Design and performance evaluation of a permanent magnet vernier machine For wind turbine generator applications

Tlali, Pushman Micheal (2019-12)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Wind power conversion has emerged as one of the attractive and rapidly growing renewable energy resources. Research in this field has indicated a crucial need of developing new or improved electrical machine technologies, as they are essential components in this application. Currently, a cascaded arrangement of mechanical gearbox and a medium- or high-speed machine is the common configuration implemented in wind turbine systems. However, to avoid gearbox issues and to improve on the system reliability, there has been a paradigm shift towards the use of direct drive generators (DDGs) with full scale converters. Since the DDGs runs at the low turbine speed, they usually have heavy structure and bulky sizes due to high torque requirements. The past decades have seen a renewed interest in permanent magnet vernier (PMV) machine, which originates from the integration of the magnetic gearing concept with the conventional permanent magnet synchronous machine (PMSM). The inherent magnetic gearing effect of this type of machine enables it to have high torque density, potential for lighter weight and more compactness than conventional PMSMs, while maintaining the similar structural simplicity. Consequently, it appears to be a suitable candidate for low-speed and/or high-torque applications such as wind turbine DDGs. Despite the above mentioned advantages, the PMV machines are notably characterized by lower power factor that may increase the converter rating requirement and subsequently the system cost. The aim of this research is to develop and evaluate the PMV machine technology for use in the wind power conversion systems. The basic research methodology employed is to first derive fundamental analytical equations that describe the unique performance characteristics of PMV machines, and then to establish a dedicated finite element method based design optimization environment for the design and analysis of PMV machines. In order to show the merits and demerits of PMV machines, a detailed comparison between an optimally designed PMV machine and a conventional PMSM of the same power rating will also be conducted. To validate the performance and design methodology used, an optimally designed prototype PMV machine is constructed, experimentally tested and compared with an existing PMSM machine. In addition, the feasibility of using PMV machine technology for large wind power applications (3MW) is also evaluated in terms of performance, costs, size and weight. The outcome from this work outlines the advantages and disadvantages of the PMV machine technology and provide insight on the potential of this technology for MW scale wind power applications.

AFRIKAANSE OPSOMMING: Windkrag omskakeling het na vore gekom as een van die aanloklike en snelgroeiende hernubare energiebronne. Navorsing in hierdie veld het gedui op die noodsaaklikheid daarvan om verbeterde elektriese masjien tegnologieë te ontwikkel, aangesien dié komponente noodsaaklik is in windkrag toepassings. Die mees algemene kon gurasie wat tans in windturbine stelsels geïmplementeer word, is 'n opstelling met 'n meganiese ratkas en 'n medium- of hoë spoed masjien in kaskade gekoppel. Ten einde ratkas probleme op te los en om die betroubaarheid van die stelsels te verbeter het 'n paradigma skuif na die gebruik van direk aangedrewe generators (DDGs) met volskaalse omsetters plaasgevind. Aangesien direk aangedrewe generators teen die lae turbine spoed loop, is hulle struktuur gewoonlik groot en swaar, as gevolg van die hoë draaimoment vereistes. In die afgelope dekades het 'n hernude belangstelling in permanente magneet vernier (PMV) masjiene ontstaan vanuit die integrasie van die magnetiese rat konsep met die konvensionele permanente magneet sinkroonmasjien (PMSM). Die inherente magnetiese rat e ek van hierdie tipe masjien stel dit in staat om 'n hoë draaimomentdigtheid, die potensiaal vir 'n kleiner gewig en 'n meer kompakte vorm as konvensionele PMSMe te hê, terwyl dieselfde eenvoudige struktuur behou kan word. Daarom blyk dit om 'n gepaste kandidaat vir lae-spoed en/of hoë-draaimoment toepassings soos wind turbine DDGs te wees. Ondanks hierdie voordele, word PMV masjiene gekarakteriseer deur 'n laer arbeidsfaktor wat die vereiste omsetter grote en gevolglik die stelsel koste mag verhoog. Die doel van hierdie navorsing is om die PMV masjien tegnologie te ontwikkel en te evalueer vir gebruik in windkrag stelsels. Die basiese navorsingsmetodologie wat gebruik is, is om eerstens fundamentele analitiese vergelykings af te lei wat die unieke werking van PMV masjiene beskryf, en om dan 'n toegewyde optimeringsomgewing vir die ontwerp en analise van PMV masjiene daar te stel, gebaseer op die eindige-element metode. Ten einde die voor- en nadele van PMV masjiene uit te lig, sal 'n gedetaileerde vergelyking tussen 'n optimaal geontwerpde prototipe PMV masjien en 'n konvensionele PMSM met dieselfde kendrywing gemaak word. Om die geldigheid van die ontwerpsmetodiek en die werkverrigting berekeninge te bevestig, is 'n optimaal geontwerpde prototipe PMV masjien gebou, eksperimenteel getoets en vergelyk met 'n bestaande PMSM masjien. Verder is die moontlikheid om PMV masjien tegnologie vir groot windkrag toepassings (3MW) te gebruik ook geëvalueer in terme van werkverrigting, koste, grote en gewig. Die uitkomste van hierdie werk werp lig op die voor- en nadele van die PMV masjien tegnologie en verskaf insig in die potensiaal van hierdie tegnologie vir MW-skaal windkrag toepassings.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107149
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