A Class Of Adaptive Output Feedback Control For Dynamic Systems With Disturbance

In recent years,the problem of nonlinear systems has been a difficult problem to be solved in control theory and applications.Researchers have gradually shifted their attention from linear systems to nonlinear systems,and nonlinear system model can describe real systems more accurately.Considering the unmeasurable state of most uncertain nonlinear systems,a class of adaptive output feedback control for nonlinear systems based on observer design is proposed in this paper.In the case that the output feedback is fully available,the problems of input nonlinearity and disturbance in the system are further solved.Simulation examples are given to verify the proposed control algorithm.The main research results of this paper are as follows:(1)Nonlinear tracking differentiator adaptive fuzzy output feedback control approach is proposed for a class of non-strict feedback systems with input saturation,unknown functions and unmeasurable states,which overcomes the problem of input saturation and algebraic loop in virtual signal.Fuzzy logic system is used to approximate saturation disturbance term and unknown function,fuzzy state observer is designed to estimate the unmeasured state of the system.The nonlinear tracking differentiator is used to estimate the differential of command signal which increase the tracking signal convergence speed and avoids the problem of “explosion of complexity”in traditional backstepping control.Filter compensation signal is designed in the controller to eliminate the filter error caused by the tracking differentiator.(2)Actuator saturation phenomenon often exists in the actual control system,which could destroy the closed-loop performance of the system and even lead to unstable behavior.Our main contribution is to provide an anti-windup recursive dynamic surface control(RDSC)for nonlinear system with unknown state and actuator saturation.The fuzzy compensator is added to perform as active disturbance rejection term in the feed forward path to avoid windup caused by input saturation.To construct output feedback control,the system is transformed into the form of pure-feedback and improved higher order sliding mode(HOSM)observer is designed to carry out future output prediction.Based on which RDSC is synthesized,only one fuzzy logic system(FLS)is used and the controller singularity is completely avoided.In addition,a numeral example and a simulation using a continuous stirred tank reactors(CSTRs)system with actuator saturation are provided and the results show that the strategy owns good robustness and effectively compensates for the disturbance caused by actuator saturation in the presence of nonlinear system with unmeasurable state.(3)An output feedback fuzzy controller with mismatched disturbance compensation is designed for a class of non-strict feedback nonlinear systems,which contain uncertain nonlinear functions and unknown external disturbances.Considering observer and controller are affected by the mismatched total disturbance signal composed of external disturbance and fuzzy approximation error,improved disturbance observation is designed to estimate and compensate the mismatched disturbance.Through the improved disturbance observer,the disturbance observation error can gently converge to an small range in finite time,and the influence of mismatched disturbance signal on the design of fuzzy state observer can be eliminated.Fuzzy logic system is used to approximate the unknown nonlinear function,and the fuzzy state observer is constructed to observe the unknown state of the system At the same time,the accurate compensation of disturbance is carried out in the controller design to improve the robustness of the system.Finally,the effectiveness of the proposed method is further verified by numerical simulation and electromechanical system.