| In practical engineering systems,due to the consideration of physical conditions,system performance and security,the system states need to meet certain constraints to achieve the expected performance indicators.If states violate the constraints,the performance degradation,instability of control system or even safety accidents may occur.Therefore,state constraints are particularly important in the field of nonlinear control.However,most of the current researches on state constraint problem is based on the assumption that the initial values of the system meet the constraints.In this paper,based on the backstepping method,the following researches for tracking control problems of nonlinear systems under the influence of state constraints,input delay and actuator fault are carried out.The main contents are as follows:Firstly,an adaptive finite-time backstepping control scheme is proposed for nonlinear system with unknown functions and input delay.In order to address the “term of explosion”problem of backstepping control,a finite-time filter is designed,and the effect of the filter error is eliminated through error compensation mechanism.The upper bound of the unknown nonlinear function is estimated by adaptive law.The input delay is compensated by Pade approximation method.According to Lyapunov stability theory,the practical finite-time stability of the closed-loop system is demonstrated,and the effectiveness of the raised control strategy is verified by simulation.Secondly,for nonlinear system with deferred full state constraints,an adaptive switching event-triggered backstepping control strategy is designed.The shifting function is established to realize that the initial values of system from violating constraints to satisfying constraints in a predefined time.Through state transformation function,the full state constraints problem is transformed into the boundedness of modified states.The radial basis function neural network(RBFNN)is applied to approximate the unknown nonlinear function.For reducing the update of controller,a composite switching event-triggered mechanism is established.Based on Lyapunov stability theory,it is proved that the closed-loop system is semi-global bounded stable,and the effectiveness of the designed control strategy is verified through simulation.Finally,an adaptive finite-time fault-tolerant backstepping control strategy is proposed for nonlinear system with actuator fault and deferred full state constraints.An exponential shifting function and a more general state transformation function are designed to ensure the initial values of the states that violates the constraints return back to the constraint ranges within a predefined time,while solving the full state constraints problem.The adaptive method and RBFNN are respectively used to dispose actuator fault and the unknown nonlinear function,and an adaptive finite-time fault-tolerant controller is established under the framework of backstepping control.Based on Lyapunov stability theory,it is demonstrated that the closed-loop system is practical finite-time stable,and the effectiveness of the proposed control strategy is verified by simulation. |
