Circumnavigation Control Technology For Unmanned Aerial Vehicles Constrained By Detection Resources Limitations

With the continuous progress of science and technology,the functions of UAVs are becoming richer and richer.Compared with manned aircraft,UAVs have many advantages,such as small size,convenient use,low cost,and strong concealment ability.As a result,it has replaced manned aircraft in some specific scenarios,and has a wide range of applications in various engineering applications,such as surveillance and tracking missions.Typical motion scenarios can be roughly divided into three categories: trajectory tracking,path following and enclosing control.Among which,circumnavigation control is a frontier technology for intelligent unmanned system,which is an important technical means for UAV to complete various complex tasks,such as target location,environmental monitoring and reconnaissance.Taking UAV as a model,this paper studies circular control methods of single UAV,multicircular circumnavigation control for UAVs with desired angular spacing,elliptical surrounding of single UAV and elliptical circumnavigation control for multiple UAVs with a desired arc length spacing,comprehensively considering detection resources limitations,transient performance enhancement and surround configuration.Specific research contents include:1)Aiming at the issue that unknown target information is arduous to obtain in encirclement scenes,a relative distance information estimator is designed to reconstruct target position information when only the relative distance between UAV and target can be measured,which solves the problem that UAV can measure the bearing information inaccurately by mounting a monocular camera in harsh climates with dust,snow or fog.In addition,with the aid of the relative range estimator to reconstruct the bearing angle,a horizontal circling guidance law including radial correction and normal circling is constructed to achieve the tracking and circling of the unknown stationary target.2)Aiming at the low efficiency and poor flexibility of a single UAV in tracking and reconnaissance of targets,by defining a coordination error relative to the adjacent angular spacing,a multicircular circumnavigation control strategy is derived for multiple UAVs connected by an undirected graph to allow for formation behaviors concerning the moving target,and ensure that each UAV could track targets with the desired circling radius and angular velocity,such that the target can be monitored realize dynamically in a full range.Besides,to avoid the requirement of target’s states being accessible for each UAV,fixed-time distributed observers are introduced to acquire the state estimates in a fixed-time sense,and the upper boundary of settling time can be determined offline irrespective of initial properties,greatly releasing the burdensome communication traffic.Finally,with the aid of fixed-time distributed observers,a distributed circular circumnavigation controller is derived to force all UAVs to collaboratively evolve along the preset circles while keeping a desired angular spacing.3)In view of the disadvantages of the lack of flexibility and adaptability,high energy consumption and low observation efficiency of the current circular encircling in complex and irregular working scenes,a more general elliptical encircling control method for UAV with distance information only,which is independent of the global information.Firstly,a relative position estimator with exponential error convergence is constructed using the existing distance data to solve the extraction of target states in the premise of limited detection condition.Then,the estimated bearing angle is calculated according to the results of the relative position estimator,by deducing the parameterized time-varying radius and tangential velocity direction related to the bearing angle,the elliptic guidance law with time-varying radius is established to maintain the control of the target.In addition,the stability analysis of system is more complicated and intractable due to the high coupling between observation errors induced by distance-based estimators and controlling errors.4)To surmount the reliance on global position data in hostile surroundings where GPS is being attacked or disrupted,by resorting to a distance-only relative position observer,a GPSfree cooperative elliptical circling controller is formulated to force all UAVs to collaboratively evolve along the prescribed ellipse.In addition,the existing researches on collaborative circling mainly focus on the deployment of adjacent separation angles to realize formation behavior,when it comes to the case of elliptical circumnavigation,the existing schemes may suffer from unavoidable aggressive maneuvers and remarkable energy expenditures stemming from the deployment of separation angles,due to that an identical separation angle no longer correspond to the same relative distance along the ellipse.By defining a novel coordinated error relative to neighboring arc length,under the premise of accessible global position,a cooperative elliptical enclosing control strategy is derived for multiple UAVs connected by a digraph to enable formation behaviors with a uniform forward speed.