Robust Global Prescribed Performance Control of Unknown Strict-Feedback Systems

This paper is concerned with the reference tracking control problem for strict-feedback systems with unknown nonlinear functions under mismatched disturbances. A tuning function-based prescribed performance control strategy is proposed to solve the problem. In the control design, the tuning function is employed to adjust the output tracking error and the intermediate tracking errors. In this way, the dependence of the performance specifications on the initial condition of the closed loop is relaxed. Then, a set of barrier functions are adopted to confine the resulting error signals, while the potential robustness of the barrier functions is thoroughly revealed. By doing so, it is guaranteed that all the real errors converge from any initial positions to the preassigned sets in the given time. The simulation results illustrate the effectiveness of the proposed control.