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Coordinated Control of Multi-UUV Formation for Spatial Curve Path Following

Author: MouChunZuo
Tutor: BianXinQian
School: Harbin Engineering University
Course: Control Theory and Control Engineering
Keywords: unmanned underwater vehicle path following coordinated formation decentralized control environment constraint
CLC: U674.941
Type: PhD thesis
Year: 2011
Downloads: 15
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Abstract

The early formation control of multiple UUVs requires only the relative position or distance information among the UUVs to be the expected values, the path of single UUV wasn’t restricted and when multi-UUV perform special tasks, such as subsea pipeline inspection, seabed maps’establishment, UUV must follow a specified path. Obviously, the traditional formation controller can not solve such a special formation problem. In this paper, formation coordinated control is discussed based on the path following (straight path and curved path) for a certain type of UUV. The main contents are as follows:Firstly, based on the coordinated path following control tasks of multi-UUV, we propose a decentralized control structure which has the time-space decoupling characteristic. Using this set-up, path following (in space) and inter-vehicle coordination (in time) are almost decoupled. The first step, a path following control law is derived that drives each vehicle to its assigned path, which is aimed at achieving space task. The second step, through the exchange of information among UUVs to design a coordinated controller aimed at achieving time task. In addition, the application of under acoustic communication is described, and graph theory notation is applied to communication topology. It has laid a theoretical foundation for controllers designed.Secondly, the problem of coordinated formation control of multi-UUV under the straight line path following is discussed based on the above architecture. For the path following control problem of a single UUV, the line-of-sight method is proposed to establish the space movement error models of UUV. Then the problem of position error’s stabilization control is turned into the asymptotic stability design of the speed error, heading error and pitch error. These controllers are designed based on feedback linearization which is convenient for engineering realization, respectively. To solve the problem of the leader failure caused the global collapse in the leader-follower method, a decentralized formation control method which is based on graph theory is proposed. This method provides the feedback channels of status messages between the multi-UUV. Vehicle coordination is achieved by adjusting the speed of each of the vehicles along its path, according to information on the status of the remaining vehicles only. Relative to the leader-follower, in which the leader can not get the followers’ status feedback information, this method has more effective information exchange between the multi-UUV and formation control.Then, the problem of coordination formation control of curve path following is discussed because of the limitations that straight line path following can not meet in practical applications. In the spatial curve path following control, the roll degree of freedom can not be ignored, and need to be considered during the manoeuvre motion. So, the "pulling" control strategy, which is based on virtual reference target, is presented. The dynamics path following controller and the kinematics path following controller have achieved the position and the speed tracking of the UUV, respectively. The Lyapunov direct method and the input-to-state stability theorem proved the stability of path following subsystem and the bound of system status and control inputs in the design of speed coordination controller. This method improves the path following control precision. To solve the underwater acoustic communication bandwidth constraints problem, only to exchange one variable coordination state of information exchange is presented. This method is corresponding to reduce the amount of communication to meet the narrow bandwidth of underwater acoustic communication constraints. Using graph theory describes the communication topology of multi-UUV and established coordination error model in the formation control. Moreover, the actuators saturation of UUV has been considered, and the formation controller contains double curve tangent function to ensure the quality of the control system.Finally, the problem of multi-UUV’s coordination path following control which has limitations of environment is discussed, considering the impacts of ocean current interference and limitation of acoustic communication. The nonlinear adaptive path following controller is designed based on backstepping under disturbance of ocean current, which compensates for the disturbance of unknown currents. LaSalle’s invariance principle is applied to prove a set of global convergence of path following subsystem. The available nonlinear part is eliminated in feedback linearization, which is avoided in this method. In the case of acoustic communication limited, logic-based communications strategy is proposed based on consensus of multi-agent, so that each UUV achieve the purpose of coordination between mulli-UUV by updating their own status estimate information. The results of simulation has shown the effectiveness of the controllers of path following and coordination formation under the condition of limited environment.

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