A modal-coherency technique for deriving dynamic equivalents

A technique for deriving dynamic equivalents is developed that combines the advantages of modal and coherency analysis. The electromechanical mode shapes are examined to find all the possible coherent groupings of machines in a given system. The results are displayed as a tree structure in which the whole interconnected power system forms the root of the tree and the various subdivisions of the system constitute the branches. The modal tree can be used to extract coherent machine groups to suit any particular application. A 24-machine test system is presented as an illustration.>