This paper presents a robust excitation controller design for power systems to improve the dynamic stability following large disturbances. The controller is designed based on the partial feedback linearization where some parts of power systems need to be linearized. The robustness of the proposed control scheme is ensured by considering uncertainties within power systems model. In this paper, the uncertainties in power systems model are considered as the structured uncertainties which need to satisfy the matching condition. The performance of the designed controller is evaluated on a single machine infinite bus (SMIB) system under major disturbances. Simulation results show the robustness of the proposed excitation controller as compared to that of normal partial feedback linearizing controller by enhancing both the transient stability and voltage regulation under severe disturbances.