Abstract: Based on a nonlinear second-order model for a single-machine infinite-bus system with TCSC, two kinds of nonlinear controller were designed using backstepping methods. With backstepping, the origin nonlinear system doesn't need to be linearized and the closed-loop error system is guaranteed to be asymptotically stable. When damping coefficients is measured inaccurately, a dynamic feedback controller can be designed using adaptive backstepping containing the real-time estimation of uncertainty parameter. The design procedure reveals that the controller designed by backstepping possesses good performances.