In this paper, a nonlinear approach is proposed for the control and state estimation of the Pantograph-Catenary system in order to maintain the contact force at a constant level. Assuming that the measures of the contact force and the train velocity are both available, we estimate the states by means of a robust nonlinear observer constructed by the incorporation of a robust sliding mode term in the Extended Kalman Filter (EKF). Secondly, we use a Feedback Linearization method to transform the original nonlinear plant into its equivalent linear one. The obtained feedback linearized system can be controlled with a large number of linear approaches that can be tuned according to the specification requirements. Using these theoretical elements, we apply a observer-based linear quadratic regulator (LQR) in order to stabilize the system and solve the reference tracking problem. The simulation results demonstrate the effectiveness of this method.