Asymptotically Adaptive Tracking Control Of Nonlinear System

Tracking control is widely used in engineering systems,such as aircraft path tracking,ship trajectory tracking,laser cutter and so on.Tracking error is an important index to measure the performance of tracking control.Compared with bounded-error tracking,asymptotic tracking control can ensure zero-error convergence.Based on adaptive control method,backstepping technique,fuzzy logical systems and nonlinear robust control method,this thesis considers adaptive fuzzy asymptotic tracking control problem of several classes of nonlinear systems.Lyapunov stability theory and MATLAB simulations are utilized to test and verify the feasibility of the designed control schemes.The major contents of this thesis include the following three parts:(1)For a class of nonstrict feedback nonlinear systems,a novel adaptive asymptotic tracking control scheme is proposed.First,the unknown nonlinear functions of the system are approximated by fuzzy logical system.According to the monotone property of fuzzy basis function,the algebraic loop problem of nonstrict feedback nonlinear systems when using backstepping recursive technique is solved.Second,the requirement of upper bound of unknown virtual control function in most existing results is removed by introducing the lower bound of unknown virtual control function into the construction of Lyapunov function.At last,the effectiveness of the asymptotic tracking control method is proved by a numerical example and a simulation experiment of a single link manipulator system.(2)For a class of nonstrict feedback nonlinear systems with external disturbance,an exponentially asymptotic adaptive tracking control scheme is raised.First of all,fuzzy logical system is used to approximate the unknown nonlinear functions of the system.The influence of unknown external disturbance on system stability is eliminated by the bound estimation method.Moreover,exponentially asymptotic convergence performance is guaranteed by introducing the exponential function into Lyapunov function and adaptive laws.Compared with the common asymptotic tracking control schemes,the proposed exponentially asymptotic tracking control method can realize faster convergence of tracking error.At last,the feasibility of the proposed exponentially asymptotic tracking control method is proved by the simulation experiments of a second-order numerical system and an electromechanical system.(3)For a class of switched nonlinear system,an adaptive asymptotic tracking control algorithm with prescribed performance is designed.First of all,the switched signals are dealt with the common Lyapunov function.In addition,a finite time performance function is introduced,which not only guarantees the transient performance of the tracking error,and makes the tracking error constrained in a range all the time,but also makes the tracking error quickly converge to a compact set within a preset interval.Furthermore,the zero-error convergence of tracking error can be realized by designing a smooth integral function.At last,the feasibility of the asymptotic tracking control scheme is evaluated by the simulation experiment of a second-order numerical system.