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  • 1.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Antonopoulos, Antonios
    ABB Corporate Research Center, Sweden.
    Harnefors, Lennart
    ABB Corporate Research Center, Sweden.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    A computationally efficient continuous model for the modular multilevel converter2014In: IEEE Journal of Emerging and Selected Topics in Power Electronics, ISSN 2168-6777, Vol. 2, no 4, p. 1139-1148, article id 6840290Article in journal (Refereed)
    Abstract [en]

    Simulation models of the modular multilevel converter (MMC) play a very important role for studying the dynamic performance. Detailed modeling of the MMC in electromagnetic transient simulation programs is cumbersome, as it requires high computational effort and simulation time. Several averaged or continuous models proposed in the literature lack the capability to describe the blocked state. This paper presents a continuous model, which is capable of accurately simulating the blocked state. This feature is very important for accurate simulation of faults. The model is generally applicable, although it is particularly useful in high-voltage dc applications.

  • 2.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Mitigation of Sub-Synchronous Control Interaction in DFIGs using a Power Oscillation Damper2017In: 2017 IEEE Manchester PowerTech, Powertech 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7980941Conference paper (Refereed)
    Abstract [en]

    The aim of this research work is to analyse subsynchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) and to design a supplementary control technique for the mitigation of SSCI. A mathematical model of the DFIG is derived and linearized in order to perform an eigenvalue analysis. This analysis pinpoints the parameters of the system which are sensitive in making sub-synchronous modes unstable and hence are responsible for causing SSCI. A power oscillation damper (POD) is designed using a residue method to make the DFIG system immune to the SSCI. The POD control signal acts as a supplementary control, which is fed to the controller of the grid-side converter (GSC). The POD signal is applied to different summation junctions of the GSC controller in order to determine the best placement of the POD for effective mitigation of SSCI and for the increased damping of the system.

  • 3.
    Bakas, Panagiotis
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. ABB Corporate Research, Sweden.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. ABB Corporate Research, Sweden.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nami, A.
    Ilves, K.
    Dijkhuizen, F.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hybrid Topologies for Series and Shunt Compensation of the Line-Commutated Converter2016In: 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 (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.

  • 4.
    Bakas, Panagiotis
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. ABB Corporate Research, Sweden.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. ABB Corporate Research, Sweden.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nami, Alireza
    ABB Corporate Research, Sweden.
    Ilves, Kalle
    ABB Corporate Research, Sweden.
    Dijkhuizen, Frans
    ABB Corporate Research, Sweden.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    A Review of Hybrid Topologies Combining Line-Commutated and Cascaded Full-Bridge Converters2017In: 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)
    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).

  • 5.
    Bakas, Panagiotis
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. ABB Corp Res, Västerås, Sweden..
    Ilves, K.
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. ABB Corp Res, Västerås, Sweden..
    Norrga, S.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nee, H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability2018In: 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe), 2018Conference 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).

  • 6.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Harnefors, Lennart
    Ilves, Kalle
    Norrga, Staffan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    A Method for the Calculation of the AC-Side Admittance of a Modular Multilevel Converter2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed)
    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.

  • 7.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    Ilves, Kalle
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation2016In: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE), IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    This paper applies a control method based on current control and sum-capacitor-voltage estimation to the direct ac/ac modular multilevel converter. As capacitor voltages are estimated, their measurements are not needed in the high-level control, which simplifies the communication between the main controller and the submodules of the converter. The stability of the internal dynamics of the converter, using the aforementioned control method, is studied using Lyapunov stability theory, proving that the system is globally asymptotically stable. The behavior of the converter is simulated focusing on three-phase 50 Hz to single-phase 16 (2)/(3) Hz conversion, which is typical for railway power supply systems of some European countries. Simulation results are in agreement with the expected behavior of the converter, both in steady-state and dynamic situations.

  • 8.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Ilves, Kalle
    Harnefors, Lennart
    Norrga, Staffan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter2019In: 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)
    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.

  • 9.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Ilves, Kalle
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Harnefors, Lennart
    Norrga, Staffan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies2019In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed)
    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. 

  • 10.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ilves, K.
    Harnefors, Lennart
    Ac-side admittance calculation for modular multilevel converters2017In: 2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia, IFEEC - ECCE Asia 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 308-312Conference paper (Refereed)
    Abstract [en]

    Power electronic converters may interact with the grid, thereby influencing dynamic behavior and resonances. Impedance and passivity based stability criteria are two useful methods that allow for studying the grid-converter system as a feedback system, whose behavior is determined by the ratio of grid and converter impedances. In this paper, the ac-side admittance of the modular multilevel converter is calculated using harmonic linearization and considering five specific frequency components of the converter variables. The proposed model features remarkable accuracy, verified through simulations, and insight into the influence of converter and control parameters on the admittance frequency characteristics, which is useful for understanding grid-converter interaction and designing the system.

  • 11.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ilves, Kalle
    Harnefors, Lennart
    Control of Modular Multilevel Matrix Converters Based on Capacitor Voltage Estimation2016In: IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), 2016, IEEE, 2016, p. 3447-3452, article id 7512848Conference paper (Refereed)
    Abstract [en]

    In this paper, a control method based on capacitor voltage estimation is applied to the modular multilevel matrix converter topology. By using such control method, capacitor voltage measurement is not needed in the high-level control. A state-space model of the converter and the control method is developed. Lyapunov stability theory is used to prove global asymptotic stability of the internal dynamics of the converter. Simulation results showing the behavior of the converter in steady-state and dynamic situations are presented.

  • 12.
    Björk, Joakim
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes2019In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 34, no 2, p. 1095-1104Article in journal (Refereed)
    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.

  • 13.
    Nikouei Harnefors, Mojgan
    et al.
    KTH, School of Electrical Engineering (EES).
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES).
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES).
    Operation Under Fault Conditions of the Stacked Polyphase Bridges Converter2016Conference paper (Refereed)
    Abstract [en]

    The stacked polyphase bridges converter consists of several submodules that, on the input dc side, all are connected in series. Whereas controller designs presented in previous studies have been found promising for realizing equal voltage sharing between submodules, the survival and stability under fault conditions have not been studied. This paper presents a control strategy that enables survival of the converter after the occurrence of a sudden short circuit of a single transistor switch. The results are verified by simulations.

  • 14.
    Nikouie, Mojgan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Wallmark, Oskar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Torque-Ripple Minimization for Permanent-Magnet Synchronous Motors Based on Harmonic Flux Estimation2018In: 2018 20TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'18 ECCE EUROPE), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    This paper presents a control algorithm to reduce the torque ripple in permanent-magnet synchronous motors. This control algorithm is based on the on-line estimation of harmonic flux linkage. Together with the on-line estimation of the flux linkage, a proportional-integral-resonant controller is introduced to suppress the torque ripple.

  • 15.
    Nikouie, Mojgan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Wallmark, Oskar
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Torque-Ripple Minimization for Permanent-MagnetSynchronous Motors Based on Harmonic Flux Estimation2018Conference paper (Refereed)
    Abstract [en]

    This paper presents a control algorithm to reduce the torque ripple in permanent-magnet synchronous motors. This control algorithm is based on the on-line estimation of harmonic flux linkage. Together with the online estimation of the flux linkage, a proportional–integral–resonant controller is introduced to suppress the torque ripple.

  • 16. Stamatiou, Georgios
    et al.
    Beza, Mebtu
    Bongiorno, Massimo
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Analytical derivation of the DC-side input admittance of the direct-voltage controlled modular multilevel converter2017In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 11, no 16, p. 4018-4030Article in journal (Refereed)
    Abstract [en]

    The input admittance of a converter, connected to other dynamic subsystems, is a useful tool to investigate whether poorly damped oscillations or even unstable conditions might occur at certain frequencies. This is of interest in applications employing the modular multilevel converter (MMC), where the internal dynamics of the converter and the increased number of control loops greatly affect the MMC's dynamic behaviour, compared to other types of converters. In this study, the dc-side input admittance of the direct-voltage controlled MMC is derived analytically and verified via small-signal perturbation in a detailed non-linear time-domain simulation model. The MMC's input admittance is parametrically studied and compared to the dc-side input admittance of an equivalent two-level converter.

  • 17. Zhang, H.
    et al.
    Wang, X.
    Harnefors, Lennart
    ABB, Västerås, Sweden.
    Gong, H.
    Hasler, J. -P
    Nee, Hans-Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    SISO Transfer Functions for Stability Analysis of Grid-Connected Voltage-Source Converters2019In: 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)
    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.

  • 18.
    Zhang, Hongyang
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. ABB, Power Grids Div, S-72164 Vasteras, Sweden.
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. ABB, Corp Res, S-72178 Vasteras, Sweden..
    Wang, Xiongfei
    Aalborg Univ, Dept Energy Technol, DK-9220 Aalborg, Denmark..
    Gong, Hong
    Aalborg Univ, Dept Energy Technol, DK-9220 Aalborg, Denmark..
    Hasler, Jean-Philippe
    ABB, Power Grids Div, S-72164 Vasteras, Sweden..
    Stability Analysis of Grid-Connected Voltage-Source Converters Using SISO Modeling2019In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, no 8, p. 8104-8117Article in journal (Refereed)
    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.

1 - 18 of 18
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