Cross-couplings are present in all the generators belonging to interconnected power systems. As is well known, the presence of these couplings is one of the major sources of voltage variations and rotor oscillations in the generators belonging to the system. To solve this problem a geometric graph-theoretic approach is proposed by which a state feedback decoupling controller is derived. The proposed controller can also assure a desired location to all the critical eigenvalues of the decoupled closed-loop system, so that the improvement of the dynamic performance of each generator is guaranteed. The capability and usefulness of the proposed technique are illustrated by considering a 14-generator 34-busbar test system.