Abstract: Derivation of nonlinear synchronous generator excitation controllers for improving power system stability is described in this paper. These controllers are based on the existing universal Higher-Order Sliding Mode control Structure (HSMCS), furnishing the system with robustness quality in the presence of disturbance. A significant aspect of the paper is the modification of the HSMCS for enhanced system dynamic performance and better robustness. The parameters of the controllers are carefully selected by simulation using MATLAB® software and various results showing system performance under network fault conditions are presented. The results show the ability of the modified controller to withstand longer fault durations of 14.7 and 14.5 cycles for a three-phase symmetrical fault located at an infinite bus and generator terminal, respectively.