抄録
Transient stability analysis is one of the most important studies related to power systems. As the scale of the power system grows, the computational effort required for this analysis increases greatly. Use of equivalents to represent certain parts of the system is a popular approach to overcome the above difficulty. Coherency based equivalents requiring the identification of coherent machines is one of widely used methods.
In this paper, a new efficient method is proposed to characterize coherent behavior of machines in power systems. The linearized set of system equations is employed to describe the dynamics of the machines which are departing from their equilibrium state. In the proposed method a theorem and a corollary are derived using the idea of perfect coherency and modal analysis. Later, a minimization technique in an inner product space is incorporated in this analysis in order to extend the idea of perfect coherency to the idea of practical coherency which is designated as close coherency throughout this paper. The practicality of the close coherency is further diversified introducing the idea of global and local coherency. Finally numerical examples are used to give a better picture of the proposed approach.
