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  • 1.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Zhou, Dao
    Song, Yipeng
    Ghandari, Mehrdad
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Blaabjerg, Frede
    Analysis and Mitigation of SSCI in DFIG Systems With Experimental Validation2020In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 35, no 2, p. 714-723Article in journal (Refereed)
    Abstract [en]

    Sub-synchronous oscillations (SSOs) in doubly-fed induction generator (DFIG)-based series compensated power systems are mainly caused by sub-synchronous control interaction (SSCI). SSCI is the most recently found type of sub-synchronous resonances. In this article, SSCI is elaborated and investigated by performing eigenvalue analysis on a mathematically modeled DFIG system. The occurrence of SSCI is observed and the results of eigenvalue analysis are validated through a down-scaled 7.5-kW experimental setup of a grid-connected DFIG. Based on the analysis, the proportional control parameters of the rotor-side converter (RSC) are found to be very sensitive towards the sub-synchronous modes of the system. The results obtained from both the simulation and the experimental analysis show that if the sensitive proportional parameters of the RSC are tuned properly, then the DFIG system can become immune to the SSCI for any level of series compensation.

  • 2.
    Dimitropoulos, Dimitrios
    et al.
    Aalborg Univ, AAU Energy, DK-9220 Aalborg, Denmark..
    Wang, Xiongfei
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems. Aalborg Univ, AAU Energy, DK-9220 Aalborg, Denmark.
    Blaabjerg, Frede
    Aalborg Univ, AAU Energy, DK-9220 Aalborg, Denmark..
    Stability Analysis in Multi-VSC (Voltage Source Converter) Systems of Wind Turbines2024In: Applied Sciences, E-ISSN 2076-3417, Vol. 14, no 8, article id 3519Article in journal (Refereed)
    Abstract [en]

    In this paper, a holistic nonlinear state-space model of a system with multiple converters is developed, where the converters correspond to the wind turbines in a wind farm and are equipped with grid-following control. A novel generalized methodology is developed, based on the number of the system's converters, to compute the equilibrium points around which the model is linearized. This is a more solid approach compared with selecting operating points for linearizing the model or utilizing EMT simulation tools to estimate the system's steady state. The dynamics of both the inner and outer control loops of the power converters are included, as well as the dynamics of the electrical elements of the system and the digital time delay, in order to study the dynamic issues in both high- and low-frequency ranges. The system's stability is assessed through an eigenvalue-based stability analysis. A participation factor analysis is also used to give an insight into the interactions caused by the control topology of the converters. Time domain simulations and the corresponding frequency analysis are performed in order to validate the model for all the control interactions under study.

  • 3.
    Yang, Zhiqing
    et al.
    Hefei University of Technology, School of Electrical Engineering and Automation, Hefei, China, 230009.
    He, Shan
    Aalborg University, Department of Energy, Aalborg, Denmark, 9220.
    Zhou, Dao
    Aalborg University, Department of Energy, Aalborg, Denmark, 9220.
    Wang, Xiongfei
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems. Aalborg University, Department of Energy, Aalborg, Denmark, 9220.
    De Doncker, Rik W.
    Institute for Power Generation and Storage Systems, RWTH Aachen University, E. ON Energy Research Center, Aachen, Germany, 52074.
    Blaabjerg, Frede
    Aalborg University, Department of Energy, Aalborg, Denmark, 9220.
    Ding, Lijian
    Hefei University of Technology, School of Electrical Engineering and Automation, Hefei, China, 230009.
    Wideband Dissipativity Enhancement for Grid-Following VSC Utilizing Capacitor Voltage Feedforward2023In: IEEE Journal of Emerging and Selected Topics in Power Electronics, ISSN 2168-6777, E-ISSN 2168-6785, Vol. 11, no 3, p. 3138-3151Article in journal (Refereed)
    Abstract [en]

    Frequency-domain dissipativity of the converter admittance provides an intuitive approach to analyze wideband resonances due to the interactions with the grid. Although the reasons for high- and low-frequency resonances are different, it is found that the proportional capacitor voltage feedforward (CVF) can affect and reshape the converter admittance in a wide frequency range. To enhance wideband dissipativity under a weak/capacitive grid, a proportional-integral (PI)-derivative CVF is proposed in this article. Specifically, high-frequency dissipativity can be guaranteed through the multisampling control (MSC) with proportional-derivative CVF. The low-frequency nondissipative region caused by the phase-locked loop (PLL) and proportional CVF can be compensated through multiorder integrations. In light of grid frequency disturbances, modified integrators are further proposed for the multiorder integrations. The proposed method also applies to the conventional double-sampling control (DSC) with regard to the low-frequency dissipativity enhancement. Finally, experiments validate the proposed control method.

  • 4.
    Zhang, Mengfan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Xu, Qianwen
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Zhang, Chuanlin
    Shanghai Univ Elect Power, Shanghai, Peoples R China..
    Nordström, Lars
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Blaabjerg, Frede
    Aalborg Univ, Aalborg, Denmark..
    Decentralized Coordination and Stabilization of Hybrid Energy Storage Systems in DC Microgrids2023In: 2023 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, PESGM, Institute of Electrical and Electronics Engineers (IEEE) , 2023Conference paper (Refereed)
    Abstract [en]

    Hybrid energy storage system (HESS) is an attractive solution to compensate power balance issues caused by intermittent renewable generations and pulsed power load in DC microgrids. The purpose of HESS is to ensure optimal usage of heterogeneous storage systems with different characteristics. In this context, power allocation for different energy storage units is a major concern. At the same time, the wide integration of power electronic converters in DC microgrids would possibly cause the constant power load instability issue. This paper proposes a composite model predictive control based decentralized dynamic power sharing strategy for HESS. First, a composite model predictive controller (MPC) is proposed for a system with a single ESS and constant power loads (CPLs). It consists of a baseline MPC for optimized transient performance and a sliding mode observer to estimate system disturbances. Then, a coordinated scheme is developed for HESS by using the proposed composite MPC with a virtual resistance droop controller for the battery system and with a virtual capacitance droop controller for the supercapacitor (SC) system. With the proposed scheme, the battery only supplies smooth power at steady state, while the SC compensates all the fast fluctuations. The proposed scheme achieves a decentralized dynamic power sharing and optimized transient performance under large variation of sources and loads. The proposed approach is verified by simulations and experiments.

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