Fixed-time output tracking control for a class of uncertain nonlinear MIMO systems

This article proposed a new fixed-time output tracking control scheme for a class of high-order MIMO nonlinear systems with unknown nonlinearities, parameter uncertainties and external disturbances. Firstly, a novel nonsingular recursive integral terminal sliding mode (ITSM) surface is designed by employing appropriate integral function and integer orders. Then the lumped system matched and mismatched uncertainties are estimated by developing a new adaptive fixed-time disturbance observer (AFTDO) based on super-twisting technique. The chattering problem existed in traditional disturbance observer (DO) can be reduced with the proposed AFTDO allowing the gains to adapt the changed derivative of lumped disturbances, effectively. Furthermore, semi-global fixed-time stability analysis is presented by means of Lyapunov stability theorem and it is proved that the system convergence time is independent of the system initial states and allowed to be arbitrarily adjusted based on practical demands. Finally, theoretical results are supported by numerical simulation and experimental results.