Browsing by Author "Hojabri, Mojgan"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Dual Two-Level Voltage Source Inverter Virtual Inertia Emulation: A Comparative Study
    (MDPI AG, 2021-02-22) Dashtaki, Mohammad Ali; Nafisi, Hamed; Khorsandi, Amir; Hojabri, Mojgan; Pouresmaeil, Edris; Department of Electrical Engineering and Automation; Renewable Energies for Power Systems; Amirkabir University of Technology; Lucerne University of Applied Sciences and Arts
    In this paper, the virtual synchronous generator (VSG) concept is utilized in the controller of the grid-connected dual two-level voltage source inverter (DTL VSI). First, the topology of the VSG and the DTL VSI are presented. Then, the state-space equations of the DTL VSI and the grid-connected two-level voltage source inverter (TL VSI), regarding the presence of the phase-locked loop (PLL) and the VSG, are given. Next, the small-signal modeling of the DTL VSI and the TL VSI is realized. Eventually, the stability enhancement in the DTL VSI compared with the TL VSI is demonstrated. In the TL VSI, large values of virtual inertia could result in oscillations in the power system. However, the ability of the DTL VSI in damping oscillations is deduced. Furthermore, in the presence of nonlinear loads, the potentiality of the DTL VSI in reducing grid current Total Harmonic Distortion (THD) is evaluated. Finally, by using a proper reference current command signal, the abilities of the DTL VSI and the TL VSI in supplying nonlinear loads and providing virtual inertia are assessed simultaneously. The simulation results prove the advantages of the DTL VSI compared with the TL VSI in virtual inertia emulation and oscillation damping, which are realized by small-signal analysis.
  • Thumbnail Image
    Item
    Improving Transient Stability of Power Synchronization Control for Weak Grid Applications
    (IEEE, 2020) Sepehr, Amir; Pouresmaeil, Mobina; Hojabri, Mojgan; Blaabjerg, Frede; Pouresmaeil, Edris; Department of Electrical Engineering and Automation; Renewable Energies for Power Systems; Lucerne University of Applied Sciences and Arts; Aalborg University
    Power synchronization control (PSC) has a promising potential to be used in interface converters of large-scale renewable generations operating under weak-grid condition. This paper presents a modified PSC-based control structure that provides an enhanced dynamic response, reinforced synchronization, and reduced vulnerability against grid transients. By utilizing a back-calculation scheme, the active power reference in the synchronization loop of PSC is configured to be adapted to the grid transients for avoiding loss of synchronization (LOS). Furthermore, the proposed control structure prevents power-injection collapse (PIC) and mitigates the dc current components of the converter caused by transients in weak grids. Performance and feasibility of the proposed control structure are highlighted and verified by simulation of various scenarios and operating conditions.