Adaptive Control For Nonlinear Systems With Actuator Faults And Time Delay

In real world,most controlled systems are inherently nonlinear,uncertain,and often affected by actuator faults and time delay.Consequently,the study of nonlinear systems with actuator faults and time delay has received much attention.In recent years,based on nonlinear system stability theory,adaptive control,backstepping technique,neural network and other design tools,the adaptive control of nonlinear systems has achieved remarkable results.However,most of the existing results need to impose strong assump-tions and the system considered has certain limitations.In view of this fact,this paper will further investigate the adaptive control problem of nonlinear control systems with actuator faults and time delay.The main contents include:1.The global adaptive control and finite-time control problems are considered for strict feedback nonlinear systems with actuator fault and unknown control coefficients.Firstly,without a priori knowledge of actuator fault and system uncertainties,a switching-type adaptive controller is designed by using the backstepping method.By tuning the controller parameter with the proposed switching mechanism,the global stability can be achieved.Secondly,the global adaptive finite-time control problem is also investigated.Similarly,by adopting adding a power integrator technique,a switching-type adaptive finite-time controller is designed and a modified switching mechanism is also proposed.It is proven that the global finite-time stability can be guaranteed by the proposed controller.Finally,two simulation examples are provided to verifly the effectiveness of the proposed methods.2.The global finite-time adaptive control problem is considered for high-order uncer-tain nonlinear systems in the presence of actuator fault and unknown control coefficients.Different from the previous results,a priori knowledge of the actuator fault and con-trol coefficients is not required.By introducing the sign function and novel coordinate transformation,a switching-type adaptive controller is designed by using adding a power integrator technique.Then based on the Lyapunov function,a modified switching mech-anism is proposed to tune the controller parameter.And global finite-time stability of the closed-loop systems is proven by using the finite-time stability theory.Finally,a simulation example combined with a comparison is provided to verify the effectiveness of the proposed method.3.The command-filter-based adaptive asymptotic tracking control problem is in-vestigated for strict feedback nonlinear systems with actuator fault and mismatching disturbances.The mismatching disturbances have been effectively compensated by in-troducing smooth functions in the virtual controllers.By introducing the sign function,the finite time stability of the compensation signals can be ensured.Then by combining the modified command filter and backstepping method,an adaptive tracking controller is designed to guarantee that system output can asymptotically track the reference signal.Furthermore,the practical finite-time adaptive control problem is studied for nonlinear systems with actuator fault.By utilizing the command filter backstepping method,an adaptive switching-type controller is designed and a novel switching mechanism is also proposed.By regulating the controller parameters online,the practical finite time sta-bility of the closed-loop systems can be ensured.Finally,two simulation examples are given to illustrate the effectiveness of the proposed method.4.The adaptive neural network control problem is considered for a class of uncertain nonlinear systems with input delay.Firstly,by using Pade approximation method,an auxiliary system is constructed to compensate the input delay based on the introduced variable.By introducing novel coordinate transformation,an adaptive state feedback controller is designed with the aid of backstepping and neural networks.Secondly,an linear observer is constructed to estimate the unmeasurable states.Similarly,an adap-tive output feedback controller is also designed by using the Pade approximation,neural networks and backstepping techniques.By using the Lyapunov stability theorem,it has been proven that all the signals in the closed-loop systems are semi-globally uniformly ultimately bounded.Finally,two simulation examples are given to illustrate the effec-tiveness of the proposed methods.