Fixed-time Formation Control For Multi-quadrotors System

In recent years,with the development of new materials,electronic machinery,control theory,etc.,rotorcraft technology has become more mature and has been widely used in various fields,such as,environmental governance,marine monitoring,express transportation,reconnaissance search,power inspection etc.However,in the face of increasingly complex application environments and diversified needs,single unmanned aerial vehicle(UAV)is limited by its size,weight,load capacity,and endurance time,so that it cannot satisfy the needs of many specific tasks.Therefore,in view of the limitations of a single rotary-wing UAV,it is very meaningful to use the coordination of multiple UAVs.Multi-UAV systems have better robustness and fault tolerance,and have broader development prospects.This thesis mainly studies the formation control method of quadrotor UAVs and then proposes a control approach.The control approach is designed by adopting the fixed-time consensus theory and event-triggered mechanism,and the feasibility of the approach is verified by numerical simulation.The main work and contributions of this thesis are represented as follows:1)In order to better deal with the problem of cooperative control of multiquadrotor UAV,a hierarchical control framework is proposed in this thesis,which can realize multi-UAV flying in the desired formation.The control framework consists of two layers: The upper layer is the cooperative control layer,where the virtual state information of the UAV can be obtained by using the fixed-time consensus theory.The lower layer is the tracking control layer,which adopts the classical PID control theory to make the real state of the UAV track the virtual state.The formation flight of the quadrotor UAV is controlled by the upper and lower layers cooperatively so that the desired formation flight can be realized quickly.In addition,the stability of the collaborative control algorithm based on fixed-time consensus is proved,and the effectiveness of the hierarchical control approach is verified by numerical simulation.2)Aiming at the problems of resource waste and heavy burden in the communication process of multi-UAV systems,this thesis further applies the eventtriggered communication mechanism to the collaborative control algorithm,and improves the collaborative controller.Under the event-triggered communication mechanism,the UAV system only performs data communication and update control input when the trigger conditions are met,which effectively reduces the number of communications and waste of communications resources.In addition,the stability of the fixed-time consensus control algorithm based on the event-triggered mechanism is proved and verified by simulation.3)In order to further verify the effectiveness and superiority of the proposed fixedtime hierarchical control approach,simulations are given to compare the performance capability of the finite-time hierarchical control approach and the proposed fixed-time hierarchical control approach.In the simulations,the performance of the multiquadrotor system under the two control approaches is analyzed by comparing the convergence rate within the specified time.Furthermore,the performance of multiquadrotor system in different initial state is compared to verify the superiority of the proposed control approach.