Course Constraint Control Of Air Cushion Vehicle Considering System Uncertainty

As a kind of high performance vehicle,the air cushion vehicle can sail on the water surface by means of the cushion lift system,so it suffers little water resistance and has speediness.Moreover,compared with conventional surface vehicles,air cushion vehicle can also travel at high speed on other special sailing surfaces,such as shoal,swamp and ice,etc.,so it also have amphibious performance.However,while the special hull structure of air cushion vehicle can make it obtain excellent performance,there are also many problems.There are a lot of nonlinear water and air resistance coefficients in the complex mathematical model of the hovercraft.These coefficients are related to the real-time motion state of the hovercraft.Due to the limitations of test methods and measurement accuracy,it is difficult to accurately obtain these coefficients in real time,and considering the effect of the random sea wind during the navigation of the hovercraft,it is difficult to obtain the ideal control precision when using the model-based nonlinear control method to control the course of the hovercraft.Therefore,it is necessary to deal with the system uncertainty caused by uncertainty of model parameters and unknown external interference when designing the hovercraft course controller.In addition,due to small water resistance,the hovercraft is prone to stall,sideslip,and heeling,etc.when turning at high speeds.Therefore,taking into account the requirements of safety,it is necessary to adopt some methods to constraint the yaw rate,sideslip angle within the safety limit during the process of course control.Aiming at the above problems,this paper studies the course control of air cushion vehicle with safety constraints considering system uncertainty.This paper focuses on the system uncertainty caused by the uncertainty of model parameters and unknown external interference in the course control process of air cushion vehicle,as well as the problem that the yaw rate and sideslip angle closely related to the safe navigation of hovercraft need to meet the constraints of safety limit.The following aspects are mainly studied:(1)In view of the influence of system uncertainty caused by model parameter uncertainty and unknown disturbance in the nonlinear dynamic model of air cushion vehicle on the accuracy of hovercraft course controller,a backstepping sliding mode course controller is designed based on the known approximate model,and a second-order sliding mode observer based on super-twisting algorithm is designed to estimate and compensate the system uncertainty.The observer can be designed independently of the controller and the uncertainty of the system can be estimated in a finite time.Simulation results show that the backstepping sliding mode course controller with observer has higher control accuracy than that one without observer.(2)In view of the navigation danger caused by the excessive yaw rate exceeding the safety limit in the course control of the air cushion vehicle,on the basis of considering the influence of system uncertainty,the yaw rate direct constraint method and indirect constraint method are adopted to realize the bounded constraint on the yaw rate in the process of course control.The auxiliary dynamic system is used to adjust the control input in the direct method,while in the indirect method,the auxiliary dynamic system is used to constrain the virtual yaw rate,and then the Log-type barrier Lyapunov function(BLF)is used to constrain the yaw rate error.The simulation results show that both of the methods can realize bounded constraint of yaw rate in course control,but compared with direct constraint method,indirect constraint method can ensure strict constraint of yaw rate.(3)On the basis of considering the yaw rate constraint in the course control of air cushion vehicle,the constraint of yaw angle is considered to avoid system overshot,and the sideslip angle constraint is considered to further ensure the safety of course control.Firstly,in view of the the limitation that the Log-type barrier Lyapunov function is used to constrain the yaw rate during the course control,unable to act directly on the system state quantities and needs to be converted into state errors.An integral barrier Lyapunov function(IBLF)is introduced to realize the constraint on the yaw states,which leads to the relaxation of the feasibility condition for constraint satisfaction.Then,IBLF is used to constrain the yaw states,at the same time the sideslip angle is constrained based on the log-type BLF to further ensure the navigation safety of the hovercraft.Finally,the simulation results show that the yaw rate,sideslip angle and yaw angle of the hovercraft in course control can meet the bounded constraint conditions.