| The design of output feedback controllers that solve the output regulation problem for nonlinear systems is considered, with emphasis on improving their transient performance. We concentrate on the output regulation of nonlinear systems using conditional servocompensators, an idea that was introduced in the earlier work of Khalil and co-researchers. The conditional servocompensator acts as a traditional servocompensator in a neighborhood of the zero-error manifold while acting as a stable system otherwise, leading to improvement in the transient response while achieving zero steady-state regulation error. The idea was introduced in a sliding mode control framework. We extend the technique of conditional servocompensators to more general feedback controllers by using Lyapunov redesign and saturated high-gain feedback.;The striking feature of our approach is the flexibility of starting with any stabilizing state feedback controller and then including a conditional servocompensator to achieve zero steady-state regulation error without degrading the transient performnace. We give regional as well as semi-global analytical results for error convergence. The flexibility offered by our design approach allows us to consider as a special case, the output regulation problem for control-constrained linear systems. Such a design approach, however, assumes the availability of all state variables to meet the control objectives, and the output feedback control can only be implemented using a full-order observer. An extension of methodology to nonlinear systems would necessitate the development of a full-order nonlinear observer. We develop a full-order high-gain observer for nonlinear systems, extending earlier work on reduced-order high-gain observers for nonlinear systems and full-order observers for linear systems. |
