Adaptive fault-tolerant output feedback control of uncertain nonlinear systems with unknown high-frequency gain sign

This article develops an adaptive control method for accommodating actuator faults in a class of unknown nonlinear systems without a priori knowledge of high-frequency gain. An adaptive high-gain K-filters with switching laws is proposed to suppress the nonlinearities which are dependent on the unmeasured states. Combining the Nussbaum-gain approach with backstepping design, an adaptive controller with high-gain function can be obtained. It is proved that the proposed control approach can guarantee that all the signals of the resulting closed-loop system are bounded and tracking error can be made as small as desired by appropriate choice of the design parameters. Simulation results are presented to show the effectiveness of the proposed scheme.