Sliding Mode Control Of Uncertain Systems In Case Of Actuator Failures

In practical engineering applications, the components of control systems (such as actuators and sensors), due to wearing and aging, suffer from failures inevitably. It will not only affect the system’s performance, but even lead to system instability. Thus, the reliable issue has always been the hotspot of control field. Meanwhile, the inevitable uncertainties of the system will reduce the performance, which must be considered in the design process. On the other hand, sliding mode control (SMC) exhibits strong robustness to parameter perturbation and external disturbance. Therefore, the study on sliding mode control of uncertain systems in case of possible failures of actuators or sensors has great theoretical and practical significance.Based on the summary and analysis of the current situation on the SMC of uncertain systems, this thesis considers the problem of sliding mode control subject to possible failures of actuators under the following conditions:two types of uncertain T-S fuzzy state-delayed systems with parameter uncertainties and external disturbance, with constrained control input and the approach combining the SMC with the adaptive control, respectively. And some innovative achievements have been made.The main results include:(1) Aiming at the problem of sliding mode control for a class of uncertain T-S fuzzy delayed systems with parameter uncertainties and external disturbance, a T-S fuzzy model is established and an integral sliding surface is designed then. In addition, a sufficient condition for the asymptotical stability of the sliding mode dynamics is derived and the reachability of the sliding surface despite the presence of parameter uncertainties, external disturbances and actuator faults is demonstrated. Finally, the resulting control law is applied to the reconfigurable flight controller of an aircraft with vectored thrust. Simulation results show the proposed method achieves good performance even if the aircraft has failures.(2) The problem of sliding mode reliable control for a class of uncertain T-S fuzzy delayed systems with constrained input (dead-zone and saturation) is investigated. A sliding mode controller based on an integral switching surface is designed, and the sufficient condition for the asymptotic stability of the sliding motion is derived. It is shown that the reachability of the sliding surface can be ensured. Finally, a numerical example is given to show the effectiveness of the proposed method. (3) Aiming at the uncertain systems with possible actuator faults, the reliable design via combining sliding mode control and adaptive control is investigated. There exist parameter uncertainties and external disturbance in the controlled system and any of the actuators may be subject to faults. Both the stability of the slidng motion and the reachability of the specified sliding surface are analyzed by linear matrix inequality (LMI) and Lyapunov stability theory. Finally, numerical simulation results are given to demonstrate the effectiveness of the proposed method.