The paper describes the problem of control of multi-machine power systems under parametric uncertainties, perturbed mechanical input power and unknown variable communication time-delay. The algorithm is proposed for the case when only relative speeds of each electrical generator are measured. The 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 scheme is illustrated by modeling of the three machine power systems.