Research On Sliding Mode Control Strategies For Several Classes Of Uncertain Nonlinear Systems

Because there are many uncertain factors in the actual engineering system,such as unmodeled dynamics,model parameter changes and unknown external disturbances,which have a subtle impact on the stability control or fast and accurate tracking control of the space object.In recent years,sliding mode control has become a research hotspot because of its strong robustness to uncertain factors such as system internal parameter perturbation,system unmodeled dynamics and external disturbance.Combined with disturbance observer,RBF neural network approximation principle and terminal sliding mode finite time control method,this paper designs three new improved sliding mode control strategies for fast and stable tracking control of uncertain nonlinear systems with unmodeled dynamics,model parameter changes and unknown external disturbances Slightly.The research contents include the following:The tracking control problem of SISO uncertain nonlinear system with system modeling simplification and peripheral disturbance is studied.A fast and stable non-singular terminal sliding mode control method is proposed,which combines RBF network and disturbance observation.First,the new nonsingular fast terminal sliding surface is designed to ensure the finite time a fast convergence of the system,and the system controller is designed by combining the smooth double power approach law.Then,RBF network is utilized to approach the unknown nonlinear function in the system model.Then,the disturbance of the controlled system is estimated by disturbance observer,and a fresh disturbance rejection control strategy is proposed by combining with sliding mode controller.Finally,the simulation method is utilized to verify verify the feasibility and effectiveness of the control scheme.The problem of tracking control for a class of second-order under actuated uncertain nonlinear systems with partial unknown model,external disturbance and noise disturbance is studied.Firstly,the Lagrangian model of the system is transformed into an affine model,and the sliding mode observer is designed according to the unique structure of the controlled system.Secondly,an external loop integral terminal sliding mode controller is designed by using the estimated state of the observer,and the output of the external loop controller is filtered by a low-pass filter.Then,the inner loop layered integral terminal controller is designed by using the layered sliding mode control method.Finally,the simulation experiment of the car inverted pendulum system shows the effectiveness of the control strategy.In this paper,a class of high order under actuated uncertain nonlinear systems with modeling part unknown and control signal disturbance is studied.Firstly,the system is decomposed into n subsystems,and a nonsingular fast terminal sliding surface is designed for each subsystem.Then,through the physical structure of the system,the layered sliding surface is designed.Then,the disturbance observer is used to estimate the unknown model generated in the process of modeling the controlled system,so as to avoid the limitation of the structure and parameters of the controlled system that need to be known in advance in the process of controller design.At the same time,due to the estimation error of disturbance observer in the process of disturbance estimation,an adaptive law is used to adjust the performance of the controller and reduce the influence of the estimation error on the control process of the system.Finally,the simulation of the double inverted pendulum system is carried out,and the simulation results show the effectiveness of the method.At last,it summarizes and analyzes the research contents of the whole paper,and points out some possible research directions to be improved.