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  • 1.
    Ahmed, Noman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Haider, Arif
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Van Hertem, Dirk
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Zhang, Lidong
    ABB Power Systems, Ludvika.
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Prospects and challenges of future HVDC SuperGrids with modular multilevel converters2011Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Konferensbidrag (Refereegranskat)
    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 the future HVDC SuperGrids. Different topologies for a SuperGrid and the possibility to use modular multilevel converters (M2Cs) are presented. A comprehensive overview of different sub-module implementations of M2C is given. An overview of short circuit behaviour of the M2C is also given, as well as a discussion on the choice between cables or overhead lines and DC-side resonance issues.

  • 2.
    Ahmed, Noman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Haider, Arif
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    M2C-BASED MTDC SYSTEM FOR HANDLING OF POWERFLUCTUATIONS FROM OFFSHORE WIND FARMS2011Ingår i: Proceedings of IET RPG-2011 / [ed] IET, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper a modular multilevel converter (M2C) basedmulti-terminal direct current (MTDC) system is proposed forthe connection of offshore wind farms. Each M2C ismodelled with 36 sub-modules per arm with a total of 216sub-modules consisting of half bridges. An open-loopconverter control method is employed for the M2Cs. Powersynchronizationcontrol is used instead of a phase-locked loop(PLL) for synchronization. A voltage controller isimplemented with power-synchronization control as an innerloop. By means of numerical simulations in PSCAD, it isshown that the system is self stabilizing both at steady stateand following power fluctuations of the wind farm.

  • 3.
    Haider, Arif
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Ahmed, Noman
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Ängquist, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Open-loop approach for control of multi-terminal DC systems based on modular multilevel converters2011Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper a multi-terminal direct current (MTDC) system with modular multilevel converters (M2Cs) is suggested. An open loop control method is used for the control of the converters. Each converter is modeled with 36 sub-modules per arm with a total of 216 sub-modules consisting of half bridges. Power-synchronization control is used instead of a phase-locked loop (PLL) for synchronization. Thus, the short circuit capacities of the ac systems are no longer limiting factors and the instability caused by the PLL in weak ac systems is avoided [10]. A direct voltage controller is implemented with power-synchronization control as an inner loop in one station. Several scenarios are analyzed to demonstrate control flexibility and ride-through capability for grid transients. By means of analytical calculations and time simulations in PSCAD/EMTDC, the validity of the proposed MTDC system is confirmed.

  • 4.
    Khan, Naveed Ahmad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem. HVDC ABB AB, Dept Syst Studies, Ludvika, Sweden.
    Vanfretti, Luigi
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem. Stattnet SF, Oslo, Norway.
    Li, Wei
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Haider, Arif
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem. HVDC ABB AB, Dept Syst Studies, Ludvika, Sweden.
    Hybrid Nearest Level and open loop control of Modular Multilevel Converters with N+1 and 2N+1 levels2014Ingår i: Power Electronics and Applications (EPE'14-ECCE Europe), 2014 16th European Conference on, IEEE conference proceedings, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper a Nearest Level Control with open loop approach for modular multilevel converter (MMC) is proposed. By using open loop approach it is possible to suppress circulating currents without using feedback controllers. Moreover, with this method, both N+1 and 2N+1 levels (N=number of sub-modules) can be obtained at the output voltage. In addition, the voltage quality is improved and the total harmonic distortion is reduced at higher and lower modulation indices by increasing the number of levels up to 2N+1. Simulation results of 3-phase MMC are presented for both 2N+1 and N+1 levels together with the description of proposed Nearest Level Control scheme.

  • 5.
    Ängquist, Lennart
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Haider, Arif
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Nee, Hans-Peter
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska maskiner och effektelektronik (stängd 20110930).
    Jiang, Hongbo
    Trafikverket, Borlänge, Sweden.
    Open-loop approach to control a Modular Multilevel Frequency Converter2011Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Frequency converters are required to supply power from the public three-phase network to railways using 16.7 Hz single-phase in their rolling stock. The emerging Modular Multilevel Converter (M2C) technology offers the possibility to make such power conversion in one step using Modular Multilevel Frequency Converters (MMFC) with full-bridge sub-modules. A detailed study of the modulation and control of such converters is presented in this paper. The voltage inserted by each arm of the MMFC is a mixture of the three-phase 50 Hz voltage and the single phase 16.7 Hz voltage. It is important that the voltage reference given to the modulator will be carefully reproduced by the converter because any deviation can introduce undesired frequency components from the single-phase side to the three-phase side and vice versa. The fact that the low frequency, single-phase load causes low-frequency ripple in the total capacitor voltage complicates the problem to generate the correct modulation pattern. In this paper it is proposed to solve that difficulty by estimating the instaneous total capacitor voltages in each arm and provide that information to the modulator. It is shown that such estimations can be performed using measured currents on the single- and three-phase sides. Stable single-phase voltage, symmetrical undistorted three-phase currents and stable converter capacitor voltages are achieved under varying loading conditions. Models in Matlab/Simulink (continuous) and EMTDC/PSCAD (discrete sub-modules) have been developed in this study.

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