Research On Formation Control Methods For Underactuated Surface Vessels Under Constraints

To make rational exploitation and utilization of resources in the sea,the formation control problem of underactuated surface vessels(USVs)has been paid more and more attention.Some achievements have been achieved in formation control community;however,there are still problems that need to be deeply studied.Actuator saturation contains amplitude saturation and rate saturation,namely input amplitude saturation and rate saturation,which always results in the decrease of system performance.More than that,USVs moving at a complex sea environment inevitably come across various dynamic ships and static obstacles,there may be a ship collision that might cause the damage of struck hull structure.Therefore,it is rewarding to investigate formation collision avoidance and obstacle avoidance control problem of USVs under constraints.Under this background,the dissertation focuses on the formation collision avoidance and obstacle avoidance control of USVs under model uncertainties,environmental disturbances,input amplitude saturation and rate saturation.The specific research contents are as follows:To solve the formation control problem of USVs with input constraints,an anti-amplitude rate saturation controller based on auxiliary dynamic system is proposed.Firstly,a disturbance observer is designed to estimate the total disturbances including environmental disturbances and model uncertainties by using velocity measurements.Secondly,an auxiliary dynamic system is developed to deal with input amplitude saturation.A fixed threshold event-trigged controller is constructed based on leader-follower approach,disturbance observer and auxiliary dynamic system.And considering input rate saturation,an auxiliary dynamic system is constructed.Then,an anti-amplitude rate saturation controller is proposed based on disturbance observer and leader-follower approach.Thirdly,based on Lyapunov stability analysis,it is proved that all signals of closed-loop system are bounded.Finally,simulation results verified that the proposed control algorithm ensure that formation control is achieved under input amplitude saturation and rate saturation.The formation collision avoidance control problem of USVs is considered under input constraints,a barrier Lyapunov function(BLF)anti-amplitude rate saturation controller is proposed.Firstly,a disturbance observer is designed to reduce the influences of environmental disturbances and model uncertainties which degrade system performance.Secondly,an auxiliary dynamic system is designed to deal with input amplitude saturation.To avoid collisions between formation,distance errors and angle errors are transformed by using the BLF.A BLF anti-amplitude saturation controller is designed based on the transformed errors,disturbance observer and auxiliary dynamic system.And considering input rate saturation,an auxiliary dynamic system is constructed.Then,a BLF anti-amplitude rate saturation controller is proposed based on the transformed errors and disturbance observer.Thirdly,based on Lyapunov stability analysis,it is proved that all signals of closed-loop system are bounded.Finally,simulation results verified that the proposed methods can realize formation control without collisions under input amplitude saturation and rate saturation.To solve the formation obstacle avoidance control problem of USVs under input constraints,an artificial potential function(APF)anti-amplitude rate saturation controller is proposed.Firstly,for the total disturbances including model uncertainties and environmental disturbances,an extended state observer(ESO)is designed to estimate the total disturbances and provide the velocity estimation.Secondly,the designed APF is introduced into control objectives,which affects positions of USVs,so collision avoidance and obstacle avoidance can be achieved.An auxiliary dynamic system is designed to deal with input amplitude saturation.An APF anti-amplitude saturation controller is designed based on the ESO,APF and auxiliary dynamic system.And considering input rate saturation,an auxiliary dynamic system is constructed.Then,an APF anti-amplitude rate saturation controller is proposed based on the ESO and APF.Thirdly,based on Lyapunov stability analysis,it is proved that all signals of closed-loop system are bounded.Finally,simulation results show the methods can ensure that USVs are driven to the desired formation without collisions under input amplitude saturation and rate saturation.In this paper,the formation collision avoidance and obstacle avoidance control problems of USVs with input constraints are investigated.And the stability analysis and simulations for the designed control methods are carried out.The results show that the fixed threshold event-trigged controller can realize formation control and reduce the action frequency of actuator.Under input amplitude saturation and rate saturation,the anti-amplitude rate saturation controller can ensure that formation control is achieved while guaranteeing the tracking precision,the BLF anti-amplitude rate saturation controller ensure that the proposed methods can realize formation control without collisions,the APF anti-amplitude rate saturation controller ensure that formation control,collision avoidance and obstacle avoidance are achieved.