The operating point of a power system changes to an unknown point with an unknown change in the mechanical input power. In this paper, a nonlinear adaptive controller is designed for excitation system of the generator based on the backstepping control technique, in order to achieve transient stability enhancement, in the presence of uncertainties in mechanical power. The designed controller guarantees the convergence of system states to new desired values corresponding to unknown mechanical power. A power system consisting of a synchronous generator connected to an infinite bus through a double circuit transmission line is used in control design and the simulation studies. Computer simulation verifies the effectiveness and the validity of the proposed control, considering faulted system with a clearance and change in network topology

Keywords: Adaptive control, Lyapunov stability, Transient stability, Mechanical power