A Nonlinear Control Method for SSSC to Improve Power System Stability

This paper presents an investigation on transient stability of power systems equipped with a flexible alternating current transmission system (FACTS) device. A static synchronous series compensator (SSSC) is considered as a FACTS device. In a power system transmission, the SSSC has two functions; first, it compensates reactive power, second, it improves transient stability. The second functionality of the SSSC system is due to its capability to raise the maximum transferable electric power (P_max) from generator to infinite bus. To raise the maximum transferable electric power (P_max), the SSSC actively and appropriately changes the line reactance. Since the control of the power system is a nonlinear problem, therefore, a nonlinear controller for the SSSC is designed and presented in this paper. The proposed nonlinear controller of the SSSC increases critical clearing time of the power systems' faults and damps out rotor oscillations of a single machine connected to an infinite bus. Unlike linear controllers, performance and operating region of the proposed nonlinear controller of the SSSC system is not restricted to a close vicinity of the generator operating point, but includes the entire region of operation. The Matlab simulations for computational analysis and the Lyapunov criteria of stability for analytical investigations are used to examine the response time and robustness of the proposed nonlinear controller.