Fault Tolerant Control System Design Based On The Adaptive Method

Based on the fact that automatic systems are becoming more and more large and complex and the control accuracy for the practical engineering systems is advanced as high as possible, fault tolerant control was a reliable technology and put forward to improve control performance. Adaptive control as an effective method can solve the problem of the systems with uncertainty and robustness, so this control method has a promising foreground in fault tolerant control fields, especially for some systems focusing on their safety such as airplane system. When something has been wrong with the actuator or sensor of the system, where nothing about the failure is known previously, adaptive control scheme is applied to the system and always can get satisfied performance, even under the condition that failure pattern is unknown. In 1991, adaptive method was applied to F-16 airplane for its failure accommodation by F.Ahmed-Zaid. But unfortunately, the major difficulty with adaptive methods is that the transient performance could not be assured due to the property of the nonlinear time-varying systems that they result in. First, in this dissertation all sorts of fault tolerant control methods and the present situation and development of adaptive schemes in fault tolerant control fields are summarized. Then failure models of the system are analyzed and presented.Model Reference Adaptive Controller (MRAC) based on the Lyapunov method as actuator failure compensator is designed for a class of continuous-time, multi-input and single-output linear time-invariant complex plants. Global stability is proved in theory for the design of the adaptive control law. The control task is to design a controller and accommodate the rest actuators in order to attain the desired performance under the condition that failure parameters are unknown. The parameters of the system and failure pattern need to be analyzed and something of the desired controller should be known in order to design the adaptive control scheme. The plant model match parameters are discussed before and after the failure happens, so the designed controller can adaptively regulate arbitrary actuator failure. According to the states and output of the reference model respectively, adaptive control schemes are presented. Adaptively parameters of the state feedback controller are regulated continuously, so ultimately the states and output both could follow after the given reference signals. Due to airplane system as a typical one, which focused much on its safety, simulation results for a linearized airplane model with actuator failure are shown to verify the efficiency of the designed adaptive methods.Considering the practical situation that the internal states are not always measurable, an adaptive control scheme based on output feedback is given for a class of continuous-time, multi-input and single-output linear time-invariant complex plants. According to the same actuator failure, simulation results for a linearized airplane model with actuator failure are shown to realize the global stability. Unfortunately, the major difficulty with MRAC method is that the transient performance could not be satisfied due to the property of the nonlinear time-varying systems that result in notwithstanding ultimately the convergence and stability of the system are assured. In this dissertation we will seek ways of improving performance of the adaptive failure compensation controller. A modified adaptive scheme including an additive feedback loop through fixed compensator, which is introduced to counteract the error caused by parameter uncertainty and the inaccuracy of parameter identification, is proposed. The adaptive algorithm used for updating parameters is kept the same as the one used by the standard MRAC system. Performance analysis of the proposed adaptive control scheme is verified based on the mean square tracking error criterion and thetracking error theory. Finally, the adaptive controllers with and without fixed compensator are compared and applied to an aircraft...