Dynamic Output Feedback by Robust Observer and Variable Structure Control

Variable structure controllers for systems with nonlinearities can be designed in conjunction with robust observers to obtain regulation. The robust observer (of the Doyle Stein class) is designed on the basis of the nominal plant dynamics (assumed linear and minimum phase), and the estimated state is used in the variable structure controller. It is shown that the closed loop system is globally asymptoticvally stable and the desired regulation is obtained provided the nonlinear perturbation is expressed by an operator with bounded L2 and L¿ norms. Applications to the control of underwater vehicles in diving maneuvers show the effectiveness of the technique.