Master of Science / Department of Electrical and Computer Engineering / Ruth Douglas Miller / This thesis presents the design of two models for permanent-magnet direct-drive wind turbines. The models are of a 10 kW and a 5 MW wind turbine, which are representative of residential scale and commercial scale turbines respectively. The models include aerodynamic and mechanical simulations through the FAST software, as well as concurrent electrical simulations through the SimPowerSystems toolbox for MATLAB/Simulink. The aim is to provide wind turbine designers and researchers with a comprehensive simulation tool that they can use to design and test many different aspects of a wind turbine. The particular novelty of these models is their high level of detail in electromechanical simulations. For each model, a generator speed controller was designed in a reference frame attached to the generator’s rotor, and was executed with a 3-phase active rectifier using space-vector pulse-width modulation. Also for each model, active and reactive power controllers were designed in a reference frame synchronous with the grid, and were executed with a 3-phase inverter using space-vector pulse-width modulation. Additionally, a blade pitch controller was designed for the 5 MW model. Validation of the models was carried out in the MATLAB/Simulink environment with satisfactory results.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This thesis investigates the viability of constructing a solid-state transformer (SST) with a series-input, parallel-output connection of full-bridge, three-level ying-capacitor converters. It focusses on the active recti er front-end of the SST which is used to control the input current to be sinusoidal and in-phase with the sinusoidal input voltage. A stack of two converters are built and tested. The input current, as well as the ying capacitor voltages of the two active recti ers in the stack, are actively controlled by a nite-state model-based predictive (FS-MPC) controller. The use of multiple ying-capacitor converters poses a problem when using FS-MPC because of the large number of possible switching states to include in the prediction equations. Three FS-MPC control algorithms are proposed to attempt to overcome the problem associated with the large number of switching states. They are implemented on an FPGA digital controller. The algorithms are compared on the bases of voltage and current errors, as well as their responses to disturbances that are introduced into the system. The simulation and experimental results that are presented shows that by interleaving the control actions for the two converters, one can obtain fast and robust responses of the controlled variables. The viability of extending the interleaving control algorithm beyond two converters is also motivated. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die moontlikheid van volbrug, drievlak vlieënde-kapasitoromsetters wat gebruik word om 'n serie-intree, parallel-uittree drywingselektroniese transformator (DET) te bou. Dit fokus op die aktiewe gelykrigter van die DET wat gebruik word om die intreestroom te beheer om sinusvormig en in fase met die sinusvormige intreespanning te wees. 'n Stapel van twee omsetters word gebou en getoets. Die intreestroom, sowel as die vlieënde kapasitorspannings van die twee aktiewe gelykrigters in die stapel, word aktief beheer met behulp van 'n eindige-toestand, model-gebaseerde voorspellende beheerder (ET-MVB). Die gebruik van veelvuldige vlieënde-kapasitoromsetters bemoeilik die implementering van 'n ET-MVB-beheerder as gevolg van die groot aantal skakeltoestande wat in die voorspellende vergelykings in ag geneem moet word. Drie ET-MVB-algoritmes word voorgestel om te poog om die probleme, wat met die groot aantal skakeltoestande geassosieer word, te oorkom. Die algoritmes word in 'n FPGA digitale verwerker geïmplementeer. Die algoritmes word vergelyk op grond van hul stroom- en spanningsfoute, asook hul reaksie op steurings wat op die stelsel ingevoer word. Die simulasie en praktiese resultate toon dat, deur die beheeraksies vir die twee omsetters te laat oorvleuel, die gedrag van die beheerde veranderlikes vinniger en meer robuust is. Die moontlikheid om die oorvleuelende beheeraksies uit te brei tot meer as twee omsetters word ook gemotiveer.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Cash can be seen as a fast moving consumer good. Approaching cash as inventory within the ATM cash management environment of a South African retail bank, provided the opportunity to apply well known industrial engineering techniques to the financial industry. This led to the application of forecasting, inventory management, operational research and simulation methods. A forecasting model is designed to address the multiple seasonalities and calendar day effects that is prevalent in the demand for cash. Special days, e.g. paydays, lead to an increase in demand for cash. The weekday on which the special day falls will also influence the demand. The multiplicative Holt-Winters method is combined with an improvised distribution method to determine the demand for cash for the region and per ATM. Reordering points are calculated and simulated to form an understanding of the effect this will have on the ATM network. Direct replenishment and the traveling salesman problem is applied and simulated to determine the difference in using one or the other. Various simulation models are build to test the operational and financial impact when certain variables are amended. It is evident that more work is required to determine the optimal combination of variable values, i.e. forecasting frequency, aggregate forecasting or individual forecasting, reorder levels, loading levels, lead times, cash swap or cash add, and the type of transportation method. Each one of these are a science in itself and cannot be seen (calculated) in isolation from the other as a change in one can affect the overall operational efficiency and costs of the ATM network. The thesis proves that significant cost savings is possible, compared to the current set-up, when applying industrial engineering techniques to a geographical ATM network within South Africa. / AFRIKAANSE OPSOMMING: Kontant kan gesien word as vinnig bewegende verbruikersgoedere. Deur kontant te benader as voorraad binne die ATM kontant bestuur omgewing van ’n Suid Afrikaanse kleinhandelsbank, het dit die geleentheid geskep om bekende bedryfsingenieurstegnieke toe te pas in die finansiële industrie. Dit het gelei tot die toepassing van vooruitskatting, voorraadbestuur, operasionele navorsing en simulasie metodes. ’n Vooruitskattingsmodel is ontwerp om die verskeie seisoenaliteite en kalenderdae effekte wat deel uitmaak van die vraag na kontant aan te spreek. Spesiale dae, bv. betaaldae, lei tot ’n toename in die vraag na kontant. Die weeksdag waarop die spesiale dag voorkom sal ook ’n invloed hê op die vraag. Die multiplikatiewe Holt-Winters metode is gekombineer met ’n geïmproviseerde verspreidingsmetode om die vraag na kontant vir die streek en per ATM the bepaal. Bestellingsvlakke is bereken en gesimuleer om ’n prentjie te skep van die invloed wat dit op die ATM netwerk sal hê. Direkte hervulling en die handelsreisigerprobleem is toegepas en gesimuleer om die verskille te bepaal tussen die gebruik van of die een of die ander. Veskeie simulasie modelle is gebou om die operasionele en finansiële impak te toets, wanneer sekere veranderlikes aangepas word. Dit is duidelik dat meer werk nodig is om die optimale kombinasie van veranderlike waardes te bepaal, bv. vooruitskatting frekwensie, totale vooruiskatting of individuele vooruitskatting, bestellingsvlakke, leitye, kontant omruiling of kontant byvoeging, en die tipe vervoermetode. Elkeen van hierdie is ’n wetenskap op sy eie en kan nie in isolasie gesien en bereken word nie, want ’n verandering van een se waarde kan die hele operasionele doeltreffendheid en kostes van die ATM netwerk beïnvloed.