Adaptive Fuzzy Predefined-Time Prescribed Performance Control for Nonlinear Systems with Input Saturation

In this article, the predefined-time prescribed performance (PTPP) adaptive fuzzy control problem is investigated for non-strict feedback nonlinear systems with input saturation and unknown external disturbances. Specifically, fuzzy logic systems and the variable separation technique are adopted to simultaneously estimate unknown nonlinear terms and eliminate the algebraic loop problem. The challenge caused by the input saturation is overcome by constructing the antisaturation auxiliary system. Moreover, with the help of the PTPP function and the nonlinear error transformation function, the tracking error converges to the preset bound within a predefined time. In contrast to asymptotic/finite/fixed-time performance controllers, the upper bound of the settling time in this paper can be assigned a priori irrespective of initial conditions. Furthermore, by combining the backstepping design framework with the dynamic surface control technique, the adaptive fuzzy PTPP control strategy is formulated, which guarantees that the tracking error can stay within the predefined domains and all signals in the closed-loop system are bounded. Finally, the feasibility of the proposed method is effectively demonstrated through a simulation example.