Browsing by Author "Nafisi, Hamed"

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    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.
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    Virtual Inertia Implementation in Dual Two-Level Voltage Source Inverters
    (2020-02) Dashtaki, Mohammad Ali; Nafisi, Hamed; Pouresmaeil, Edris; Khorsandi, Amir; Department of Electrical Engineering and Automation; Renewable Energies for Power Systems; Amirkabir University of Technology
    In this paper, the implementation of virtual inertia in a dual two-level voltage source inverter (DTL VSI) configuration is investigated. The derivative control method is employed to provide virtual inertia. The virtual synchronous generator (VSG) topology is presented, and its elements are introduced. According to the frequency changes, the active power reference is generated. Moreover, the control structure is designed and presented to control the DTL VSI properly. By means of the derivative control method, the DTL VSI participates in the frequency regulation, and the frequency oscillations during contingencies are confined. The results show that the controller follows its reference in all cases. The potentiality of the proposed controller is confirmed through MATLAB simulations. Compared to the conventional DTL VSI, the rate of change of frequency (ROCOF) and frequency nadir are reduced during disturbances.