Dynamic stability enhancement of composite mode oscillations of interconnected power systems by means of a hybrid power system stabilizer is discussed. The proposed hybrid PSS is of a two-level structure composed of a local mode and a global PSS inter-area mode damping. The input of the global stabilizer is the center of inertia speed deviation of slow-coherent generators. This work is mainly focused on the practical considerations in implementation of the proposed stabilizer. The optimum allocation of this stabilizer is discussed. An index of mode-input-assignability, by which the best sites of the stabilizer can be identified, is introduced. For practical applications, an estimation for the approximation of the input of the global PSS is introduced. An approximated value of the center of inertia speed is obtained from a suitable combination of the rotor speed data of a few properly selected key generators.
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