In this paper, a novel approach for the design of nonlinear excitation control of power system generators is proposed. The method is developed using a flatness-based adaptive fuzzy control methodology. The considered power system can be written in the canonical form and the resulting excitation control signal is shown to be nonlinear. In case of unknown power system parameters due abnormalities, the nonlinear functions appearing in the control signal can be approximated using adaptive fuzzy systems. Simulation results show that the proposed controller can enhance the transient stability of the power system under a three-phase to ground fault occurring near the generator terminals.