Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
System Aspects and Modulation Strategies of an HVDC-based Converter System for Wind Farms
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

 

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.
Series
Trita-EE, ISSN 1653-5146 ; 2009:018
Keyword [en]
Isolated AC/DC Converter, Mutual Commutation, Soft Switching, Voltage Source Converter, Cycloconverter, Modulation Strategies, Medium-Frequency Transformer, HVDC Transmission, Wind Power, Wind Farms
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-10267ISBN: 978-91-7415-292-0 (print)OAI: oai:DiVA.org:kth-10267DiVA: diva2:213688
Public defence
2009-05-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100802Available from: 2009-05-12 Created: 2009-04-28 Last updated: 2010-08-03Bibliographically 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
4. Modulation strategies for a mutually commutated converter system in wind farms
Open this publication in new window or tab >>Modulation strategies for a mutually commutated converter system in wind farms
2007 (English)In: 2007 European Conference on Power Electronics and Applications, EPE, 2007, 1221-1230 p.Conference paper, Published paper (Refereed)
Abstract [en]

A novel mutually commutated converter (MCC) system consisting of a voltage source converter (VSC) and a cycloconverter connected by a medium-frequency (MF) transformer is adapted for the power collection and conversion in large wind farms. Different modulation strategies based on space vectors are described and evaluated with regard to the very restrictive constraints on the modulation and commutation of the thyristor valves in the cycloconverter. This paper shows that a feasible and effective modulation strategy can be found in order to provide the desired reference voltage vector during every single modulation interval and under all operating conditions. The proposed current clamping control strategy is based on stopping the gate pulses of the conducting thyristor valve during a certain dead-time whenever the current in the corresponding phase leg becomes zero.

Keyword
modulation strategy, vector control, wind energy, adjustable speed generation system, HVDC
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-14303 (URN)10.1109/EPE.2007.4417478 (DOI)000255993600134 ()2-s2.0-51049112239 (Scopus ID)978-90-75815-11-5 (ISBN)
Conference
2007 European Conference on Power Electronics and Applications, EPE; Aalborg; Denmark; 2 September 2007 through 5 September 2007
Note

QC 20100802

Available from: 2010-08-02 Created: 2010-08-02 Last updated: 2014-10-29Bibliographically approved
5. Space Vector Modulation for Mutually Commutated Isolated Three-Phase Converter Systems
Open this publication in new window or tab >>Space Vector Modulation for Mutually Commutated Isolated Three-Phase Converter Systems
2008 (English)In: 39th IEEE Power Electronic Specialists Conference (PESC 08) Rhodes, GREECE, JUN 15-19, 2008, 2008, 4465-4471 p.Conference paper, Published paper (Refereed)
Abstract [en]

Converter systems consisting of a voltage source converter and a cycloconverter connected by a medium-frequency transformer have several attractive properties. They offer bidirectional AC/DC conversion as well as voltage transformation and isolation by the transformer. Furthermore, it is possible to achieve soft-switching conditions for all semiconductor devices by consistently commutating the two converters in alternation; hence the name "mutually commutated converter system". Such a commutation scheme, however, imposes certain restrictions on the modulation of the converter system. A newly proposed space vector oriented modulation method promises superior performance compared to carrier-based modulation methods. This paper describes the implementation of the considered space vector modulation on the example of a 40 WA prototype converter system. The experimental results show that the evaluated space vector modulation is particularly beneficial at low output voltages due to its inherent nature of maximizing the zero voltage vectors.

Series
IEEE power electronics specialists conference records, ISSN 0275-9306
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-14304 (URN)000260398502252 ()2-s2.0-52349101714 (Scopus ID)
Note
QC 20100802Available from: 2010-08-02 Created: 2010-08-02 Last updated: 2010-08-02Bibliographically approved
6. Control Strategies for Mutually Commutated Converter Systems without Cycloconverter Turn-off Capability
Open this publication in new window or tab >>Control Strategies for Mutually Commutated Converter Systems without Cycloconverter Turn-off Capability
2008 (English)In: EEE POWER ELECTRONICS SPECIALISTS CONFERENCE RECORDS, 2008, 1344-1350 p.Conference paper, Published paper (Refereed)
Abstract [en]

Mutually commutated converter systems consisting of a voltage source converter and a cycloconverter connected by a medium-frequency transformer allow bidirectional AC/DC conversion as well as voltage transformation and isolation by the transformer. However, such converter systems require an extra power conversion stage compared to conventional converter systems, which may result in low system efficiency despite the soft-switching commutation scheme. In order to reduce the power losses in the cycloconverter, it is desirable to utilize fast thyristors instead of IGBTs. As a consequence, the cycloconverter valves lack turn-off capability because a thyristor can not be turned off by its gate. This paper describes and evaluates the most common control strategies in order to control a thyristor-based cycloconverter in a mutually commutated converter system. The behaviour of the cycloconverter depends strongly on the chosen control strategy when one of the output currents approaches zero, which may inherently affect the harmonic properties of the output voltages and currents. Experimental results from a 20 kVA prototype show that it is possible to successfully operate a mutually commutated converter system without turn-off capability.

Series
IEEE power electronics specialists conference records, ISSN 0275-9306
Keyword
Electric inverters, Electric rectifiers, Electric switchgear, Power electronics, Thyristors, Ac/dc conversion, Control strategies, Converter system, Cyclo converter, Fast thyristors, Harmonic properties, Output currents, Output voltages, Power conversion stage, Power losses, Soft-switching, System efficiencies, Turn-off, Voltage transformation, Voltage-source converter, Control systems
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-14305 (URN)10.1109/PESC.2008.4592121 (DOI)000260398500215 ()2-s2.0-52349110730 (Scopus ID)978-1-4244-1667-7 (ISBN)
Conference
39th IEEE Power Electronic Specialists Conference (PESC 08) Rhodes, GREECE, JUN 15-19, 2008
Note

QC 20100802

Available from: 2010-08-02 Created: 2010-08-02 Last updated: 2014-12-16Bibliographically approved
7. Design Considerations for Medium-Frequency Power Transformers in Offshore Wind Farms
Open this publication in new window or tab >>Design Considerations for Medium-Frequency Power Transformers in Offshore Wind Farms
2009 (English)In: 2009 13th European Conference on Power Electronics and Applications, EPE '09, IEEE , 2009, 757-768 p.Conference paper, Published paper (Refereed)
Abstract [en]

In a recently proposed converter system for offshore wind farms, single-phase medium-fire (MF) transformers replace the conventional three-phase line-frequency transformers that convert the electricity from the wind turbine generators to high voltage. MF operation allows a reduction of the transformer size and weight, thus leading to a compact and efficient design, which minimizes the installation and maintenance costs, This paper presents design considerations for dry-type single-phase MF power transformers in offshore wind farms. Recent transformer problems in large wind turbines have shown that a thorough and careful magnetic, electric, and thermal design is required to ensure the reliability and performance of the transformers. As a result, a suitable design for a 3 MW wind turbine transformer is proposed.

Place, publisher, year, edition, pages
IEEE, 2009
Keyword
Transformer, Design, Single phase system, Wind Energy
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-14306 (URN)000275384100085 ()2-s2.0-72949120842 (Scopus ID)978-1-4244-4432-8 (ISBN)
Conference
13th European Conference on Power Electronics and Applications (EPE 2009) Barcelona, SPAIN, SEP 08-10, 2009
Note

QC 20100802

Available from: 2010-08-02 Created: 2010-08-02 Last updated: 2014-10-09Bibliographically approved

Open Access in DiVA

spikblad(105 kB)28 downloads
File information
File name SPIKBLAD01.pdfFile size 105 kBChecksum SHA-512
5a31f9fa99eda01f54da9d40cdb4abd76358d1f0b4289c778efa694f1a4d8d9975e1b3b4d45d4d825b90fc085b1729346da2fe23b76c489b0eded3e168a1d1c7
Type spikbladMimetype application/pdf
fulltext(2556 kB)2038 downloads
File information
File name FULLTEXT02.pdfFile size 2556 kBChecksum SHA-512
131ec8b5a3909aa1b05b3a85e785cb15db0b6b5ade4a4a94a36e1d374e85e2e5e797ed418aad0b8747fd5573b8d24537b1451708d5b77c1bb065b84aeb138dbe
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Meier, Stephan
By organisation
Electrical Machines and Power Electronics
Other Electrical Engineering, Electronic Engineering, Information EngineeringOther Electrical Engineering, Electronic Engineering, Information Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 2040 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 849 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf