Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In this study a new type of gearless, direct-drive wind generator, which can be connected directly to the grid,
is proposed. The working characteristics of this generator are based upon the principles of the permanent
magnet induction generator (PMIG). By omitting the need for a gearbox and power electronic converter this
generator type has several advantages regarding cost and reliability. Although the PMIG is proposed in
previous studies as favourable for wind power generation, the mechanical complexity and difficult
construction associated with these types of generators, seems to be the main reason why these generator
systems are not used.
The design methods presented in this study are intended to alleviate these constructional issues by proposing
the split-PMIG (S-PMIG), where the stator winding and the induction cage-rotor windings are
electromagnetically separated. The machine is basically split into two permanent magnet (PM) machines, a
grid connected synchronous generator (SG) unit and a turbine connected induction generator (IG) unit. These
two units are mechanically linked by a common PM-rotor. To evaluate this concept a finite element (FE)
design analysis is done independently for both machine components. The emphasis of the design
optimisation is the minimisation of the cogging torque, while still having a decent performing, easily
constructible generator. This generator should also have low load ripple content. Cogging torque can result in
the failure of the turbine to start up, especially at low wind speeds. As this is a directly grid connected
generator, torque ripple transferred to the common PM-rotor can destabilise the generator.
Based upon the FE designs a preliminary S-PMIG system is constructed and practically evaluated. Due to the
modular nature of the design it is possible to implement the synchronous generator part of the S-PMIG in
conjunction with a grid-connected solid state converter (SSC). This allows for a useful comparison with the
S-PMIG system. Promising results are obtained from initial tests of the S-PMIG directly connected to the
grid. It is shown that the operation of this generator is stable under a wide range of wind load conditions.
However, some important machine design issues are identified from these practical results, which could
prove vital in the implementation of future S-PMIG designs. / AFRIKAANSE OPSOMMING: In hierdie studie word 'n nuwe ratkaslose direk-aangedrewe wind generator voorgestel, wat direk aan die
krag netwerk gekoppel kan word. Hierdie generator is gebaseer op die beginsels waarop permanente magneet
induksie generators (PMIG’s) werk. Deur die ratkas en drywings-elektroniese omsetter uit te laat, het hierdie
generator verskeie voordele rakende koste en betroubaarheid. Alhoewel vorige studies hierdie generator
voorstel as 'n belowende opsie vir gebruik in wind-energie-stelsels, lyk dit of die meganiese kompleksiteit en
moeilike konstruksie die hoof rede is hoekom hierdie generator stelsels tans nie gebruik word nie.
Die ontwerpsmetodes wat in hierdie studie voorgestel word poog om die genoemde konstruksie probleme op
te los deur die gesplete-PMIG (S-PMIG), waar die stator wikkelings en die induksie masjien kou-rotor
wikkelings elektromagneties ontkoppel is, voor te stel. Hierdie masjien is basies verdeel in twee permanente
magneet (PM) masjiene, 'n netwerk gekoppelde sinchroongenerator (SG) eenheid en 'n turbine gekoppelde
induksie generator (IG) eenheid. Hierdie twee eenhede word gekoppel deur 'n gemeenskaplike PM-rotor. Om
hierdie konsep te evalueer word eindige element analise onafhanklik vir beide masjiene gedoen. Die fokus
van die ontwerp optimering is die minimalisering van die vertandingsdraaimoment, terwyl die generator
steeds goed presteer en maklik is om te vervaardig. Vertandingsdraaimoment kan tot die gevolg hê dat die
turbine versuim om te begin draai, veral by lae windsnelhede. Dit is ook belangrik dat die generator 'n lae
rimpel inhoud onder las bevat. Omrede hierdie generator direk aan die netwerk gekoppel is, kan
draaimoment pulsasies, oorgedra aan die gemeenskaplike PM-rotor, die masjien destabiliseer.
Gebaseer op die eindige element ontwerpe, is 'n voorlopige gesplete-PMIG gebou en prakties geëvalueer. As
gevolg van die modulêre struktuur van die ontwerp, is dit moontlik om die SG gedeelte van die gesplete-
PMIG saam met 'n drywings-elektroniese omsetter te implementeer. Dit laat toe vir 'n nuttige vergelyk tussen
die twee stelsels. Belowende eerste toets resultate is verkry van die gesplete-PMIG direk gekoppel aan die
netwerk. Daar word gewys dat hierdie generator stabiel oor 'n wye operasionele gebied kan funksioneer.
Verskeie belangrike masjien ontwerpsfaktore word ook uitgelig met die praktiese evaluering van die
gesplete-PMIG. Hierdie faktore kan uiters belangrik wees in die ontwerp en implementering van toekomstige
gesplete-PMIG stelsels. / Sponsored by the Centre for Renewable and Sustainable Energy Studies
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6689 |
| Date | 03 1900 |
| Creators | Potgieter, Johannes H. J. |
| Contributors | Kamper, M. J., University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering., Stellenbosch University. Faculty of Engineering. Centre for Renewable and Sustainable Energy Studies |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 88 p. : ill. |
| Rights | University of Stellenbosch |
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