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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6489 |
| Date | 03 1900 |
| Creators | Gule, Nkosinathi |
| Contributors | Kamper, M. J., University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 91 p. : ill. |
| Rights | University of Stellenbosch |
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