The problem of disturbances compensation in multi-machine power systems under parametric uncertainties and perturbed mechanical input power is considered. The solution is proposed for the case when only relative speed of each electrical generator is available for measurement. The proposed control algorithm synchronizes the multi-machine power system with the required accuracy in the normal mode and under symmetrical 3-phase short circuit faults which occur on transmission lines. Efficiency of the proposed scheme is illustrated by modeling of the three-machine power system.