Research On Fixed Time Control Of Trajectory Tracking And Formation Consistency Of Autonomous Underwater Vehicle

Autonomous Underwater Vehicle(AUV,Autonomous Underwater Vehicle),as an intelligent tool for assisting ocean exploration,is widely used in civil and military fields such as resource exploration,military reconnaissance,and marine environment monitoring.It has attracted the attention of scientific researchers from all over the world.With the increasing competition for territorial waters resources,the theoretical and technical research on related applications of underwater robots continues to deepen,and it has great practical significance to carry out high-performance control research.This subject takes autonomous underwater robots as the research object,based on the fixed time theory,event-triggered mechanism,back-stepping,filter technology,integral sliding mode algorithm and other theories,in order to tackle with the AUV's own under-drive,strong nonlinearity,system uncertainty,system's initial state soundness,disturbance super randomness,input saturation nonlinearity,actuator dead zone characteristics,etc.,and the trajectory tracking control of single AUV and the coordinated formation control of multiple AUV have been studied respectively.The main works are as follows:(1)In view of the under-driven AUV horizontal stabilization control problem with external disturbances,and consider the strong coupling and under-driving characteristics in the system,the input transformation and state transformation methods are used to make the AUV dynamic model couple into a cascaded system form.A fixed-time control strategy based on a fixed-time expansion state observer is proposed to make the subsystem converge in a fixed time,and the stability analysis of the subsystem is given.A fixed time control law based on a fixed time extended state observer was proposed for the horizontal plane stabilization control of an underactuated AUV with external disturbance.According to the stability of the cascaded system and the equivalence principle of the transformation model,the AUV can achieve fixed time convergence,and the convergence time is independent of the initial state of the system.Further,aiming at the fixed-time tracking control problem of the under-driven vertical plane AUV with external ocean current interference and input dead-zone,the non-linear part of the dead zone of the system and the external ocean current disturbance are equivalent to a composite disturbance,and a linear sliding mode fixed time super-twisting sliding mode disturbance observer is designed for real-time estimation.In order to improve the convergence rate of the observer,a fixed time sliding mode super-twisting interference is designed to estimate the compound disturbance,an adaptive fixed-time sliding mode control method based on a fixed-time sliding mode super-twisting disturbance observer is proposed to realize the fixed-time trajectory tracking control of the AUV,and the system convergence time has nothing to do with the initial value of the system.(2)Aiming at the three-dimensional trajectory tracking control problem of a fully-driven five-degree-of-freedom AUV,and considering the saturation input and the interference of external ocean currents of the system,an adaptive fixed-time integral sliding mode control method based on an event trigger mechanism is proposed.Regard the system's saturated input nonlinear term and external environmental disturbance as the system's compound disturbance,a fixed-time adaptive law for the upper bound of the compound disturbance is designed;By introducing a static threshold event-triggered strategy,in order to solve the problem of limited system transmission network resources.An adaptive fixed-time integral sliding mode event-triggered controller is designed to make the AUV track the desired trajectory within a fixed time.The convergence time of the system only depends on the design parameters of the controller,and has nothing to do with the initial state of the system.Based on the Lyapunov stability theory,the stability proof and the exclusion of Zeno behavior are given.(3)Considering the existence of external disturbances,model parameter perturbation,communication network limited by limited bandwidth and communication resources in multi-AUV systems,a fixed-time convergent integral sliding mode disturbance observer(AFSIMDO)is designed.Based on AFSIMDO and backstepping method,an anti-disturbance formation controller based on fixed time relative threshold event-triggered is proposed.The proposed control strategy enables the system to achieve fixed-time formation while reducing the number of triggers of the formation controller to save communication resources,and the system convergence time has nothing to do with the initial value of the system.Furthermore,for the problem of multi-AUV system with external disturbance,model parameter perturbation and limited input,a fixed-time dynamic threshold event-triggered anti-saturation formation controller based on AFSIMDO is proposed.This strategy enables the system to increase the controller trigger interval while realizing a fixed-time formation,and can make a balance choice between system control performance and reducing the number of controller triggers.The system convergence time does not depend on the initial state of the system.Based on the Lyapunov stability theory,the stability proof and the exclusion of Zeno behavior are given.(4)Considering the problems of limited communication resources,system external disturbance,model parameter perturbation and actuator saturation input,a fixed time radial basis function neural network disturbance observer(FRBFDO)is constructed.Combined with virtual-leader follower algorithm and backstepping method,a fixed-time event-triggered anti-saturation formation controller is designed for the follower multi-AUV to ensure the actual fixed time convergence of the closed-loop system by using a method based on the fusion of FRBFDO and static event-triggered control strategy.Based on the Lyapunov stability theory,the stability proof and the exclusion of Zeno behavior are given.