Finite Time Adaptive Control For Nonlinear Systems With Input/State Delays

For nonlinear systems,it is more difficult to design effective controllers for them than for linear systems because they are often affected by external disturbances and their own faults.In addition,due to the complexity of the nonlinear system and its environment,the system shows the characteristics of time delay,which deeply affects the stability of the system.And the conventional asymptotic stability control is sometimes difficult to meet the control requirements of the actual system.Therefore,it is of great practical significance to introduce a finite time control method to solve this kind of problem.Based on this,this thesis will focus on the nonlinear system with time delay as the controlled object,combining the finite time control,fuzzy logic control,backstepping control and Lyapunov stability theory,etc.,to study the adaptive control problem and system stability in detail.The main works and innovations are as follows:(1)An adaptive control method is proposed to solve the finite time tracking control problem for nonlinear systems with input delays.Firstly,Pade fitting technique is used to reduce the disturbance of input delay,and compensation system is introduced to ensure the accuracy of system reliability analysis and the conservatism of control results;Secondly,fuzzy logic control is introduced to approximate unknown functions;Finally,an adaptive control strategy is proposed to ensure the finite time stability of the system,and the closed-loop signal has semi global finite time stability.(2)A finite time adaptive fault-tolerant control method is proposed for tracking control of a class of nonlinear systems with unknown state delays and actuators.First,the finite cover lemma and fuzzy logic system are applied to deal with nonlinear functions with state delays;Secondly,an adaptive fault-tolerant controller is constructed based on backstepping control method to compensate actuator faults;Finally,the stability of the system is analyzed through the finite time stability theorem,and it is proved that the proposed control method can be stable in finite time when the system has actuator faults,and all closed-loop system signals are semi global finite time stable.(3)In order to verify the effectiveness of the proposed control method,a strict feedback nonlinear system with input and state delays is taken as an example to conduct simulation experiments.The experimental results show that the output signal of the system has good tracking performance in limited time,and the tracking error is controlled in the neighborhood near the origin.At the same time,the finite time stability control method is compared with Lyapunov asymptotic stability control method,and the results show that the control effect of the former is better than that of the latter.