On the disturbance decoupling problem for a class of nonlinear time delay systems

Considers a class of SISO nonlinear time delay systems with delays on the state and the input. Based on the concept of relative degree associated to this class of systems, the authors give necessary and sufficient conditions for the solvability of the nonlinear disturbance decoupling problem (NDDP). Since the control law needed for the solvability of the NDDP for this system is noncausal the authors propose a causal solution based on an approximate representation of the nonlinear time delay system around an equilibrium point