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 suggest a second‐order sliding mode based control scheme that avoids the direct measurement of the contact force, which is quite unpractical in real applications. The idea is to estimate the contact force using the measured displacements of the upper and lower pantograph frames. Unlike the contact force, the frames displacements can be measured accurately and reliably in practice. The estimation method, based on the algebraic observability theory, entails the use of real‐time sliding‐mode differentiators. It makes use explicitly of the mechanical characteristics of the upper frame only. The considered second‐order sliding mode control scheme 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.