Adaptive Fault Tolerant Control With Prescribed Performance And Its Applications To Underwater Vehicle

In recent years,with the improvement of modern science and artificial intelligence,control systems become more complex.While meeting the performance requirements,the probability of failure rate of sensor,actuator and components of the system is greatly increasing.Among these faults,actuator fault is the most common fault due to its frequent use.In order to improve system reliability and system stability,many effective fault tolerant control(FTC)approaches have been proposed in literature.However,most of the existing works in literature only focused on the steady-state performance of the controlled system,and transient performance cannot draw enough attention.In this work,based on adaptive control,backstepping control and neural networks,and combining prescribed performance control with fault tolerant control,several adaptive fault tolerant control schemes are proposed for nonlinear systems with actuator faults.The main contents of this work are summarized as follows:Firstly,for a class of nonlinear systems with unmodeled dynamics,actuator bias faults and prescribed performance,combining nonlinear fault tolerant theory with prescribed performance control,an adaptive fault tolerant control scheme with prescribed performance is proposed.In order to eliminate the unmodeled dynamics,a dynamic signal is introduced.The tracking error is transformed by the construction of performance function and error transformation function.From theoretical analysis,all signals in the closed-loop control system are semi-globally uniformly ultimately bounded.Finally,the validity of this scheme is proved by the steering control subsystem of autonomous underwater vehicle(AUV).Secondly,based on neural networks and backstepping control,a prescribed performance adaptive fault tolerant control scheme is proposed for a class of nonlinear systems with unmodeled fault and external disturbance.By introducing a transformation function,the initial constrained tracking error is first transformed into an unconstrained signal.Thus,the initial system is transformed into a nonlinear system with uniform structure.The controller designed in this scheme guarantee that the output tracking error meets the prescribed performance and all signals of the closed-loop system are bounded.The simulation results on autonomous underwater vehicle show the effectiveness of the proposed scheme.Thirdly,by using command filters with backstepping technique,an adaptive fault tolerant control scheme with prescribed performance is proposed for a class of nonlinear systems with unmodeled dynamics and unmodeled faults,where the computation of the first derivatives of virtual control signals at each step in classical backstepping design is avoided and the complexity of controller design is reduced.In addition,the original system is transformed into an equivalent system with the same structure by introducing the prescribed performance function and error transformation function.Finnaly,based on Lyapunov theory,it is proved that all the signals in the closed-loop system are semi-globally uniformly ultimately bounded and the tracking error satisfies the prescribed performance.Finally,a simulation study clarifies and verifies the approach.Fourthly,for a class of dynamic systems with actuator fault,the problem of active fault-tolerant control is discussesed,and an active fault-tolerant control sheme is designed to ensure that all the signals in the closed-loop system are semi-globally uniformly ultimately bounded,where the controller singularity is avoided without projection algorithm.The scheme first calculates time delay due to fault diagnosis,i.e.,the time spent on fault diagnosis,and its influence on system performance is analyized.Further,the analytical expression of the time delay is derived strictly.Further,the quantitative analysis of system performance which is degraded by the time delay is developed,and the conditions that the magnitudes of the faults should be satisfied such that the faulty system controlled by the normal controller remains bounded even stable during the time delay are derived.In addition,the corresponding solution to the adverse effect of the time delay is proposed.Finally,the simulation results show the proposed control algorithm has a very reliable efficiency.