Output Feedback Control For A Class Of Nonlinear Systems

In practical engineering control systems,nonlinearity is widespread.With the complexity of modern engineering systems,research on nonlinear systems has become one of the hotspots of general concern.In recent decades,a lot of research has been done on the design of control methods for nonlinear systems based on backstepping,and some remarkable results have been achieved.By applying backstepping technology,dynamic surface control technology and adaptive control theory,this paper studies the output feedback control problem based on backstepping technique for a class of strict feedback uncertain nonlinear systems.Based on this,the adaptive output feedback asymptotic tracking control problem based on dynamic surface control technology for the nonlinear system is proposed.First of all,the problem of adaptive output feedback backstepping control is considered for a class of uncertain nonlinear systems in strict-feedback form with unknown parameters.A simplified output feedback control method based on adaptive high gain observer is proposed to achieve desired tracking performance,where the observer is developed for jointly estimating system states and parameters.Compared with other classical methods,the proposed control strategy does not need to design the adaptive updating laws at each step to estimate unknown parameters,thus greatly reducing the computational burden.In addition,the nonlinear functions of system are admitted to include system states,instead of only depending on the measured output.On the other hand,compared with the output feedback control method using fuzzy control or neural network,this paper does not use any approximation technology and achieves global tracking control results.Besides,via the Lyapunov scheme,it can be proven that tracking error of the system is global bounded,the range of which is regulable by selecting suitable design parameters.Finally,the numerical simulation example is provided to verify the boundness of the presented approach.Secondly,based on the above results,the problem of the adaptive output feedback asymptotic tracking control is considered for a class of uncertain nonlinear systems in strictfeedback form.By using the nonlinear filters,a novel dynamic surface output feedback controller based on the adaptive high-gain observer is designed to achieve the asymptotic tracking.Different from the previous results,the proposed control strategy uses dynamic surface technology to pass the virtual controller through a nonlinear filter with a time-varying integral function,so it not only effectively avoids the issue of "explosion of complexity" of the controller in the traditional backstepping process,but also achieves the performance of asymptotic tracking.Moreover,through the Lyapunov method,it is proved that all the signals of the closed-loop system are bounded and the tracking error asymptotically converges to zero,which is the purpose of asymptotic tracking.The effectiveness of the method is verified by simulation results.