Output–Feedback Regulation of the Contact-Force in High-Speed Train Pantographs

One of the main problems in high-speed train transportation systems is to counteract the fast variations of the contact force between the catenary and the pantograph collector end. The variation of the catenary equivalent stiffness, due to the suspending system, originates mechanical oscillations whose frequency and magnitude are larger and larger as the train speed increases. Such oscillations cause electric arcs that damage the mechanical structure and compromise the collection of the current from the supply wire, degradating the overall performance. Active pantographs offer the possibility of affecting the contact force evolution by suitably modifying a control torque applied at the lower arm of the pantograph. We consider the equivalent stiffness of the catenary as an uncertainty to compensate for by suitable robust control techniques, and, under the assumption that a noisy measure of the actual contact force is available, we propose an output-feedback control scheme based on higher-order sliding modes and high-gain observers. That combination allows for an almost-complete rejection of the undesired oscillations of the contact force, as confirmed by simulations, and is very attractive for real-time implementation purposes, due to its simplicity and robustness.