System Aspects and Modulation Strategies of an HVDC-based Converter System for Wind Farms
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
In this thesis, a new HVDC-based converter system for wind farms is investigated. It is based on a mutually commutated soft-switching converter system and provides a unique integrated solution for the wind turbine generator drive systems, the wind turbine interconnection, and the power conversion for HVDC transmission.
In a wind farm, the mutually commutated converter system is a distributed system. A medium-frequency collection grid connects the converter station, equipped with a single-phase voltage source converter and a medium-frequency transmission transformer, with the wind turbines, each containing a cycloconverter and a medium-frequency distribution transformer. In this thesis, various system aspects regarding the application of a distributed mutually commutated converter system in a wind farm are investigated. Special attention is paid to the design of a medium-frequency collection grid that has an acceptable level of transient overvoltages, the design of medium-frequency transformers with suitable magnetic, electric and thermal properties, and the development of a strategy to commutate the voltage source converter during low power generation.
In order to adapt the mutually commutated converter system for an application in a wind farm, it had to be further developped. Different carrier-based and space-vector oriented modulation methods have been investigated. It turns out that for any load angle there is a quasi-discontinuous pulse width modulation strategy that can produce the same pulse patterns as space vector modulation. In addition, a modulation strategy has been developed that allows to replace the IGBTs in the cycloconverter with cheap, robust, and reliable fast thyristors, despite their absence of turn-off capability. The feasibility of different modulation strategies for mutually commutated converter systems has been verified on a down-scaled prototype converter system with both IGBT- and thyristor-based cycloconverters.
Finally, a feasible wind farm layout is proposed, which considerably reduces the energy generation costs for large winds farms distant to a strong grid connection point. As a consequence, the proposed solution may facilitate the establishment of remotely located wind farms.
Place, publisher, year, edition, pages
Stockholm, Sweden: KTH , 2009. , viii, 80 p.
Trita-EE, ISSN 1653-5146 ; 2009:018
Isolated AC/DC Converter, Mutual Commutation, Soft Switching, Voltage Source Converter, Cycloconverter, Modulation Strategies, Medium-Frequency Transformer, HVDC Transmission, Wind Power, Wind Farms
Other Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
IdentifiersURN: urn:nbn:se:kth:diva-10267ISBN: 978-91-7415-292-0OAI: oai:DiVA.org:kth-10267DiVA: diva2:213688
2009-05-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Ooi, Boon-Teck, Prof.
Nee, Hans-Peter, Prof.
QC 201008022009-05-122009-04-282010-08-03Bibliographically approved
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