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  • 1.
    Ahmed, Noman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Haider, Arif
    Van Hertem, Dirk
    ESAT/ELECTA, K.U.Leuven, Belgium.
    Zhang, Lidong
    ABB Power Systems HVDC, Ludvika.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    HVDC SuperGrids with modular multilevel converters - The power transmission backbone of the future2012Inngår i: International Multi-Conference on Systems, Signals and Devices, SSD 2012, IEEE , 2012, s. 6198119-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In order to transmit massive amounts of power generated by remotely located power plants, especially offshore wind farms, and to balance the intermittent nature of renewable energy sources, the need for a stronger high voltage transmission grid is anticipated. Due to limitations in ac power transmission the most likable choice for such a grid is a high-voltage dc (HVDC) grid. However, the concept of the HVDC grid is still under active development as different technical challenges exist, and it is not yet possible to construct such a dc grid. This paper deals with prospects and technical challenges for future HVDC SuperGrids. Different topologies for a SuperGrid and the possibility to use modular multilevel converters (M2Cs) are presented. A comprehensive overview of different submodule implementations of M2C is given as well as a discussion on the choice between cables or overhead lines, the protection system for the dc grid and dc-side resonance issues.

  • 2.
    Ahmed, Noman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Antonopoulos, Antonios
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling. ABB Corporate Research.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Performance of the modular multilevel converter with redundant submodules2015Inngår i: IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society, Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 3922-3927, artikkel-id 7392712Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The modular multilevel converter (MMC) is the state-of-the-art voltage-source converter (VSC) topology used for various power-conversion applications. In the MMC, submodule failures can occur due to various reasons. Therefore, additional submodules called the redundant submodules are included in the arms of the MMC to fulfill the fault-safe operation requirement. The performance of the MMC with redundant submodules has not been widely covered in the published literature. This paper investigates the performance of the MMC with redundant submodules in the arms. Two different control strategies are used and compared for integrating redundant submodules. The response of the MMC to a submodule failure for the two strategies is also studied. Moreover, the operation of the MMC with redundant submodules is validated experimentally using the converter prototype in the laboratory.

  • 3.
    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.

  • 4.
    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.

  • 5.
    Ali, Muhammad Taha
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Effect of control parameters on infliction of sub-synchronous control interaction in DFIGs2016Inngår i: 2016 IEEE International Conference on Power and Renewable Energy (ICPRE), IEEE conference proceedings, 2016, s. 72-78, artikkel-id 7871175Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This research work deals with the analysis of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs). The time-invariant model of the DFIG is linearized to perform eigenvalue analysis and to obtain the participation factor of each state variable for unstable modes. The sensitivity of system eigenvalues related to sub-synchronous modes is analyzed with respect to all the proportional and integral parameters of the controllers in the rotor-side-converters and grid-side-converters. The major contribution of this research work is the outcomes based on eigenvalue analysis that clearly point out the control parameters to which sub-synchronous modes are highly sensitive. The effect of series compensation level on DFIG system and on the sensitivity of converter control parameters is also studied.

  • 6.
    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.

  • 7.
    Antonopoulos, Antonios
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling. ABB, Sweden.
    Ilves, Kalle
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Global Asymptotic Stability of Modular Multilevel Converters2014Inngår i: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 61, nr 2, s. 603-612Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Modular multilevel converters require that the controller is designed so that the submodule capacitor voltages are equalized and stable, independent of the loading conditions. Assuming that the individual capacitor-voltage sharing is managed effectively, an open-loop strategy has been designed to ensure that the total amount of energy stored inside the converter always will be controlled. This strategy, using the steady-state solutions of the dynamic equations for controlling the total stored energy in each converter arm, has proven to be effective. The intention of this paper is to explain in a rigorous way the mechanism behind the suggested strategy and to prove that, when this open-loop strategy is used, the system becomes globally asymptotically stable. Experimental verification on a three-phase 10-kVA prototype is presented.

  • 8.
    Antonopoulos, Antonios
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ilves, Kalle
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Stability Analysis of Modular Multilevel Converters With Open-Loop Control2013Inngår i: 39th Annual Conference of the IEEE Industrial Electronics Society, IECON 2013, IEEE , 2013, s. 6316-6321Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Modular multilevel converters (M2Cs) require that the controller is designed so that the submodule capacitor voltages are equalized and stable, independent of the loading conditions. Provided that the individual capacitor voltage sharing is managed effectively, an open-loop strategy can been designed to ensure that the total amount of energy stored inside the converter always will be controlled. This strategy, using the steady-state solutions of the dynamic equations for controlling the total stored energy in each converter arm, has proven to be effective. The intention of this paper is to explain in a rigorous way the mechanism behind the suggested strategy, and to prove that, when this open-loop strategy is used, the system becomes globally asymptotically stable.

  • 9.
    Antonopoulos, Antonios
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Optimal selection of the average capacitor voltage for modular multilevel converters2013Inngår i: 2013 IEEE Energy Conversion Congress and Exposition, ECCE 2013, IEEE , 2013, s. 3368-3374Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Variable-speed drives have reduced voltage requirements when operating below the base speed. In a modular-multilevel-converter-based (M2C-based) motor drive it is then possible to operate with reduced voltage in the submodule capacitors, than at the base speed. In this sense, a greater capacitor-voltage ripple can be accommodated, without exceeding the maximum peak-capacitor voltage. This paper presents an analytical investigation for the optimal selection of the average capacitor voltage for M2Cs, when the motor is operating with rated torque, below the base speed. This method does not require any power exchange between the converter arms, so it keeps the conduction losses at the minimum level. Additionally, the method decreases the switching losses, due to the decreased capacitor-voltage level. The overall ratings of the converter remain the same as in the base-speed operation. It is shown that this method can be applied at a speed range between the base speed and down to approximately one third of it, i.e, an operating range that covers the requirements for typical pump- and fan-type applications. The results obtained from the analytical investigation are experimentally verified on a down-scaled laboratory prototype M2C.

  • 10.
    Antonopoulos, Antonios
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Optimal Selection of the Average Capacitor Voltage for Variable-Speed Drives With Modular Multilevel Converters2015Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, nr 1, s. 227-234Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Variable-speed drives have reduced voltage requirementswhen operating below the base speed. In a modularmultilevel-converter-based (M2C-based) motor drive it is thenpossible to operate with reduced voltage in the submodulecapacitors, than at the base speed. In this sense, a greatercapacitor-voltage ripple can be accommodated, without exceedingthe maximum peak-capacitor voltage. This paper presents ananalytical investigation for the optimal selection of the averagecapacitor voltage for M2Cs, when the motor is operating withrated torque, below the base speed. This method does not requireany power exchange between the converter arms, so it keepsthe conduction losses at the minimum level. Additionally, themethod decreases the switching losses, due to the decreasedcapacitor-voltage level. The overall ratings of the converterremain the same as in the base-speed operation. It is shownthat this method can be applied at a speed range betweenthe base speed and down to approximately one third of it,i.e, an operating range that covers the requirements for typicalpump- and fan-type applications. The results obtained from theanalytical investigation are experimentally verified on a downscaledlaboratory prototype M2C.

  • 11.
    Antonopoulos, Antonios
    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.
    Ilves, Kalle
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Modular multilevel converter AC motor drives with constant torque from zero to nominal speed2014Inngår i: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 50, nr 3, s. 1982-1993Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Modular multilevel converters are shown to have a great potential in the area of medium-voltage drives. Low-distortion output quantities combined with low average switching frequencies for the semiconductor devices create an ideal combination for very high-efficiency drives. However, the large number of devices and capacitors that have to conduct the fundamental-frequency current require more complex converter control techniques than its two-level counterpart. Special care needs to be taken for starting and operation at low speeds, where the low-frequency current may cause significant unbalance between the submodule capacitor voltages and disturb the output waveforms. In this paper, principles for converter operation with high torque in the whole speed range are investigated. Experimental results from a down-scaled 12-kVA prototype converter running a loaded motor at various speeds between standstill and the rated speed are also provided.

  • 12.
    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.

  • 13.
    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).

  • 14.
    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).

  • 15.
    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 thyristors: 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.

  • 16.
    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.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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.

  • 20.
    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.

  • 21.
    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. 

  • 22.
    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.

  • 23.
    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.

  • 24.
    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.

  • 25.
    Harnefors, Lennart
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling. ABB, Sweden.
    Antonopoulos, Antonios
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ilves, Kalle
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Global asymptotic stability of current-controlled modular multilevel converters2015Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, nr 1, s. 249-258, artikkel-id 6883248Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, previously developed stability results for open-loop sum-capacitor-voltage control of modular multilevel converters are extended. To give improved damping, circulating-current feedback is included in the control law. With the output-current control loop and a first-order measurement lag taken into account, global asymptotic stability is proven. Careful consideration of the on-line sum-capacitor-voltage reference computation is given, since this is the most critical part of the control system.

  • 26. Harnefors, Lennart
    et al.
    Antonopoulos, Antonios
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Global asymptotic stability of modular multilevel converters with measurement lag and circulating-current control2013Inngår i: Power Electronics and Applications (EPE), 2013, IEEE , 2013, s. 1-10Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, previously developed stability results for open-loop sum-capacitor-voltage control of modular multilevel converters are extended. To obtain improved damping, circulating-current feedback is included in the control law. A first-order measurement lag is added to this feedback. With these additions, global asymptotic stability is proven. Careful consideration of the online control-law computation is given, since this is the most critical part of the control system. Experimental results verify the theory.

  • 27.
    Harnefors, Lennart
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Antonopoulos, Antonios
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Dynamic Analysis of Modular Multilevel Converters2013Inngår i: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 60, nr 7, s. 2526-2537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theory for the dynamics of modular multilevel converters is developed in this paper. It is shown that the sum capacitor voltage in each arm often can be considered instead of the individual capacitor voltages, thereby significantly reducing the complexity of the system model. Two selections of the so-called insertion indices, which both compensate for the sum-capacitor-voltage ripples, are considered. The dynamic systems which respectively result from these selections are analyzed. An effective dc-bus model, which takes into account the contribution from the submodule capacitors, is obtained. Finally, explicit formulas for the stationary sum-capacitor-voltage ripples are derived.

  • 28.
    Harnefors, Lennart
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Hinkkanen, Marko
    School of Electrical Engineering, Aalto University, Espoo, Finland.
    Wallmark, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Guest editorial - Special issue on permanent-magnet synchronous reluctance machines and their applications2016Inngår i: IET Electric Power Applications, ISSN 1751-8660, E-ISSN 1751-8679, Vol. 10, nr 5, s. 311-Artikkel, forskningsoversikt (Annet vitenskapelig)
  • 29. Harnefors, Lennart
    et al.
    Jansson, Magnus
    Ottersten, Rolf
    Pietiläinen, Kai
    Unified Sensorless Vector Control of Synchronous and Induction Motors2003Inngår i: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, IEEE transactions on industrial electronics, Vol. 50, nr 1, s. 153-160Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a unified theory for sensorless fluxestimation and vector control of induction motors and nonsalientpermanent-magnet synchronous motors (PMSMs) is developed.It is shown that an estimator and vector controller for one of themotor types can also be applied to the other, with only minormodifications necessary. Two candidate estimators are considered:a variant of the well-known “voltage model” (VM) and aphase-locked-loop-type speed and position estimator. These areapplied to both motor types, and evaluated experimentally. Forthe nonsalient PMSM, an important result is that synchronizationcan be guaranteed from any initial rotor position.

  • 30.
    Harnefors, Lennart
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Antonopoulos, Antonios
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Dynamic modeling of modular multilevel converters2011Inngår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Theory for the dynamics of modular multilevel converters is developed in this paper. It is shown that the sum capacitor voltage in each arm often can be considered instead of the individual capacitor voltages, thereby significantly reducing the complexity of the system model. A selection of the so-called insertion indices, which compensates for the sum-capacitor-voltage ripples, is considered. The system which results for this selection is analyzed, and is shown to be asymptotically stable. Finally, explicit formulas for the steady-state sum-capacitor-voltage ripples are derived.

  • 31. Harnefors, Lennart
    et al.
    Pietiläinen, Kai
    Gertmar, Lars
    Torque-Maximizing Field-Weakening Control: Design, Analysis, and Parameter Selection2001Inngår i: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 48, nr 1, s. 161-168Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The torque-maximizing field-weakening controlscheme proposed by Kim and Sul is developed further. Theperformance under imperfect field orientation conditions isinvestigated, and it is shown that an overestimated—rather thanan underestimated—model leakage inductance should be used. Aslightly modified algorithm, which offers better robustness andreduced computational complexity, is presented. The importance,for good performance, of combining the scheme with currentand speed controllers featuring antiwindup and improved disturbancerejection is emphasized. The dynamics of the resultingclosed-loop system are analyzed. Obtained in the process are rulesfor selection of all controller parameters, allowing tuning withouttrial-and-error steps. Good performance of the resulting systemis verified experimentally.

  • 32. Harnefors, Lennart
    et al.
    Pietiläinen, Kai
    Jansson, Magnus
    Voltage Sag Ride-Through for Line-Connected Syn-chronous Motors Through Flux Control2003Inngår i: PEDS 2003 : FIFTH INTERNATIONAL CONFERENCE ON POWER ELECTRONICS AND DRIVE SYSTEMS, VOLS 1 AND 2, PROCEEDINGS / [ed] Tseng, K.J., 2003, Vol. 2, s. 1219-1223Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, the voltage sag ride-through capabilities of the line-connected electrically excited synchronous motors with damper windings (EESMs) is investigated. Two aspects are investigated, first the capability to keep the nominal speed and second the damping of speed oscillations by controlling the flux. We will design a voltage sag ride-through controller and show through simulations that the proposed controller has good speed oscillation damping capability and that the ride-through capability is improved.

  • 33.
    Harnefors, Lennart
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem. ABB Corporate Research, Västerås, Sweden .
    Yepes, Alejandro G.
    Vidal, Ana
    Doval-Gandoy, Jesus
    Passivity-Based Controller Design of Grid-Connected VSCs for Prevention of Electrical Resonance Instability2015Inngår i: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 62, nr 2, s. 702-710Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The time delay in the current control loop of a grid-connected voltage-source converter (VSC) may cause destabilization of electrical resonances in the grid or in the VSC's input filter. Instability is prevented if the input admittance of the VSC can be made passive. This paper presents an analytical controller design method for obtaining passivity. The method is equally applicable to single-and three-phase systems, i.e., in the latter case, for both stationary-and synchronous-frame control. Simulations and experiments verify the theoretical results.

  • 34.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Antonopoulos, Antonios
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Hans-Peter, Nee
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Circulating current control in modular multilevel converters with fundamental switching frequency2012Inngår i: Conference Proceedings - 2012 IEEE 7th International Power Electronics and Motion Control Conference - ECCE Asia, IPEMC 2012, IEEE , 2012, s. 249-256Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The modular multilevel converter is a suitable topology for high-voltage applications as it combines very low switching frequency and excellent harmonic performance. In fact, it has been shown that the modular multilevel converter can even be operated at the fundamental switching frequency. If the circulating current is not controlled, a second-order harmonic component will appear. This component increases the resistive losses and the capacitor voltage ripple. Different control methods have been developed for eliminating this component in the circulating current. These are, however, based on continuous representations of the system and no control method suitable for fundamental switching frequency have yet been proposed. This paper presents a control method that combines a fundamental switching frequency scheme with an active control of the circulating current. The controller is verified experimentally on a 10-kVA laboratory prototype with five submodules per arm. The experimental validation is performed in both inverter and rectifier modes.

  • 35.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Antonopoulos, Antonios
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Capacitor Voltage Ripple Shaping in Modular Multilevel Converters Allowing for Operating Region Extension2011Inngår i: IECON 2011: 37TH ANNUAL CONFERENCE ON IEEE INDUSTRIAL ELECTRONICS SOCIETY, New York: IEEE , 2011, s. 4403-4408Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The second-order harmonic in the circulating current of a modular multilevel converter (M2C) influences the capacitor voltage ripple. If no measures are taken to control it, it is not possible to operate the converter with unity modulation index. An open-loop method that precalculates the instantaneous values of the circulating current and the capacitor voltages is used, in order to control the circulating current. A desired second-order harmonic is intentionally induced in the circulating current in order to make the peak of the capacitor voltage coincide with the maximum requested voltage, aiming either to extend the limits of the instantaneous available voltage or avoid unnecessarily high capacitor voltages. A method for numerical estimation of the appropriate amplitude and phase of the induced second-order harmonic is described. The method is experimentally evaluated on a three-phase down-scaled laboratory prototype. From the experiments it was found that significantly improved operating conditions could be obtained.

  • 36.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Bessegato, Luca
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Semi-Full-Bridge Submodule for Modular Multilevel ConvertersManuskript (preprint) (Annet vitenskapelig)
  • 37.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Analysis and operation of modular multilevel converters with phase-shifted carrier PWM2013Inngår i: 2013 IEEE Energy Conversion Congress and Exposition, ECCE 2013, IEEE , 2013, s. 396-403Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The modular multilevel converter is a suitable topology for high-voltage high-power applications since the cascaded submodules can generate high-voltage waveforms with excellent harmonic performance at low switching frequencies. Many publications have been presented on the modulation and control of this converter type, some of which are based on phase-shifted carrier modulation. This paper presents an analysis of how the switching frequency affects the capacitor voltages, circulating current and alternating voltage at phase-shifted carrier modulation. It is found that integer multiples of the fundamental frequency should be avoided as they can cause the capacitor voltages to diverge. Suitable switching frequencies are then defined for which the arm and line quantities will be periodic and symmetric in the upper and lower arms. The theoretical results are then validated by both simulations and experimental results.

  • 38.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Analysis and Operation of Modular Multilevel Converters With Phase-Shifted Carrier PWM2015Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, nr 1, s. 268-283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many publications have been presented on the modulation and control of the modular multilevel converter, some of which are based on phase-shifted carrier modulation. This paper presents an analysis of how the switching frequency affects the capacitor voltages, circulating currents, and alternating voltages using phase-shifted carrier modulation. It is found that switching frequencies that are integer multiples of the fundamental frequency should be avoided as they can cause the capacitor voltages to diverge. Suitable switching frequencies are derived for which the arm and line quantities will be periodic with symmetric operating conditions in the upper and lower arms. Thus, the practical outcome of this paper is a detailed description of how the switching frequency should be chosen in order to achieve advantageous operating conditions. The theoretical results from the analysis are validated by both simulations and experimental results.

  • 39.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    ABB Corporate Research, Västerås, Sweden .
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Predictive sorting algorithm for modular multilevel converters minimizing the spread in the submodule capacitor voltages2013Inngår i: 2013 IEEE ECCE Asia Downunder - 5th IEEE Annual International Energy Conversion Congress and Exhibition, IEEE ECCE Asia 2013, IEEE , 2013, s. 325-331Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The modular multilevel converter is a suitable topology for bidirectional ac-dc conversion in high-voltage high-power applications. By connecting submodule circuits in series, a high-voltage waveform with excellent harmonic performance can be achieved with a very high efficiency and low switching frequency. The balancing of the capacitor voltages will, however, become increasingly difficult as the switching frequency is reduced. Although the capacitor voltages can be kept balanced over time even at the fundamental switching frequency, the spread and thus also the peak variation in the capacitor voltages will typically increase at lower switching frequencies. This paper presents a capacitor voltage balancing strategy which aims to combine a low switching frequency with a low capacitor voltage ripple. This is done by a predictive algorithm that calculates the amount of charge that must be stored in the submodule capacitors during the following fundamental frequency period. The converter is then controlled in such a way that the stored charge in the submodule capacitors is evenly distributed among all the submodules when the capacitor voltages reach their maximum values. In this way, it is possible to limit the peak voltage in the capacitor at switching frequencies as low as 2-3 times the fundamental frequency. The capacitor voltage balancing strategy is first validated by simulation results at 110 Hz switching frequency. It is observeved that when the proposed method is used, the capacitor voltage ripple is 35% lower compared to the case when a conventional sorting algorithm is used. The capacitor voltage balancing strategy is also validated experimentally at 130 Hz switching frequency. The experimental results show that it is possible to combine the proposed method with previously presented circulating-current control methods.

  • 40.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    ABB Corporate Research, Västerås, Sweden .
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Predictive Sorting Algorithm for Modular Multilevel Converters Minimizing the Spread in the Submodule Capacitor Voltages2015Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, nr 1, s. 440-449Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The balancing of the capacitor voltages in modular multilevel converters becomes increasingly difficult when the switching frequency is reduced. Typically, a reduced switching frequency will increase the spread in the capacitor voltages and, thus, the voltage ripple in the individual submodules. This paper presents a capacitor voltage balancing strategy which aims to combine a low switching frequency with a low capacitor-voltage ripple. This is done by a predictive algorithm that controls the converter in such a way that the stored charge in the submodule capacitors is evenly distributed among all the submodules when the capacitor voltages reach their maximum values. In this way, it is possible to limit the peak voltages in the submodule capacitors at switching frequencies as low as 2-3 times the fundamental switching frequency. The proposed capacitor voltage balancing strategy is validated by both simulations and experimental results with 130-Hz and 140-Hz switching frequency. In the simulations, the capacitor voltage ripple was reduced by 24% compared to the case when a conventional sorting algorithm is used, and the experimental results show that it is possible to combine the proposed voltage balancing strategy with a circulating-current controller.

  • 41.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Analysis of arm current harmonics in modular multilevel converters with main-circuit filters2012Inngår i: International Multi-Conference on Systems, Signals and Devices, SSD 2012 - Summary Proceedings, IEEE , 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In a modular multilevel converter the circulating current that flows through each phase leg can affect the performance and efficiency of the converter. If measures are not taken to control the circulating current, it will inevitably contain a second-order harmonic. There are various solutions for eliminating this second-order harmonic. One of the proposed solutions includes a main-circuit filter that is tuned to block the second-order harmonic in the circulating current. This paper presents an analytical relation between the ac-side current and the higher-order harmonics in the circulating current when such a filter is used. It is found that when third-order harmonic injection is used, a large fourth-order harmonic component may appear in the circulating current. This is verified by simulating a 32-MVA converter designed for grid connected applications. The simulation results support the conclusion that it is essential to take this effect into consideration when designing the main-circuit filter.

  • 42.
    Ilves, Kalle
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Taffner, Franz
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Antonopoulos, Antonios
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    A submodule implementation for parallel connection of capacitors in modular multilevel converters2013Inngår i: Power Electronics and Applications (EPE), 2013 15th European Conference on, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The modular multilevel converter is a suitable converter topology for high-voltage high-power applications and consists of series-connected submodules. Typically, these submodules are half-bridges with dc capacitors. A voltage ripple in the submodule capacitors is inevitable due to the current flowing in the arms. The converter should therefore be controlled in such a way that the capacitor voltages are kept balanced and close to their nominal values over time. This paper presents a new submodule circuit which alleviates the balancing of the capacitor voltages. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current rating of the switches can be chosen such that the combined power rating of the semiconductors is the same as for equivalent half-bridge submodules. The proposed submodule circuit provides the possibility of connecting the two capacitors in parallel when the intermediate voltage level is used. This will reduce the capacitor voltage ripple, especially at low switching frequencies and thus allow for a reduction of the size, weight, and cost of the submodule capacitors. The proposed submodule circuit is validated by both simulation results and experiments on a laboratory prototype. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages.

  • 43.
    Leksell, Mats
    et al.
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Harnefors, Lennart
    Malardalen University, Sweden.
    Jansson, Magnus
    Direct Sensorless Speed Control of PM-Motors - a simple and effective sensorless method2001Inngår i: 32nd Annual Power Electronics Specialists Conference, IEEE , 2001, Vol. 2, s. 805-810Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a method for sensorless speed control of non-salient permanent magnet synchronous motors (PMSM). Special attention is put on the startup and synchronization of the motor, which are crucial for good performance of the drive system. The method merges both estimation and control of speed into one combined algorithm. Good performance is verified theoretically and experimentally.

  • 44.
    Malik, Naveed ur Rehman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Sadarangani, Chandur
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Cosic, Alija
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling. ABB CRC Västerås.
    Experimental Validation of a Rotating Power Electronic Brushless Doubly-Fed Induction Generator for Variable-Speed OperationManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    This paper investigates through experiments a differenttopology of a brushless doubly-fed induction generatorwith a rotating power electronic converter: the rotatingpower electronic brushless doubly-fed induction generator (RPEBDFIG),operated with variable speed and torque. The theorybehind the operation of the generator is presented, its dynamicmodel and control aspects are discussed, and closed-loop controlof the generator is implemented and verified through experimentson an 11-kW prototype. The measurement results show stableoperation for variable speed and torque regions. Moreover, itis shown that the integrated rotating exciter is sufficient torecover slip power and deliver to the grid, hence, verifyingsuccessful brushless operation. Besides, it is verified that thegenerator operates well in both regions of operation, i.e., the subsynchronousand super-synchronous modes, and is stable undertorque transients added by the rotating exciter.

  • 45.
    Malik, Naveed ur Rehman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Sadarangani, Chandur
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Cosic, Alija
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling. ABB CRC Västerås.
    Variable Reactive Power Control of a Rotating Power Electronic Brushless Doubly-Fed GeneratorManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    This paper considers reactive power control of anew topology of a brushless doubly-fed generator—the rotatingpower electronic brushless doubly-fed induction generator (RPEBDFIG).It consists of a doubly-fed induction generator (DFIG),on whose rotor two power electronic converters and a rotatingexciter are mounted and rotating with its shaft. The rotatingexciter and power electronic converters supply reactive powerfrom the rotor of the DFIG, thus manipulating the powerfactor at the stator terminals. Theory for variable-reactive-poweroperation is developed and verified through experiments on an11-kW prototype.

  • 46.
    Malik, Naveed ur Rehman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Sadarangani, Chandur
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Harnefors, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling. ABB CRC Västerås.
    Low-Voltage Ride-Through of a 2-MW Rotating Power Electronic Brushless Doubly-Fed GeneratorManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    This paper presents results for unsymmetrical lowvoltageride-through (LVRT) of a 2-MW brushless doubly-fedinduction generator with rotating power electronic converters.The behavior of the generator during various voltage dips isexamined and explained. The dual vector control of the generator,which assists the generator in riding through unsymmetricalfaults, and minimizes electrical and mechanical oscillations, ispresented. Furthermore, studies of the impact of phase-anglejumps and various magnitudes of voltage dips on the operationof the generator are presented.

  • 47.
    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.

  • 48.
    Nikouie Harnefors, Mojgan
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Wallmark, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Jin, Lebing
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Harnefors, Lennart
    ABB, Corporate Research, Sweden.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    DC-link stability analysis and controller design for the stacked polyphase bridges converter2017Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 32, nr 2, s. 1666-1674, artikkel-id 7451258Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stacked polyphase bridges (SPB) converter consists of several submodules that all are connected in series to a voltage source. The total dc-link voltage should split in a balanced way among the submodules. This does not always occur inherently. This paper presents an analysis of the capacitor voltage stability for the SPB converter. From the analysis, criteria for stability are derived and three alternatives of a suitable balancing controller are designed. The proposed controller alternatives and their associated stability properties are verified on an experimental setup and by simulation.

  • 49.
    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.

  • 50.
    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.

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