Analytical characterization of nonlinear modal interaction in power systems with UPFC

In this paper, the oscillations due to a Unified Power Flow Controller (UPFC) interacting with the power system are analyzed. The UPFC is an important component which belongs to the Flexible AC Transmission Systems (FACTS) devices. One of its main applications arises on damping oscillations in power systems. Basically, the nonlinear oscillations are characterized by the modal series method, which is an analytical approach that allows to obtain an uncoupled terms of linear and nonlinear contributions of a nonlinear system, in this case the UPFC connected to the power system. The nonlinear contributions of power system and UPFC variables are analyzed when controller parameters are varied, carrying out the modal analysis through the study of eigenvalues trajectories and nonlinear interaction indices. Time domain simulations are performed under different parameters scenarios of the synchronous machine-infinite busbar-UPFC that are followed after a disturbance operating conditions. A comparative analysis between linear response and nonlinear modal series time solution are described.