Research On Several Methods Of Fault Tolerant Control For Time Delay Systems

Fault-tolerant control is an important approach to improving the safety and reliability for dynamic systems. Hence, the study on fault-tolerant control technology has both theoretical and practical importances. At present, it has drawn wide attention, and has been one of the main topics in control science. Time delay is commonly encountered in various engineering systems, such as chemical processes, long transmission lines in pneumatic, hydraulic and rolling mill systems, furthermore, these can be regarded as time delay systems. Time delay usually results in unsatisfactory performances and is frequently a source of instability. The methods of fault-tolerant control for time delay systems are studied systematically in this dissertation. The main contributions of this dissertation can be summarized as follows:Robust reliable control design problem for uncertain systems with time-varying state delay as well as actuator failures in the input channels is discussed. A sufficient condition is established such that the quadratic stability of the closed-loop system is ensured for both the nominal system and the system with possible actuator failures. The condition is a delay-dependent one. A reliable state feedback controller is synthesized within the framework of linear matrix inequalities(LMIs). As compared with the delay-independent conditions, the result proposed has the merit of being less conservative.The fault tolerant control design problem for uncertain time-delay systems with both sensor and actuator failures is discussed. A memoryless and memory state feedback control, which can decrease the influence of time delay, is designed to guarantee the integrity of the system together with the prescribed H_∞performance index. The sufficient condition for the existence of the solution is formulated in terms of LMIs.Active fault-tolerant control problem of multi-state delay system is studied. Based on generalized internal model control (GIMC) two fault-tolerant control design methods are proposed. In the first method, based on Youla controller parameterization and GIMC, the feedback controller architecture includes two parts: one part for performance and the other part for robustness. The feedback control system will be solely controlled by the performance controller when there is no fault and the robust controller will be active when there are faults. In the second method, based on GIMC, firstly, the residual signal is generated by means of a co-prime factorization method. Secondly, a new performance index is proposed by converting the fault diagnosis (FD) problem to a H∞robust control problem. And then a post-filter is designed as a robust controller which can make the filtered residual signal close to the fault signal so that the fault estimation purpose can be fulfilled simply. This method may be regarded as a H∞bridge between FD and fault tolerant control, the relationship of residual signal and the real fault signal is established. Some illustrative design examples are used to demonstrate the validity and applicability of the proposed approaches. Some comparisons are made based on the simulation results.Fault tolerant control for uncertain systems with time varying state-delay is studied. Based on sliding mode controller design, a fault tolerant control method is proposed. By means of the feasibility of some LMIs, delay dependent sufficient condition is derived for the existence of a linear sliding surface which guarantees quadratic stability of the reduced-order equivalent system restricted to the sliding surface. A reaching motion controller, which can be seen as a fault tolerant controller and can retain the stability of the closed loop system in the present of uncertainties, disturbances and actuator fault, is designed. A numerical simulation shows the effectiveness of the approach.An active fault-tolerant control scheme of linear parameter varying time-delay system (LPVTD) is proposed. Under the assumption that the parameters are convex and the system matrices can be of affine parameter dependence, by a linear fractional transformation (LFT), the design of a fault filter can be equal to the design of a H∞controller. The existence condition and the method to get the gain of the controller are proposed, based on which fault compensation can be realized. The idea that transform the fault diagnosis and fault tolerant control problem to a H∞control problem can be easily extended to other kinds of systems.The fault accommodation problem for time-delay systems with parametric faults is studied. The progressive accommodation strategy which based on the Newton-Raphson scheme is adopted to solve this problem. This accommodation scheme significantly reduces the degradation of performance and the risk associated with system instability resulted from the time delay induced by fault accommodation algorithms to provide a solution. Consider that in the real situations, it takes some time for the controller to compute and apply the fault tolerant control after the fault been detected. So the delays should be considered and thus the method proposed is more applicable in practice.