Research On Key Issues And Methods Of Formation Control Of Unmanned Underwater Vehicles With Collision Avoidance Under Unknown Disturbances

With the ocean development and exploration,the Unmanned Underwater Vehicle(UUV)has attracted extensive attention because of its flexibility,low cost,and autonomous decision ability.Due to the large ocean area and the limited speed of unmanned underwater vehicles,the research on the UUV formation has become a hot spot in recent years.The unmanned underwater vehicle formation has the characteristics of high efficiency,strong robustness,and large coverage,but it also encounters many challenges in practical applications.For example,the problem of the coordination of the formation of the UUV formation during the execution of the mission,the problem of collision avoidance within the formation,and the ability to resist external disturbances,which are the key issues for the successful completion of the operation of the UUV formation.Therefore,in the context of the UUV formation performing exploration tasks in the ocean,this paper conducts an in-depth study on the key issues and methods in the coordinated UUV formation control with collision avoidance in the presence of unknown external disturbances.The main research contents are as follows:(1)In this paper,according to the functions and performance of UUVs,the distributed formation architecture is used as the basic system structure of the formation;At the same time,graph theory is adopted to establish the communication system of the UUV formation;And the collision avoidance system of the formation is formed by using the sensor equipment and modules equipped with the unmanned underwater vehicle.Because the mathematical model of the UUV has the characteristics of nonlinearity and coupling,which brings many difficulties to the design of the formation controller,the feedback linearization method is applied to convert the nonlinear and coupled mathematical model into a second-order linear model.The system model and feedback linearization mathematical model of UUV formation are the theoretical basis for subsequent research.(2)Aiming at the unknown external disturbances and communication limitation caused by the complex underwater environment of the ocean and poor underwater acoustic communication signals,a fixed-time UUV formation control method with collision avoidance based on bi-limited homogeneous integral sliding mode is proposed.Firstly,considering the problem of limited communication,a fixed-time-based distributed observer is designed,according to each follower’s own state information and the state information of other followers which can communicate with in the communication topology.The follower can estimate the position information and speed information of the leader in a fixed time.Secondly,a three-dimensional space collision avoidance controller based on artificial potential field method is designed to solve the collision problem in the formation system,and the designed potential function structure is simple and easy to implement in engineering applications.It is also can avoid the local minimum problem.Thirdly,further considering the influence of unknown external disturbances on the formation system,based on bi-limited homogeneous theory and integral sliding mode control,a fixed-time collision avoidance controller for unmanned underwater vehicle formation is designed,which can ensure that the followers can quickly converge to the preset formation within a fixed time and compensate for unknown external disturbances meanwhile,to enhance the robustness of the formation system.Finally,the effectiveness of the proposed control method is verified by simulation comparison experiments.(3)In view of the unmeasurable velocity state problem caused by the failure of sensors and the influence of measurement noise on the measurement accuracy of the sensors,considering the unknown external disturbances,an adaptive neural network UUV formation control method based on filtered high-gain observer with collision avoidance is proposed.Firstly,considering the problem of unmeasured velocity state,a filtered high-gain observer is designed,which can not only ensure the real-time estimation of the velocity state information of the unmanned underwater vehicle itself,but also resist the influence of measurement noise on the state observer to avoid the problem of observer failure caused by noise.Secondly,considering the failure of the state observer caused by the misalignment of inertial navigation in high latitudes,the high latitude unmanned underwater vehicle initial state information alignment method based on grid coordinate system is proposed,which can solve the problem of inertial navigation inaccuracy and ensure that the state observer can obtain accurate position state information and improve the accuracy of observed velocity state.Thirdly,considering the influence of unknown disturbances on the UUV formation,according to the universal approximation characteristic of radial basis function(RBF)neural network,an adaptive RBF neural network update law is designed to ensure the stability of the formation system and compensate for the effects of unknown external disturbances.At the same time,combined with the filtered high-gain observer and artificial potential field method,an adaptive RBF neural network formation controller with collision avoidance based on the filtered high-gain observer is designed,and the Lyapunov stability proof is used to ensure the stability of the formation system.Finally,the superiority of the filtered high-gain observer and the effectiveness of the proposed control method are verified by comparative simulation experiments.(4)In view of the higher requirements of transient performance indicators such as error overshoot and convergence time of UUV formation system with the unknown external disturbances,an unmanned underwater vehicle formation control method with collision avoidance based on prescribed performance control is proposed.Firstly,considering the requirement to improve the transient performance and steady-state performance of the system to develop the stability and safety of the formation,and to solve the chattering problem caused by excessive overshoot during collision avoidance,a prescribed performance function is designed to transform the problem of coordinated formation control with collision avoidance into system constraints and boundary conditions.Then,to control the system performance easily,an error conversion function is designed to convert the constrained formation system into an unconstrained system to ensure the unconstrained system state is bounded and the state error of UUV formation can be constrained within a preset constraint boundary.Subsequently,to solve the influence of unknown external disturbances on the formation system,a finite-time sliding mode disturbance observer is designed,which can estimate unknown external disturbances quickly and accurately.Combining with dynamic surface technology,prescribe performance method,adaptive control technology,backstepping method and disturbance observer,a formation control method for UUV with collision avoidance based on prescribed performance is proposed.Lyapunov stability theory proves that the error of the system is bounded.Finally,the effectiveness and efficiency of the proposed method are verified by simulation comparison experiments.