Thesis (MEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: This thesis describes the development of a distributed ground support system to be used in the small satellite program at the University of Stellenbosch. A literature study was done to determine the current trends in ground support design. These trends are presented together with an analysis of the SUNSAT groundstation software. New technologies in the field of distributed systems are discussed and used in the design of a distributed ground support system. The design centres around a servicesbased architecture where services are distributed on the network. The design is evaluated according to attributes exhibited by effective distributed systems. Certain services were implemented to demonstrate the feasibility of the design. The implementations are discussed and suggestions are made for future improvements and fields of possible further study. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwikkeling van 'n verspreide-grondstasie-sisteem vir gebruik in die Universiteit van Stellenbosch se satelliet-program. Eerstens is 'n literatuurstudie gedoen om die huidige verwikkelinge in die veld van satellietondersteuning-ontwikkeling vas te stel. Hierdie verwikkelinge word bespreek en gebruik om die SUNSAT-grondstasie sagteware te evalueer. Nuwe tegnologieë in die veld van verspreide stelsels word ondersoek en bespreek. Die ontwerp van die grondstasie is gebaseer op 'n verspreide dienste argitektuur. Die ontwerp word beskryf en geëvalueer aan die hand van kenmerke tipies van 'n effektiewe verspreide stelsel. Om die werkbaarheid van die ontwerp te toon, is sekere van die dienste geïmplimenteer, en die funksionering daarvan word bespreek. Voorstelle word ook gemaak oor moontlike toekomstige navorsing wat gedoen kan word.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: After SUNSAT was launched in 1999 and the possibility of developing another micro satellite emerged, areas of possible improvement were identified. Among the suggestions that emerged was the idea of developing an on-board computer for a micro satellite, using one of the new generation low power processors. The processor had to meet guideline specifications derived from the experience gained by researchers and students involved with the SUNSAT project. This thesis covers the process of choosing one of these processors and the subsequent testing of the feasibility of using it in an on-board computer. The feasibility test included comparing the processor's specifications to those required and designing an evaluation board for this processor to test its ease of use and programmability. / AFRIKAANSE OPSOMMING: Nadat SUNSAT in 1999 gelanseer is en die moontlikheid vir die ontwikkeling van In soortgelyke satellite ontstaan het, is areas vir verbetering op bestaande stelsels geidentifiseer. Die idee om In nuwe generasie verwerker met lae kragverbruik as In aanboord rekenaar te gebruik, was een moontlikheid wat ondersoek moes word. Die verwerker moes aan riglyne gemeet, word wat afgelei is uit die ondervinding wat deur navorsers en studente tydens die SUNSAT projek opgedoen is. Die tesis dek die proses wat gevolg is om In verwerker te kies en die daaropvolgende toetsing om die bruikbaarheid van die verwerker as In aanboord rekenaar te bepaal. As deel van die toetsing is die verwerker se spesifikasies teen die verlangde spesifikasies opgeweeg, en In evaluasiebord is ontwikkel om die gemaklikheid van die gebruik en programmering van die verwerker te bepaal.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The topic of microwave frequency discriminators is introduced. Various applications and implementation techniques of these devices are given and discussed. This thesis may serve as reference foundation for future research on this topic. Discriminators are developed at both S- and X-band, with high linearity and good sensitivity. The systems used to implement these devices are developed as well. The S-band discriminator is used in a direct FM demodulation system, which works well. / AFRIKAANSE OPSOMMING: Hierdie is 'n inleiding tot die onderwerp van mikrogolf frekwensie diskrimineerders. Verskeie toepassings en implementeringstegnieke van hierdie toestelle word genoem en bespreek. Hierdie tesis kan dien as verwysings-raamwerk vir toekomstige navorsing oor hierdie onderwerp. Diskrimineerders is ontwikkel by beide S- en X-band, met 'n goeie lineariteit en sensitiwiteit. Die stelsels wat gebruik word om hulle te implementeer, is ook ontwikkel. Die S-band diskrimineerder is gebruik in 'n direkte FM demodulasie sisteem en werk goed.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The bandwidth of standard HV measurement devices such as capacitive voltage transformers is too limited in order to measure wideband phenomena. This thesis is concerned with the investigation into a non- intrusive HV transient voltage measurement facility using standard substation HV current transformers (CI's) configured in a transconductance topology. The sensing, summation and integration of the CT capacitive earth currents are investigated. This thesis also reports on the development of a optically isolated link using optical fibre for signal transfer and a computer based data acquisition system. / AFRIKAANSE OPSOMMING: Standaard hoogspannings (HS) meettoerusting soos kapasitiewe spannmgs transformators het beperkte bandwydte vir die meet van wyeband verskynsels. Hierdie tesis handel oor die implementering van 'n HS meetstelsel wat op meinbrekende wyse oorgangsverskynsels meet deur middel van HS stroomtransformators wat in 'n transkonduktansie topologie gekonfigureer is. Die meet, sommasie en integrasie van kapasitoewe grondstrome word ondersoek. Hierdie tesis doen ook verslag aangaande die ontwikkeling van 'n optiese geisoleerde koppelvlak wat gebruik word vir seinoordrag en 'n rekenaar gebasseerde data versamelaar. / pdv201406

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This project relates to the unexplained failure of 33kV porcelain line post insulators in ESKOM's Southern Region. An initial investigation suggested that the failures could probably be due to a combination of internal manufacturing flaws and the effects of lightning. The failures all occurred in insulators based on a new design that uses a metal spindle for mechanical attachment to a power line structure embedded in the insulator base. This thesis investigates the non-destructive detection of internal flaws in porcelain line post insulators. The research was structured as follows: • The examination of the manufacturing process and materials used to determine the cause, location and nature of internal flaws. • An electrical field simulation study to verify whether a void in the sulphur cement will experience discharge activity when exposed to systeni nominal voltage or lightning potential. • The identification of non-destructive techniques (NDT) that are potentially viable for determining the presence of insulator internal flaws. • The design of NDT experiments for X-ray, partial discharge (PD) detection and ultrasonic testing. These experiments were evaluated for their effectiveness in determining the presence of internal flaws and their usefulness as a quality control measure in the insulator manufacturing process. The main findings are: The major cause of insulator internal flaws is the fast setting sulphur cement used for cementing the metal spindle (mechanical attachment) to the porcelain body of the insulator. The field simulation study shows that a discharge in a 3mm diameter spherical void on the insulator's axis of symmetry will occur if the insulator is exposed to lightning potential. High energy X-raying is an effective technique for exposing the location, nature, size and number of flaws in the insulator, but is impractical due to the high Xraying cost and over-utilisation of the only high energy X-ray facility in the RSA. The PD experiment was effective in revealing the presence of internal flaws, but the location, nature, size and number of flaws cannot be determined. The experiment is time consuming and is therefore not suitable for quality control in the insulator manufacturing process. A preliminary investigation into the suitability of ultrasonic testing techniques encountered major technical difficulties. Further investigation into the use of ultrasonic 3D imaging techniques is recommended. / AFRIKAANSE OPSOMMING: Hierdie projek hou verband met die onverklaarbare faling van 33kV porselein staaftipe isolators in ESKOM se Suidelike Streek. 'n Aanvanklike ondersoek het daarop gedui dat die falings veroorsaak is deur 'n kombinasie van interne vervaardigingsfoute en die effek van weerlig. Die falings het almal plaasgeving op isolators waarvan die vashegtingsbout direk in die porselein versink is. Die doel van hierdie navorsingsprojek is om nie-vernietigende toetsmetodes (NVT) te ondersoek, teneinde interne foute in die tipe isolators op te spoor. Die tesis is soos volg gestruktureer: • Die ondersoek van die vervaardigingsproses en die materiale wat gebruik word, ten einde die oorsaak, posisie en aard van hierdie foute vas te stel. • 'n Simulasie van die elektriese veld om vas te stelof 'n holte in die swaelsement ontladings salondervind onder die invloed van nominale spanning en weerlig. • Die indentifisering van nie-vernietignde toetsmetodes wat gebruik kan word om die teenwoordigheid van interne foute te bepaal. • Die ontwerp van NVT eksperimente vir X-straal, gedeeltelike ontlading ("PD") deteksie en ultrasoniese toetsing. Hierdie eksperimente is geëvalueer om hul effektiwiteit om die teenwoordigheid van interne foute vas te stel, asook hul nuttigheid as 'n kwaliteitsbeheermaatreël in die iso latorvervaardigingsproses. Die hoofbevindinge is: Die hoofoorsaak van die interne foute is die vinnig-stollende swael-sement wat gebruik word om die metaalinsetsel aan die porselein te heg. Die veldsimulasies het getoon dat 'n ontlading in 'n 3mm sferiese holte op die isolator se simmetrie-as sal plaasvind as die isolator aan weerligpotensiaal onderwerp word. Hoë-energie-X-strale is 'n effektiewe tegniek om die posisie, aard, grootte en aantal foute in die isolator vas te stel. Dit is egter onprakties as gevolg van die hoë koste en oorbenutting van die enigste hoë-energie-X-straal-fasiliteit in die RSA. Die ontladingsdeteksie eksperiment was effektief om die teenwoordigheid van interne foute aan te dui, maar die posisie, aard; grootte en getal foute kan nie bepaal word nie. Die eksperiment is tydrowend en is daarom nie geskik vir kwaliteitsbeheer van die isolatorvervaardigingsproses nie. 'n Voorlopige ondersoek na die geskiktheid van ultrasoniese toetsmetodes het groot tegniese stuikelblokke opgelewer. Verdere ondersoek van die gebruik van ultrasoniese 3D-beeldtegnieke word aanbeveel.

Thesis (MEng) -- University of Stellenbosch, 1991. / ENGLISH ABSTRACT: A two-dimensional Coupled Element Method (CEM) for solving electromagnetic scattering problems involving lossy, inhomogeneous, arbitrarily shaped cylinders, was investigated and implemented. The CEM uses the Finite Element Method (FEM) to approximate the fields in and around the scatterer and the Boundary Element Method (BEM) to approximate the far-field values. The basic CEM theory is explained using the special, static electric field problem involving the solution of Laplace's equation. This theory is expanded to incorporate scattering problems, involving the solution of the Helmholtz equation. This is done for linear as well as quadratic elements. Some of the important algorithms used to implement the CEM theory are discussed. Analytical solutions for a round, homogeneous- and one layer coated PC cylinder are discussed and obtained. The materials used in these analytical solutions can be lossy as well as chiral. The CEM is validated by comparing near- and far-field results to the analytical solution. A comparison between linear and quadratic elements is also made. The theory of the CEM is further expanded to incorporate scattering from chiral media / AFRIKAANSE OPSOMMING: 'n Gekoppelde Element Metode (GEM) wat elektromagnetiese weerkaatsingsprobleme, van verlieserige, nie-homogene, arbitrere voorwerpe kan oplos, is ondersoek en geimplimenteer. Die GEM gebruik die Eindige Element Metode (EEM) om die velde in en om die voorwerp te benader. 'n Grenselementmetode word gebruik om die vervelde te benader. Die basiese teorie van die GEM word verduidelik deur die toepassing daarvan op die spesiale geval van 'n statiese elektriese veld- probleem. Hierdie probleem verlang die oplossing van Laplace se vergelyking. Die teorie word uitgebrei om weerkaatsingsprobleme te kan hanteer. Die weerkaatsingsprobleme verlang die oplossing van 'n Helmholtz-vergelyking. Hierdie teorie word ontwikkel vir lineere sowel as kwadratiese elemente. Van die belangrike algoritmes wat gebruik is om die GEM-teorie te implimenteer, word bespreek. Analietise oplossings vir ronde, homogene en eenlaag bedekte perfek geleidende silinders word bespreek en verkry. Die material wat in die oplossings gebruik word, kan verlieserig of kiraal wees. Die GEM word bekragtig deur naby- en verveld resultate te vergelyk met ooreenkomstige aitalitiese oplossings. Die lineere en kwadratiese element- resultate word ook met mekaar vergelyk. Die GEM-teorie is verder uitgebrei sodat weerkaatsing vanaf kirale materiale ook hanteer kan word.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The aim of this study is to critically evaluate the voltage injection position sensorless control technique as applied to the reluctance synchronous machine (RSM) drive and to implement the technique on a 5.5 kW RSM and a 110 kW RSM. The technique is evaluated by using an accurate mathematical model of the RSM in a simulation package, called Simuwin. The negative effects that cross-magnetisation and the slotted air-gap have on the technique are intensively investigated. It was showed that these effects can cause an error in the position estimation of up to 30°. The TMS320F240 DSP was used as the controller for the RSM drives to implement the position sensorless control technique. Measurements on both RSM drives confirm the simulated results. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om die spannings-injeksie posisie sensorlose beheer tegniek soos toegepas op die reluktansie sinchroon masjien (RSM) aandryfstelsel, krities te evalueer en te implementeer op 'n 5.5 kW RSM en op 'n 110 kW RSM. Die tegniek is geevalueer deur 'n akkurate wiskundige model van die RSM saam te stel en die model te gebruik in 'n simulasie pakket, genaamd Simuwin. Daar is veral klem gele op die negatiewe invloed wat kruis-magnetisering en 'n gegleufde lug-spleet op die tegniek het. Dit is bewys dat hierdie eienskappe van die RSM 'n fout in die posisie afskatting van tot 30° kan veroorsaak. Die TMS320F240 DSP is gebruik as beheerder vir die RSM aandryfstelsels om sodoende posisie sensorlose beheer op altwee masjiene toe te pas. Metings op albei stelsels bevestig die simulasies.

The purpose with this project is to develop a model of the whole power system of Gotland in the power system simulation software PSS/E. A model of the whole power system of Gotland has earlier been used in the power system simulation software Simpow but now there is a need to develop a model in PSS/E. In the power system of Gotland there are several components that need to be modelled such as lines, loads, transformers, shunt impedances, synchronous machines, asynchronous machines, an HVDC Classic link and an HVDC Light link. These components are modelled in the Simpow model and needs to be converted to the PSS/E model. The aim is to develop a model in PSS/E that is as equal as possible to the model in Simpow. Especially the HVDC Light link at Gotland has been investigated in the project. A problem with converting data from Simpow to PSS/E is that the models of several components differ in Simpow and PSS/E. Lines and shunt impedances can be modelled in the same way but the models for loads, transformers, synchronous machines, asynchronous machines, the HVDC Classic link, and the HVDC Light link differ in Simpow and PSS/E. The models in Simpow are converted to the models in PSS/E in an as equal way as possible. The results in PSS/E are analyzed and compared with the Simpow model. In the project we have also made a test of fault simulations in time-domain simulations in PSS/E. The aim with this test is to verify the PSS/E calculations when a three-phase or a single-phase fault is applied. The reason for that is that PSS/E only calculates using positivesequence components and therefore only is able to calculate exact during circumstances of symmetrical loads and faults. The result shows that the calculations for both symmetrical and unsymmetrical faults in PSS/E are correct concerning the positive-sequence components. A drawback in PSS/E is, however, that we do not have any information concerning the negativeand zero-sequence  components, which results in that we cannot calculate the three phasequantities.

Thesis (PhD (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / A strategy for the design of an effective, practically feasible, robust, computationally efficient autopilot for three dimensional manoeuvre flight control of Unmanned Aerial Vehicles is presented. The core feature of the strategy is the design of attitude independent inner loop acceleration controllers. With these controllers implemented, the aircraft is reduced to a point mass with a steerable acceleration vector when viewed from an outer loop guidance perspective. Trajectory generation is also simplified with reference trajectories only required to be kinematically feasible. Robustness is achieved through uncertainty encapsulation and disturbance rejection at an acceleration level. The detailed design and associated analysis of the inner loop acceleration controllers is carried out for the case where the airflow incidence angles are small. For this case it is shown that under mild practically feasible conditions the inner loop dynamics decouple and become linear, thereby allowing the derivation of closed form pole placement solutions. Dimensional and normalised non-dimensional time variants of the inner loop controllers are designed and their respective advantages highlighted. Pole placement constraints that arise due to the typically weak non-minimum phase nature of aircraft dynamics are developed. A generic, aircraft independent guidance control algorithm, well suited for use with the inner loop acceleration controllers, is also presented. The guidance algorithm regulates the aircraft about a kinematically feasible reference trajectory. A number of fundamental basis trajectories are presented which are easily linkable to form complex three dimensional manoeuvres. Results from simulations with a number of different aircraft and reference trajectories illustrate the versatility and functionality of the autopilot. Key words: Aircraft control, Autonomous vehicles, UAV flight control, Acceleration control, Aircraft guidance, Trajectory tracking, Manoeuvre flight control.

Thesis (DEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / The Finite Element Method (FEM) as applied to Computational Electromagnetics (CEM), can beused to solve a large class of Electromagnetics problems with high accuracy and good computational efficiency. For solving wide-band problems time domain solutions are often preferred; while time domain FEM methods are feasible, the Finite Difference Time Domain (FDTD) method is more commonly applied. The FDTD is popular both for its efficiency and its simplicity. The efficiency of the FDTD stems from the fact that it is both explicit (i.e. no matrices need to be solved) and second order accurate in both time and space. The FDTD has limitations when dealing with certain geometrical shapes and when electrically large structures are analysed. The former limitation is caused by stair-casing in the geometrical modelling, the latter by accumulated dispersion error throughout the mesh. The FEM can be seen as a general mathematical framework describing families of concrete numerical method implementations; in fact the FDTD can be described as a particular FETD (Finite Element Time Domain) method. To date the most commonly described FETD CEM methods make use of unstructured, conforming meshes and implicit time stepping schemes. Such meshes deal well with complex geometries while implicit time stepping is required for practical numerical stability. Compared to the FDTD, these methods have the advantages of computational efficiency when dealing with complex geometries and the conceptually straight forward extension to higher orders of accuracy. On the downside, they are much more complicated to implement and less computationally efficient when dealing with regular geometries. The FDTD and implicit FETD have been combined in an implicit/explicit hybrid. By using the implicit FETD in regions of complex geometry and the FDTD elsewhere the advantages of both are combined. However, previous work only addressed mixed first order (i.e. second order accurate) methods. For electrically large problems or when very accurate solutions are required, higher order methods are attractive. In this thesis a novel higher order implicit/explicit FETD method of arbitrary order in space is presented. A higher order explicit FETD method is implemented using Gauss-Lobatto lumping on regular Cartesian hexahedra with central differencing in time applied to a coupled Maxwell’s equation FEM formulation. This can be seen as a spatially higher order generalisation of the FDTD. A convolution-free perfectly matched layer (PML) method is adapted from the FDTD literature to provide mesh termination. A curl conforming hybrid mesh allowing the interconnection of arbitrary order tetrahedra and hexahedra without using intermediate pyramidal or prismatic elements is presented. An unconditionally stable implicit FETD method is implemented using Newmark-Beta time integration and the standard curl-curl FEM formulation. The implicit/explicit hybrid is constructed on the hybrid hexahedral/tetrahedral mesh using the equivalence between the coupled Maxwell’s formulation with central differences and the Newmark-Beta method with Beta = 0 and the element-wise implicitness method. The accuracy and efficiency of this hybrid is numerically demonstrated using several test-problems.