Study On Finite-Time/Fixed-Time Cooperative Formation Control Of Unmanned Surface Vehicles

Over the last decade,plenty of researches have been conducted on Unmanned Surface Vehicles(USVs),which are widely used to perform tasks,such as searching and rescuing,oil spill collection,marine surveillance,environmental monitoring,bathymetric mapping and marine floor investigation.These tasks are usually complex and cannot be fulfilled in finite time by individual USV.Therefore,there is an increasing need for utilizing multiple vehicles to perform complex works,which can improve the overall performance and efficiency of USVs.This thesis focuses on the study of the finite-time/fixed-time formation cooperative control of USVs,and the main results are as follows:1.The mathematical model of the USVs with three degrees of freedom is established.In the process of establishing the model,the origin and significance of every parameter in the model are briefly introduced,and two common coordinate systems are analyzed.In order to control the USVs formation system in finite time and fixed time,the mathematical models of USVs are transformed into the cascade systems by utilizing the states and inputs transformations.2.The finite time formation cooperative control problem of unmanned surface vehicles is studied.Under the premise of knowing the initial states of the systems,the theory of finite time stability is used to construct a two-staged controller,which is proposed to make USVs complete the formation with desired speed.The controller consists of two stages.The first stage is to steer every USV to the desired position based on the “adding a power integrator” law,then the second step is to obtain the desired angle and velocity utilizing the nonlinear control law.Simulation results illustrate the effectiveness of the proposed method.3.The fixed time formation cooperative control problem of unmanned surface vehicles is studied.When the initial states of the systems are unknown,the fixed time stability theories are utilized to achieve the formation of USVs.The proposed two-staged formation control method makes USVs with external disturbance asymptotically track the desired trajectory with desired speed.The control strategy includes two stages.Firstly,a disturbance observer is introduced to estimate the value of external disturbance,after that,every USV is steered to the desired gathering position in fixed time.Then,USVs are controlled to obtain a desired forward speed along with the heading angle.It is a fact that the fixed time control method can also accelerate the convergence of the formation system,however this theory is different from the finite time control method.The reason lies in this: the convergence time is depend on parameters of the controller.Simulation results are given to illustrate the effectiveness of the scheme.