多无人艇固定时间自适应分布式协同编队控制

Fixed-time adaptive distributed cooperative formation control for multiple unmanned surface vessels

针对在实际海洋环境中由复杂恶劣海况导致的局部通讯条件下多无人艇协同编队控制问题,本文提出一种固定时间自适应分布式控制策略.首先,考虑只有部分跟随无人艇能够直接获取虚拟领航者的状态信息,为每艘跟随无人艇设计固定时间分布式观测器,在固定时间内实现对虚拟领航者位置和速度的估计.然后,在估计信息的基础上,采用反步法为每艘跟随无人艇设计固定时间自适应局部控制器,在固定时间内实现对由虚拟领航者产生的期望轨迹的跟踪.特别地,在局部控制器设计过程中,采用参数自适应机制对模型不确定和外界扰动进行补偿,在保证控制精度的同时避免抖振现象.同时,本文给出了所提出的固定时间观测器与局部控制器的稳定性分析,经数学证明,所提出的观测器和控制器能够保证每艘跟随无人艇均能够在固定时间内完成对虚拟领航者的位置和速度的估计并使位置和速度跟踪误差在固定时间内收敛至零的邻域内.最后,设计对比仿真,将本文所提控制策略和目前常用的PD控制器的控制性能进行对比,仿真结果表明所提出的控制策略在控制精度和收敛速度上具有更优越的表现.

Compared with a single unmanned surface vessel(USV),multiple USVs have the advantages of strong maneuverability,high reliability,and low cost.Multiple USVs have potential oceanic transportation,resource exploration,and maritime rescue applications.However,cooperative formation control of multiple USVs is a significant yet challenging problem.The main difficulties arise from the limited communication and the existence of model uncertainties and external perturbations.Therefore,this paper proposes a fixed-time adaptive distributed control strategy consisting of a fixed-time distributed observer and local controller for cooperative formation control of multiple USVs under local communication in complex marine environment.First,a fixed-time distributed observer is constructed for each follower USV to estimate the virtual leader’s position and velocity in fixed time by considering that only a portion of follower USVs can directly access the state information from the virtual leader.Based on the estimated information,a fixed-time local controller is designed for each follower USV to track the desired trajectory generated by the virtual leader in a fixed time using the backstepping method.In particular,in the local controller design process,a parameter adaptive mechanism is introduced to estimate the square of the upper bound of the lumped disturbance term,including model uncertainty and external disturbance to compensate for them.Thus,the proposed controller is smooth to guarantee the control accuracy,and the chattering phenomenon can be avoided simultaneously.Stability analysis of the proposed fixed-time observer and local controller is also presented.Mathematical proofs show that the proposed observer and controller can ensure that each USV can complete the position estimation and virtual leader velocity in a fixed time,thereby making the tracking error converge to the zero neighborhood in a fixed time.Finally,USVs with the proposed control strategy can follow the virtual leader and maintain the formation as shown in the simulation.Additionally,a comparative simulation is designed,where the control performance of the proposed strategy is compared with that of the commonly used PD controller under the same condition.The simulation results show that the proposed controller has superior control accuracy and convergence rate in controlling the USVs to track the desired position and velocity of the demanded formation.Moreover,the chattering phenomenon of the control inputs is significantly suppressed.