Dynamic Surface Control of a Class of Uncertain Nonlinear Systems in the Presence of Actuator Saturation and Unknown External Disturbance

Actuator saturation is one of the most common constraints of the system input. In this paper, a dynamic surface control scheme is presented for a class of uncertain nonlinear systems in the presence of actuator saturation and unknown external disturbance. In the proposed scheme, the multi-input multi-output adaptive wavelet network as a nonlinear-in-parameter approximator is designed to approximate the uncertain dynamics of the system without requiring any prior knowledge. Translation and dilation parameters of wavelets and weights of the network are updated based on the adaptive laws. The nonsmooth nonlinear saturation constraint is approximated by a smooth function of input signal. Also, a nonlinear disturbance observer is designed to estimate the unknown external disturbance. Then, the nonlinear disturbance observer-based dynamic surface control scheme is proposed. The proposed scheme guarantees that all signals of the closed-loop system are uniformly ultimately bounded and the tracking error can be made small by proper selection of the design parameters. In the proposed scheme, because of using wavelet network and dynamic surface control approach, both of “curse of dimensionality” and “explosion of complexity” problems are eliminated, simultaneously. Simulation results verify the proper performance and effectiveness of the proposed controller.