Observer-based parameter estimation in Liénard systems

A general excitation condition is provided for parameter identification in so-called Liénard second order nonlinear systems. This condition allows a quite simple observer design for asymptotic state and parameter estimation. Such a condition has already been very recently shown to be satisfied for Van der Pol ocillators Besançon et al. (2010), and is further checked here for nonlinear pendulum equations, for which illustrative simulation results are provided.