Performance of turbo coded DS-CDMA systems in correlated and uncorrelated satellite communication channels

Word processed copy.Includes bibliographical references (leaves 82-88).This thesis aims at presenting the perfonnance of turbo codes in the correlated and uncorrelated satellite fading channel. Turbo codes are known to give very good perfonnance results in A WGN channels, especially for very large input message length codes or interleaver sizes. It can be shown that good perfonnance of the turbo codes can be achieved with small interleaver sizes in a satellite channel

Analysis and evaluation of brush-DC equivalent controlled multiphase cage induction machine drive

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

Modeling and Vector Control of a Cage+Nested-Loop Rotor Brushless Doubly Fed Induction Motor

The brushless doubly fed induction machine (BDFIM) is being considered as a possible solution for low-speed wind energy generator applications. It has been proposed as an alternative to the doubly fed induction machine (DFIM) due to its robust rotor structure as well as low operational maintenance requirements. However, due to its complicated control philosophy, higher overall machine size due to the extra set of control windings in the stator, and slightly lower efficiency, it is yet to be adopted in commercial applications. In this paper, a simplified vector control scheme for the control winding of a cage+nested-loop (cage+NL) rotor BDFIM is proposed. Experimental results are compared with simulations to validate the effectiveness of the proposed control scheme

Design and Evaluation of a Laminated Three-Phase Rotary Transformer for DFIG Applications

In doubly fed induction generators (DFIGs), the rotor is excited through slip-ring and brush assemblies. These slip-ring and brush assemblies often require frequent routine maintenance, which affects the reliability of the DFIG. Alternatively, a contact-less energy transfer system, such as a rotary transformer, can be utilized in place of the slip rings. In DFIGs, the rotor frequency is very low, under 5 Hz, and this can lead to a huge rotary transformer since the transformer size is inversely proportional to its operating frequency. However, in a rotor-tied DFIG, whereby the rotor is connected directly to the grid whilst the stator is connected to a back-to-back converter, the rotor frequency becomes the grid frequency and can lead to a reasonably sized rotary transformer. In this paper, the design methodology of a three-phase rotary transformer that can be used in rotor-tied DFIG applications is proposed. The rotary transformer is coupled to the power windings of the rotor-tied DFIG and can improve its reactive power capabilities. The proposed methodology is validated with finite element analysis in 3D and can be used for an efficient design process with the proposed error correction. The proposed methodology is then applied in the design of a 6 kVA rotary transformer. Remarkable practical results are presented to demonstrate the effectiveness of the methodology. The rotary transformer is subsequently coupled to a rotor-tied DFIG and an acceptable performance is demonstrated for the entire system

Design and Evaluation of a Laminated Three-Phase Rotary Transformer for DFIG Applications

In doubly fed induction generators (DFIGs), the rotor is excited through slip-ring and brush assemblies. These slip-ring and brush assemblies often require frequent routine maintenance, which affects the reliability of the DFIG. Alternatively, a contact-less energy transfer system, such as a rotary transformer, can be utilized in place of the slip rings. In DFIGs, the rotor frequency is very low, under 5 Hz, and this can lead to a huge rotary transformer since the transformer size is inversely proportional to its operating frequency. However, in a rotor-tied DFIG, whereby the rotor is connected directly to the grid whilst the stator is connected to a back-to-back converter, the rotor frequency becomes the grid frequency and can lead to a reasonably sized rotary transformer. In this paper, the design methodology of a three-phase rotary transformer that can be used in rotor-tied DFIG applications is proposed. The rotary transformer is coupled to the power windings of the rotor-tied DFIG and can improve its reactive power capabilities. The proposed methodology is validated with finite element analysis in 3D and can be used for an efficient design process with the proposed error correction. The proposed methodology is then applied in the design of a 6 kVA rotary transformer. Remarkable practical results are presented to demonstrate the effectiveness of the methodology. The rotary transformer is subsequently coupled to a rotor-tied DFIG and an acceptable performance is demonstrated for the entire system

A Review of the Advancements in the Design of Brushless Doubly Fed Machines

Research interest on brushless doubly fed induction machines (BDFMs) is increasing, as they offer higher reliability compared to doubly fed induction generators (DFIGs) in wind turbines. At the moment, BDFMs do not have a definitive structure nor design process, as literature is rife with different approaches to designing BDFMs. In this paper, a comprehensive review of the design of BDFMs from available literature is conducted. The evolution of cascade induction machine systems to contemporary BDFMs is first illustrated. Pioneering research work in the evolution which have influences on modern BDFM designs are highlighted. Relevant research on different aspects of present day BDFM design are then discussed. BDFM design and optimization methodologies applied in available literature are also explored