UDE-based Robust Control for a Class of Nonaffine Nonlinear Systems with Uncertainties and Output Constraint

In this paper, we study the robust control problem of a class of nonaffine nonlinear systems based on uncertainty and disturbance estimator (UDE) under unknown system dynamics and output constraint. A proposed UDE control method is used to estimate uncertainties that contain the uncertainty of parameters. The prominent feature of UDE is to avoid the construction of inverse operators. The control design requires only the bandwidth information of uncertainty. Moreover, the barrier Lyapunov function (BLF) is used directly to address the problem of output constraint. The remarkable feature of the BLF compared to the Lyapunov function based on pure tracking error is to relax the feasible initial output signal to the whole constraint range. Based on the control of UDE, by using Lyapunov’s stability theory, the consistent boundary of the closed-loop system is obtained. Through the simulation studies of model uncertainty and external disturbance, the validity of the proposed UDE-based control method is proved and compared with the traditional UDE control method.