Static disturbance-to-output decoupling for nonlinear systems with arbitrary disturbance relative degree

Static disturbance-to-output decoupling problem for nonlinear systems with arbitrary disturbance relative degree is addressed in this paper without resorting to a high-gain design. A systematic design method is developed for the design of the disturbance compensation gain in the control law. It is shown that the influence of the disturbance can be eliminated from the output channel in steady state with the proposed design method. More interesting, the exact disturbance decoupling methods turn out to be special cases of the proposed control law. The feasibility of extending the proposed method to unmeasurable disturbance case is also investigated by integrating a nonlinear disturbance observer. It is further discussed that the proposed method can be extended to multiple disturbance cases with almost no modification. Simulation example of a missile shows that the proposed method is effective in rejecting disturbance with arbitrary relative degree.