Anti-disturbance Control For Several Classes Of Nonlinear Systems Based On Disturbance Observers

Uncertainties such as the unmodeled dynamics,the variation of parameters and the unknown disturbances widely exist in practical engineering systems,which affect the stability of the control system to a certain degree.With the requirement of control precision is more and more high,the research of high precision anti-disturbance control method has become one of the hot research topics.However,in most cases,the external disturbance and the uncertainty of the control system can not be measured directly.Therefore,in order to improve the performance of the control system and meet the requirements of high precision control,it is very important to study the estimation methods of the disturbances and uncertainties.In recent years,as an effective method of disturbance estimation,disturbance observer based control(DOBC)has attracted extensive attention.The basic idea of DOBC is to estimate the unknown disturbance by designing a disturbance observer,and then compensate it in the feed-forward channel,so as to achieve the purpose of attenuate the disturbance effectively.In this dissertation,based on the DOBC method,combining with adaptive control,Back-stepping method,sliding mode control and stochastic control,a series of anti-disturbance control strategies are proposed for several classes of nonlinear multi-source disturbance systems.The main contents include the following aspects:Based on adaptive disturbance observer,an anti-disturbance control strategy is proposed for a class of nonlinear disturbance systems whose main part is linear.The disturbance is modeled by an exogenous system,which represents partial known information.Firstly,the adaptive disturbance observer is constructed for the disturbance.Furthermore,based on adaptive disturbance observer,the anti-disturbance control scheme named as ADOBC is presented for the nonlinear system.Finally,a simulation example is given to verify the effectiveness of the proposed method.The problem of anti-disturbance control is researched for a class of more general nonlinear system with multi-source disturbances.The disturbance can be classified into two parts.One represents a constant or harmonic disturbance,which is generated by an exogenous system.The other is an unknown time-varying diturbance.For the first kind of disturbance,the disturbance observer is constructed,and the disturbance estimation error system is uniformly ultimately bounded.For the second kind of disturbance,Adaptive back-stepping method is used to attenuate it.By combining the disturbance observer with adaptive back-stepping method,a composite hierarchical anti-disturbance control strategy is proposed for the nonlinear system.Finally,simulation results show that the proposed control strategy is correct and effective.The disturbance is extended from the general constant or harmonic disturbance to the disturbance whose variation rate is bounded,which extends the description scope of the disturbances.For a class of nonlinear multi-source disturbance system,the disturbance can be divided into two parts.The first satisfies the derivative-bounded condition,the second is unknown time-varying disturbance.For the first kind of disturbance,a disturbance observer is constructed.By combining the disturbance observer with adaptive back-stepping method,an anti-disturbance control method is proposed for the nonlinear system.Simulation results proved the correctness and the effectiveness of the proposed control strategy.Manipulator system is a kind of nonlinear system with strong coupling,including measurement error,friction,load variation and unmodeled dynamics,etc.First of all,the disturbance can be divided into two categories.One is a constant or harmonic disturbance,which can be generated by the exogenous system with uncertainty.The other is the norm-bounded disturbance.Independent of the controller design,the disturbance observer is constructed to estimate and compensate for the first type of disturbance.Terminal sliding mode control(TSM)is used to attenuate the second type of disturbance.Combining the disturbance observer with the terminal sliding mode control(TSM),a composite DOBC and final sliding mode control strategy is proposed.Finally,a simulation example shows that the proposed control strategy has better anti-disturbance ability.For a class of linear stochastic system with multi-source disturbance,the disturbace can be divided into two parts.The first represents the disturbance with partiallly known information,which can be generated by the exogenous system.The second is the standard Wiener process.The disturbance observer independent of the controller design is constructed to estimate the first disturbance.The second part of disturbance is attenuated by the conventional stochastic controller.The composite DOBC and stochastic control method is proposed by integrating the disturbance observer with stochastic control to improve the ability of anti-disturbance for the linear stochastic systems.Finally,simulation examples prove the validity of the proposed method.Finally,a summarization of the research contents is made at the end of this dissertation,in which the future direction of the study is pointed out.