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Research On Sliding Mode Control Strategies For A Class Of Under-actuated Nonlinear Systems

Posted on:2022-01-26Degree:MasterType:Thesis
Country:ChinaCandidate:G Y YangFull Text:PDF
GTID:2518306737956879Subject:Control Engineering
Abstract/Summary:PDF Full Text Request
The number of actuators in the underactuated mechanical system is less than the number of degrees of freedom to be controlled.Therefore,many traditional nonlinear control methods are not directly applicable.Moreover,in practical engineering applications,the controlled objects generally have uncontrollable factors such as unmodeled dynamics,model uncertainties and external disturbances,it is extremely important for their control algorithms to be robust to these uncertainties.Sliding mode variable structure control is essentially nonlinear control,which can be divided into convergence and arrival phases,with fast response and excellent robustness to system uncertainty.The article combines the nonlinear disturbance observer to estimate the system uncertainty and the idea of finite time convergence of the terminal sliding mode function to design two new terminal sliding mode control algorithms for the tracking and stabilization control of a class of underdriven systems;for the problem of jitter and insufficient convergence rate in the convergence phase of the sliding mode control algorithm,a new improved convergence law is designed.The research contents are as follows:Consider class of fourth-order underactuated system,in allusion to its strong coupling characteristics,and the problem of insufficient accuracy and reaching speed in tracking control,a decoupled global fast terminal sliding mode control based on nonlinear disturbance observer is proposed.The fourth-order nonlinear system was decomposed into two second-order subsystems,and an intermediate variable was introduced to design the global fast terminal sliding mode surface,respectively.An improved double power reaching law was designed,and the control law of the system was solved by using the equivalent control method and the fuzzy double power reaching law;Meanwhile,to eliminate the influence of system disturbance on the control effect,a hyperbolic tangent nonlinear disturbance observer is designed to evaluate the systematic uncertainty as well as the disturbance and compensate to the controller.The proposed control scheme has better control performance compared with other control algorithms through the simulation of the tracking control of the first-level trolley inverted pendulum system.A class of fourth-order underactuated systems is considered,and a decoupled time-varying fast terminal sliding mode control strategy based on a nonlinear disturbance observer is proposed for its robust coupling characteristics,as well as the problems of severe jitter and insufficient convergence speed in stabilization control.Combined with the decoupling algorithm,the time-varying parameters are calculated using a nonlinear function about the system state to design the sliding mode surface of each subsystem respectively.The controller adopts a modified time-varying fast terminal sliding mode control algorithm to realize that each of the two subsystems converges to the equilibrium point at a fixed time;meanwhile,a hyperbolic tangent nonlinear disturbance observer is used to eliminate the influence of system perturbations on the control effect.Finally,the method is applied to the stability control of the cart inverted pendulum system,and its effectiveness and superiority can be verified from the comparative simulation results and through numerical analysis compared with the existing decoupled sliding mode control algorithm.Considering the inevitable chattering in the control of the sliding-mode variable structure,a segmented fast multi-power convergence law is proposed to ensure the fast astriction of the convergence phase while inhibiting the chattering,combining the advantages of the doublepower and fast-power convergence laws when they are distant from and are near the equilibrium point,respectively.By introducing a nonlinear function,this is used in the design of the exponential term of the reaching law,so that the system can achieve fast convergence at all steps of the convergence process with fixed time convergence characteristics.The reaching law can achieve convergence of the sliding mode surface to the steady-state error bound in finite time when there are unmeasurable parameters of the model and external disturbances in the system.And the method is used in the stabilization control of the cart inverted pendulum system,and its availability and superiority can be confirmed through comparative simulation and numerical analysis.In conclusion,the research on sliding mode control in a class of underactuated systems is summarized,and the shortcomings of the research content of the article and the research directions that can be improved are pointed out.
Keywords/Search Tags:Underactuated system, Terminal sliding mode control, Reaching law, Non-linear disturbance observer, Inverted pendulum system
PDF Full Text Request
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