Rapid Impedance Measurement Method for DFIG-Based Wind Turbines with Transient Characteristic Analysis Under Large Disturbance Conditions

Doubly-fed induction generator (DFIG)-based wind turbines connected to weak grids risk instability during low-voltage ride-through (LVRT) state under transient large disturbances due to improper active/reactive current injections. This paper proposes a sweep-frequency-based wide-band impedance measurement method to rapidly characterize DFIG impedance during normal operation and transient disturbances, and comparisons of the impedance characteristics between these conditions are presented. Impedance measurements results under varying voltage sag depths during transient events reveal impedance behaviors of the DFIG in different operating states. Simulation validation through ADPSS (Advanced Digital Power System Simulator) platform successfully reproduces oscillation risk issues, which confirming the accuracy of both the proposed measurement method and transient impedance analysis results.