On The Attitude And Trajectory Tracking Control For A Coaxial Eight-rotor Unmanned Aircraft

Over the last decade, the unmanned aerial vehicle(UAV) has played an importantrole and shown broad application prospects in the military and civilian fields. Its relatedresearch has received more and more attention from engineers and technicians.Especially in recent years, a quad-rotor aircraft attracted broad attention has become aresearch focus in the UAV field with a simple mechanical structure and flexible flightmode. However, quad-rotor with only four drive units has restricted mobility. Owing tothe small coefficient proportion between thrust and gravity, quad-rotor has low loadcapacity and short flight time. In the meantime, it is not configured with enoughinstitutions redundancy, which results in weak reliability. Therefore, a new coaxialeight-rotor UAV is proposed in the paper. The same compact construction as quad-rotoris guaranteed by the coaxial design of the eight-rotor. Furthermore, the eight-rotorprovides four more drive units than quad-rotor, which results in much higher drivecapacity and greater payload capacity, as well as stronger robustness. In addition, thecoaxial design scheme enhances the actuator fault redundancy, which makes the entiresystem have higher reliability. This paper focuses on the issues that the attitude andtrajectory tracking control, as well as ground control station software system design,which lays a good foundation and guarantee for achieving autonomous flight. The maincontents of this paper include the following aspects:Research the dynamic characteristic of the coaxial eight-rotor UAV. The analysis ofthe dynamics and the establishment of a dynamic model are the foundation of attitudeand trajectory tracking control. Firstly, the mechanical structure and flight theory of theeight-rotor are analyzed. The aircraft can be seen as a rigid body with six degrees offreedom via reasonable simplification. Then, the dynamic model of the eight-rotor can beobtained based on the related dynamic knowledge. Next, the autonomous controlarchitecture of the coaxial eight-rotor system is established based on the idea of stratifiedhierarchical intelligent control. Finally, the high efficient and practical autonomouscontrol architecture is formed through modular division, which provides a clear directionfor the eight-rotor UAV to achieve autonomous flight.Design the attitude stability controller for the coaxial eight-rotor UAV so as toachieve the basic requirement of autonomous level. The task is to ensure that threeattitude angles of aircraft can track the desired input stably and the attitude angle errorshave desired convergence characteristics. On account of the parameter uncertainty ofdynamic model and unmodeled aerodynamic which influence the performance of attitudecontrol, a set of attitude control algorithms are designed based on the backsteppingalgorithm. Considering the parameter uncertainties of dynamic model and externaldisturbances, robust backstepping sliding mode control with adaptive radial basis function neural network as attitude controller is proposed. The controller can effectivelyestimate and compensate the influence of disturbances in the flight system. The validityand robustness of the attitude controller has been demonstrated by numericalsimulations.Design the trajectory tracking controller for the coaxial eight-rotor UAV, which is theimportant part of the eight-rotor to realize autonomous flight and also is the guarantee toperform a variety of tasks. According to the coupling characteristics of the coaxialeight-rotor, active disturbance rejection controller(ADRC) based on Particle SwarmOptimization and linear active disturbance rejection controller(LADRC) are designed,respectively. Simulations have demonstrated that both controllers have favorable controlperformance in the presence of disturbances, especially, LADRC with simplerimplementation has higher real-time and more suitable for engineering application.Address the issue that the eight-rotor easily reaches actuator saturation on the yawmovement. It has much weaker drive ability on yaw movement in comparison with othertwo attitude movements(pitch and roll) through theoretical analysis. Thereby, it issignificantly easier to reach actuator saturation on the yaw movement. Aimed at thisproblem, firstly, static anti-windup compensator based on LMI is introduced in LDARCcontroller of yaw attitude. The simulation has corroborated the anti-windup compensatorcan effectively weaken the influence of actuator saturation and enhance yaw trackingperformance. Next, because PID yaw controller is applied in the practical engineering, inview of integral saturation problem in PID controller, a double closed loop yawanti-windup controller combined by PD method with variable structure and variablecoefficient PI method is proposed in the paper. Variable structure and variable coefficientPI (VSVCPI)method carries out saturated strategy under certain conditions so as toenhance the ability to resist disturbances. The validity of the yaw anti-windup controllerhas been demonstrated via both numerical simulations and eight-rotor prototypeexperiments. The PD-VSVCPI yaw controller has been applied in practical engineering.Develop a set of functional ground control station software system. Firstly, theengineering design requirements of ground station software system are analyzed. Theoverall structure of the ground station software is built based on the idea of functionmodularization. The technologies of serial port communication, navigation electronicmaps, mission management and database have been implemented, respectively, so as tomake the operator to real-time monitor flight status. Finally, the ground station test hascorroborated that the designed ground station software system is a fully functional, easilyoperated and friendly man-machine interactive platform that can completely meet themission demand.Finally, the main content and innovation of this dissertation are summarized, andthen the further researches are discussed.