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  • 1.
    Ahmed, Noman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Antonopoulos, Antonios
    ABB Corporate Research Center, Sweden.
    Harnefors, Lennart
    ABB Corporate Research Center, Sweden.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    A computationally efficient continuous model for the modular multilevel converter2014Inngår i: IEEE Journal of Emerging and Selected Topics in Power Electronics, ISSN 2168-6777, Vol. 2, nr 4, s. 1139-1148, artikkel-id 6840290Artikkel i tidsskrift (Fagfellevurdert)
    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, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ghandari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Mitigation of Sub-Synchronous Control Interaction in DFIGs using a Power Oscillation Damper2017Inngår i: 2017 IEEE Manchester PowerTech, Powertech 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, artikkel-id 7980941Konferansepaper (Fagfellevurdert)
    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.
    Ali, Muhammad Taha
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ghandhari, Mehrdad
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Optimal tuning and placement of POD for SSCI mitigation in DFIG-based power system2019Inngår i: 2019 IEEE Milan PowerTech, PowerTech 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, artikkel-id 8810891Konferansepaper (Fagfellevurdert)
    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.

  • 4.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik. ABB Corporate Research, Sweden.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik. ABB Corporate Research, Sweden.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Nami, A.
    ABB Corporate Research, Sweden.
    Ilves, K.
    ABB Corporate Research, Sweden.
    Dijkhuizen, F.
    ABB Corporate Research, Sweden.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Hybrid Topologies for Series and Shunt Compensation of the Line-Commutated Converter2016Inngår i: 8th International Power Electronics and Motion Control Conference - ECCE Asia, IPEMC 2016-ECCE Asia, Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 3030-3035, artikkel-id 7512779Konferansepaper (Fagfellevurdert)
    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.

  • 5.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik. ABB Corporate Research, Sweden.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik. ABB Corporate Research, Sweden.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Nami, Alireza
    ABB Corporate Research, Sweden.
    Ilves, Kalle
    ABB Corporate Research, Sweden.
    Dijkhuizen, Frans
    ABB Corporate Research, Sweden.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    A Review of Hybrid Topologies Combining Line-Commutated and Cascaded Full-Bridge Converters2017Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 32, nr 10, s. 7435-7448, artikkel-id 7750589Artikkel, forskningsoversikt (Fagfellevurdert)
    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).

  • 6.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB Corporate Research, Västerås, Sweden.
    Ilves, K.
    ABB Corporate Research, Västerås, Sweden.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB Corporate Research, Västerås, Sweden.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability2018Inngår i: 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe), 2018Konferansepaper (Fagfellevurdert)
    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).

  • 7.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ilves, Kalle
    ABB Corporate Research.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid alternate-common-arm converter with director thyristorsImpact of commutation time on the active-power capability: Impact of commutation time on the active-power capability2019Inngår i: 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 , 2019Konferansepaper (Annet vitenskapelig)
    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.

  • 8.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ilves, Kalle
    ABB Corporate Research.
    Okazaki, Yuhei
    ABB Corporate Research.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB Corporate Research.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid alternate-common-arm converter with high power capability: potential and limitationsInngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikkel i tidsskrift (Annet vitenskapelig)
    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.

  • 9.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Okazaki, Yuhei
    ABB Corporate Research.
    Ilves, Kalle
    ABB Corporate Research.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Design considerations and comparison of hybrid line-commutated and cascaded full-bridge converters with reactive-power compensation and active filtering capabilities2019Konferansepaper (Annet vitenskapelig)
    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.

  • 10.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    Ilves, Kalle
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    A Method for the Calculation of the AC-Side Admittance of a Modular Multilevel Converter2018Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 11.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Harnefors, Lennart
    Ilves, Kalle
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Östlund, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation2016Inngår i: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE), IEEE, 2016Konferansepaper (Fagfellevurdert)
    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.

  • 12.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ilves, Kalle
    Harnefors, Lennart
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter2019Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, nr 8, s. 7206-7220, artikkel-id 8514034Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 13.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ilves, Kalle
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Östlund, Stefan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies2019Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikkel i tidsskrift (Fagfellevurdert)
    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. 

  • 14.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ilves, K.
    Harnefors, Lennart
    Ac-side admittance calculation for modular multilevel converters2017Inngår i: 2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia, IFEEC - ECCE Asia 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 308-312Konferansepaper (Fagfellevurdert)
    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.

  • 15.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ilves, Kalle
    Harnefors, Lennart
    Control of Modular Multilevel Matrix Converters Based on Capacitor Voltage Estimation2016Inngår i: IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), 2016, IEEE, 2016, s. 3447-3452, artikkel-id 7512848Konferansepaper (Fagfellevurdert)
    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.

  • 16.
    Björk, Joakim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes2019Inngår i: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 34, nr 2, s. 1095-1104Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 17.
    Nikouei Harnefors, Mojgan
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Wallmark, Oskar
    KTH, Skolan för elektro- och systemteknik (EES).
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES).
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES).
    Operation Under Fault Conditions of the Stacked Polyphase Bridges Converter2016Konferansepaper (Fagfellevurdert)
    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.

  • 18.
    Nikouie, Mojgan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Wallmark, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Torque-Ripple Minimization for Permanent-Magnet Synchronous Motors Based on Harmonic Flux Estimation2018Inngår i: 2018 20TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'18 ECCE EUROPE), IEEE , 2018Konferansepaper (Fagfellevurdert)
    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.

  • 19.
    Nikouie, Mojgan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Wallmark, Oskar
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Torque-Ripple Minimization for Permanent-MagnetSynchronous Motors Based on Harmonic Flux Estimation2018Konferansepaper (Fagfellevurdert)
    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.

  • 20. Stamatiou, Georgios
    et al.
    Beza, Mebtu
    Bongiorno, Massimo
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Analytical derivation of the DC-side input admittance of the direct-voltage controlled modular multilevel converter2017Inngår i: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 11, nr 16, s. 4018-4030Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 21. Zhang, H.
    et al.
    Wang, X.
    Harnefors, Lennart
    ABB, Västerås, Sweden.
    Gong, H.
    Hasler, J. -P
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    SISO Transfer Functions for Stability Analysis of Grid-Connected Voltage-Source Converters2019Inngår i: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 55, nr 3, s. 2931-2941, artikkel-id 8640057Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 22.
    Zhang, Hongyang
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB, Power Grids Div, S-72164 Vasteras, Sweden.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. 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 Modeling2019Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, nr 8, s. 8104-8117Artikkel i tidsskrift (Fagfellevurdert)
    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.

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