Large-scale integration of wind power brings great challenges for power system stability. Because of the randomness of wind speed and generator parameter uncertainties, it is difficult for conventional Proportional- Integral-Differential (PID) control to achieve a satisfactory control performance for a Doubly-Fed Induction Generator (DFIG). In this paper, a novel Robust Passive Control (RPC) is proposed to improve the stability of a power system. First, the generator nonlinearities, parameter uncertainties, unmodelled dynamics and wind speed randomness are aggregated into a perturbation. Then, fast perturbation estimation is achieved by a nonlinear Extended State Observer (ESO) in real-time. Online complete compensation of perturbation is realized by RPC. Subsequently, considerable system damping can be injected to improve the transient responses of the DFIG under various operating conditions. Finally, four cases, such as step change of wind speed, voltage drop at power grid, inter-area type disturbance and generator parameter uncertainties are simulated and studied. Simulation results verify the effectiveness and robustness of RPC under various operating conditions. This work is supported by National Natural Science Foundation of China (No. 61963020).