A Less Intrusive Solution To Stablize 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 paper. 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 operations over a wide range of grid strength. The proposed control can be used to upgrade a commissioned VSC with inner current loop intact; it also offers a non-intrusive solution to stabilize VSCs externally. The effectiveness of the proposed approach and schemes are verified by analysis in frequency domain and case studies in time domain including change of grid strength and fault-ride-through