Composite disturbance-observer-based control and variable structure control for non-linear systems with disturbances

A novel type of control scheme combining the disturbance-observer-based control (DOBC) with variable structure control (VSC) is proposed for a class of continuous non-linear systems subject to disturbances. The disturbances are supposed to include two parts. One in the input channel is generated by an exogenous system with uncertainty, which can represent the harmonic signals with modelling perturbations. The other is supposed to have the bounded H₂ norm. The disturbance observers based on regional pole placement and D-stability theory are presented, which can be designed separately from the controller design. By integrating DOBC with VSC laws, the disturbances can be rejected and the desired dynamic performances can be guaranteed for continuous systems in finite time with known and unknown non-linear dynamics, respectively. Simulations for a flight control system are given to demonstrate the effectiveness of the results and compare the proposed results with the previous schemes.