Abstract: Most of the existing nonlinear excitation controllers of power systems are designed in state feedback approaches,so generator rotor angles and some variables’ differentiations have to be measured.Besides that,these controllers drive relative rotor angles to reference values,thus they can’t assure voltage regulation of generators during variation of the network parameters or the system operating point changes.This paper presented a novel output feedback based method for nonlinear excitation controller design.New model transformations were proposed for nonlinear models of single-machine-infinite-bus systems and multi-machine systems respectively.Both systems were transformed to uncertain linear ones where deviations of generator terminal voltage,rotor speed and generator active power output became state variables.And then the new controllers were designed by applying a robust control theory based on linear matrix inequality（LMI）.Rotor angles and any variable’s differentiations don’t need to be measured for the proposed controllers.The controllers don’t rely on any pre-selected system operating point,and the controllers are adapt to variations of the system network parameters,and can well restrain disturbance and assure voltage regulations of generators.Simulation results verified the conclusions.