Frequency-change analysis of nonlinear system using spectrum (Fast Fourier Transform) theory

The study of nonlinear behavior near an equilibrium point is of considerable importance in power system. In this paper, some systematic procedures based on normal form (NF) theory are proposed for studying the influence of high order terms arising from the Taylor series expansion of the system model on power system dynamic behavior. Using this method, a third-order model of the power system is proposed in which weak system nonlinearities are explicitly represented. Analytical expressions are then developed that provide near approximate solutions to system performance. To check the validity of the frequency-change method, experiments were obtained using single-machine infinite-bus system using a classical representation. The purpose of these experiments is to find the phase difference between the classical model and the nonlinear equivalents.