Accurate Trajectory Tracking Control Of An Unmanned Surface Vehicle

Unmanned surface vehicles have many advantages such as compact structure,flexible to control and strong maneuverability,etc.,and have been widely applied in various areas including military and civil applications,maritime and research applications,etc.With the continuous implementing and developing of the marine strategy,corresponding researches of unmanned surface vessels have been highly-regarded by many countries.As the basis of various tasks,trajectory tracking is one of the most important research fields of the motion control of unmanned surface vehicles,and has become the focus of current research.Traditional model-based control methods are no longer applicable when considering the complex marine disturbances and unmodelled vehicle dynamics,which makes high-precision tracking problem of unmanned surface vehicles much challenging but has more practical significance.In this thesis,accurate trajectory tracking problem of an unmanned surface vehicle without exact vehicle dynamics will be extensively solved by virtue of disturbance observer based finite-time control techniques.Firstly,an integral sliding mode based finite time control scheme for tracking of an unmanned surface vehicle is proposed.Accurate tracking performance can be achieved for an unmanned surface vehicle without external disturbances,which realizes finite-time control property,has faster convergence rate and higher control accuracy.The entire closed-loop system stability can be guaranteed by Lyapunov theorem,which leads to zero tracking performance.Simulation studies further demonstrate the effectiveness of the proposed control law.Then,to eliminate the influence of ocean disturbances on unmanned surface vessels,disturbance observer based technique is employed to develop the finite-time disturbance observer,and the negative homogeneity theorem is further applied to design finite-time trajectory tracking control schemes.Finally,not only external disturbances can be effectively compensated with zero approximation errors,but also both trajectory and velocity tracking errors can be stabilized to zero in a finite time.Simulation studies demonstrate the effectiveness and superiority of the proposed control schemes.In addition,in order to make the work more practical,the tracking problem is further researched for an unmanned surface vehicle with completely unknown dynamics.Specifically,the known hydrodynamic dynamics and external disturbances are merged together into a lumped uncertainty term,and the unknown observer is further designed to realize exact unknown estimation.Then tracking control law is designed on the basis of the nonsingular terminal sliding mode technique and the unknown observer,which achieves accurate tracking performance even without complete vehicle model.Both theories and simulation results can guarantee the effectiveness of the proposed control schemes.