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The electromagnetic behavior of magnetic devices used in power electronics circuitry, is studied in order to predict their performance within a context of desirable circuit parameters. Past efforts have focused on simplifications widely used in electric machinery applications. Due to the greatly increased operating frequencies of today's circuits (in the upper kHz and lower MHz region), the operation and design of magnetic components greatly differs from those of 60 Hz machinery. A set of models based on assumptions that are unique to the these devices used in power electronics are put forth. The entire approach is based on deriving models from solutions of the field equations, rather than using older, less accurate circuit analogies. More importantly, models are needed for accurate design and optimization processes of complete power electronic systems, in which the magnetic components form a small part. Solutions are sought without using the popular simplifications at very low and very high frequencies, since they are not accurate at intermediate frequencies encountered in power electronics. The conductors used in transformers and inductors are modelled in these high frequency regions. / Ph. D.

Permanent magnet brushless DC motors that have found wide application in high performance servo drives need absolute rotor position sensors. However, the cost of the position sensor limits the use of brush less DC motors for low performance applications such as automotive and home appliances. A sensorless starting scheme for brushless DC motors is studied in this thesis. A hardware implementation of the starting scheme has been instrumented. The modeling and simulation of the sensorless starting performance of brushless DC motors have been accomplished to gain the insight into the process. The experimental results confirm the theoretical prediction that the permanent magnet brush less DC motor can be started without a position sensor. The experimental setup with individual subsystems are described in detail. / Master of Science

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The multiphase induction machine drive has been under investigation for the last half century. Although it offers several attractive advantages over the conventional three-phase induction machine drive, it is restricted to highly specialised applications. One aspect of the multiphase induction machine drive is the complexity of the control algorithm for decoupled flux and torque control. The complexity, arising from the required coordinate transformations, increases with increase in the number of phases of the machine. Recently, a method that allows the control of a six-phase induction machine drive without any coordinate transformations was developed and tested. This new control technique allows the control of the machine to be similar to that of dc machines through the use of special trapezoidal-shaped stator current waveforms. These stator phase current waveforms consist of field (flux) and torque current components, with flat-topped amplitudes allowing a stator phase to act alternately in time as either a flux or a torque producing phase. The idea is to have a number of stator phases acting as flux producing phases, whilst the remaining phases act as torque producing phases at each time instance. This dissertation takes a further step in the research on this particular control technique. As the control method relates directly to the brush-dc machine operation, in this dissertation, the control method is defined as a “brush-dc equivalent” (BDCE) control method. First, in this dissertation, a simple analytical method is developed to determine a defined optimal ratio of the number of field to the number of torque phases of a multiphase induction machine that utilises trapezoidal stator current waveforms. The method is applied to induction machines with up to fifteen stator phases. Finite element analysis is used to verify the validity of the developed criterion and to verify the square-like air gap flux density. Secondly, in this dissertation, an analytical method for predicting and evaluating the rotor bar current waveform of a cage multiphase induction machine is proposed. The method is based on the Fourier transform and the winding function theory under linear condition assumptions. The method also allows for the calculation of the electromagnetic torque and rotor bar losses. Skin effect is considered in the calculation of the rotor bar resistance of the machine. Again, finite element analysis is used to verify the analytically calculated results. The developed method can be expanded and used to evaluate the rotor current waveform of any multiphase induction machine supplied with any stator current waveforms. The BDCE control method is implemented on a prototype nine-phase cage-rotor induction machine drive. A nine-phase inverter and control system are developed for supplying the nine-phase induction machine with the trapezoidal stator current waveforms. Rotor current waveform measurements are taken on a specially designed rotor to verify the analytically predicted waveform. The linear relationship of the developed torque and torque current of the proposed BDCE control method is verified through measurements. Through the comparison of analytical calculated results with finite element calculated and measured results, it is shown in this dissertation that the developed analytical techniques can be used in the design and performance analysis of multiphase induction machines. Also, from the results, it is clear that the new control technique works remarkably well even in the flux weakening region. However, outstanding aspects, such as efficiency and generated torque quality of the proposed drive still need to be investigated further. / AFRIKAANSE OPSOMMING: Die multifase induksiemasjien aandryfstelsel word in die laaste halwe eeu al in navorsing ondersoek. Alhoewel dit verskeie aantreklike voordele bied bo die konvensionele driefase induksiemasjien aandryfstelsel, is dit beperk tot hoogs gespesialiseerde aanwendings. Een aspek van die multifase induksiemasjien aandryfstelsel is die kompleksiteit van die beheer algoritme vir ontkoppelde vloed en draaimoment beheer. Die kompleksiteit, wat voortspruit uit die vereiste koördinaat transformasies, neem toe met toename in die aantal fases van die masjien. Onlangs is 'n metode wat die beheer van ’n sesfase induksiemasjien sonder enige koördinaat transformasies doen, ontwikkel en getoets. Hierdie nuwe beheertegniek maak die beheer van die masjien soortgelyk aan dié van GS masjiene deur die gebruik van spesiale trapezium-vormige statorstroom golfvorms. Hierdie stator fasestroom golfvorms bestaan uit veld- (vloed-) en draaimoment-stroom komponente met plat amplitudes, sodat 'n statorfase om die beurt in tyd optree as óf' ’n vloed of 'n draaimoment genereerde fase. Die idee is om 'n aantal statorfases te hê wat as vloed genereerde fases dien, terwyl die oorblywende fases as draaimoment genereerde fases optree op enige tydstip. Hierdie tesis neem 'n verdere stap in die navorsing op hierdie spesifieke beheertegniek. Met die beheermetode wat direk verband hou met borsel-GS masjien werking, word in hierdie proefskrif die beheermetode as 'n "borsel-GS ekwivalente" ["brush-DC equivalent" (BDCE)] beheermetode gedefinieer. In die eerste plek word in hierdie proefskrif 'n eenvoudige analitiese metode ontwikkel om ’n gedefinieerde optimale verhouding van die aantal veld tot die aantal draaimoment fases van 'n multifase induksiemasjien te bepaal, wat van trapesoïdale statorstroom golfvorms gebruik maak. Die metode word toegepas op induksiemasjiene met tot vyftien statorfases. Eindige element analise is gebruik om die geldigheid van die ontwikkelde kriterium te verifieer en om die vierkantvormige luggaping vloeddigtheid te verifieer. In die tweede plek word in hierdie proefskrif 'n analitiese metode vir die voorspelling en evaluering van die rotorstaafstroom golfvorm van 'n kourotor multifase induksiemasjien voorgestel. Die metode is gebaseer op die Fourier transform en die wikkelingsfunksie teorie onder lineêre-toestand aannames. Die metode wend hom ook daartoe tot die berekening van die elektromagnetiese draaimoment en rotorstaafverliese. Die huideffek word in ag geneem in die berekening van die rotorstaafweerstand van die masjien. Weereens is eindige element analise gebruik om die analitiese berekende resultate te verifieer. Die ontwikkelde metode kan uitgebrei en gebruik word om die rotorstroom golfvorm van van enige multifase induksiemasjien te evalueer wat gevoer word met enige statorstroom golfvorms. Die BDCE beheermetode is toegepas op 'n prototipe negefase kourotor induksiemasjien. 'n Negefase omsetter en beheerstelsel is ontwikkel vir die toevoer van die trapesoïdale statorstroom golfvorms aan die negefase induksiemasjien. Die rotorstroomgolfvorm metings is geneem op 'n spesiaal ontwerpte rotor om die analitiese voorspelde golfvorm te verifieer. Die lineêre verwantskap tussen die ontwikkelde draaimoment en draaimomentstroom van die voorgestelde BDCE beheermetode is geverifieer deur metings. Deur die analitiese berekende resultate met die eindige element berekende en gemete resultate te vergelyk, wys hierdie proefskrif dat die ontwikkelde analitiese tegnieke gebruik kan word in die ontwerp en werkverrigting analise van ’n multifase induksiemasjien. Vanuit die resultate is dit ook duidelik dat die nuwe beheertegniek besonder goed werk, selfs in die vloedverswakking spoedgebied. Egter, uitstaande aspekte soos effektiwiteit en genereerde draaimoment kwaliteit van die voorgestelde aandryfstelsel moet nog verder ondersoek word.

The development of an online method for the early detection of a stator turn insulation deterioration is the objective of the research at hand. A high percentage of motor breakdowns is related to the failure of the stator insulation system. Since most of the stator insulation failures originate in the breakdown of the turn-to-turn insulation, the research in this realm is of great significance. Despite the progress that has been made in the field of stator turn fault detection methods, the most popular and the best known ones are still limited to the detection of solid turn faults. The time span between a solid turn fault and the breakdown of the primary insulation system can be as short as a few seconds. Therefore, it is desirable to develop a method capable of detecting the deterioration of the turn insulation as early as possible and prior to the development of a solid turn fault. The different stresses that cause the aging of the insulation and eventually lead to failure are described as well as the various patterns of an insulation failure. A comprehensive literature survey shows the methods presently used for the monitoring of the turn insulation. Up to now no well-tested and reliable online method that can find the deterioration of the turn insulation is available. The most commonly used turn insulation test is the surge test, which, however, is performed only when the motor is out of service and disconnected from the supply. So far no research at all has been conducted on the application of an online surge test. The research at hand examines the applicability of the surge test to an operating machine. Various topologies of online surge testing are examined with regard to their practicability and their limitations. The most practical configuration is chosen for further analysis, implementation and development. Moreover, practical challenges are presented by the non-idealities of the induction machine like the eccentricity of the rotor and the rotor slotting, and have to be taken into account. Two solutions to eliminate the influence of the rotor position on the surge waveform are presented. Even though the basic concepts of online surge testing can be validated experimentally by a machine with a solid turn fault, it is preferable to use a machine with a deteriorated turn insulation. Therefore, a method, which does not require complex and expensive hardware, to experimentally emulate the turn insulation breakdown is implemented. The concepts at any stage of the work are supported by simulations and experimental results. In addition, the theory of surge testing is further developed by giving new definitions of the test's sensitivity, i.e., the frequency sensitivity and the error area ratio (EAR) sensitivity.

This dissertation presents an investigation of miniaturized magnetic induction and permanent magnet (PM) machines, intended for use in a microengine. Similar to a macroscale turbogenerator, a microengine comprises a small, gas-fueled turbine engine for converting chemical fuel energy into mechanical power and an integrated electrical generator for converting mechanical power to electrical power. The microengine system is proposed as a revolutionary, high power-density source for portable electronics. In this research, miniaturized magnetic induction machines and PM machines were designed, fabricated, and characterized. Both types of machines used axially directed magnetic fields and were nominally 10 mm in diameter and 1.5-2.3 mm in thickness. Innovative microfabrication techniques were developed to demonstrate the feasibility of integrating magnetic machines within a bulk-micromachined, silicon-based microengine system. Two-phase, eight-pole induction machines were constructed within silicon substrates using Cu coils in a laminated, slotted ferromagnetic NiFe or CoFeNi stator core. Silicon etching, wafer bonding, and electrodeposition were used to form all of the magnetic machine components. The induction machines were characterized in motoring mode using tethered rotors and demonstrated motoring torques of up to 2.5 uN-m. Also, three-phase, eight-pole, surface wound PM machines were built using a hybrid microfabrication/assembly approach. The stators were fabricated by electroplating Cu coils on ferromagnetic NiFeMo (Moly Permalloy) substrates. The rotors were formed by assembling a magnetically patterned SmCo PM with a FeCoV (Hiperco 50) back iron. The PM machines were tested as generators with free-spinning rotors, powered by an air-driven spindle, and demonstrated 2.6 W of mechanical-to-electrical power conversion with continuous DC power generation of 1.1 W at 120 krpm rotor speed. The primary contributions of this work are (1) the demonstration of microfabricated magnetic machines integrated within bulk-micromachined silicon and (2) the demonstration of multi-watt power conversion from a microfabricated PM generator. These achievements represent progress in the ongoing development of silicon-based microengines, but in addition, the fabrication technologies and device structures may find application in other microsystems.

Advanced material handling systems' impact on flexible manufacturing systems (FMS) have increased the efficiency and work rate over conventional manufacturing assemblies. The interaction of automated guided vehicles (AGVs), roller conveyors and conveyor belts with robots and machine tools forms highly sophisticated assembly operations. Whilst material handling in FMS today is conventionally used to transport assembly units from one work station to another, it does not take an active role in the manufacturing process. With manufacturers implementing more advanced manufacturing principles to perform agile manufacturing, there is a growing need to implement "smarter" material handling systems that would perform essential, integral roles in the assembly process. This research outlines the development of a cordless linear synchronous motor (CLSM) material handling system. The CLSM incorporates a permanent magnet courier that moves without tether restrictions on an integrated reverse air bearing system which eliminates friction. The CLSM provides a material handling system with enhanced travel, flexibility and accuracy. The CLSM material handling system is designed to integrate with overhead manipulators and part feeders to form a comprehensive flexible manufacturing system. This research covers the 2-D finite element modeling (FEM) used to determine the CLSM's optimal parameters. The development of the motor windings design and construction, together with the control system for the CLSM, is also covered. The CLSM novel air bearing system is outlined and compared to other conventional linear bearing systems. The possible impact of the CLSM on current manufacturing systems is explored to determine the validity of the research project and possible further research opportunities. / Thesis (M.Sc.Eng)-University of Natal, Durban, 2000.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 170-177).

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.

Este trabalho propõe uma metodologia de projeto de controladores para o amortecimento de oscilações eletromecânicas de baixa frequência em sistemas elétricos de potência. O problema de controle é estruturado na forma de desigualdades matriciais, as quais permitem a busca por uma solução numérica para o problema de controle. Os controladores de amortecimento baseados na realimentação dinâmica de saída, gerados por metodologias de projeto na forma de desigualdades matriciais, geralmente apresentam ordem elevada. Além disso, projetos considerando sistemas de potência de médio porte demandam elevado tempo computacional. Nesse contexto, o presente trabalho propõe uma metodologia de projeto capaz de gerar controladores de ordem reduzida. A metodologia proposta adota um índice de desempenho que possibilita a redução do tempo computacional demandado no projeto. O índice de desempenho adotado para o sistema em malha fechada é a energia do sinal de saída do sistema. Essa energia corresponde à integral do valor quadrático do sinal adotado como saída do sistema. A metodologia proposta permite especificar um índice de desempenho apenas para aos modos de resposta de interesse do sistema, contornando as limitações das metodologias baseadas em posicionamento regional de polos. A relação entre o valor da energia do sinal de saída do sistema e seu fator de amortecimento é estabelecida por meio de uma equação algébrica. Neste trabalho, a metodologia é aplicada na geração de controladores de amortecimento para geradores síncronos. Entretanto, o procedimento proposto é genérico o suficiente para ser aplicado a outros tipos de geradores (gerador de indução empregado em unidades eólicas, por exemplo), a dispositivos FACTS (do Inglês, Flexible AC Transmission System) assim como a outros tipos de sistemas dinâmicos. A metodologia gerou um controlador eficaz para um caso onde a formulação baseada no tradicional posicionamento regional de polos é incapaz de gerar um controlador que assegure uma boa margem de estabilidade para o modo de resposta de interesse. / This work proposes a methodology for the design of controller to damp low frequency electromechanical oscillations in power systems. The control problem is structured in the form of matrix inequalities, which allows obtaining a numerical solution for the control problem. The damping controllers based on dynamic output feedback, generated by design methodologies in the form of matrix inequalities, usually presents high order. In addition, the design of this controller, considering large power systems, usually requires excessive computational effort. In this context, this work proposes a methodology for the design of reduced order controllers. The proposed methodology employs a performance index that is less costly in terms of computational effort when compared to the one with the traditional regional pole placement. The adopted performance index for the closed loop system is the energy of the system output. This energy corresponds to the integral of the signal squared regarding the system output. The proposed methodology allows specifying a performance index only for the response modes of interest, overcoming the limitations of the methodologies based on regional pole placement. The relation between the energy value of the output signal of the system and its damping factor is established by means of an algebraic equation. In this paper, the methodology is applied to generate damping controller for synchronous generators. However, the proposed procedure is general enough to be applied to other kinds of power plants (wind generation, for example), to FACTS devices, as well as to other dynamic systems. The methodology has generated an effective controller for a case where the formulation based on the regional pole placement is unable to generate a controller which assures a good stability margin for the response mode of interest.