Abstract: The excitation control problem in multimachine power systems was discussed. In order to avoid the conservatism which comes from estimating the upper bound of the disturbance or magnifying the equation simply， a control method of nonlinear large disturbance rejection was proposed by using backstepping method combined with minimax method. Considering that the system may get large disturbance suddenly from the generator which has occurred mechanical power disturbance， a controller of nonlinear large disturbance rejection was designed. It was indicated that the multimachine power system had good robustness and insensitivity about largedisturbance. Simulation results showed that the proposed control program can effectively improve the transient stability of multimachine power systems.

Key words: multimachine power systems, excitation control, large disturbance rejection, backstepping, minimax