This paper presents a new robust control methodology to improve the power system transient stability and voltage regulation in interconnected power systems including dynamic loads. The inclusion of dynamic load model significantly increases the nonlinearity of the system. The automatic voltage regulation (AVR) and power system stabiliser (PSS) design problems are coordinated for the augmentation of stability. The nonlinear behaviour of power systems has been represented in this paper by an uncertain term, derived from the Cauchy remainder of the Taylor series expansion. An IEEE benchmark test system has been used to demonstrate the performance of the designed controller. Large disturbance simulations demonstrate that the proposed controller enhances voltage stability as well as transient stability of a power system during severe transients.