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.

Impedance measurement as a function of frequency is being increasingly used for the detection of organic molecules. The main building block required for this is a sinusoidal oscillator whose frequency can be varied in the range of a few KHz to tens of MHz. The thesis describes the design of Integrated CMOS Oscillator Circuits. There are 2 designs presented in the thesis, one of which is based on the Wien Bridge and the other, on an LC architecture. They provide both in-phase and quadrature outputs needed for the determination of the real and imaginary parts of complex impedances. The inductor in the LC tank is realized by gyration of a capacitor. This needs two variable transconductance elements. Linear transconductance elements with decoupled transconductance gm and output conductance go is presented. A novel circuit for detecting and controlling the amplitude of oscillation is described. A current mode technique to scale the capacitance is also discussed. Since this oscillator is used in an inexpensive hand-held instrument, both power consumption and chip area must be minimized. A comparison between the Wien Bridge and the LC tank based oscillator is presented. Simulation results pertaining to the design of the different blocks of the circuit are made available. / text

Darbe nagrinėjami ir tiriami nuolatinės srovės keitikliai atsinaujinančios energijos šaltiniams. Pateikiami duomenys apie bendrą elektros energijos gamybą ir gamybą iš atsinaujinančių energijos šaltinių Lietuvoje ir pasaulyje. Pirmajame skyriuje nagrinėjamos pagrindinės nuolatinės srovės keitiklių struktūros, pateikiamos jų topologijos, analizuojamos išraiškos parametrams skaičiuoti, pateikiami valdančiųjų signalų formavimo algoritmai ir signalų epiūros. Antrajame skyriuje nagrinėjamos nuolatinės srovės keitiklių (inverterių), keičiančių nuolatinės srovės šaltinio įtampą į kintamąją įtampą, struktūros. Analizuojamos šių keitiklių topologijos, valdymo principai, signalų epiūros, signalų formavimo algoritmai, inverterių savybės, nagrinėjamos išraiškos parametrams apskaičiuoti. Trečiajame skyriuje analizuojamas inverterio išėjimo filtras. Pateikiamos pagrindinės šio filtro topologijos, aptariamos jų savybės, pateikiamos signalų epiūros, analizuojamos išraiškos filtro parametrams apskaičiuoti. Ketvirtajame skyriuje pateikiami inverterio su išėjimo filtru modeliavimo ir eksperimentinio tyrimo rezultatai. Tyrimams suprojektuotas ir surinktas 1 kW galios inverteris su filtru, jo darbo valdymui ir valdančiųjų signalų inverterio raktams formavimui panaudotas mikrokompiuteris su mikrovaldikliu. Gauti tyrimų rezultatai pritaikyti kuriant keitiklį saulės elementų baterijoms. Kiekvieno skyriaus pabaigoje pateikiamos išvados. Baigiamojo darbo pabaigoje pateikiamos apibendrinančios išvados. / The work focuses on direct current (DC) converters for alternative energy sources. The data about the general production of electricity and the production of electricity from alternative energy sources in Lithuania and in the world is presented. In the first section the structures and topologies of DC-DC converters are analyzed, the signal formation algorithms and plots of the signals are given and discussed. In the second section the structures and topologies of DC-AC (Alternating Current) converters are analyzed, the signal formation algorithms and plots of the signals are presented. In the third section the output filter is analyzed. The topologies, characteristics, signal plots and equations are presented. In the fourth section the simulation and experimental investigation results are presented and discussed. The 1 kW DC-AC converter with output filter was designed for experimental investigation and a microcontroller-based microcomputer was used for generation of signals for control of converter output transistors. The obtained investigation results were employed for development of the converter for the solar panel. Conclusions in the each section of the thesis are given. General conclusions are formulated at the end of the work. Thesis consist of: 88 p. text without appendixes, 77 pictures, 9 tables, 28 bibliographical entries. Appendixes included.

<p style="text-align: justify;">Rad se bavi problemom smanjenja proizvodnje<br />električne energije fotonaponske elektrane u<br />uslovima promenljivog zračenja. Predlaže se novi<br />metod analize rada u uslovima senčenja putem makro- i<br />mikrorekonfiguracije FN polja, koja povećava<br />proizvodnju električne energije.</p> / <p>The paper presents the problem of reducing electricity<br />production of PV power plant under variation of solar<br />radiation conditions. The author proposed a new method of<br />analysis PV power plant works under partial shading<br />condition trough micro- and macroconfiguration of PV array.</p>

Desde a idealização das máquinas elétricas girantes, o motor de indução linear (MIL) fora também considerado viável e, ao longo do tempo, foi pesquisado e foram desenvolvidas novas tecnologias para sua melhoria e para o seu acionamento. Muitos trabalhos acadêmicos foram realizados em todos os centros de pesquisa do mundo e, no Brasil, os primeiros a estudá-lo com rigor científico foram os professores Morency Arouca e Délio Pereira Guerrini, no início da década de 70, no departamento de Engenharia Elétrica da EESC/USP. Até hoje no Brasil, pouco se desenvolve neste campo de estudo da Engenharia Elétrica e, quando se desenvolve, ficam restritos à simulações e levantamentos de parâmetros característicos aos MIL\'s específicos. O presente trabalho tem como objetivo fazer uma explanação teórica e matemática que servirá de base ao estudo e compreensão do MIL e propor uma aplicação ao mesmo: o MIL acionado por inversor de freqüência e utilizado para obtenção de posicionamento com auxílio de simulação computacional de algumas malhas de controle para tal posicionamento. / Since the rotating machines had been idealized, the Linear Induction Motor (LIM) has been researched and, along the time, new technologies are being developed in order to improve it. Many academic works were accomplished in several research centers and universities around the world. In Brazil, the first ones to study it with scientific approach were Professors Morency Arouca and Délio Pereira Guerrini, in the early 70\'s. Even nowadays, works are seldom developed, and most of them are dedicated to simulation of the LIM or obtaining of parameters of specific LIM\'s. The present work has as objective to study the mathematical and theoretical modeling, which will be used as basis in order to study and understand the LIM and to propose an application: the LIM fed by Frequency Inverter, used in order to obtain positioning, with simulation of specific control systems.

A instalação de geração distribuída nas redes de distribuição e de subtransmissão de energia elétrica tem apresentado significativo crescimento em âmbito mundial, impulsionada pelos benefícios que pode proporcionar aos sistemas elétricos, pela necessidade de diversificação da matriz energética dos países, pela desregulamentação do setor de energia elétrica em diversos países e pela necessidade de gerar energia elétrica de forma sustentável. No entanto, para que os geradores distribuídos possam de fato beneficiar a operação das redes elétricas, seus impactos técnicos devem ser cuidadosamente estudados, sobretudo em redes de distribuição, as quais foram inicialmente planejadas para operar com fluxo de potência unidirecional. Dentre esses impactos, destaca-se a elevação do nível de curto-circuito da rede, pois correntes de curto-circuito com valores elevados podem causar violação das capacidades dos equipamentos em suportar os esforços térmicos e dinâmicos e também provocar a perda da coordenação entre os dispositivos de proteção contra sobrecorrente. Neste contexto, este trabalho analisa a influência de geradores distribuídos baseados em inversores na corrente de curto-circuito trifásica em um sistema de distribuição de energia, e sobretudo, comprova que sua contribuição no valor da corrente de falta não supera o dobro de sua corrente nominal. Além disso, com base nesta comprovação, apresenta duas estratégias para inserção desse tipo de gerador nos cálculos de curto-circuito de um sistema de distribuição de energia elétrica. As duas estratégias apresentam resultados satisfatórios, utilizam conceitos básicos de circuitos elétricos, independem de dados minuciosos dos inversores e são validadas através de aplicações numéricas com resultados confrontados aos obtidos das simulações. / The installation of distributed generation in distribution and subtransmission systems has shown significant growth worldwide, driven by the benefits it can provide to electrical systems, the need to diversify the energy sources, deregulation of the electricity industry in several countries and the need to generate electricity in a sustainable manner. However, in order to evaluate if distributed generators benefit the operation of power networks, their technical impacts should be carefully studied, especially in distribution networks, which were originally designed to operate with unidirectional power flow. Among the aforementioned impacts, there is the increase of the short circuit level in the distribution network, since high short-circuit currents may exceed the capabilities of equipment to support the dynamic and thermal stresses and also cause loss of coordination between the overcurrent protection devices. Within this context, this thesis analyzes the influence of inverter based distributed generators on three-phase short circuit currents in a power distribution systems. Especially it confirms that the contribution to the fault current does not exceed twice its rated value. Furthermore, based on this issue, this work presents two strategies for the inclusion of this type of generator in short circuit calculations. Both strategies presented satisfactory results, use basic concepts of electrical circuits, they do not depend on detailed data from the inverters and the results are validated by using simulation results.

This thesis presents a new DC/AC inverter circuit which is based on a switched-capacitor circuit topology with reduced components (power switch and capacitor) count for low power applications. The proposed circuit has distinct features of both voltage boost-up and near sinusoidal (multi-level/staircase) AC output voltage. The main idea is to utilise a simple circuit technique called resonant-based Double Switch Single Capacitor Switched-Capacitor (DSSC SCC) with variable duty cycle Pulse Width Modulation (PWM) control technique in such a way that multi-level voltage can be realised across a capacitor. In order to show the superiority of the applied technique, comparisons with other techniques/circuits configurations are presented. The circuit technique can significantly reduce the number of multiple stages of switched-capacitor circuit cells of the recent switched-capacitor multi-level inverter topology. The proposed inverter (with integrated DSSC SCC technique) can generate a line-frequency with 13-levels near sinusoidal AC output voltage with low total harmonics distortion. The output voltage can be achieved with the least number of components use and only a single DC source is used as an input. The proposed inverter topology is also reviewed against other inverter-based switched-capacitor circuit topology and the well-known multi-level inverter topology. The proposed inverter has shown a tremendous reduction in the total harmonics distortion and circuit component count in comparison with the recent Switched-Capacitor Boost multi-level inverter and the classical Cascaded H-Bridge multi-level inverter. Mathematical analysis shows the design of the proposed inverter and PSPICE simulation result to verify the design is also presented. The practical experiment implementation of the proposed system is presented and proves the correct operation of the proposed inverter topology by showing consistency between simulation results and practical results.

A instalação de geração distribuída nas redes de distribuição e de subtransmissão de energia elétrica tem apresentado significativo crescimento em âmbito mundial, impulsionada pelos benefícios que pode proporcionar aos sistemas elétricos, pela necessidade de diversificação da matriz energética dos países, pela desregulamentação do setor de energia elétrica em diversos países e pela necessidade de gerar energia elétrica de forma sustentável. No entanto, para que os geradores distribuídos possam de fato beneficiar a operação das redes elétricas, seus impactos técnicos devem ser cuidadosamente estudados, sobretudo em redes de distribuição, as quais foram inicialmente planejadas para operar com fluxo de potência unidirecional. Dentre esses impactos, destaca-se a elevação do nível de curto-circuito da rede, pois correntes de curto-circuito com valores elevados podem causar violação das capacidades dos equipamentos em suportar os esforços térmicos e dinâmicos e também provocar a perda da coordenação entre os dispositivos de proteção contra sobrecorrente. Neste contexto, este trabalho analisa a influência de geradores distribuídos baseados em inversores na corrente de curto-circuito trifásica em um sistema de distribuição de energia, e sobretudo, comprova que sua contribuição no valor da corrente de falta não supera o dobro de sua corrente nominal. Além disso, com base nesta comprovação, apresenta duas estratégias para inserção desse tipo de gerador nos cálculos de curto-circuito de um sistema de distribuição de energia elétrica. As duas estratégias apresentam resultados satisfatórios, utilizam conceitos básicos de circuitos elétricos, independem de dados minuciosos dos inversores e são validadas através de aplicações numéricas com resultados confrontados aos obtidos das simulações. / The installation of distributed generation in distribution and subtransmission systems has shown significant growth worldwide, driven by the benefits it can provide to electrical systems, the need to diversify the energy sources, deregulation of the electricity industry in several countries and the need to generate electricity in a sustainable manner. However, in order to evaluate if distributed generators benefit the operation of power networks, their technical impacts should be carefully studied, especially in distribution networks, which were originally designed to operate with unidirectional power flow. Among the aforementioned impacts, there is the increase of the short circuit level in the distribution network, since high short-circuit currents may exceed the capabilities of equipment to support the dynamic and thermal stresses and also cause loss of coordination between the overcurrent protection devices. Within this context, this thesis analyzes the influence of inverter based distributed generators on three-phase short circuit currents in a power distribution systems. Especially it confirms that the contribution to the fault current does not exceed twice its rated value. Furthermore, based on this issue, this work presents two strategies for the inclusion of this type of generator in short circuit calculations. Both strategies presented satisfactory results, use basic concepts of electrical circuits, they do not depend on detailed data from the inverters and the results are validated by using simulation results.

As máquinas elétricas rotativas são hoje a principal forma de transformação da energia elétrica em mecânica motriz e os motores de indução trifásicos têm grande relevância dentro do setor produtivo. A garantia de um correto funcionamento torna-se vital para eficácia e competitividade da empresa dentro do setor fabril. Assim sendo, um correto diagnóstico e classificação de falhas de funcionamento dos motores em operação pode fornecer maior segurança no processo de tomada de decisão sobre a manutenção, aumentar a produtividade e eliminar os riscos e os danos aos processos como um todo. A proposição deste trabalho baseia-se na análise das correntes de estator no domínio da frequência com sinais injetados na máquina juntamente com a modulação de alimentação para o diagnóstico do motor sem defeitos, com falhas de curtocircuito nos enrolamentos do estator e com falhas de rotor. A proposta é validada numa ampla faixa de frequências de operação bem como de regimes de conjugado de carga. São analisados os desempenhos individuais de cinco técnicas de classificadores de padrões, sendo proposta a utilização de: i) Perceptron Multicamadas, ii) Máquina de Vetores de Suporte, iii) k-Vizinhos Próximos, iv) Árvore de Decisão C 4.5 e v) Naive Bayes. Complementarmente, é desenvolvido um comparativo dos métodos de classificação de padrões para avaliar a precisão de classificação frente aos diversos níveis de severidade das falhas. Resultados experimentais com motor de 1 cv são apresentados para validar a proposta. / Rotating electric machines are today the main form of transformation of electrical energy in motor mechanics and three-phase induction motors have great relevance within the productive sector. Thus a correct diagnosis and classification of failures of the engines in operation can provide security in the decision making process on maintenance, increase productivity and eliminate risks and damages to processes as a whole. The purpose of this paper is based on the analysis of the stator currents in the frequency domain with signals injected into the machine together with the power modulation for the diagnosis of motor faultless, stator winding short-circuit faults and rotor faults. Considering also, for validation of the proposal is validated on a broad range frequency of operation as well as load torque. We analyze the individual performances of five standard classifier techniques, proposing the use of: i) Multilayers Perceptron, ii) Support Vector Machine, iii) k-Nearest Neighbor, iv) C 4.5 Decision Tree and v) Naive Bayes. Complementarily, a comparison of the methods of classification of standards is developed to evaluate the accuracy of classification against the different levels of severity of the failures. Experimental results with 735.5 w and 1.471 w engines are presented to validate the proposal.

Increased government funding and incentives in recent years has led to an increase in the number of grid-tied renewable energy sources as their economic benefits become more renowned. Unfortunately, the outputs of these renewable resources are often highly variable, resulting in undesirable voltage disruptions that are harmful to sensitive loads. In addition to the energy variability of renewable energy sources, random voltage sags, swells and disruptions are already a major issue in power systems. Recent advances in power electronic devices have provided a platform for new solutions to the voltage support problem in power systems. One promising solution is the Dynamic Voltage Regulator (DVR), a series compensating device used to protect a sensitive load that is connected downstream from voltage sag or swell. For this thesis, the design, modeling, and analysis of a DVR system were performed using PSCAD software. Results from simulation demonstrate the DVR’s effectiveness in protecting a sensitive load from load and source side voltage disturbances as well as regulate the load bus voltage to its rated value.