Adaptive fuzzy fault-tolerant control with guaranteed tracking performance for nonlinear strict-feedback systems

In this study, we propose two backstepping-based adaptive fuzzy fault-tolerant control (FTC) methods for a class of nonlinear strict-feedback systems with actuator failures. First, a traditional FTC (TFTC) method is considered. Our analysis shows that TFTC has poor tracking performance due to the existence of approximation errors and external disturbances. Inspired by the idea that the magnitudes of control inputs decrease as the error of the last step decreases in the backstepping procedure, we propose a new prescribed performance FTC (NPP-FTC) method based on the improved error transformation technique. Compared with previous methods where only the output tracking error is guaranteed within the prescribed performance bound (PPB), we show that the state tracking error for each step between the intermediate control and virtual control remains within the PPB regardless of actuator faults. The main advantage of the NPP-FTC method is that the tracking errors and magnitudes of the control inputs can be reduced by adjusting the PPB parameters of the errors in the first and last steps. Our simulation results demonstrate the effectiveness of the proposed NPP-FTC method.