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Hybrid Converters for HVDC Transmission
KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. (Power Electronics)ORCID iD: 0000-0002-7739-9668
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The line-commutated converter (LCC) and the voltage-source converter (VSC) are the two main converter technologies utilized in high-voltage direct current (HVDC) transmission applications. Depending on the application requirements, one technology might be more advantageous than the other. On the one hand, the LCC features technological maturity, high efficiency, and high power-transfer capability, but it lacks the ability to independently control active and reactive power and to ride through ac faults. On the other hand, the VSC overcomes the shortcomings of the LCC and offers more functionality, as it features the ability to independently control active and reactive power, ac-fault ride through capability, black-start capability, and superior harmonic performance. Yet, it is less mature, less efficient, and has lower power-transfer capability than the LCC. Thus, the combination of the LCC and the VSC topologies could yield hybrid converters that leverage the complementary characteristics of both technologies and thus are optimized for HVDC applications. Therefore, the main objective of this thesis is to investigate existing and derive new hybrid converters that combine the complementary characteristics of the LCC and VSC technologies.

The hybrid converters investigated in this thesis are divided in two main categories, namely: (a) current-source; and (b) voltage-source hybrid converters. The former category includes hybrid converters that are based on the LCC structure and utilize a VSC part either for compensating the reactive power consumed by the LCC, or for active filtering of the LCC current harmonics, or for independently controlling active and reactive power, or for achieving a combination of these functionalities. Four different current-source hybrid converters have been investigated and compared in terms of functionality, conduction losses, and semiconductor requirements.

The second category includes more complex circuits that combine thyristors and modular VSC elements in ways that enable these hybrid converters to operate as VSCs and to achieve high active-power capability. Two new voltage-source hybrid converters are analyzed and compared in terms of active-power capability, semiconductor requirements, and controllability. This study reveals that the hybrid alternate-common-arm converter (HACC) is the most interesting circuit; thus, an in-depth analysis is performed for this converter. The theoretical analysis shows that, under certain operating conditions, the HACC can transfer twice the active power of the full-bridge modular multilevel converter (FB-MMC) with lower semiconductor rating per unit of active power. Yet, if the total commutation time of the thyristors and/or the power angle are increased beyond certain values, the active-power capability of the HACC is reduced. Finally, simulation and experimental results are provided in order to verify the theoretical analysis and prove the feasibility of the HACC.

Abstract [sv]

Linjekommuterade (LCC) och spänningsstyva (VSC) omvandlare är de två huvudteknologier som används i högspänd likströmsöverföring (HVDC). Beroende på applikationskraven kan den ena varianten vara mer fördelaktig än den andra. LCC är teknologiskt mogen, har hög effektivitet och hög överföringskapacitet, men det saknar förmåga att styra den reaktiva effekten oberoende av den aktiva effekten. LCC är också känslig för ac-linjefel. VSC har inte dessa brister och erbjuder dessutom möjlighet till så kallad “black start”. Den harmoniska prestandan är överlägsen. Dock är tekniken mindre mogen, har något lägre verkningsgrad och lägre överföringskapacitet än LCC. Sålunda kan kombinationen av LCC- och VSC-teknologierna ge hybridomvandlare som utnyttjar de komplementära egenskaperna och därför lämpar sig väl i HVDC-applikationer. Huvudsyftet med denna avhandling är att undersöka befintliga och utveckla nya hybridomvandlare som kombinerar de komplementära egenskaperna hos LCC- och VSC-teknologierna.

Omvandlarna som undersöks i denna avhandling är uppdelade i två huvudkategorier: (a) strömstyv och (b) spänningsstyv. Den förstnämnda kategorin innefattar hybridomvandlare som är baserade på LCC-strukturen och använder en VSCdel antingen för att kompensera den förbrukade reaktiva effekten, för aktiv filtrering av strömövertonerna som genereras av LCC-omvandlaren, för att oberoende styra aktiv och reaktiv effekt eller för att uppnå en kombination av dessa funktioner. Fyra olika strömstyva hybridomvandlare har undersökts och jämförts med avseende på funktionalitet, ledningsförluster och halvledarkrav.

Den andra kategorin innehåller mer komplexa kretsar som kombinerar tyristorer och modulära VSC-element på sätt som gör det möjligt för dessa hybridomvandlare att fungera som VSC och för att uppnå hög överföring av aktiv effekt. Två nya spänningsstyva hybridomvandlare analyseras och jämförs med avseende på aktiv effekt, halvledarkrav och styrbarhet. Denna studie visar att den så kallade "hybrid alternate-common-arm converter" (HACC) är den mest intressanta topologin. Därför utförs en djupgående analys för denna omvandlare. Den teoretiska analysen visar att HACC under vissa driftsförhållanden kan överföra två gånger den aktiva effekten hos en modulär multinivåomvandlare med fullbryggor (FB-MMC) med lägre halvledarbehov per enhet av aktiv effekt. Dock reduceras överföringsförmågan om den totala kommuteringstiden för tyristorerna och/eller effektvinkeln överskrider vissa värden. Slutligen redovisas simuleringar och experimentella resultat för att verifiera den teoretiska analysen och påvisa fördelarna med HACC-topologin.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2019. , p. 144
Series
TRITA-EECS-AVL ; 2019:62
Keywords [en]
High-voltage direct current (HVDC), hybrid alternate-common arm converter (HACC), hybrid converters, line-commutated converters (LCCs), modular multilevel converters (MMCs), thyristors
Keywords [sv]
"Hybrid alternate-common-arm converter" (HACC), hybrid omvandlare, högspänd likströmsöverföring (HVDC), linjekommuterade omvandlare (LCC), modulära multinivåomvandlare (MMC), tyristorer
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-262704ISBN: 978-91-7873-266-1 (electronic)OAI: oai:DiVA.org:kth-262704DiVA, id: diva2:1362111
Public defence
2019-11-20, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, SP8
Note

QC 20191018

Available from: 2019-10-18 Created: 2019-10-18 Last updated: 2019-10-18Bibliographically approved
List of papers
1. A Review of Hybrid Topologies Combining Line-Commutated and Cascaded Full-Bridge Converters
Open this publication in new window or tab >>A Review of Hybrid Topologies Combining Line-Commutated and Cascaded Full-Bridge Converters
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2017 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 32, no 10, p. 7435-7448, article id 7750589Article, review/survey (Refereed) Published
Abstract [sv]

This paper presents a review of concepts for enabling the operation of a line-commutated converter (LCC) at leading power angles. These concepts rely on voltage or current injection at the ac or dc sides of the LCC, which can be achieved in different ways. We focus on the voltage and current injection by full-bridge (FB) arms, which can be connected either at the ac or dc sides of the LCC and can generate voltages that approximate ideal sinusoids. Hybrid configurations of an LCC connected at the ac side in series or in parallel with FB arms are presented. Moreover, a hybrid configuration of an LCC connected in parallel at the ac side and in series at the dc side with an FB modular multilevel converter (MMC) is outlined. The main contribution of this paper is an analysis and comparison of the mentioned hybrid configurations in terms of the capability to independently control the active (P) and reactive power (Q).

Place, publisher, year, edition, pages
IEEE Press, 2017
Keywords
Topology, Power conversion, Thyristors, Harmonic analysis, Power capacitors
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-203775 (URN)10.1109/TPEL.2016.2631250 (DOI)000401320000004 ()2-s2.0-85019413296 (Scopus ID)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, SP8
Note

QC 20170405

Available from: 2017-03-16 Created: 2017-03-16 Last updated: 2019-10-18Bibliographically approved
2. Hybrid alternate-common-arm converter with high power capability: Potential and limitations
Open this publication in new window or tab >>Hybrid alternate-common-arm converter with high power capability: Potential and limitations
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(English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Other academic) Submitted
Abstract [en]

This paper studies a new hybrid converter thatutilizes thyristors and full-bridge (FB) arms for achieving higherpower capability than the full-bridge (FB) modular multilevel converter (MMC) with reduced semiconductor requirements. The study covers the theoretical analysis of the energy balancing,the dimensioning principles, the maximum power capability, and the limitations imposed by the discontinuous operation of theconverter. Based on the analysis of these aspects, the theoretical analysis is concluded by identifying the design constraints that need to be fulfilled for achieving the maximum power capabilityof the converter. It is concluded that the maximum power capability can be achieved for a certain range of modulation indices and is limited by both the commutation time of the thyristors andthe power angle. Finally, simulation and experimental results that confirm the theoretical analysis and the feasibility of the studied converter are presented and discussed.

Place, publisher, year, edition, pages
IEEE
Keywords
DC-AC power conversion, HVDC transmission, Thyristors
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-262701 (URN)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, SP8
Note

QC 20191018

Available from: 2019-10-18 Created: 2019-10-18 Last updated: 2019-10-21Bibliographically approved
3. Hybrid Topologies for Series and Shunt Compensation of the Line-Commutated Converter
Open this publication in new window or tab >>Hybrid Topologies for Series and Shunt Compensation of the Line-Commutated Converter
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2016 (English)In: 8th International Power Electronics and Motion Control Conference - ECCE Asia, IPEMC 2016-ECCE Asia, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 3030-3035, article id 7512779Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents two concepts for enabling the operation of a line-commutated converter (LCC) at leading power angles. The concepts are based on voltage or current injection at the ac side of an LCC, which can be achieved in different ways. However, this paper focuses on the voltage and current injection by series-connected full-bridge cells that can generate voltages that approximate ideal sinusoids. Thus, hybrid configurations of an LCC connected at the ac side in series or in parallel with fullbridge cells are presented. Finally, these hybrid configurations are compared in terms of voltage and current rating.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2016
Keywords
DC-AC power converters, HVDC transmission, static VAr compensators
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-197894 (URN)10.1109/IPEMC.2016.7512779 (DOI)000390949703032 ()2-s2.0-84983358969 (Scopus ID)978-1-5090-1210-7 (ISBN)
Conference
8th IEEE International Power Electronics and Motion Control Conference, IPEMC-ECCE Asia 2016, Hefei, China, 22 May 2016 through 26 May 2016
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, SP8
Note

QC 200161212. QC 20191018

Available from: 2016-12-08 Created: 2016-12-08 Last updated: 2019-10-18Bibliographically approved
4. Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability
Open this publication in new window or tab >>Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability
Show others...
2018 (English)In: 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe), 2018Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the basic operating principles of a new hybrid converter that combines thyristors and full-bridge (FB) arms for achieving high active-power capability. This converter consists of a modular multilevel converter (MMC) equipped with additional common arms, which alternate between the upper and lower dc poles. This alternation is achieved by the thyristors that are utilized as director switches and allow the parallel connection of the common arms and the arms of the MMC. The main contributions of this paper are the analysis of the operating principles, the simulation verification of the functionality of the proposed converter, and the comparison of the latter with the full-bridge modular multilevel converter (FB-MMC).

Keywords
HVDC power convertors;thyristors;hybrid converter;modular multilevel converter;converter circuit;HVDC
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-239574 (URN)000450299300042 ()
Conference
2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, SP8
Note

QC 20181210. QC 20191018

Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2019-10-18Bibliographically approved
5. Design considerations and comparison of hybrid line-commutated and cascaded full-bridge converters with reactive-power compensation and active filtering capabilities
Open this publication in new window or tab >>Design considerations and comparison of hybrid line-commutated and cascaded full-bridge converters with reactive-power compensation and active filtering capabilities
Show others...
2019 (English)Conference paper, Published paper (Other academic)
Abstract [en]

This paper compares two hybrid topologies that combine the line-commutated converter (LCC) with cascaded full-bridge (FB) converters. The latter are utilized for compensating the reactive power and filtering the current harmonics of the LCC. The method that was developed for dimensioning these hybrid topologies is presented in detail. This method is utilized for calculating the arm voltage and current waveforms, which are used to estimate other important quantities, such as conduction losses and energy variations. Finally, the studied converters are compared in terms of voltage/current ratings, semiconductor requirements, conduction losses, and energy variations.

Keywords
Converter circuit, HVDC, Multilevel converters, Thyristor.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-262671 (URN)978-9-0758-1530-6 (ISBN)
Conference
2019 21st European Conference on Power Electronics and Applications (EPE'19 ECCE Europe)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, SP8
Note

QC 20191018

Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-10-18Bibliographically approved
6. Hybrid alternate-common-arm converter with director thyristors: Impact of commutation time on the active-power capability
Open this publication in new window or tab >>Hybrid alternate-common-arm converter with director thyristors: Impact of commutation time on the active-power capability
Show others...
2019 (English)In: Proc. 2019 21st European Conference on Power Electronics and Applications (EPE'19 ECCE Europe), IEEE and EPE Association, Genova, Italy, Sep. 2-6, 2019, Genova, Italy: IEEE and EPE Association , 2019Conference paper, Published paper (Other academic)
Abstract [en]

This paper investigates the impact of the thyristor commutation time on the peak currents and the active power capability of the hybrid alternate-common-arm converter (HACC). This converter employs director thyristors for the alternate connection of a common arm in parallel to the main arms. The parallel connection enables current sharing among the arms, which allows the HACC to transfer higher output power without increasing the peak arm current. It is shown that the active-power capability of the HACC is doubled for a certain current-sharing factor, which, however, is altered by the thyristor commutation time. Therefore, the impact of the commutation time on the active-power capability of the HACC is investigated theoretically. Finally, this analysis is verified by simulation results.

Place, publisher, year, edition, pages
Genova, Italy: IEEE and EPE Association, 2019
Keywords
Converter circuit, HVDC, Multilevel converters, Thyristor.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-262670 (URN)978-9-0758-1530-6 (ISBN)
Conference
2019 21st European Conference on Power Electronics and Applications (EPE'19 ECCE Europe), Genova, Italy, Sep. 2-6, 2019
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, SP8
Note

QC 20191018

Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-10-21Bibliographically approved

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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
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  • de-DE
  • en-GB
  • en-US
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  • nn-NO
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  • Other locale
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