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Tolerance Band Adaptation Method for Dynamic Operation of Grid-Connected Modular Multilevel Converters
KTH, School of Electrical Engineering (EES), Electric power and energy systems. ABB Corporate Research Vasteras, Sweden.ORCID iD: 0000-0001-8788-0415
KTH, School of Electrical Engineering (EES), Electric power and energy systems.ORCID iD: 0000-0002-8565-4753
2016 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, no 99, 1-1 p.Article in journal (Refereed) PublishedText
Abstract [en]

The use of modular multilevel converters (MMC) in high-voltage direct current (HVDC) transmission systems has grown significantly in the past decade. The efficiency, cell capacitor voltage ripple and dynamic performance are three contradictory aspects of the MMC which are related to the converter switching scheme. Previously introduced tolerance band-based schemes enable efficient and simple control for grid-connected MMCs. This paper addresses the dynamic operation of tolerance band switching schemes by proposing a dynamic boundary setting technique for steady-state operation and a switching scheme scheduling controller for transient fault handling. The performance of proposed methods are validated in a realistic point-to-point HVDC link, modeled in real-time digital simulator (RTDS) where two converters with 512 cells per arm are implemented. Utilizing the proposed methods will enable efficient implementation of tolerance band-based schemes for different operating points, and also a robust transient fault handling.

Place, publisher, year, edition, pages
IEEE , 2016. no 99, 1-1 p.
Keyword [en]
Capacitors, Converters, HVDC transmission, Harmonic analysis, Integrated circuits, Steady-state, Switche, HVDC transmission, Power conversion, Switching frequency, Switching loss
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-182748DOI: 10.1109/TPEL.2016.2521480ISI: 000380116600020ScopusID: 2-s2.0-84978646167OAI: diva2:905651

QC 20160311

Available from: 2016-02-23 Created: 2016-02-23 Last updated: 2016-09-16Bibliographically approved
In thesis
1. Modulation of Modular Multilevel Converters for HVDC Transmission
Open this publication in new window or tab >>Modulation of Modular Multilevel Converters for HVDC Transmission
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The outstanding features of modular multilevel converters (MMC) have recently gained much attention in the high-voltage direct-current (HVDC) transmission field. Power quality, converter cost and system performance are three crucial aspects of HVDC MMCs which are directly linked to the converter modulation and switching schemes. High power quality and performance require high switching frequency and large cell capacitor whereas low switching frequency and small cell capacitor are needed to reduce the converter cost.

The main objective of this thesis is to propose a practical switching method for HVDC MMCs which balances the aforementioned contradictory requirements. A mathematical analysis of the converter switching pattern, against the power quality and converter cost, has been conducted to formulate an optimization problem for MMCs. Different objective functions are studied for the formulated optimization problem such as converter loss minimization, voltage imbalance minimization and computational burden minimization. This thesis proposes three methods to address different objective functions. Ultimately, a real-time simulator has been built to practically verify and investigate the performance of the proposed methods in a realistic point-to-point HVDC link.

The most significant outcome of this thesis is the tolerance band-based switching scheme which offers a direct control of the cell capacitor voltage, low power losses, and robust dynamic performance. As a result, the converter switching frequency can reach frequencies as low as 70 Hz (with the proposed cell tolerance band (CTB) method). A modified optimized CTB method is proposed to minimize the converter switching losses and it could reduce the converter switching losses by 60% in comparison to the conventional phase shifted carrier modulation method.

It is concluded intelligent utilization of sorting algorithm can enable efficient HVDC station operation by reducing the converter cost.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 57 p.
TRITA-EE, ISSN 1653-5146 ; 2016:139
HVDC, switching schemes, modulation, high power converters, power grids
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
urn:nbn:se:kth:diva-192607 (URN)978-91-7729-098-8 (ISBN)
Public defence
2016-10-07, Sal D3, Kungl Tekniska Högskolan, Lindstedtsvägen 5, Stockholm, 10:00 (English)

QC 20160916

Available from: 2016-09-16 Created: 2016-09-15 Last updated: 2016-09-16Bibliographically approved

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