Adaptive Fuzzy Control for Nonlinear Systems in Nonstrict-Feedback Form with Full State Constraints: A Feasibility Condition Free Approach

In this paper, we aim to solve the full state constrained control problem for nonstrict-feedback nonlinear systems subject to completely unknown nonlinearities, unknown control gains and external disturbances. The full state constraints are assumed to be asymmetric and time-varying. Fuzzy logic systems (FLSs) are utilized to approximate the completely unknown nonlinearities. A shifting function is first introduced to remove the feasibility condition on the virtual controllers while using the traditional barrier Lyapunov functions (BLFs). Then, a dynamic surface control (DSC) based adaptive fuzzy controller is developed to prevent the state constraints from being violated. The main feature of this paper lies in that a unified structure for both symmetric and asymmetric full state constraints is constructed without feasibility condition, and the Lyapunov stability of the closed-loop system is proven. Simulation results are given to demonstrate the effectiveness of the proposed control structure.