In this paper, the nonlinear modal analysis based on modal series method is employed to study the effects of SVC control system parameters on the nonlinear interaction between Static VAr Compensator (SVC) and the steam power plant turbine-generator set. For this purpose, a second-order representation of a power system equipped with SVC is developed and then by using the modal series method, the SVC nonlinear torsional interaction assessed under different conditions. The results show that in a stressed power system, the SVC parameters such as voltage regulator gain and firing delay of thyristor have important effects on the increasing of the nonlinear interaction with torsional modes. In this case, an adverse increase in the torsional oscillations amplitudes occurs, and this may lead to a significant reduction in the lifetime of the shaft in oscillation periods. Furthermore, the results of nonlinear modal analysis are validated through simulating the nonlinear power system equations in the time domain.

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