No abstract / Thesis (M.Sc.-Electronic Engineering)-University of Natal, 1992.

This dissertation investigates the role that is played by high temperatures of air gaps on the breakdown voltage levels under DC positive and negative polarity applied voltages. Due to past experience of AC transmission lines tripping as a result of sugar-cane fires that occur under these lines during cultivation seasons, this study was initiated to investigate this effect under DC applied voltages. Results were obtained from laboratory work conducted and these were closely analysed to understand the behaviour of air gaps under these conditions. A 17mm2 square-cut brass rodrod electrode configuration was used to carry out these tests at the various air gap temperatures. These were induced by a gas burner for both the positive and negative polarities at 200C – 3000C for the 10 mm – 150 mm air gap range and 200C – 1500C for the 200 mm – 500 mm air gap range. Later particles were introduced into the air gap to determine the subsequent behaviour. These were introduced vertically from the top into an air gap via a vibrating micro sieve mechanism to regulate the consistency of the introduction of these particles in the air gap. A reduction of 55% and 50% was observed on the breakdown voltage under positive and negative polarity applied voltages respectively from ambient conditions to 3000C. Additionally the breakdown behaviour of both negative and positive DC was found to be linear which is similar to the AC case. However, air gaps subjected to positive DC applied voltages were found to portray an inferior dielectric strength as opposed to the equivalent negative DC polarity. The study found that the effect of particles in the air gap is practically negligible and that for practical purposes, only the temperature effect plays a role due to the reduced air density at high temperatures. Empirical models for both the positive and negative DC polarities have been proposed by the study that incorporate the effect of the temperature in the air gap to enable the determination or prediction of the breakdown voltage level at various temperatures. These models may be utilised for DC transmission line design for servitudes in areas that are known to be prone to fires. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Solar photovoltaic (PV) systems are distributed energy sources that are an environmentally friendly and renewable source of energy. However, solar PV power fluctuates due to variations in radiation and temperature levels. Furthermore, when the solar panel is directly connected to the load, the power that is delivered is not optimal. A maximum peak power point tracker is therefore necessary for maximum efficiency. A complete PV system equipped maximum power point tracking (MPPT) system includes a solar panel, MPPT algorithm, and a DC-DC converter topology. Each subsystem is modeled and simulated in a Matlab/Simulink environment; then the whole PV system is combined with the battery load to assess the overall performance when subjected to varying weather conditions. A PV panel model of moderate complexity based on the Shockley diode equation is used to predict the electrical characteristics of the cell with regard to changes in the atmospheric parameter of irradiance and temperature. In this dissertation, five MPPT algorithms are written in Matlab m-files and investigated via simulations. The standard Perturb and Observe (PO) algorithm along with its two improved versions and the conventional Incremental Conductance (IC) algorithm, also with its two-stage improved version, are assessed under different atmospheric operating conditions. An efficient two-mode MPPT algorithm combining the incremental conductance and the modified constant voltage methods is selected from the five ones as the best model, because it provides the highest tracking efficiencies in both sunny and cloudy weather conditions when compared to other MPPT algorithms. A DC-DC converter topology and interface study between the panel and the battery load is performed. This includes the steady state and dynamic analysis of buck and boost converters and allows the researcher to choose the appropriate chopper for the current PV system. Frequency responses using the state space averaged model are obtained for both converters. They are displayed with the help of Bode and root locus methods based on their respective transfer functions. Following the simulated results displayed in Matlab environment for both choppers, an appropriate converter is selected and implemented in the present PV system. The chosen chopper is then modeled using the Simulink Power Systems toolbox and validates the design specifications. The simulated results of the complete PV system show that the performances of the PV panel using the improved two-stage MPPT algorithm provides better steady state and fast transient characteristics when compared with the conventional incremental conductance method. It yields not only a reduction in convergence time to track the maximum power point MPP, but also a significant reduction in power fluctuations around the MPP when subjected to slow and rapid solar irradiance changes. / Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2011.

This research work deals with the application of the phase shifting transformer in improving the steady state performance and voltage stability of transmission network that has transmission lines at different voltage levels running in parallel to each other. Transmission power system networks are usually developed using lines built at a certain voltage level initially. As power demand requirements increase, building of the new lines at the same voltage level becomes necessary. However, lesser and lesser improvements in transfer capacity are realised when the additional lines are built. This prompts utilities to consider higher voltages for future lines as these have a higher transfer capacity. Utilities usually lay, i.e., they build in parallel, newer, higher voltage transmission lines along side the existing lower voltage ones. Power flow in power system is mainly influenced by impedances of equipment. If the combined impedance of the existing, lower voltage transmission system is relatively less than the impedance of the newer, higher voltage ones, power may primarily flow through it rather than via the newer, parallel higher voltage transmission network. This may lead to a serious underutilisation of the newer infrastructure with a higher transmission capacity. Transmission networks similar to the one described above are common throughout the world. This study was undertaken towards finding solutions to the problem of under utilisation of such transmission lines. The study was performed by first reviewing the literature on the use of phase shifting transformers to redirect power flow in transmission networks throughout the world. This was followed by analysis of the theory on how and what determines the power flow in power networks. Several simulations of varying the phase of the phase shifting transformer were performed on the Cape network, as a case study, to investigate the impact on the power flow distribution and voltage stability performance of the 765 kV and 400 kV transmission lines carrying power to the Western Cape. In this dissertation, it has been demonstrated that a phase shifting transformer can be used to alter the power flow patterns so that power flows are restructured or redistributed, such that power which originally flowed via the low impedance, lower voltage system is transferred to the parallel higher voltage transmission system of lines. It is shown that once the power flows are redistributed, steady state and voltage stability performance of the total system can be enhanced and an increase in its power transfer capacity can be realised. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Wireless sensor networks are battery operated computing and sensing devices that collaborate to achieve a common goal for a specific application. They are formed by a cluster of sensor nodes where each sensor node is composed of a single chip with embedded memory (microprocessor), a transceiver for transmission and reception (resulting in the most energy consumption), a sensor device for event detection and a power source to keep the node alive. Due to the environmental nature of their application, it is not feasible to change or charge the power source once a sensor node is deployed. The main design objective in WSNs (Wireless Sensor Networks) is to define effective and efficient strategies to conserve energy for the nodes in the network. With regard to the transceiver, the highest consumer of energy in a sensor node, the factors contributing to energy consumption in wireless sensor networks include idle listening, where nodes keep listening on the channel with no data to receive; ovehearing, where nodes hears or intercept data that is meant for a different node; and collision, which occurs at the sink node when it receives data from different nodes at the same time. These factors all arise during transmission or reception of data in the Transceiver module in wireless sensor networks. A MAC (Medium Access Control) protocol is one of the techniques that enables successful operation while minimizing the energy consumption in the network. Its task is to avoid collision, reduce overhearing and to reduce idle listening by properly managing the state of each node in the network. The aim, when designing a MAC protocol for WSNs is to achieve a balance amongst minimum energy consumption, minimum latency, maximum fault-tolerance and providing QoS (Quality of Service). To carefully achieve this balance, this dissertation has proposed, designed, simulated and analyzed a new cooperative MAC scheme with an overhearing avoidance technique with the aim of minimizing energy consumption by attempting to minimize the overhearing in the WSN. The new MAC protocol for WSNs supports the cooperative diversity and overhearing communications in order to reduce the effects of energy consumption thus increase the network lifetime, providing improved communication reliability and further mitigating the effects of multipath fading in WSNs. The MAC scheme in this work focuses on cooperation with overhearing avoidance and reducing transmissions in case of link failures in order to minimize energy consumption. The cooperative MAC scheme presented herein uses the standard IEEE 802.15.4 scheme as its base physical model. It introduces cooperation, overhearing avoidance, receiver based relay node selection and a Markov-based channel state estimation. The performance analysis of the developed Energy Efficient Distributed Receiver based MAC (E2DRCMAC) protocol for WSNs shows an improvement from the standard IEEE 802.15.4 MAC layer with regard to the energy consumption, throughput, reliability of message delivery, bit error rates, system capacity, packet delay, packet error rates, and packet delivery ratios. / M.Sc.Eng. University of KwaZulu-Natal, Durban 2013.

Thesis (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The main aim of this research programme was to compare the relative performance of different insulator materials used in South Africa when subjected to a severe marine pollution environment. A test programme and procedure, test facility and instrumentation were established. Some novel instrumentation and monitoring equipment were developed and built specifically for this research programme, supported by data analysing software programs. In order to compare material performance only, all non-material design variables between the test insulators had to be removed (e.g. creepage distance, connecting length, inter-shed spacing, profile, etc.). To achieve this some of the test insulators had to be specially manufactured. Leakage current, electrical discharge activity, climatic and environmental data was collected successfully over a one-year test period, starting with new test insulators. The peak and energy values of the leakage current were identified as the two main parameters needed to describe the leakage current activity on the test insulators. A correlation was found between the climatic and environmental data and the leakage current data, and it was found that the leakage current can be determined successfully from some of the climatic and environmental parameters monitored by using multiple regression techniques. Surface conductivity and energy were found to be the best parameters to show the maximum and continuous interaction of the insulator material surface with the electrolytic pollution layer. A natural ageing and pollution test procedure was developed, which has become a South African standard and is gaining international acceptance. A model and hypothesis are proposed to describe the electrical discharge activity that takes place on the test insulators and explain the difference in leakage current performance of the various materials. Keywords: Insulator, Pollution, High Voltage, Leakage current, Material performance. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie navorsingsprogram was om die relatiewe prestasie van verskillende isolatormateriale wat in Suid-Afrika gebruik word te vergelyk in 'n swaar besoedelde marine omgewing. 'n Toetsprogram en prosedure, toets fasiliteit en instrumentasie is gevestig. 'n Paar nuwe instrumente en moniteer toerusting is ontwikkel en gebou spesifiek vir hierdie navorsingsprogram, gesteun deur data analise sagteware programme. Ten einde slegs materiaalprestasie te vergelyk, moes alle nie-materiaal ontwerpsveranderlikes tussen die toetsisolators verwyder word (bv. kruipafstand, konnekteer lengte, tussen-skerm spasiëring, profiel, ens.). Om dit reg te kry moes sommige van die toetsisolators spesiaal vervaardig word. Lekstroom, elektriese ontladingsaktiwiteit, klimaat en omgewingsdata is suksesvol versameloor 'n een-jaar toetsperiode, beginnende met nuwe toets isolators. Die piek en energie waardes van die lekstroom is identifiseer as die twee hoof parameters wat nodig is om die lekstroomaktiwiteit op die toetsisolators te beskryf. 'n Korrelasie is gevind tussen die klimaat- en omgewingsdata en die lekstroom data, en dit is gevind dat die lekstroom data suksesvol bepaal kan word van sekere van die klimaat- en omgewingsparameters wat gemoniteer is deur veelvoudige regressie tegnieke te gebruik. Oppervlakskonduktiwiteit en energie is gevind die beste parameters te wees om die maksimum en kontinue interaksie van die isolatormateriaaloppervlak met die elektrolitiese besoedelingslaag aan te toon. 'n Natuurlike veroudering en besoedeling toetsprosedure is ontwikkel, wat 'n Suid-Afrikaanse standaard geword het en besig is om internastionale aanvaarding te wen. 'n Model en hipotese word voorgestelom die elektriese ontladingsaktiwiteit wat op die toetsisolators plaasvind te beskryf en om die verskil in lekstroomprestasie van die verskeie materiale te verduidelik. S/eufelwoorde: Isolator, Besoedeling, Hoog Spanning, Leek stroom, Materiaal prestasie.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: This thesis covers the development of a multilevel cascaded inverter for the purpose of costeffective transformerless series dip compensation. Of all known power quality problems, voltage dips are the greatest reason for concern. Dips/sags occur more frequently than outages and therefore tend to be more costly for industry as modem technical equipment becomes all the more sensitive to the quality and reliability of supply. A number of devices already exist to compensate for this problem, but the cost of most of these systems does not always justify the financial losses they compensate for. All of these systems are using transformers and/or large filter components that contribute to the size, price and losses to quite a large extent. Series injection dip compensators offer the advantage of only having to compensate for the decrease in supply voltage during a dip. This results in a significant reduction in the converter ratings and energy storage requirements compared to conventional uninterruptible power supplies or shunt injection power quality devices. Existing inverter topologies, including multilevel inverters, were therefore studied and compared as possible solutions for cost-effective transformerless series dip compensation. On the basis of these considerations the multilevel cascaded inverter seems to be the most cost-effective option. The relatively low harmonic content of its unfiltered output also eliminates the need for a large output filter. A single-phase dip compensator, with this topology, was designed and built according to specifications stated by Eskom, the main utility in South Africa. Batteries as energy storage and automotive MOSFETs as switching components, proved to be most cost-effective options for the specified power ratings. Control algorithms for dip compensation with the multilevel inverter were also developed. Some of these algorithms are based on existing techniques, but two new algorithms were also developed to implement force commutation of the thyristors and to share the power dissipation in the dip compensator. Simulations indicated that these algorithms could be suitable and sufficient for their application. This dip compensator with its control algorithms was tested with a dip generator, developed at the University of Stellenbosch, for different types of loads. The experimental results confirmed the simulations and showed a very good performance for the specified conditions. An optimised design of this dip compensator will make it a cost-effective solution for dip compensation. / AFRIKAANSE OPSOMMING: Hierdie tesis dek die ontwikkeling van 'n multivlakwisselrigter, in kaskade, met koste-effektiewe transformatorlose duik kompensasie as mikpunt. Van al die bekende toevoerkwaliteit probleme wek duike in die spanning die meeste kommer. Duike kom meer gereeld voor as kragonderbrekings en neig daarom om 'n groter onkoste te wees vir die industrie soos wat moderne tegnologiese toerusting al hoe meer sensitief raak vir die kwaliteit en betroubaarheid van die toevoer. 'n Aantal toestelle wat vir hierdie probleem kompenseer bestaan reeds, maar die koste van hierdie stelsels regverdig nie altyd die finansiële verliese wat hulle moet elimineer nie. Al hierdie stelsels gebruik transformators en/of groot filter komponente wat grootliks bydra tot die grootte, prys en verliese van hierdie stelsels. Serie-injeksie kompenseerders het die voordeel dat hulle net kompenseer vir die verlies in die toevoerspanning tydens die duik. Dit het 'n beduidende vermindering in die omsetterkenwaardes en energiestoorvereistes tot gevolg in vergelyking met ononderbroke kragbronne (UPS) of newe-injeksie toevoerkwaliteit toestelle. Daarom IS bestaande wisselrigtertopologië, insluitende multivlakwisselrigters, bestudeer en vergelyk as moontlike oplossings vir koste-effektiewe serie duik-kompensasie. Van al hierdie moontlikhede lyk die multivlakwisselrigter, in kaskade, na die mees koste-effektiewe opsie. Die relatiewe lae harmoniese inhoud van sy ongefilterde uittree elimineer die behoefte aan 'n groot uittreefilter. 'n Enkelfase duik kompenseerder, met hierdie topologie, is ontwerp en gebou volgens die spesifikasies wat vasgestel is deur Eskom, die hoof elektriese kragvoorsiener in Suid-Afrika. Dit het geblyk dat batterye, en MOSFETte uit die motorbedryf, die mees koste-effektiewe opsies bied vir onderskeidelik die energiestoor en skakelkomponente. Beheeralgoritmes VIr duik kompensasie met die multivlakwisselrigter is ook ontwikkel. Sommige van hierdie algoritmes is gebaseer op bestaande tegnieke, maar twee nuwe algoritmes is ook ontwikkel vir die kommutering van die tiristors en die deling van die drywingsverkwisting in die duik kompenseerder. Simulasies dui aan dat hierdie algoritmes geskik en voldoende kan wees vir hulle toepassing. Hierdie duik kompenseerder met sy beheeralgoritmes is getoets vir verskillende tipes laste met 'n duikgenerator wat ontwikkel is by die Universiteit van Stellenbosch. Die eksperimentele resultate bevestig dit wat verkry is uit die simulasies en wys 'n goeie werkverrigting vir die gespesifiseerde kondisies. 'n Geoptimeerde ontwerp van hierdie duik kompenseerder sal dit 'n koste-effektiewe oplossing maak vir duik kompensasie.

Thesis (MSc (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Knowledge of the magnetic fields in the domain of electrical machines is required in order to model machines accurately. It is difficult to solve these fields analytically because of the complex geometries of electrical machines and the non-linear characteristics of the materials used to build them. Thus, finite element analysis, which can be used to solve the magnetic field accurately, plays an important part in the design of electrical machines. When designing electrical machines, the task of finding an optimal design is not simple because the performance of the machine has a non-linear dependence on many variables. In these circumstances, numerical optimisation using finite element analysis is the most powerful method of finding optimal designs. In this thesis, the work of improving an existing finite element simulation package, formerly known as the Cambridge package among its users, and the use of this package in the optimisation of electrical machine designs, is presented. The work involved restructuring the original package, expanding its capabilities and coupling it to numerical optimisers. The developed finite element package has been dubbed SEMFEM: the Stellenbosch Electrical Machines Finite Element Method. The Cambridge package employed the air-gap element method, first proposed by Razek et. al. [2], to solve the magnetic field for different positions of the moving component in a time-stepped finite element simulation. Because many new machine topologies have more than one air-gap, the ability to model machines with multiple air-gaps is important. The Cambridge package was not capable of this, but during the course of this work, the ability to model machines with multiple air-gaps using the air-gap element method was implemented. Many linear electrical machines have tubular, axisymmetric topologies. The functionality to simulate these machines was newly implemented because the original program was not capable of analysing these machines. Amongst other things, this involved the derivation of the coefficients of an axisymmetric air-gap element’s stiffness matrix. This derivation, along with the original air-gap element derived by Razek et. al. [2] and the extension of the method to the Cartesian coordinate system by Wang et. al. [29, 30], completes the derivation of all two-dimensional air-gap elements. In order to speed the numerical optimisation process, which is computationally expensive, parallelisation was introduced in two areas: at the level of the finite element simulation and at the level of the optimisation program. The final product is a more powerful, more usable package, geared for the optimisation of electrical machines. / AFRIKAANSE OPSOMMING: Kennis van die magnetiese velde in die gebied van elektriese masjiene word benodig om masjiene akkuraat te modelleer. Dit is moeilik om hierdie velde analities op te los as gevolg die komplekse geometrieë van elektriese masjiene en die nie-lineêre karakteristieke van die materiale wat gebruik word om hulle te bou. Dus speel eindige element analise ’n belangrike rol in die ontwerp van elektriese masjiene omdat dit gebruik kan word om die magnetiese veld akkuraat te bepaal. Wanneer elektriese masjiene ontwerp word, is dit nie ’n eenvoudige taak om ’n optimale ontwerp te vind nie omdat die werkverrigting van die masjien nie-lineêr afhanklik is van baie veranderlikes. Onder hierdie omstandighede is numeriese optimering, tesame met eindige element analise, die kragtigste metode om optimale ontwerpe te vind. In hierdie tesis word die verbetering van ’n bestaande eindige element simulasie pakket, wat onder gebruikers van die pakket as die Cambridge pakket bekend staan, en die gebruik van hierdie pakket vir die optimering van elektriese masjiene, voorgelê. Die werk het die herstrukturering van die oorspronklike pakket, die uitbreiding van die pakket se vermoëns en die koppeling van die pakket aan numeriese optimeerders behels. Die ontwikkelde eindige element pakket word SEMFEM genoem: die Stellenbosch Elektriese Masjiene Finite Element Method. Die Cambridge pakket het van die lugspleet element metode, soos oorspronlik deur Razek et. al. [2] voorgestel, gebruik gemaak om die magnetiese veld vir verskillende posisies van die bewegende komponent in ’n tyd-stapsgewyse eindige element simulasie op te los. Omdat baie nuwe masjien topologieë meer as een lugspleet het, is die vermoë om masjiene met meer as een lugspleet te kan modelleer belangrik. Die Cambridge pakket was nie hier toe in staat nie, maar die vermoë om masjiene met meervoudige lugsplete te modelleer is gedurende hierdie werk geïmplementeer. Baie lineêre masjiene het tubulêre, assimmetriese topologieë. Die funksionaliteit om hierdie masjiene te simuleer is nuut geïmplementeer omdat die oorspronlike program nie in staat was om hierdie masjiene te analiseer nie. Dit het onder andere behels dat die koeffisiënte van ’n assimmetriese lugspleetelement se styfheidsmatriks afgelei moes word. Hierdie afleiding, tesame met die oorspronlike lugspleetelement afgelei deur Razek et. al. [2] en die uitbreiding na die Cartesiese koördinaatstelsel deur Wang et. al. [29, 30], voltooi die afleiding van alle twee-dimensionele lugspleet elemente. Om die numeriese optimeringsproses, wat tipies tydsgewys duur is, te versnel, is parallellisering op twee vlakke ingebring: op die vlak van die eindige element simulasie en op die vlak van die optimeringsprogram. Die finale produk is ’n kragtiger, meer bruikbare pakket, goed aangepas vir die optimering van elektriese masjiene.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In this study a new type of gearless, direct-drive wind generator, which can be connected directly to the grid, is proposed. The working characteristics of this generator are based upon the principles of the permanent magnet induction generator (PMIG). By omitting the need for a gearbox and power electronic converter this generator type has several advantages regarding cost and reliability. Although the PMIG is proposed in previous studies as favourable for wind power generation, the mechanical complexity and difficult construction associated with these types of generators, seems to be the main reason why these generator systems are not used. The design methods presented in this study are intended to alleviate these constructional issues by proposing the split-PMIG (S-PMIG), where the stator winding and the induction cage-rotor windings are electromagnetically separated. The machine is basically split into two permanent magnet (PM) machines, a grid connected synchronous generator (SG) unit and a turbine connected induction generator (IG) unit. These two units are mechanically linked by a common PM-rotor. To evaluate this concept a finite element (FE) design analysis is done independently for both machine components. The emphasis of the design optimisation is the minimisation of the cogging torque, while still having a decent performing, easily constructible generator. This generator should also have low load ripple content. Cogging torque can result in the failure of the turbine to start up, especially at low wind speeds. As this is a directly grid connected generator, torque ripple transferred to the common PM-rotor can destabilise the generator. Based upon the FE designs a preliminary S-PMIG system is constructed and practically evaluated. Due to the modular nature of the design it is possible to implement the synchronous generator part of the S-PMIG in conjunction with a grid-connected solid state converter (SSC). This allows for a useful comparison with the S-PMIG system. Promising results are obtained from initial tests of the S-PMIG directly connected to the grid. It is shown that the operation of this generator is stable under a wide range of wind load conditions. However, some important machine design issues are identified from these practical results, which could prove vital in the implementation of future S-PMIG designs. / AFRIKAANSE OPSOMMING: In hierdie studie word 'n nuwe ratkaslose direk-aangedrewe wind generator voorgestel, wat direk aan die krag netwerk gekoppel kan word. Hierdie generator is gebaseer op die beginsels waarop permanente magneet induksie generators (PMIG’s) werk. Deur die ratkas en drywings-elektroniese omsetter uit te laat, het hierdie generator verskeie voordele rakende koste en betroubaarheid. Alhoewel vorige studies hierdie generator voorstel as 'n belowende opsie vir gebruik in wind-energie-stelsels, lyk dit of die meganiese kompleksiteit en moeilike konstruksie die hoof rede is hoekom hierdie generator stelsels tans nie gebruik word nie. Die ontwerpsmetodes wat in hierdie studie voorgestel word poog om die genoemde konstruksie probleme op te los deur die gesplete-PMIG (S-PMIG), waar die stator wikkelings en die induksie masjien kou-rotor wikkelings elektromagneties ontkoppel is, voor te stel. Hierdie masjien is basies verdeel in twee permanente magneet (PM) masjiene, 'n netwerk gekoppelde sinchroongenerator (SG) eenheid en 'n turbine gekoppelde induksie generator (IG) eenheid. Hierdie twee eenhede word gekoppel deur 'n gemeenskaplike PM-rotor. Om hierdie konsep te evalueer word eindige element analise onafhanklik vir beide masjiene gedoen. Die fokus van die ontwerp optimering is die minimalisering van die vertandingsdraaimoment, terwyl die generator steeds goed presteer en maklik is om te vervaardig. Vertandingsdraaimoment kan tot die gevolg hê dat die turbine versuim om te begin draai, veral by lae windsnelhede. Dit is ook belangrik dat die generator 'n lae rimpel inhoud onder las bevat. Omrede hierdie generator direk aan die netwerk gekoppel is, kan draaimoment pulsasies, oorgedra aan die gemeenskaplike PM-rotor, die masjien destabiliseer. Gebaseer op die eindige element ontwerpe, is 'n voorlopige gesplete-PMIG gebou en prakties geëvalueer. As gevolg van die modulêre struktuur van die ontwerp, is dit moontlik om die SG gedeelte van die gesplete- PMIG saam met 'n drywings-elektroniese omsetter te implementeer. Dit laat toe vir 'n nuttige vergelyk tussen die twee stelsels. Belowende eerste toets resultate is verkry van die gesplete-PMIG direk gekoppel aan die netwerk. Daar word gewys dat hierdie generator stabiel oor 'n wye operasionele gebied kan funksioneer. Verskeie belangrike masjien ontwerpsfaktore word ook uitgelig met die praktiese evaluering van die gesplete-PMIG. Hierdie faktore kan uiters belangrik wees in die ontwerp en implementering van toekomstige gesplete-PMIG stelsels. / Sponsored by the Centre for Renewable and Sustainable Energy Studies

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The slip synchronous permanent magnet generator (SSG) is a direct-driven direct-grid connected generator developed to alleviate the need for expensive gearboxes and solid-state power converters on wind turbine generators. This study identifies certain key areas where the current wind turbine generator (WTG) system does not comply with the grid code for wind energy facilities (WEF) as specified by the National Energy Regulator of South Africa. The current WTG system does not have a reactive power compensation device. The main focus in this study is the development of an on-load tap changer (OLTC) transformer to control the terminal voltage of the generator. By controlling the terminal voltage of the generator the excitation-mode of the SSG can be changed allowing for control over the reactive power output of the SSG. An OLTC transformer utilising a solid-state assisted mechanical diverter circuit is built and tested to determine the viability of using an OLTC as a reactive power control device. Practical test results show that the OLTC can successfully control the terminal voltage of the SSG without interrupting the load current. The required accuracy regarding power factor control capability was not met due to the large change in reactive power output per tap change operation. A method of using small shunt capacitor banks to provide additional reactive power in between consecutive tap changes is evaluated in simulation. Simulation results show that the addition of these small shunt capacitor banks dramatically improves the reactive power control accuracy. Additionally the grid code specifies that a WEF must have the ability to curtail the active power output during frequency disturbances. The effects of frequency disturbances on the SSG output is simulated and it was found that the SSG will comply with the minimum connection requirements as specified in the grid code. A method of using an IGBT switched DC load to limit the active power output of the WEF is developed and simulated. From the simulation results it was found that the proposed active power curtailment device will meet the minimum power curtailment response time requirements as specified in the grid code. / AFRIKAANSE OPSOMMING: Die glip sinchroon permanente magneet generator (SSG) is ʼn direkte dryf, direkte netwerk gekoppelde wind generator wat ontwikkel is om behoefte aan duur ratkaste en drywing elektroniese omsetters te verlig. Hierdie studie identifiseer sekere sleutel areas waar die huidige wind generator opstelling nie aan die netwerk kode spesifikasie soos uiteengesit deur die Nasionale Energie Reguleerder van Suid-Afrika voldoen nie. Die wind turbine generator stelsel beskik nie oor ʼn reaktiewe drywing beheer meganisme nie. Die belangrikste fokus in hierdie studie is die ontwikkeling van ʼn transformator tap wisselaar wat gebruik sal word om die generator se terminale spanning te beheer. Deur die terminaal spanning te beheer kan die opwekking modus van die generator verander word om dan die uittree reaktiewe drywing te beheer. ʼn Tap wisselaar wat gebruik maak van ʼn drywingelektronies gesteunde meganiese skakelaar is ontwikkel en getoets om die lewensvatbaarheid van die tegniek te ondersoek. Praktiese toets resultate toon dat die tap wisselaar suksesvol beheer oor die generator se terminaal spanning kon uitvoer, sonder om die las-stroom te onderbreuk. Ongelukkig is die vereiste akkuraatheid ten opsigte van die reaktiewe drywing beheer nie gehaal nie. Die rede hiervoor is dat die verandering in uittree reaktiewe drywing baie groot is vir opeenvolgende tap verstellings. ʼn Metode waar twee klein kapasitor banke geskakel word om reaktiewe drywing te lewer, tussen opeenvolgende tap veranderinge, is deur middel van simulasie ondersoek. Die simulasie resultate toon aan dat die toevoeging van die kapasitors ʼn drastiese verbetering in die beheerbaarheid van die uittree reaktiewe drywing het. Verder spesifiseer die netwerk kode ook dat ʼn wind plaas oor die vermoë moet beskik om die aktiewe drywing te verminder tydens ʼn netwerk frekwensie versteuring. Die effek wat ʼn frekwensie versteuring op die SSG het, is deur middel van simulasie ondersoek en daar is gevind dat die SSG aan die netwerk verbinding spesifikasie sal voldoen. ʼn Metode waarby ʼn IGBT geskakelde GS las gebruik word om die aktiewe drywing van die wind generator te beperk is ondersoek en gesimuleer. Vanaf die simulasie resultate is daar gevind dat die drywing beperkings toestel aan die minimum drywing en reaksie tyd spesifikasies soos vereis sal voldoen.