Adaptive Fixed-Time Prescribed Performance Command-Filtered Control for Nonlinear Systems with Unknown Control Gains and Actuator Faults

This paper investigates the adaptive prescribed performance fixed-time control problem for uncertain strict-feedback nonlinear systems in the presence of unknown control coefficients and actuator faults. A switching-based control strategy is developed to address the uncertainty in control coefficients, where adaptive parameters are adjusted online according to design requirements. To regulate the transient and steady-state behavior, a fixed-time prescribed performance function is incorporated into the control design, ensuring that the tracking error evolves within predefined bounds. The command filter technique is employed to simplify the backstepping procedure and avoid the issue of complexity growth, while filter-induced errors are compensated using auxiliary signals. Rigorous Lyapunov analysis establishes that all closed-loop signals remain bounded and that the tracking error converges to a small neighborhood of zero within a fixed time, independent of initial conditions. The effectiveness of the proposed method is demonstrated through numerical simulations and a practical example.