Development of coherency-based time-domain equivalent model using structure constraints

A new method is proposed to develop dynamic equivalents of coherent machines represented by detailed models. The method estimates the parameters of an equivalent synchronous machine and an equivalent excitation system using a noniterative procedure. The equivalent parameters are determined by structure preservation of the coefficient matrices in a time-domain representation of the machines. The development of dynamic equivalents by the reported procedure requires much less computation time than the existing frequency-domain procedure. The derived equivalent can be used with conventional transient stability programs without any modification. Validation test of the proposed equivalencing procedure on a 50 machine power system is reported in the paper.