Implementation of a Hybrid Power System Stabilizer

Dynamic stability enhancement of composite mode oscillations of interconnected power system by means of a hybrid power system stabilizer is discussed here. The proposed Hybrid PSS is of a two-level structure composed of a local PSS for local mode and a global PSS for inter-area mode damping as in Fig. 1. The input of the global stabilizer is the center of inertia speed deviation of slow-coherent generators. The present paper is mainly focused on the practical considerations in implementation of the proposed stabilizer. First, the optimum allocation of this stabilizer is discussed. We introduce an index of "modeinput-assignability," by which the best sites of the stabilizer can be identified. Next, for practical applications, an estimation method for the approximation of the input of the global PSS is introduced. Here, 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." Lightly damped or even negative damping oscillatory modes associated with rotor dynamics of synchronous generators are widely experienced in practice. When the individual power grids are interconnected with AC tie-lines, it forces the generating units to participate in both local and inter-area oscillations, which are referred to "composite mode oscillations." Our research is concerned with the dynamic stability enhancement of interconnected power systems through stabilization of composite mode electromechanical oscillations.