Grid-forming compensation Control Strategy Based on Virtual Impedance

With the increase of new energy sources penetration rate, the inertia of the system decreases, and the short-circuit ratio (SCR) at the point of common coupling (PCC) drops significantly, which makes the power grid show the characteristics of weak power grid or even extremely weak grid, so that there is a risk of resonance and instability when the grid-following converters which are currently widely applied are connected to the weak power grid. Additionally, the impedance of the local grid often fluctuates drastically due to factors such as the number of grid-connected devices, loads, and system operation modes, leading to alternating strong and weak grid characteristics. Conventional grid-following and grid-forming converters cannot fully meet the requirements of power grid. To address the stability issues of converters under varying grid strengths, this paper proposes a grid-forming compensation control strategy based on virtual impedance. The strategy achieves impedance reshaping of the converter system by inserting a virtual impedance before the voltage-current dual-loop of grid-forming control, and improves the control performance under strong grid conditions. Finally, simulations verify the correctness of the theoretical analysis and the effectiveness of the proposed method.