Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: This thesis covers the development of a multilevel cascaded inverter for the purpose of costeffective
transformerless series dip compensation. Of all known power quality problems, voltage
dips are the greatest reason for concern. Dips/sags occur more frequently than outages and therefore
tend to be more costly for industry as modem technical equipment becomes all the more sensitive to
the quality and reliability of supply. A number of devices already exist to compensate for this
problem, but the cost of most of these systems does not always justify the financial losses they
compensate for. All of these systems are using transformers and/or large filter components that
contribute to the size, price and losses to quite a large extent. Series injection dip compensators
offer the advantage of only having to compensate for the decrease in supply voltage during a dip.
This results in a significant reduction in the converter ratings and energy storage requirements
compared to conventional uninterruptible power supplies or shunt injection power quality devices.
Existing inverter topologies, including multilevel inverters, were therefore studied and compared as
possible solutions for cost-effective transformerless series dip compensation. On the basis of these
considerations the multilevel cascaded inverter seems to be the most cost-effective option. The
relatively low harmonic content of its unfiltered output also eliminates the need for a large output
filter. A single-phase dip compensator, with this topology, was designed and built according to
specifications stated by Eskom, the main utility in South Africa. Batteries as energy storage and
automotive MOSFETs as switching components, proved to be most cost-effective options for the
specified power ratings. Control algorithms for dip compensation with the multilevel inverter were
also developed. Some of these algorithms are based on existing techniques, but two new algorithms
were also developed to implement force commutation of the thyristors and to share the power
dissipation in the dip compensator. Simulations indicated that these algorithms could be suitable
and sufficient for their application. This dip compensator with its control algorithms was tested with
a dip generator, developed at the University of Stellenbosch, for different types of loads. The
experimental results confirmed the simulations and showed a very good performance for the
specified conditions. An optimised design of this dip compensator will make it a cost-effective
solution for dip compensation. / AFRIKAANSE OPSOMMING: Hierdie tesis dek die ontwikkeling van 'n multivlakwisselrigter, in kaskade, met koste-effektiewe
transformatorlose duik kompensasie as mikpunt. Van al die bekende toevoerkwaliteit probleme wek
duike in die spanning die meeste kommer. Duike kom meer gereeld voor as kragonderbrekings en
neig daarom om 'n groter onkoste te wees vir die industrie soos wat moderne tegnologiese
toerusting al hoe meer sensitief raak vir die kwaliteit en betroubaarheid van die toevoer. 'n Aantal
toestelle wat vir hierdie probleem kompenseer bestaan reeds, maar die koste van hierdie stelsels
regverdig nie altyd die finansiële verliese wat hulle moet elimineer nie. Al hierdie stelsels gebruik
transformators en/of groot filter komponente wat grootliks bydra tot die grootte, prys en verliese
van hierdie stelsels. Serie-injeksie kompenseerders het die voordeel dat hulle net kompenseer vir die
verlies in die toevoerspanning tydens die duik. Dit het 'n beduidende vermindering in die
omsetterkenwaardes en energiestoorvereistes tot gevolg in vergelyking met ononderbroke
kragbronne (UPS) of newe-injeksie toevoerkwaliteit toestelle. Daarom IS bestaande
wisselrigtertopologië, insluitende multivlakwisselrigters, bestudeer en vergelyk as moontlike
oplossings vir koste-effektiewe serie duik-kompensasie. Van al hierdie moontlikhede lyk die
multivlakwisselrigter, in kaskade, na die mees koste-effektiewe opsie. Die relatiewe lae harmoniese
inhoud van sy ongefilterde uittree elimineer die behoefte aan 'n groot uittreefilter. 'n Enkelfase duik
kompenseerder, met hierdie topologie, is ontwerp en gebou volgens die spesifikasies wat vasgestel
is deur Eskom, die hoof elektriese kragvoorsiener in Suid-Afrika. Dit het geblyk dat batterye, en
MOSFETte uit die motorbedryf, die mees koste-effektiewe opsies bied vir onderskeidelik die
energiestoor en skakelkomponente. Beheeralgoritmes VIr duik kompensasie met die
multivlakwisselrigter is ook ontwikkel. Sommige van hierdie algoritmes is gebaseer op bestaande
tegnieke, maar twee nuwe algoritmes is ook ontwikkel vir die kommutering van die tiristors en die
deling van die drywingsverkwisting in die duik kompenseerder. Simulasies dui aan dat hierdie
algoritmes geskik en voldoende kan wees vir hulle toepassing. Hierdie duik kompenseerder met sy
beheeralgoritmes is getoets vir verskillende tipes laste met 'n duikgenerator wat ontwikkel is by die
Universiteit van Stellenbosch. Die eksperimentele resultate bevestig dit wat verkry is uit die
simulasies en wys 'n goeie werkverrigting vir die gespesifiseerde kondisies. 'n Geoptimeerde
ontwerp van hierdie duik kompenseerder sal dit 'n koste-effektiewe oplossing maak vir duik
kompensasie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52592 |
| Date | 12 1900 |
| Creators | Visser, Abraham Johannes |
| Contributors | Mouton, H. du T., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 175 p. : ill. |
| Rights | Stellenbosch University |
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