Formation Control Of Small UAV Swarm In Complex Environment

In recent years,Unmanned Aerial Vehicle(UAV)swarm has been rapidly developed because of their potential applications.Generally,UAV swarm needs to achieve group behaviors of the cluster in a distributed collaborative manner through local interaction,so as to more effectively complete collaborative tasks.The existing formation control methods have many problems,which restrict the practical application of UAV swarm.For the problems of timeliness,multi-constraints,and connectivity preservation,this thesis investigates the fully distributed formation control method on the basis of consensus,finite-time and fixed-time stability.The proposed formation control methods promote the development of UAV swarm formation control,which is of great significance in theoretical and future engineering applications.The main works and contributions of this thesis are as follows:(1)In view of the robustness and timeliness problems,distributed finite-time formation control method with shorter convergence time and higher accuracy is proposed.To ensure that the formation control method is fully distributed,a fixed-time observer is designed to accurately estimate the state of the leader.In order to solve the problem of larger real-time measurement error of the speed,a finite-time state observer is designed to accurately estimate the speed based on the position and formation control input.To suppress the influence of uncertain disturbances on control performance,a distributed finite-time formation control method is proposed by using integral sliding mode.To solve the problem that the Lyapunov function cannot be constructed for finite-time stability of the time-delay system,a distributed finite-time formation control method based on the extended Artstein’s transformation is proposed for UAV swarm with timedelay.Then,a distributed finite-time formation control method is proposed to solve the input saturation caused by the performance of small UAV platform.Rigorous proof is given by using Lyapunov stability theory and finite-time stability theory.Finally,simulation examples are given to verify the effectiveness of the proposed finite-time control methods.(2)In view of the finite-time formation control protocol that cannot satisfy the requirements in scenarios(such as predefined convergence time,estimate the stabilization time in advance,etc.),a distributed fixed-time formation control method is proposed and the upper bound of the settling time is rigorously derived offline regardless of initial states.To solve the problem of larger real-time measurement error of the speed,a fixed-time state observer is designed to accurately estimate the UAV speed,and an auxiliary vector system is innovatively constructed to prove the fixed-time stability.To suppress the influence of uncertain disturbances on control performance,a fixed-time disturbance observer is designed to accurately estimate the uncertain disturbances and speed of the UAV,which is introduced as equivalent compensation.By using Artstein extended transformation and hyperbolic tangent function,a distributed fixed-time formation control method is proposed to solve the time-delay and input saturation.Mathematical proof is given and some stability conditions are derived.Moreover,the settling time depends on the parameters of state observer and control protocol.Finally,simulation examples are given to verify the effectiveness of the proposed fixed-time control methods.(3)Aiming at the problem of communication resource waste and frequent response of actuators caused by continuous communication and continuous update of controllers,distributed event-triggered finite/fixed-time formation control methods are proposed to achieve formation control of small UAV swarm with lower channel occupancy and lower control energy loss.First,a distributed event-triggered finite-time formation control protocol is developed and the corresponding triggering function is designed to generate event sequences.The UAV can only update the calculation of the control input when the event is triggered,thereby effectively reducing information transmission and the number of responses from the implementing agency.Then,an event-triggered distributed fixed-time formation control protocol is proposed and a corresponding triggering function is designed to generate event sequences.It is proved that the settling time can be theoretically estimated offline regardless of initial states.Further,the stability analysis is carried out by using the finite/fixed-time stability theory and the Lyapunov stability theory,and it is proved that the proposed triggering function can effectively avoid Zeno behavior.Finally,the simulation results verify the effectiveness of the proposed event-triggered control scheme.(4)UAV swarm topology connectivity preservation control method and aggregation,dissolution,formation transformation,formation maintenance control strategy are proposed.Aiming at the problems of the local minimum value and the inability to guarantee the control accuracy,a new class of non-negative bounded artificial potential functions is designed.By introducing the formation error coefficient and artificial potential function,finite-time and fixed-time formation control protocol is proposed to preserve the initial interaction topology.Rigorous proof is performed through finite/fixed-time stability,non-smooth analysis and Lyapunov stability.According to the characteristics of UAV swarm,a strategy of formation assembly and dissolution is proposed,and the assembly is divided into three processes: determination of aggregation areas and aggregation points,optimal allocation of aggregation points and UAVs,and forming a formation.The dissolution can be seen as the reverse process of aggregation.Then,by changing the geometric constraints,the formation transformation strategy is given to switch the basic equilibrium state of the formation.Finally,numerical simulations verify the effectiveness of the main results.Settling time is a main performance index to measure the superiority of the control method.At present,most of the existing UAV formation control methods are asymptotically stable,and their timeliness is poor,which is difficult to satisfy the applications of UAV swarm formation control.Aiming at the constraints of timeliness,disturbance,time-delay,input saturation,and larger real-time speed measurement errors,this thesis investigates distributed finite-time formation control of small UAV swarm.Compared with asymptotic stability control,it has higher control accuracy,faster convergence speed,better robustness and anti-disturbance performance.Although the finite-time formation control can converge in a finite time,its settling time depends on the initial state of the individuals of UAV swarm,which limits the practical application.Therefore,this thesis further investigates distributed fixed-time formation control of small UAV swarm.Considering that the communication capabilities and carrying energy of small UAV are usually limited,event-triggered formation control scheme is investigated on the basis of finite/fixed-time formation control.Considering that the UAV need to be kept within the communication distance,a connectivity preservation control scheme is proposed by utilizing consensus and bounded artificial potential function.