Disturbance rejection in nonlinear systems based on equivalent-input-disturbance approach

This paper presents a new system configuration and a design method that improves disturbance rejection performance for a nonlinear system. The equivalent-input-disturbance (EID) approach is used to construct an EID estimator that estimates the influence of exogenous disturbances and nonlinearities on the output of the system. Sufficient stability conditions for state- and output-feedback control are derived in terms of linear matrix inequalities. New EID-based control laws that combines an EID estimate with a state- or an output-feedback control laws ensure good control performance. A numerical example illustrates the design method. A comparison between the EID-based control, the conventional disturbance observer, the disturbance-observer-based-control, and the sliding mode control methods demonstrates the validity and superiority of the EID-based control method.