This paper proposes a methodology for the computation of robust controls that guarantee robustness in a wide range of operating condition of a power system; such as contingencies, uncertainties and delays in the signals. This paper proposes a detailed modeling of uncertainties of the power system as additive uncertainties of the plant under the theory of robust control, and also a methodology for defining in a correct way sensitivity matrices used in the computation of robust controls and based on the model uncertainties and control purposes (damping of electromechanical oscillations). It is also proposed the computation of robust controls in two stages guaranteeing robustness and damping, and the analysis of performance of the control against delay times in control signals.