Composite disturbance-observer-based control and H∞ control for complex systems

A new type of control scheme combined with the distance-observer-based control and H_infin control is proposed for a class of discrete-time complex models with exogenous disturbances. The unknown external disturbances are supposed to include two parts. One is generated by an exogenous system with uncertainty, which can represent the harmonic signals with modeling perturbations. The other is supposed to have the bounded H₂-norm. The novel composite control scheme combined is applied to reject and attenuate the disturbances for such uncertain nonlinear discrete-time models. Parametric uncertainties exist both in concerned plant and in exogenous subsystem. By integrating the disturbance observers with H_infin control laws, the first type of disturbances can be estimated and rejected, and the second one can be attenuated. Simulations are given to demonstrate the effectiveness of the results and compare the proposed results with the previous schemes.