Adaptive Control of Constrained Nonlinear Systems With Intermittent Faults: A Fixed‐Time Fault‐Tolerant Framework Based on Projection Operator

ABSTRACT This article investigates the problem of adaptive fixed‐time fault‐tolerant control for nonlinear systems with time‐varying intermittent faults and asymmetric output constraints. For this purpose, a novel adaptive law based on the projection operator technique is developed to estimate time‐varying intermittent faults, which eliminates the problem that the estimated value increases continuously with the accumulation of fault times. Considering that the fault estimation time needs to be less than the minimum time interval of intermittent faults, the fixed‐time design methodology is introduced to ensure that the relationship between the above two can be quantitatively analyzed. Then, a novel adaptive fixed‐time fault‐tolerant control strategy is put forward for the closed‐loop system, in which a universal barrier function is adopted to remain the system output in the time‐varying asymmetric constraint condition invariably. The theoretical analysis indicates that the developed strategy can guarantee the boundedness of all signals in the closed‐loop system in a fixed‐time. Finally, two examples, one of which involves the rotary steerable drilling tool systems are provided to demonstrate the feasibility and validity of the put forward scheme.