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Publications (10 of 21) Show all publications
Bessegato, L., Ilves, K., Harnefors, L., Norrga, S. & Östlund, S. (2019). Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies. IEEE transactions on power electronics
Open this publication in new window or tab >>Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies
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2019 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed) In press
Abstract [en]

Modular multilevel converters (MMCs) can be configured to perform ac/ac conversion, which makes them suitable as railway power supplies. In this paper, a hierarchical control scheme for ac/ac MMCs for railway power supplies is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. These models allow for analyzing the stability of the interconnected system using the impedance-based stability criterion and the passivity-based stability assessment. Finally, the findings presented in this paper are validated experimentally, using a down-scaled MMC. 

Keywords
Modular multilevel converters, ac/ac converters, current control, voltage control, admittance, frequency-domain analysis, linearization techniques, stability, railway engineering.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-248130 (URN)
Note

QC 20190404

Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-08-19Bibliographically approved
Bakas, P., Okazaki, Y., Ilves, K., Norrga, S., Harnefors, L. & Nee, H.-P. (2019). Design considerations and comparison of hybrid line-commutated and cascaded full-bridge converters with reactive-power compensation and active filtering capabilities. In: : . Paper presented at 2019 21st European Conference on Power Electronics and Applications (EPE'19 ECCE Europe).
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
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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
Bessegato, L., Ilves, K., Harnefors, L. & Norrga, S. (2019). Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter. IEEE transactions on power electronics, 34(8), 7206-7220, Article ID 8514034.
Open this publication in new window or tab >>Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter
2019 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, no 8, p. 7206-7220, article id 8514034Article in journal (Refereed) Published
Abstract [en]

The stability of a modular multilevel converter connected to an ac grid can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. The converter control parameters have a strong impact on the admittance and they can be adjusted for achieving system stability. This paper focuses on the admittance-shaping effect produced by different current-control schemes, either designed on a per-phase basis or in the $dq$ frame using space vectors. A linear analytical model of the converter ac-side admittance is developed, including the different current-control schemes and the phase-locked loop. Different solutions for computing the insertion indices are also analyzed, showing that for a closed-loop scheme a compact expression of the admittance is obtained. The impact of the control parameters on the admittance is discussed and verified experimentally, giving guidelines for designing the system in terms of stability. Moreover, recommendations on whether a simplified admittance expression could be used instead of the detailed model are given. The findings from the admittance-shaping analysis are used to recreate a grid-converter system whose stability is determined by the control parameters. The developed admittance model is then used in this experimental case study, showing that the stability of the interconnected system can be assessed using the Nyquist stability criterion.

Place, publisher, year, edition, pages
IEEE Press, 2019
Keywords
Modular multilevel converters, admittance, current control, stability, frequency-domain analysis, linearization techniques.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-238818 (URN)10.1109/TPEL.2018.2878600 (DOI)000469912200014 ()2-s2.0-85055681354 (Scopus ID)
Note

QC 20181113

Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2019-06-26Bibliographically approved
Björk, J., Johansson, K. H. & Harnefors, L. (2019). Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes. IEEE Transactions on Power Systems, 34(2), 1095-1104
Open this publication in new window or tab >>Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes
2019 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 34, no 2, p. 1095-1104Article in journal (Refereed) Published
Abstract [en]

This paper considers power oscillation damping (POD) using active power modulation of high-voltage dc transmissions. An analytical study of how the proximity between interarea modal frequencies in two interconnected asynchronous grids puts a fundamental limit to the achievable performance is presented. It is shown that the ratio between the modal frequencies is the sole factor determining the achievable nominal performance. To illustrate the inherent limitations, simulations using a proportional controller tuned to optimize performance in terms of POD are done on a simplified two-machine model. The influence of limited system information and unmodeled dynamics is shown. The analytical result is then further validated on a realistic model with two interconnected 32-bus networks.

Place, publisher, year, edition, pages
IEEE, 2019
Keywords
Controllability, frequency control, HVDC transmission control, interarea oscillations, power oscillation damping, small-signal stability
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-245892 (URN)10.1109/TPWRS.2018.2876554 (DOI)000459509400024 ()2-s2.0-85055035094 (Scopus ID)
Note

QC 20190811

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-11Bibliographically approved
Bakas, P., Ilves, K., Norrga, S., Harnefors, L. & Nee, H.-P. (2019). Hybrid alternate-common-arm converter with director thyristors: Impact of commutation time on the active-power capability. 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: . Paper presented at 2019 21st European Conference on Power Electronics and Applications (EPE'19 ECCE Europe), Genova, Italy, Sep. 2-6, 2019. Genova, Italy: IEEE and EPE Association
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
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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
Ali, M. T., Ghandhari, M. & Harnefors, L. (2019). Optimal tuning and placement of POD for SSCI mitigation in DFIG-based power system. In: 2019 IEEE Milan PowerTech, PowerTech 2019: . Paper presented at 2019 IEEE Milan PowerTech, PowerTech 2019; Milan; Italy; 23 June 2019 through 27 June 2019. Institute of Electrical and Electronics Engineers (IEEE), Article ID 8810891.
Open this publication in new window or tab >>Optimal tuning and placement of POD for SSCI mitigation in DFIG-based power system
2019 (English)In: 2019 IEEE Milan PowerTech, PowerTech 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, article id 8810891Conference paper, Published paper (Refereed)
Abstract [en]

The phenomenon of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) is investigated and the optimal tuning and placement of a power oscillation damper (POD) for its mitigation is proposed in this paper. The effect of the POD on the DFIG system is studied by placing it at all the summation junctions of rotor-side converter (RSC) and grid-side converter (GSC) controllers, turn by turn. Five local signals are examined as different input signals to the POD out of which three local signals gave promising results. These signals include the DFIG's active power, the magnitude of the DFIG's apparent power, and the magnitude of the current through the transmission line. Residues are calculated for each POD placement and for each input to the POD. The calculated residues are studied along with the root-locus plots to see the effect of the POD on the mitigation of SSCI and the stability of the DFIG-based system.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2019
Keywords
Doubly-fed induction generator, Eigenvalue analysis, Participation factor, Sub-synchronous control interaction
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-262636 (URN)10.1109/PTC.2019.8810891 (DOI)2-s2.0-85072344809 (Scopus ID)9781538647226 (ISBN)
Conference
2019 IEEE Milan PowerTech, PowerTech 2019; Milan; Italy; 23 June 2019 through 27 June 2019
Note

QC 20191018

Available from: 2019-10-18 Created: 2019-10-18 Last updated: 2019-10-18Bibliographically approved
Zhang, H., Wang, X., Harnefors, L., Gong, H., Hasler, J.-P. -. & Nee, H.-P. (2019). SISO Transfer Functions for Stability Analysis of Grid-Connected Voltage-Source Converters. IEEE transactions on industry applications, 55(3), 2931-2941, Article ID 8640057.
Open this publication in new window or tab >>SISO Transfer Functions for Stability Analysis of Grid-Connected Voltage-Source Converters
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2019 (English)In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 55, no 3, p. 2931-2941, article id 8640057Article in journal (Refereed) Published
Abstract [en]

Converter-grid interaction is of great interest in a weak-grid condition. This paper presents a single-input-single-output (SISO) open-loop transfer function for the stability analysis of grid-connected voltage-source converters. Differing from the conventional input impedance method and the eigenvalue analysis, an alternative multi-input-multi-output closed-loop system is developed in the paper and it eventually yields an SISO open-loop transfer function. This enables the application of a single Nyquist curve for analyzing the overall system stability. The model is validated against time-domain simulations as well as experimental results showing excellent accuracy for predicting the system stability.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers Inc., 2019
Keywords
Multi-input-multi-output (MIMO), Nyquist stability criterion, single-input-single-output (SISO), voltage-source converter (VSC), weak grid, Closed loop systems, Eigenvalues and eigenfunctions, MIMO systems, Stability criteria, System stability, Telecommunication repeaters, Time domain analysis, Multi input multi output, Single input single output, Voltage source converters, Transfer functions
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-252523 (URN)10.1109/TIA.2019.2898978 (DOI)000466033700073 ()2-s2.0-85064988163 (Scopus ID)
Note

QC 20190613

Available from: 2019-06-13 Created: 2019-06-13 Last updated: 2019-06-13Bibliographically approved
Zhang, H., Harnefors, L., Wang, X., Gong, H. & Hasler, J.-P. (2019). Stability Analysis of Grid-Connected Voltage-Source Converters Using SISO Modeling. IEEE transactions on power electronics, 34(8), 8104-8117
Open this publication in new window or tab >>Stability Analysis of Grid-Connected Voltage-Source Converters Using SISO Modeling
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2019 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, no 8, p. 8104-8117Article in journal (Refereed) Published
Abstract [en]

The interaction of a grid-connected voltage-source converter with a weak grid is of significant interest. In this paper, the converter together with the grid impedance is modeled as a single-input single-output (SISO) system. Provided that certain assumptions hold, this allows us to apply the standard SISO Nyquist stability criterion for stability analysis and controller design. The derivedmodel is verified against time-domain simulations and experiments. Themethod facilitates the design of the converter control system with adequate stability margins.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2019
Keywords
Multi-input multi-output (MIMO), Nyquist stability criterion, single-input single-output (SISO), voltage-source converter (VSC), weak grid
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-254067 (URN)10.1109/TPEL.2018.2878930 (DOI)000469912200081 ()
Note

QC 20190626

Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-06-26Bibliographically approved
Bessegato, L., Harnefors, L., Ilves, K. & Norrga, S. (2018). A Method for the Calculation of the AC-Side Admittance of a Modular Multilevel Converter. IEEE transactions on power electronics
Open this publication in new window or tab >>A Method for the Calculation of the AC-Side Admittance of a Modular Multilevel Converter
2018 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed) Published
Abstract [en]

Connecting a modular multilevel converter to anac grid may cause stability issues, which can be assessed byanalyzing the converter ac-side admittance in relation to the gridimpedance. This paper presents a method for calculating theac-side admittance of modular multilevel converters, analyzingthe main frequency components of the converter variables individually.Starting from a time-averaged model of the converter,the proposed method performs a linearization in the frequencydomain, which overcomes the inherent nonlinearities of theconverter internal dynamics and the phase-locked loop usedin the control. The ac-side admittance obtained analytically isfirstly validated by simulations against a nonlinear time-averagedmodel of the modular multilevel converter. The tradeoff posedby complexity of the method and the accuracy of the result isdiscussed and the magnitude of the individual frequency componentsis shown. Finally, experiments on a down-scaled prototypeare performed to validate this study and the simplification onwhich it is based.

Keywords
Modular multilevel converters, admittance, linearization techniques, frequency-domain analysis, stability.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-238815 (URN)10.1109/TPEL.2018.2862254 (DOI)000464911900018 ()2-s2.0-85050974319 (Scopus ID)
Note

QC 20181113

Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2019-05-14Bibliographically approved
Bakas, P., Ilves, K., Harnefors, L., Norrga, S. & Nee, H.-P. (2018). Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability. In: 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe): . Paper presented at 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe).
Open this publication in new window or tab >>Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability
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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
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3107-7073

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