This paper presents a new methodology for the synthesis of power system stabilizers (PSSs) and speed governors in order to satisfy some recent objectives and constraints imposed by the evolution of large-scale interconnected power systems. As a consequence of the increasing size of these systems, the frequency of some inter-area modes diminishes so much so that these oscillatory phenomena interact with the dynamics of the speed governors. These low-frequency inter-area modes are also more spread (i.e., they involve a larger number of generators) than the other inter-area modes of the system. This two particularities require several supplementary levels of coordination when tuning the PSSs and the governors of the machines involved in these oscillatory phenomena. To ensure this, the synthesis of the aforementioned regulators is done using a new control model which takes into account the key interactions of the dynamics of the power system. It thus allows the coordination of control actions among several generators as well as between the electrical and mechanical paths. This control framework ensures also an optimal trade-off performance/robustness. Validation simulations have been carried out with the Eurostag software on a realistic large-scale model of the interconnected European power system.