Output feedback stabilization and restricted tracking for cascaded systems with bounded control

In this note we discuss the problems of output feedback stabilization for a class of cascaded systems and of (approximate) output regulation for general nonlinear systems. It is shown that (global) output feedback stabilization for a class of systems in feedforward form can be achieved with a dynamic feedback law, yielding bounded control, and relying on the introduction of a reduced order observer. The above result, together with standard tools borrowed from the nonlinear output regulator theory, is instrumental to construct dynamic control laws achieving (approximate) disturbance rejection and output tracking in the presence of (bounded) disturbance/reference signals generated by a known exosystem.