| Unmanned surface vehicle formation has become one of the hot research issues in the field of marine control due to its advantages of high efficiency and unmanned.Compared with a single ship,the USV formation can efficiently carry out the complex marine missions,such as marine search and rescue,seabed exploration,military strikes and so on.In this thesis,the multiple USV formation is taken as the research object,and three existing problems are deeply studied,i.e.,“limited communication bandwidth”,“not specific operation scene” and “not considering the constraints of marine practice”.Combined with the Backstepping method,a robust adaptive formation control algorithm is designed based on the event-triggered communication mechanism.Then,all signals of the closed-loop system are proved to be with the semi-global uniform ultimate bounded(SGUUB)stability by using the Lyapunov analysis.Finally,some simulation examples are carried out in the MATLAB platform under the simulated sea state to verify the effectiveness and superiority of the proposed control algorithm.The main contribution of this thesis can be summarized as the following threefold:(1).During the formation navigation,the position information can be obtained by GPS and electronic compass,but the speed information of each other cannot be obtained in real time between individual ships.Therefore,aiming at the unknowable and unmeasurable speed information in the traditional leader-follower method,this thesis proposed an improved leader-follower framework,whose advantages are as follows: In the leader layer,the virtual leader ship is introduced to program the real-time reference path for the whole formation.For the follower layer,the adaptive virtual ship is introduced to generate the smooth reference signal for followers.By resorting to the Backstepping method,the adaptive velocity vector is derived to address the problem that the speed information of the leader ship is unknowable and unmeasurable to the follower ship.(2).With the requirement of specific ocean engineering tasks,this thesis developed a cooperative guidance and control integration strategy for autonomous maritime search operation for USVs.Firstly,a parallel search guidance principle is designed to generate the desired position and heading angle signals for the virtual leader ship,so as to enable the formation to independently execute the maritime search operation.Different from the traditional LOS guidance,the proposed parallel search guidance effectively solves the problem that traditional LOS guidance can only be used for the course-keeping control in the straight section,and can be directly applied to the maritime search scene of multi-ships formation.Therefore,it can improve the efficiency and safety factor of search and rescue in the open sea.Furthermore,an event-triggered mechanism with the minimum threshold is introduced in the control part,which effectively alleviates the unnecessary wear of the actuating devices and the frequency occupancy of the communication channel.(3).The problem of limited communication bandwidth between ships is not considered in the existing control methods,that is,in the communication topology,each ship needs to broadcast its status information to its neighbors in real time,so as to ensure the maintenance of the formation.However,the continuous signal transmission will lead to excessive channel occupancy burden and the high occupancy frequency,even causes the unnecessary waste of the communication resource.Therefore,a novel inter-ships distributed event-triggered communication mechanism is designed in this thesis,which enables the status information of USV to be sent only when the triggered condition is satisfied.That can avoid the continuous monitoring of the status of neighboring ships,thus reducing the frequency of information transmission and further saving the communication resources of the control system on the premise that the control performance meets the requirements. |
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