Research On Active Disturbance Rejection Prescribed Finite-Time Tracking Control For Nonlinear Systems

Most of modern military and civil engineering systems are based on strict feedback nonlinear models,systems such as ships,aircraft.The control of such systems is one of the hot topics in control theory.Because these control systems are often affected by factors such as external interference and dead-zones caused by their own physical characteristics.These factors will cause the decline of control performance and affect the control precision of the system.Therefore,it’s of engineering significance to study the control problems of nonlinear systems with dead-zones.In recent years,active disturbance rejection control,finite-time control and prescribed performance control have become the forefront of the research.The research content of this thesis combines these control methods,which has certain theoretical significance.The main research contents of this thesis are as follows:(1)The finite-time tracking control strategy with prescribed performance constraints is proposed for a class of strict feedback nonlinear systems with dead-zone and external disturbances.By introducing adaptive neural network to estimate parameters,the prescribed finite-time state feedback tracking controller for dead-zone nonlinear systems is designed based on backstep method.The proposed control strategy avoids the Lyapunov stability criterion for the traditional finite time control,and transforms it into a more general bounded stability criterion.The setting time of the system can be set according to the requirements,so that the setting time of the finite-time control is independent of the initial conditions of the system.The method employs tracking differentiator to solve the differential explosion problem caused by the derivative of virtual control law,and compares with the method employing neural network to solve the problem.By comparing the simulation results of the two controllers,the effectiveness and superiority of the proposed strategy are illustrated.(2)The problem of finite time bounded H_∞ event-triggered tracking control for a class of strict feedback nonlinear systems with unknown external disturbances and input dead-zones is studied.An active disturbance rejection finite-time H_∞event-triggered tracking control strategy with prescribed performance constraints is proposed.In the design process of the controller,an improved prescribed performance function is used to make the parameter selection of the prescribed performance function independent of the initial conditions of tracking errors,and to ensure that the tracking error of the system can satisfy the needs of the given prescribed performance.the extended state observer and bounded H_∞ control are used to compensate and restrain the internal uncertainties and external disturbance.The introduction of event-triggered input mechanism can greatly reduce the frequency of the actuator.In this strategy,the tracking differentiator is used to solve the differential explosion problem caused by the derivative of the virtual control law.The stability of the closed-loop system is proved by the qualitative analysis of the Lyapunov function.The simulation results show that the proposed control strategy is effective,the actuator doesn’t exist Zeno phenomenon and the system has H_∞ performance against external disturbance.