Output feedback CNF control for output regulation problem of linear system with input saturation

To improve the transient performance, the composite nonlinear feedback (CNF) control technique is introduced to solve the output regulation problem of linear systems with input saturation. Under the assumption that both the states of plant and exo-system are not measurable for feedback, an full state observer is designed to construct an output feedback CNF control law. The output feedback CNF controller is constructed based on a state feedback control law that solves the output regulation problem and the state observer. The solvability of the output regulation problem by output feedback CNF control is established which shows that the nonlinear feedback part does not change the solvability condition of the output regulation problem. The introducing of nonlinear feedback part in the CNF control law provides an extra degree of freedom to improve the transient performance. By appropriately choosing the linear feedback gain and the nonlinear feedback gain in the CNF control law can significantly improve the transient performance of the controlled output which is illustrated by a disturbance rejection problem.