Fixed-Time Anti-Disturbance Control For Systems With Disturbances Based On Disturbance Estimation

In engineering practices,the control systems are often exposed to elaborate and varied circumstances,so,it is unavoidably affected by disturbances.Moreover,owing to actual requirements,the systems are required to be higher and higher in terms of control accuracy,convergence rate and so on.Hence,in this article,the disturbance observer is constructed to estimate the disturbance,based on this,the fixed-time control matters are researched for systems under the existence of different disturbance situations.the article consists of the following three parts:In part one,the question of fixed-time control is researched for nonlinear systems under the existence of multiple disturbances,where multiple disturbances are classified as an external disturbance and a bounded disturbance with unknown upper boundary.The external disturbance is estimated by devising an adaptive nonlinear disturbance observer.Then,based on the estimated information,a composite fixed-time control(CFTC)tactic is presented by combining the H_∞control tactic and the fixed-time control theory,which guarantees that the system has faster convergence rate and stronger the capability of anti-disturbance.In part two,the matter of fixed-time tracking is researched for systems under the existence of unmeasurable states,unknown nonlinear term and external disturbance,where the external disturbance is modeled as an exogenous system containing the unknown nonlinear term.The unknown nonlinear terms are approximate by using the neural network(NN)within a fixed time,based on this,a composite adaptive fixed-time observer(CAFTO)is devised to estimate states and disturbance concurrently,which contains a disturbance observer and a state observer.Then,based on the estimation values,a NN-based adaptive fixed-time tracking control(NNBAFTC)strategy is presented,which can make that the system has faster tracking speed and higher tracking accuracy.In part three,the matter of fixed-time control is investigated for stochastic nonlinear systems under the existence of multiple disturbances,where multiple disturbances are classified as the derivative bounded disturbance with unknown upper boundary,the unknown bounded disturbance and the white noise.The derivative bounded disturbance is estimated by constructing a fixed-time stochastic disturbance observer(FTSDO),based on this,a fixed-time composite control(FTCC)tactic is put forward by combining the H_∞control tactic,the stochastic control theory and the fixed-time control theory.It can guarantee that the system achieves the expected control objectives of high control accuracy,fast convergence speed and strong robustness.