An improved current controller to ensure the robust performance of grid-connected converters under weak grid Conditions

Voltage Source Converters (VSCs) operating in very weak grids with low Short Circuit Ratio (SCR) are known to meet stability challenges. This article investigates instability of a grid connected current-controlled converter under weak grid conditions, which is often attributed to the dynamic interaction between the phase-locked loop (PLL) and system impedance networks. To accomplish this object, available approaches are overviewed, and their advantages and disadvantages are briefly explained. Then a simple yet effective technique based on the joint operation of virtual impedance technique and an amplitude estimation strategy is presented to tackle their shortcomings. The effectiveness of the proposed strategy is finally evaluated using the simulation results.