A Less-Intrusive Approach to Stabilize VSC Transmission Against Highly Variable Grid Strength

A less-intrusive solution to stabilize a voltage source converter (VSC) over an unknown grid strength is presented in this article. The existence of equilibrium point is investigated as a prerequisite to stabilization. By partially imposing grid forming control, a simple auxiliary outer loop is proposed to exhaust the physical limit of power delivery in steady state and provide support to fault-ride-through (FRT) operations over a wide range of grid strength. The proposed control can be used to upgrade a commissioned VSC with inner current loop intact and overcome the impact of negative voltage sensitivity; it also offers a robust nonintrusive solution to stabilize VSCs externally. The effectiveness of the proposed schemes is verified by analysis in frequency domain and simulations in electromagnetic transient (EMT) time domain considering change of grid strength and FRT.