Contact force estimation and regulation in active pantographs: An algebraic observability approach

In this paper we extend our previous work concerning the regulation of the contact force in active train pantographs with wire-actuators. In particular, we consider the problem of estimating the contact force, instead of measuring it, by means of the measured displacements of the upper and lower pantograph frames. The estimation method, based on the algebraic observability theory, entails the use of real-time sliding-mode differentiators. It makes use explicitly of the upper frame mechanical characteristics, but does not require any other information concerning the system model. We consider our previously proposed second-order sliding mode control scheme, which also includes proper linear compensating cascade filters devoted to cope with the de-stabilizing effects of the resonant wire actuator. We show that such a control scheme can be effectively combined with the given contact force estimation method.