Research On Path Following For Underactuated Unmanned Surface Vehicle Based On Time Varying Lookahead Distance Line Of Sight Guidance Law

Unmanned surface vehicle(USV)is a miniaturized and intelligent working platform,which is widely used in military and civil fields.Path following is the basic function of unmanned surface vehicle motion control system,and also one of the key technologies to realize autonomous navigation and various tasks.However,unmanned surface vehicle generally has no transverse thruster,so it is easy to be disturbed by environmental factors in the ocean or river,which requires high stability,high efficiency and robustness of the controller.In this paper,the path following controller is designed from two aspects: one is to design the lookahead distance self-tuning of the line of sight algorithm;the other is to adjust the parameters of the traditional PID controller by using fuzzy logic.Through the comparison of simulation experiments,the superiority of lookahead distance self-tuning and the good robustness of fuzzy adaptive PID path following controller are verified.A three degree of freedom mathematical model of the "Qihang" unmanned surface vehicle is established.Two kinds of coordinate systems are introduced to describe the motion state of unmanned surface vehicle,and the basic composition of "Qihang" unmanned surface vehicle and the assumptions of simplifying the modeling of unmanned surface vehicle are introduced.Based on these assumptions,the kinematic model,dynamic model and a propeller model simplified into a first order system are established.The inertia matrix coefficient of the dynamic model,damping matrix coefficient,thrust reduction factor and propeller flow coefficient are calculated.We compare the simulated data of throttle speed experiment and turning experiment with the actual data and compare the maneuvering response coefficient of the model with the real ship to verify the accuracy of the "Qihang" unmanned surface vehicle.The line of sight guidance algorithm is used to calculate the desired course,and the derivation process of straight line and curve guidance algorithm is introduced.For the traditional constant lookahead Distance Guidance calculation,the time-varying lookahead distance formula is designed and the influence on the system stability is analyzed.By analyzing the time-varying lookahead distance formula proposed by Fossen and Wan,it is found that there is a functional relationship between the set parameters and the minimum lookahead distance and tracking error.The reliability of the function relationship is verified by simulation in different ship models.In order to improve the maneuver performances of the unmanned surface vehicle,the PID control algorithm is combined with the fuzzy logic to realize the online self-tuning of PID parameters.The fuzzy self-adaptive PID path following controller is formed by combining the time-varying lookahead distance line of sight guidance law and fuzzy self-adaptive PID algorithm,and the simulation experiments are carried out under the model of "Qihang" unmanned surface vehicle.Compared with the conventional PID control,the fuzzy self-adaptive PID path following controller has better dynamic response and robustness.In addition,combined with the path planning waypoint design,the simulation shows the necessity of waypoint fitting.