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Novel voltage source converter based HVDC transmission system for offshore wind farms
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Offshore wind farms have recently emerged as promising renewable energy sources. For increasing distances between offshore generation and onshore distribution grid, HVDC transmission systems based on voltage source converters can be a feasible and competitive solution. This thesis presents a comprehensive evaluation of a novel integrated wind farm topology that includes the generator drive system, the turbine interconnection and the HVDC transmission.

In the proposed concept, every wind turbine is connected to a single-phase medium-frequency collection grid via a distribution transformer and a cycloconverter, which allows the wind turbines to operate at variable speed. The collection grid is connected to an HVDC cable via a transmission transformer and a single-phase voltage source converter. This thesis evaluates in detail the principle of operation, which is also verified with system simulations in PSCAD.

The proposed concept promises several potential benefits. Converter switching losses and stress on the semiconductors for example can be considerably reduced by applying a soft-switched commutation scheme in all points of operation. Single-phase medium-frequency transformers have comparably low losses and their compact size and low weight implies an important benefit in an offshore environment. In addition, the voltage source converter is considerably simplified by the reduction to one phase leg, which implies a substantial cost saving.

Several technical challenges are identified and critically evaluated in order to guarantee the feasibility of the proposed concept. Especially the design of the medium-frequency collection grid is crucial as unwanted system resonances can cause dangerous overvoltages. Most of the technical challenges concern the specific characteristics of the proposed concept. The insulation of the single-phase medium-frequency transformers for example needs to withstand the high voltage derivatives. This thesis contains also considerations regarding the dimensioning and optimization of different system components.

A survey of different transmission systems for the grid connection of wind farms shows the potential of the proposed concept, which addresses several problems associated with electrical systems of wind farms. Both the requirements for variable-speed operation of the wind turbines and an interface for HVDC transmission are fulfilled in a cost-effective way. Compared to conventional voltage source converter based HVDC transmission systems, the initial costs are reduced and the expected annual energy production is increased. In addition, the proposed voltage source converter based HVDC transmission system can fully comply with recent requirements regarding the grid connection of wind farms.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , x, 112 p.
Series
Trita-ETS, ISSN 1650-674X ; 2005:15
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-568ISBN: 91-7178-206-0 (print)OAI: oai:DiVA.org:kth-568DiVA: diva2:14453
Presentation
2005-12-12, sal V3, KTH, Teknikringen 33, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101213Available from: 2005-12-28 Created: 2005-12-28 Last updated: 2010-12-13Bibliographically approved
List of papers
1. New topology for more efficient AC/DC converters for future offshore wind farms
Open this publication in new window or tab >>New topology for more efficient AC/DC converters for future offshore wind farms
2004 (English)In: Proceedings of the 4th Nordic Workshop on Power and Industrial Electronics, Norpie ’04, Trondheim, Norway, June 2004, 2004, 1-6 p.Conference paper, Published paper (Refereed)
Abstract [en]

The concept of a novel soft-switching AC/DC converteris applied for use in future offshore wind farms. A voltagesource converter with capacitive snubbers and cycloconverters,connected via a medium frequency AC bus, promises substantialbenefits. This paper presents this new topology and describes itsprinciple of operation. Furthermore, a comparison with state-ofthe-art adjustable speed generators reveals the potential of thisnew concept.

Keyword
Wind power, Wind turbine, Power electronics, Power converter, Offshore, Soft-switching
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-14300 (URN)
Conference
4th Nordic Workshop on Power and Industrial Electronics, Norpie ’04, Trondheim, Norway, June 2004
Note
QC 20100802Available from: 2010-08-02 Created: 2010-08-02 Last updated: 2011-11-17Bibliographically approved
2. New Voltage Source Converter Topology for HVDC Grid Connection of Offshore Wind Farms
Open this publication in new window or tab >>New Voltage Source Converter Topology for HVDC Grid Connection of Offshore Wind Farms
2004 (English)In: Proceedings of the 11th International Power Electronics and Motion Control Conference, EPEPEMC ’04, Riga, Latvia, September 2004, 2004, 1-7 p.Conference paper, Published paper (Refereed)
Abstract [en]

Large offshore wind farms are recently emerging aspromising alternative power sources. Long distances betweenoffshore generation and onshore distribution grid demand new solutions for their connection to the AC network. HVDC systems based on voltage source converters (VSC) are a promisingalternative to conventional AC transmission above a certain cablelength. This paper presents a new VSC transmission topology for HVDC grid connection of offshore wind farms.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-14301 (URN)
Note
QC 20100802Available from: 2010-08-02 Created: 2010-08-02 Last updated: 2011-11-15Bibliographically approved
3. Benchmark of annual energy production for different wind farm topologies
Open this publication in new window or tab >>Benchmark of annual energy production for different wind farm topologies
2005 (English)In: PESC Record - IEEE Annual Power Electronics Specialists Conference, 2005, Vol. 2005, no 1581918, 2073-2080 p.Conference paper, Published paper (Refereed)
Abstract [en]

Wind power generation has become an established alternative power source. Especially large wind farms in remote or offshore locations are emerging strongly. Their grid connection demands new transmission solutions as distances increase. A newly proposed voltage source converter (VSC) based HVDC transmission system looks promising compared to conventional AC and DC transmission systems. This paper presents a benchmark of the estimated annual energy production (AEP) of a 200 MW wind farm depending on the transmission distance and the average wind speed. The proposed system is compared to two state-of-the-art wind farm topologies: Variable-speed wind turbines with doubly-fed induction generators (DFIG) and either AC or DC transmission systems. The benchmark comprises detailed drive-train, converter, transformer, distribution and transmission loss models. The total system losses as well as the loss distribution between the different components as a function of the transmission distance and the average wind speed allows important conclusions for future wind farm projects.

Series
IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE RECORDS, ISSN 0275-9306
Keyword
Asynchronous generators, Benchmarking, Electric power transmission, Power converters, Wind power, Wind turbines, Alternative power sources, Energy production, Wind farm topologies, Wind power generation, Power generation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-14302 (URN)10.1109/PESC.2005.1581918 (DOI)000237036502019 ()2-s2.0-33847766467 (Scopus ID)0-7803-9033-4 (ISBN)
Conference
36th Annual IEEE Power Electronic Specialists Conference (PESC 05) Recife, BRAZIL, JUN 12-16, 2005
Note
QC 20100802Available from: 2010-08-02 Created: 2010-08-02 Last updated: 2011-10-14Bibliographically approved

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