This paper investigates the low-voltage ride-through (LVRT) performance of a proposed sensorless vector control method for the doubly-fed induction generators (DFIGs) under power grid voltage sags. The sliding-mode observer (SMO) is used to estimate the rotor position and speed information for the vector control of the DFIG. The performance of the SMO is compared with the model reference adaptive system (MRAS)-based sensorless method over a wide operating speed range. The effectiveness of the proposed sensorless vector control scheme under power grid voltage sags is demonstrated by simulation results for a 2-MW DFIG-based wind energy conversion system (WECS) in MATLAB/Simulink and experimental results for a 200-W DFIG-based WECS simulator.