This paper presents a nonlinear controller for type 2 static synchronous compensator (STATCOM) systems to obtain the settling time of the reactive current and the convergence rate of the internal dynamics. To make the STATCOM system an input affine system, dynamic extension algorithm is used. Taking the reactive current as the output, we input-output linearized the dynamically extended system and put it in the normal form in order to apply integral sliding mode control for regulating the tracking error of reactive current. Stability of internal dynamics is also shown by using a composite Lyapunov equation. Locally asymptotic stability of the tracking error is proved. The proposed method reduces the ripple of active current and DC voltage without sacrificing reactive current. Simulation results are illustrated to show the effectiveness of the proposed method.