compact one for testing the latching elements and off-chip interface. The dissertation concludes with an overview of the circuits necessary for the implementation of a fully functional SPGA. / AFRIKAANSE OPSOMMING: Die ontwikkeling van ’n gereedskapstel vir die ontwerp van supergeleier FPGA’s (SPGA’s) word bespreek. Eerstens word ’n stroombaanoptimeerder, wat met genetiese algoritmes funksioneer, ontwikkel en geëvalueer. Daarna word tegnieke en ’n program ontwikkel om driedimensionele segmentmodelle te genereer waaruit FastHenry die induktansie van stroombaanstrukture kan bepaal. Die vermoë om toevalsveranderinge by die dimensies van die modelle te voeg, is ook ingesluit. Hierdie gereedskap word dan gebruik om nuwe grendelelemente te ontwerp waarmee herprogrammeerbare Rapid Single Flux Quantum (RSFQ) stroombane gebou kan word. ’n Sirkulêre proses word gevolg, waarvolgens uitlegte na stroombaandiagramme teruggeskakel kan word (deur elementonttrekkings) en, indien nodig, heroptimeer kan word. Twee programmeerbare frekwensiedelers word daarna ontwerp; een om die pulsvervoer- en skakelstrukture, asook programmeringsargitektuur van ’n SPGA te toets, en ’n ander, kompakter een om die grendelelemente en warmlogika koppelvlakke mee te toets. Die proefskrif sluit af met ’n oorsig oor die stroombane benodig vir die implementering van ’n volledig funksionele SPGA.

Thesis (PhD) -- Stellenbosch University, 2005. / ENGLISH ABSTRACT: The effective use of borehole radar in geophysical exploration requires accurate knowledge of the dielectric properties of the geological system in which it is employed. The attenuation and propagation velocity of pulses through rock must be known in order to plan and interpret experimental data. Conventional destructive methods for the measurement of hard rock cores require the careful preparation of samples. This firstly necessitates the selection of sampling position and the resulting estimation of rock properties based on sparse measurements, and secondly results in the loss of material and thus data. The ready availability of cylindrical borehole core samples invites the use of a nondestructive means of measuring their properties. A novel design for a flexible guarded capacitor which conforms to a core's cylindrical surface is presented here. T he proposed device has numerous advantages over previous methods. No material is lost to sample preparation and a detailed characterisation of the entire core, including inclusions and transitions between rock types, may be performed. A detailed methodology for the rapid construction of a robust capacitor is given. Guidelines for its operation to achieve repeatable and accurate measurements of the complex dielectric constant of samples of varying homogeneity in the 1- 25 MHz frequency range are presented. The increased amount of data collected from complete core samples is analysed statistically, and amongst other things allows the estimation of the rock's homogeneity. Comparisons of the dielectric properties measured in the laboratory to propagation velocity estimates obtained from crosshole borehole shoots show that a more homogeneous sample is a better predictor of bulk propagating conditions. Detailed studies of the dielectric properties of economically important diamondiferous and platiniferous geological systems show that borehole radar is a feasible tool for the high resolution delineation of ore bodies and other geological targets. / AFRIKAANSE OPSOMMING: Die effektiewe gebruik van boorgatradar in geofisiese eksplorasie benodig akkurate kennis van die dielektriese eienskappe van die geologiese sisteme waarin dit gebruik word. Kennis van die verswakking en voortplantingsnelheid van pulse deur die rots word benodig om eksperimente te beplan en gemete data te interpret eer. Vir konvensionele destruktiewe meetmetodes van harde rotskerne is noukeurige voorbereiding van monsters noodsaaklik. Hierdie proses vereis eerstens 'n keuse van meetposisies en die afskatting van rotseienskappe gebaseer op verspreide metings, en lei tweedens tot die verlies van materiaal en dus data. Die beskikbaarheid van silindriese bom·gat kernmonsters maak dit moontlik om die kerneienskappe op n nie-destruktiewe manier te meet. Die ontwerp van 'n nuwe buigbare afgeskermde kapasitor wat op 'n silindriese kernoppervlak pas, word hier voorgestel. Die toestel het verskeie voordele bo huidige metodes. Geen materiaal word gedurende monstervoorbereiding verloor nie, en 'n volledige beskywing van die eienskappe van die hele kern , met insluitings en oorgange tussen rotstipes, kan verkry word. 'n Gedetaileerde prosedure vir die vinnige konstruksie van 'n robuuste kapasitor word gegee. Die gebruik van die toestel vir herhaalbare en akkurate metings van die komplekse dielektriese konstante van verskillend homogene monsters in die 1- 25 MHz frekwensie bereik word beskryf. Die groter hoeveelheid data wat deur middel van hierdie metode van hele kernmonsters verkry kan word , word statisties geanaliseer, en laat onder andere 'n skatting van die rots se homogeniteit toe. Vergelykings van laboratoriumgemete rotseienskappe met veldskattings van voortplant ingsnelhede wys dat 'n meer homogene monster tot 'n beter afskatting van werklike voortplantingstoestande lei. Studies van die dielektriese eienskappe van ekonomies belangrike diamanthoudende en platinumryk geologiese sisteme wys dat boorgatradar geskik is vir hoe resolusie uitkenning van ertsligame en ander geologiese teikens.

Dissertation (Ph.D)--University of Stellenbosch, 1999. / ENGLISH ABSTRACT: System identification has been sufficiently formalized for linear systems, but not for empirical identification of non-linear, multivariate dynamic systems. Therefore this dissertation formalizes and extends non-linear empirical system identification for the broad class of nonlinear multivariate systems that can be parameterized as state space systems. The established, but rather ad hoc methods of time series embedding and nonlinear modeling, using multilayer perceptron network and radial basis function network model structures, are interpreted in context with the established linear system identification framework. First, the methodological framework was formulated for the identification of non-linear state space systems from one-dimensional time series using a surrogate data method. It was clearly demonstrated on an autocatalytic process in a continuously stirred tank reactor, that validation of dynamic models by one-step predictions is insufficient proof of model quality. In addition, the classification of data as either dynamic or random was performed, using the same surrogate data technique. The classification technique proved to be robust in the presence of up to at least 10% measurement and dynamic noise. Next, the formulation of a nearly real-time algorithm for detection and removal of radial outliers in multidimensional data was pursued. A convex hull technique was proposed and demonstrated on random data, as well as real test data recorded from an internal combustion engine. The results showed the convex hull technique to be effective at a computational cost two orders of magnitude lower than the more proficient Rocke and Woodruff technique, used as a benchmark, and incurred low cost (0.9%) in terms of falsely identifying outliers. Following the identification of systems from one-dimensional time series, the methodological framework was expanded to accommodate the identification of nonlinear state space systems from multivariate time series. System parameterization was accomplished by combining individual embeddings of each variable in the multivariate time series, and then separating this combined space into independent components, using independent component analysis. This method of parameterization was successfully applied in the simulation of the abovementioned autocatalytic process. In addition, the parameterization method was implemented in the one-step prediction of atmospheric N02 concentrations, which could become part of an environmental control system for Cape Town. Furthermore, the combination of the embedding strategy and separation by independent component analysis was able to isolate some of the noise components from the embedded data. Finally the foregoing system identification methodology was applied to the online diagnosis of temporal trends in critical system states. The methodology was supplemented by the formulation of a statistical likelihood criterion for simultaneous interpretation of multivariate system states. This technology was successfully applied to the diagnosis of the temporal deterioration of the piston rings in a compression ignition engine under test conditions. The diagnostic results indicated the beginning of significant piston ring wear, which was confirmed by physical inspection of the engine after conclusion of the test. The technology will be further developed and commercialized. / AFRIKAANSE OPSOMMING: Stelselidentifikasie is weI genoegsaam ten opsigte van lineere stelsels geformaliseer, maar nie ten opsigte van die identifikasie van nie-lineere, multiveranderlike stelsels nie. In hierdie tesis word nie-lineere, empiriese stelselidentifikasie gevolglik ten opsigte van die wye klas van nielineere, multiveranderlike stelsels, wat geparameteriseer kan word as toestandveranderlike stelsels, geformaliseer en uitgebrei. Die gevestigde, maar betreklik ad hoc metodes vir tydreeksontvouing en nie-lineere modellering (met behulp van multilaag-perseptron- en radiaalbasisfunksie-modelstrukture) word in konteks met die gevestigde line ere stelselidentifikasieraamwerk vertolk. Eerstens is die metodologiese raamwerk vir die identifikasie van nie-lineere, toestandsveranderlike stelsels uit eendimensionele tydreekse met behulp van In surrogaatdatametode geformuleer. Daar is duidelik by wyse van 'n outokatalitiese proses in 'n deurlopend geroerde tenkreaktor getoon dat die bevestiging van dinamiese modelle deur middel van enkelstapvoorspellings onvoldoende bewys van die kwaliteit van die modelle is. Bykomend is die klassifikasie van tydreekse as 6f dinamies Of willekeurig, met behulp van dieselfde surrogaattegniek gedoen. Die klassifikasietegniek het in die teenwoordigheid van tot minstens 10% meetgeraas en dinamiese geraas robuust vertoon. / Vervolgens is die formulering van In bykans intydse algoritme vir die opspoor en verwydering van radiale uitskieters in multiveranderlike data aangepak. 'n Konvekse hulstegniek is V:oorgestel en op ewekansige data, sowel as op werklike toetsdata wat van 'n binnebrandenjin opgeneem is, gedemonstreer. Volgens die resultate was die konvekse hulstegniek effektief teen 'n rekenkoste twee grootte-ordes kleiner as die meer vermoende Rocke en Woodrufftegniek, wat as meetstandaard beskou is. Die konvekse hulstegniek het ook 'n lae loopkoste (0.9%) betreffende die valse identifisering van uitskieters behaal. Na aanleiding van die identifisering van stelsels uit eendimensionele tydreekse, is die metodologiese raamwerk uitgebiei om die identifikasie van nie-lineere, toestandsveranderlike stelsels uit multiveranderlike data te omvat. Stelselparameterisering is bereik deur individuele ontvouings van elke veranderlike in die multidimensionele tydreeks met die skeiding van die gesamenlike ontvouingsruimte tot onafhanklike komponente saam te span. Sodanige skeiding is deur middel van onafhanklike komponentanalise behaal. Hierdie metode van parameterisering is suksesvc1 op die simulering van bogenoemde outokatalitiese proses toegepas. Die parameteriseringsmetode is bykomend in die enkelstapvoorspelling van atmosferiese N02-konsentrasies ingespan en sal moontlik deel van 'n voorgestelde omgewingsbestuurstelsel vir Kaapstad uitmaak. Die kombinasie van die ontvouingstrategie en skeiding deur onafhanklike komponentanalise was verder ook in staat om van die geraaskomponente in die data uit te lig. Ten slotte is die voorafgaande tegnologie vir stelselidentifikasie op die lopende diagnose van tydsgebonde neigings in kritiese stelseltoestande toegepas. Die metodologie is met die formulering van 'n statistiese waarskynlikheidsmaatstaf vir die gelyktydige vertolking van multiveranderlike stelseltoestande aangevul. Hierdie tegnologie is suksesvol op die diagnose van die tydsgebonde verswakking van die suierringe in 'n kompressieontstekingenj in tydens toetstoestande toegepas. Die diagnostiese resultate het die aanvang van beduidende slytasie in die suierringe aangedui, wat later tydens fisiese inspeksie van die enjin met afloop van die toets, bevestig is. Die tegnologie sal verder ontwikkel en markgereed gemaak word.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / The design of an electrically small planar antenna for compact circular polarization is presented. After an in-depth study of the performance limitations on electrically small antennas and an investigation into the working of various existing electrically small antennas, the design, simulation and measurement of the proposed antenna element is presented in detail.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / Nonlinear transistor modeling is becoming increasingly popular due to the demand for high linearity and high efficiency microwave amplifiers. The available models often fail to accurately predict the higher order harmonics and intermodulation distortion, which are essential when designing high-linearity amplifier circuits. This thesis describes the design of hardware and software used for the development of nonlinear CAD models. A multiline TRL calibration kit is designed and manufactured so that the characterisation of a LDMOSFET, with a RF output power capability of 10W, can be performed using an adaptive-bias S-parameter measurement algorithm. Verification standards are also manufactured and used to determine the measurement accuracy after calibration. A series of GUIs are developed to ease the model extraction process. The extraction of the small-signal model parameters is performed between 0.4 and 3 GHz, and the extraction of the parameter values for the Fager large-signal model is then performed. An improved model is defined that implements two nonlinear charge sources in stead of the three nonlinear capacitors used in the Fager model. The nonlinear charge equations are formulated using the voltage-derivatives of the calculated nonlinear charge at each port of the device. By accurately modeling the voltagederivatives of the charge, where the voltages are functions of time, the prediction of the current produced by each of the charge sources is improved. The nonlinear models are verified against the MET model, and all three models are compared to measured data. It is shown that the models are able to accurately predict the single-tone and two-tone output harmonics for class-AB operation, and in many cases the predictions outperform that of the MET model. The single-tone output power is also verified for class-C operation. Although this prediction is not extremely accurate, it is found that the correct trend for the output harmonic power can be predicted.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This research project investigates the design, modelling and application of an open-air capacitive voltage sensor assembly for the measurement of wideband High Voltage signals on three-phase transmission lines. The advantages and disadvantages of conventional methods used to measure these voltages are reviewed and the advantages of the open-air capacitive sensor are established. The main research objective of this project involves extending the application of previously developed single-phase capacitive sensor topologies to three-phase applications. A three-phase set of mobile, compact and relatively inexpensive capacitive voltage sensors for open-air application under overhead transmission lines are designed and constructed, including a data acquisition triggering system for the measurement of transient waveforms. Equivalent circuit models, using a Thévenin equivalent approach, are developed for the three-phase sensor topology and the associated three-phase transmission line configuration. A number of different methods for simplifying the associated Thévenin equivalent impedance and voltage equations are evaluated. The decoupling of the voltage waveforms measured by the individual sensors for a three-phase transmission line configuration is subsequently examined with the view to derive mathematical relationships for determining the phase conductor voltages from the measured sensor voltages. The performance of the sensor assembly is experimentally evaluated under laboratory conditions as well as field conditions. An outdoor HV test facility, representing a scaled three-phase flat transmission line structure, is developed for evaluation of the three-phase sensor topology in a controlled environment. The methodology for decoupling the phase voltages and reconstructing the phase conductor voltages from the voltages induced on the sensors is evaluated using measured data obtained with this HV test facility. It is shown that the three-phase capacitive voltage sensor topology as applied in the test facility delivers good results for the measurement of three-phase transient voltage waveforms.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / Outside the confines of cities and metropolitan areas, telecommunications may still be required. Farmers may, for example, want to communicate with each other or with local municipality or law enforcement. Various factors may make the application of fixed infrastructure telecommunications networks to rural situations like these unfeasible. Fixed infrastructure may prove to be ineffective due to geographic, social or monetary reasons. Ad hoc networking seems like an intriguing solution to these elements of the rural telecommunications problem. Instead of using the client-server architecture approach, ad hoc networks use a peer-to-peer network architecture that allows the network to change in a more dynamic fashion. Hosts of such a network can join or leave the network dynamically and will share in the forwarding responsibility. Routing is done dynamically. Transceiver range is still an issue. To counteract this problem satellites can be used to extend the communications range of a network. Communication with a satellite can be added by using gateway hosts that are equipped to establish satellite up- or downlinks. Even if one such gateway host is deactivated, ad hoc network hosts should be able to find alternative gateways (if such alternative gateways exist). For this thesis, various MAC and Network protocols will be evaluated. One protocol set will be selected and adapted to a low-bandwidth situation. Cross layer design will be used in an attempt to decrease overhead of this strategy. A simulation model was devised to predict system performance. These simulations was followed by interpretation of results which rendered a theoretical basis with which network behaviour can be explained and even predicted. A tool-like framework has, in effect, been developed for the simulation and development of ad hoc network protocols. Novel approaches to protocol behaviour analysis have also been devised.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This project was initiated by ARMSCOR to research the feasibility of an unmanned aerial vehicle launching from and landing on a South African Navy ship. The objective of this project was to develop a strong basis for other similar projects.

Thesis (MScIng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Primary health care telemedicine services require the acquisition and transmission of patient data including high quality still and video images via telecommunication networks. The objective of this thesis is to investigate the implementation of a generalpurpose medical camera as an alternative to the complex and costly CCD based cameras generally in use at present. The design is based on FillFactory’s SXGA (1280 ×1024) CMOS image sensor. A low-cost Altera Cyclone FPGA is used for signal interfacing, filtering and colour processing to enhance image quality. A Cypress USB 2.0 interface chip is employed to isochronously transfer video data up to a maximum rate of 23.04 MBytes per second to the PC. A detailed design and video image results are presented and discussed; however the camera will need repackaging and an approval for medical application by medical specialists and concerned bodies before releasing it as full-fledged product. / AFRIKAANSE OPSOMMING: Primêre gesondheidssorg telemedisyne dienste moet hoëkwaliteit televisiebeelde van hul pasiënte verkry deur van telekommunikasienetwerke gebruik te maak. Die doel van hierdie tesis is om die toepassing van n meerdoelige mediese kamera te ondersoek as n alternatief tot duur, komplekse CCD-gebaseerde kameras wat huidiglik gebruik word. Die ontwerp is gebaseer op n hoëkwaliteit CMOS beeldsensor. n Goedkoop Altera Cyclone FPGA word gebruik vir seinkoppelvlak, filtering en kleurprosessering om die kwaliteit van die beeld te verhoog. n Hoëspoed USB 2.0 poort word gebruik om die data teen die nodige spoed te versend. n Gedetailleerde ontwerp, en die beeldresultate word voorgelê en bespreek. Die kamera moet egter eers deur mediese spesialiste en relevante beheerliggame goedgekeur word voordat dit as n volledige produk vrygestel kan word.