Predefined-time asymmetric prescribed performance adaptive control of uncertain nonlinear systems with dead-zone nonlinearities

This paper investigates a predefined-time asymmetric prescribed performance adaptive control scheme for a class of uncertain nonlinear systems subject to unknown dead-zone nonlinearities, parametric uncertainties, and external disturbances. A modified tuning function together with a tangent-based error transformation is proposed to achieve asymmetric prescribed performance for arbitrary initial tracking errors. The proposed design provides enhanced flexibility in shaping transient performance while facilitating analysis. Dynamic surface control is incorporated to eliminate the repeated differentiation of virtual control laws. In addition, unified adaptive laws are developed to simultaneously compensate for parametric uncertainties, disturbances, and dead-zone effects without requiring prior knowledge of uncertainty/disturbance bounds or dead-zone parameters. The proposed approach guarantees that the tracking error remains within the prescribed performance bounds for all time and enters a prescribed steady-state region within a user-specified predefined settling time. Lyapunov-based analysis establishes the semi-global uniform ultimate boundedness of all closed-loop signals while guaranteeing the desired prescribed performance. Simulation results demonstrate the effectiveness of the proposed control scheme.