Research On Adaptive Control Of Uncertain Nonlinear Systems With Time-varying Parameters

In recent decades,adaptive control research for nonlinear systems has produced many important results that have played a very important role in the development of the entire adaptive control field.However,some algorithms for adaptive stabilization control of nonlinear systems with time-invariant parameters are not suitable for uncertain nonlinear systems with time-varying parameters.Therefore,the adaptive stabilization control of uncertain nonlinear systems with time-varying parameters is an important research direction that needs to be deeply explored in the field of control.For the adaptive stabilization control of uncertain nonlinear systems with time-varying parameters,this thesis applies a method called congelation of variables,which is extended to several classes of uncertain nonlinear systems with time-varying parameters.The specific research contents are as follows:(1)A class of adaptive output feedback suppression control problems for uncertain nonlinear systems with time-varying parameters is studied.In the presence of unknown timevarying parameters and unknown control direction of the system,the congelation of variables method is applied to deal with the unknown time-varying parameters.At the same time,due to the unmeasurable part of the state of the system under the output feedback,a new adaptive control scheme is obtained by combining the new adaptive observer design and the classical backstepping method,and by introducing the tuning functions to simplify the parameter estimation process.The set output feedback controller can ensure that the output of the system converges to zero asymptotically when there are unknown time-varying parameters in the system,and at the same time ensure the boundedness of all closed-loop signals of the system.(2)For a class of uncertain nonlinear systems under time-varying sensor attacks,due to the influence of sensor attacks,multiple parameters of the system will become unknown and time-varying,which is difficult to handle.To solve this problem,a new adaptive control scheme is proposed.The scheme uses the congelation of variables method and Nussbaum function to deal with the unknown time-varying parameters and unknown time-varying control gains caused by the sensor attack,and uses the tuning functions to simplify the process of parameter estimation,and the final designed controller can ensure the state of the system is asymptotic.converges to zero while ensuring the boundedness of all closed-loop signals of the system.(3)Based on the above research contents,the adaptive control problem of uncertain nonlinear systems under both time-varying sensor attack and time-varying actuator attack is further studied.In view of the influence of sensor attack and actuator attack in the system,there will be various types of unknown time-varying parameters in the system.Therefore,an improved adaptive control scheme is proposed to solve this problem.By combining congelation of variables method and Nussbaum function to deal with multiple unknown timevarying parameters and unknown time-varying control gains caused by sensor and actuator attacks,and using tuning functions to avoid over-parameterization problems,the designed controller can be In the case of unknown time-varying parameters and unknown time-varying control gains of the type,the state of the system is guaranteed to converge to zero asymptotically,while the boundedness of all closed-loop signals of the system is ensured.