Disturbance-observer-based model-free adaptive active fault-tolerant consensus control for MASs with TVDAF

This paper investigates the problem of consensus control for multi-agent systems (MASs) with both actuator faults and external disturbances. Firstly, a disturbance-observer-based model-free adaptive consensus control scheme is presented for the fault-free case. Interestingly, based on the fault-free control scheme, a novel fault detection mechanism with an adjustable time-varying threshold is developed to detect actuator faults and trigger alarms, which avoids false alarms due to the large changes in the desired output. Next, by using the fault detection mechanism and the radial basis function neural network (RBFNN), two disturbance-observer-based model-free adaptive active fault-tolerant control (AFTC) schemes are respectively proposed, one each for the cases of known time-varying-direction actuator faults (KTVDAF) and unknown time-varying-direction actuator faults (UTVDAF). It is worth mentioning that an improved Nussbaum function that has better freedom of frequency adjustment is developed to deal with the issue of UTVDAF. Furthermore, by introducing the disturbance separation method, the effect of external disturbances on the fault detection results is avoided, and the control accuracy and fault tolerance ability are improved. Finally, the feasibility of the developed control schemes is confirmed through rigorous math proofs and computer simulations.