Fault-Tolerant Control For Nonlinear Systems Based On Adaptive Approach

Modern engineering systems are developing towards larger and more complicated scale, and the demands for plant safety and reliability are higher. However, the faults on control systems occur inevitably, and the nonlinear characters usually exist in engineering systems, which make the above-mentioned demands are difficult to be satisfied. Hence, the fault-tolerant problem for nonlinear systems has been led to greater attention, and also is one of the hot and difficult topics focused by international scientific association. In this thesis, the fault-tolerant problems for nonlinear systems are investigated by adaptive approach, based on the existing literatures. The main research contents are given as follows:First, the design problem of adaptive observer and adaptive fault-tolerant controller for nonlinear systems is studied with time-varying delay and the unknown upper bound of nonlinear term in this paper. First of all, the adaptive observer is utilized to give a real time estimation of the fault. Then, an adaptive fault-tolerant controller is constructed according to the information of real time diagnosis. The asymptotic stability of the closed-loop system is proved by Lyapunov theory both in normal case and in fault case.Second, a new adaptive fault-tolerant method for nonlinear systems is presented. By constructing a novel Lyapunov functional, we design a new fault-tolerant controller based on robust adaptive observer without the knowledge of upper bounds of nonlinear function, external disturbances, modeling uncertainties and external fault inputs. The resulting closed-loop system is shown to be asymptotically stable. And, in contrast with the existing literatures, the proposed method can make the dynamic performance of closed-loop system better.Then, we focus on investigating the adaptive tracking control problem of a class of nonlinear system with non-symmetric actuator dead-zone fault. Based on extended observer, a new adaptive tracking control method is proposed. The restriction that all states of the systems must be fully measured is cancelled. Under the condition that the dead-zone model parameters and the upper bound of uncertain nonlinear term are all unknown, the adaptive controller we designed can eliminate the effect of actuator dead-zone fault well, and ensure bounded-error tracking. Moreover, the chatter phenomenon of controller can be eliminated well by selecting appropriate design parameters.In the end, the tracking fault-tolerant control problem for a class of unmatched nonlinear systems is investigated. Considering the actuator dead-zone fault, the adaptive fault-tolerant control approach is proposed based on backstepping method, which can assure that tracking error of the fault closed-loop system is uniform ultimate-bounded. Furthermore, the design method of smooth controller is presented.