Double–Stage photovoltaic generator augmented with FLL–based synthetic inertia emulator

Distributed virtual inertia (DVI) is a promising method in frequency support provision for power system transition toward ≈100% power electronic–based generation. In this approach, the inertia power is provided by discharging or charging dc capacitors adhered to the grid–tied inverters distributed in the grid. However, the dc–bus voltage drifts with the time from its nominal in the conventional DVI technique. Herein, we suggest a modified DVI–based frequency regulator which addresses the aforesaid issue. The inverter controller comprises two main loops: 1) inner current loop and 2) outer voltage loop augmented with the proposed synthetic inertia emulator, whereby measured grid frequency oscillations are transmuted to the synthetic inertia support. The proposed controller is utilized in a double–stage photovoltaic generator. The synchronization of generator with the host grid is performed using a fast but accurate frequency–locked loop (FLL) implemented in the synchronous reference frame. The small–signal state–space realization illustrates that the generator stability is scarcely sensitive to the dc–link capacitance changes, while the grid strength and the FLL controller gains significantly affect the stability. The efficacy of the proposed control scheme is verified by time–domain simulation results in MATLAB/Simulink. The grid frequency response depicts that the frequency rate of change is improved by 14.6% if the proposed synthetic inertia emulator is employed.