Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The slip synchronous-permanent magnet generator (SS-PMG) is a direct-driven, direct-to-grid generator
for wind turbine applications. This investigation focuses on achieving automated grid connection and
low voltage ride-through for a small-scale SS-PMG. To reduce cost and complexity, components such
as blade pitch controllers and frequency converters are avoided. Instead, electromagnetic braking is
employed to control turbine speed prior to grid synchronisation and compensation resistances are used
to facilitate grid fault ride-through.
The conditions under which the SS-PMG can be successfully synchronised with the grid are determined,
indicating a need for speed control. An evaluation of electromagnetic braking strategies reveals
that satisfactory speed control performance can be achieved when employing back-to-back thyristors to
switch in the braking load. Simulations show that controlled synchronisation can be executed successfully
under turbulent wind conditions. All controllable parameters are held within safe limits, but the
SS-PMG terminal voltage drop is higher than desired.
Compensation is developed to allow the SS-PMG to ride through the voltage dip profile specified by
the Irish distribution code. It is found that a combination of series and shunt resistances is necessary to
shield the SS-PMG from the voltage dip, while balancing active power transfer. The flexibility offered by
thyristor switching of the shunt braking load is instrumental in coping with turbulent wind conditions
and unbalanced dips. The South African voltage dip profile is also managed with conditional success.
Following on from the theoretical design, the grid connection controller is implemented for practical
testing purposes. Protection functions are developed to ensure safe operation under various contingencies.
Before testing, problems with the operation of the thyristors are overcome.
Practical testing shows that grid synchronisation can be undertaken safely by obeying the theoretically
determined conditions. The speed control mechanism is also shown to achieve acceptable dynamic
performance. Finally, the SS-PMG is incorporated into a functioning wind turbine system and automated
grid connection is demonstrated under turbulent wind conditions.
Future investigations may be focused on optimal control strategies, alternative solid-state switching
schemes, and reactive power control. Low voltage ride-through should also be optimised for the South
African dip profile and validated experimentally. / AFRIKAANSE OPSOMMING: Die glip-sinchroon permanente magneet generator (GS-PMG) is ‘n direkte dryf, direkte netwerkgekoppelde
generator vir windturbine toepassings. Hierdie ondersoek fokus op die bereiking van ’n
ge-outomatiseerde netwerkkoppeling en lae spanning deurry vir ‘n kleinskaalse GS-PMG. Om kostes
en kompleksiteit te verminder, word komponente soos lemsteekbeheerders en frekwensie-omsetters
vermy. In plaas daarvan word elektromagnetiese remwerking gebruik om die turbine spoed, voorgaande
net-werksinchronisasie, te beheer, en word kompensasieweerstande gebruik om netwerkfoutdeurry
te handhaaf.
Die omstandighede waaronder die GS-PMG suksesvol met die netwerk gesinchroniseer kan word, is
vasgestel en dit het die behoefte aan spoedbeheer uitgewys. ‘n Evaluering van elektromagnetiese remstrategië
wys uit dat ’n bevredigende spoedbeheervermoë verkry kan word as anti-parallelle tiristors
gebruik word om die remlas te skakel. Simulasies wys dat beheerde netwerksinchronisasie suksesvol
uitgevoer kan word, selfs onder turbulente windtoestande. Alle beheerbare parameters is binne veilige
perke gehou, maar die GS-PMG se klemspanningsval is gevind as hoë as verwag.
Kompensasie is ontwikkel om die GS-PMG toe te laat om deur die spanningsvalprofiel, soos gespesifieer
deur die Ierse distribusiekode, te ry. Dit is gevind dat ‘n kombinasie van serie- en parallelle
weerstande nodig is om die GS-PMG teen die spanningsval te beskerm, terwyl aktiewe drywingsoordrag
gebalanseer word. Die buigbaarheid wat verkry word met die tiristorskakeling van die parallele
weerstand is noodsaaklik in die hanteering van turbulente windtoestande en ongebalanseerde spanningsvalle.
Die Suid-Afrikaanse spanningsvalprofiel is ook met voorwaardelike sukses hanteer.
In opvolg van die teoretiese ontwerp is die netwerkkoppelingsbeheerder vir praktiese toetsdoeleindes
in werking gestel. Beskermingsfunksies is ontwikkel om veilige werking onder verskeie gebeurlikhede
te verseker. Die probleme met die werking van die tiristors is oorkom voor die aanvang van die
toetse.
Die praktiese toetse bewys dat netwerksinchronisasie veilig gedoen kan word deur die teoretiese
bepaalde voorwaardes te volg. Dit is ook getoon dat met die spoedbeheermeganisme aanvaarbare dinamiese
gedrag verkry kan word. Ten laaste is die GS-PMG in ‘n werkende windturbinestelsel geïnkorporeer
en outomatiese netwerkkoppeling is onder turbulente windtoestande gedemonstreer.
Toekomstige ondersoeke kan toegespits word op optimale beheerstrategië, alternatiewe vaste toestand
skakelingskemas en reaktiewe drywingsbeheer. Lae spanning deurry moet nog vir die Suid-
Afrikaanse spanningsprofiel ge-optimeer en eksperimenteel bevestig word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/19980 |
| Date | 03 1900 |
| Creators | Hoffmann, Ulwin |
| Contributors | Kamper, M. J., 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 | 184 p. : ill. |
| Rights | Stellenbosch University |
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