Composite Saturating Control Based Disturbance Observer For A Class Of Nonlinear Systems

In recent years, the problem of anti-disturbance control for nonlinear systems has beenreceived more and more attention. Disturbance-observer-based control (abbreviate DOBC)approach can deal with the problem of anti-disturbance control for a class of nonlinearsystems. DOBC strategy depends on the idea of feed-forward compensation, and the influenceof the external disturbance can be estimated by a disturbance observer, then compensated inthe feed-forward channel. With the development of DOBC, the composite control strategieswith the combination of DOBC and other control scheme have been presented.In practical systems, the control input of most systems has constraints, namely thesaturation. It is difficult to guarantee the stability of the system when the input of the systemis too large owing to the saturation. Therefore, it should not only consider the disturbance, butalso take into account the influence of saturation to solve the problem of anti-disturbancecontrol for nonlinear systems.This paper considers the existence of external disturbance and saturation for a class ofnonlinear systems. A disturbance observer is designed to estimate the disturbance and asaturating controller is constructed to reject the effects of saturation. By integrating DOBCwith saturation control, the strategy of composite saturating control is proposed based on thedisturbance observer to solve the control problem for a class of nonlinear systems.Firstly, the problem of anti-disturbance control is investigated for a class of continuousnonlinear systems with disturbance and nonlinear saturation based on the compositesaturating control strategy in this paper. A disturbance observer is designed to estimate theexternal disturbance. Simultaneously, by considering the influence of nonlinear saturation, asaturating controller is designed to reject the saturation. By integrating DOBC with saturationcontrol, the composite saturating control strategy is proposed.Secondly, for a class of discrete nonlinear systems with disturbance and nonlinearsaturation, the composite saturating control strategy is extended to discrete nonlinear systems.Due to the discrete system characteristics, the disturbance observer is designed to estimate theinterference and the saturating controller is designed to reject the influence of saturation.Finally, for a class of special nonlinear systems, a reduced order disturbance observer is designed to estimate the disturbance. Based on the backstepping method, The anti-disturbancecontrol for a class of nonlinear systems can be solved by the saturating controller.