Straight-path Following Control Of Ship Based On Fractional Order Sliding Mode

In the actual movement,surface ship have the characteristics of the strong nonlinear,big inertia,large time delay,susceptibility to disturbances of wind,ocean current and wave and model parameter uncertainties,so it is a difficult task to improve the accuracy and the stability of the ship path following control.Sliding mode control has good anti-disturbance ability,strong robustness that is simple and easy to realize the control algorithm,which has been deeply applied in the reserch of ship movement.The fractional differential operator has the characteristics of memory,heredity and accuracy.Therefore,this paper combines the fractional calculus theory with the sliding mode control to be applied to path following control of ship.which can improve the control performance of path following on the basis of conventional sliding mode control.In order to realize the convergence of position error,different fractional-order sliding mode controllers are designed respectively according to the concerning whether or not to consider the uncertainties uncertainties of the model.In the kinematics loop,the speed virtual control law is designed.In the dynamic loop,the different fractional order sliding mode surfaces of velocity tracking error of surge and sway are designed respectively.The designed fractional order sliding mode controller can achieve the convergence of ship position tracking error by indirectly controlling the velocity tracking error of surge and sway.In order to validate the control effect of the fractional order sliding mode controller,the MATLAB Simlink toolbox is used to simulate the designed fractional order sliding mode controller.Under the condition of no interference and superposition interference,the experiment and theoretical analysis make clear that the designed fractional order sliding mode controller can keep the convergence of position tracking error in the effective time and tracking the desired trajectory quickly and stably,which shows good steady-state error and dynamic control performance,the whole process is smooth,no chattering,good stability,strong anti-interference ability.It can be seen that the designed straight-path following control of ship based on fractional order sliding mode has strong robustness to model parameter uncertainties and external time-varying disturbances.