Research On Design Of Flight Control System For Quadrotor Unmanned Aerial Vehicle

Quadrotor unmanned aerial vehicle(UAV),is a novel and compact aircraft with good maneuverability.In comparison with fixed-wing UAV,quad-rotor UAV possesses many advantages,such as strong flexibility,simple mechanical structure capability of vertical takeoff and landing,high reliability,etc.It has wide application prospects in military,civil,college education and so on.Quad-rotor UAV is a six-degree-of-freedom,four-input under-actuated system with the features of nonlinearity,multivariable and strong coupling.The design of a stable hardware system and control algorithm is to ensure the good performance of quad-rotor UAV.This paper concentrates on the nonlinear model,multi-sensor data fusion and flight control of a quadrotor,and the main research contents of this paper include:Firstly,the research status,applications,main technology and the development prospects of quadrotors.According to the basic structure of UAV,its flight principle is elaborated.Moreover,the airframe and navigation coordinate subsystem describing the flight movements of the quadrotor aircraft are established.In addition,the coordinate transformation matrix between the two coordinate systems are given.Based on a series of reasonable assumptions,the nonlinear dynamic equations are set up and the key parameters in the model are measured based on the actual parameters.Secondly,a quadrotor UAV platform is established.The entire UAV system has included two parts that the Attitude and Heading Reference System(AHRS)and the flight control system.Position,attitude and velocity signals feedback to control system is provided by AHRS,in which data acquisition from all sensors is conducted.The accuracy of the information provided by the system directly affects the control effect of the aircraft.In the flight control system,the microprocessor calculates the control of each motor by running the flight control algorithm and convert it to PWM signal.Thirdly,according to the design scheme,suitable devices are selected.Two PCB boards are designed and producted and a large number of hardware and software debugging tests are carried out.Hierarchical and structured software is developed after the design and implementation of hardware.The software system includes three parts: the underlying driving program,the functional modules program and the application program.Fourthly,in the AHRS,by taking the advantages of MEMS three-axises gyroscope,accelerometer and magnetometer into consideration,an extended Kalman filter(EKF)based on quaternion is introduced to posture optimal attitude estimation of quadrotors for the flight control system.In the flight control system,according to the nonlinear dynamics model of the system,the UAV attitude controller and position controller are designed based on the cascade PID.Moreover,in order to reduce the actuator saturation of the attitude controller,an attitude controller of multi-mode PID is designed.Finally,the the designed algorithms are used to simulate linear trajectory and fixed-point flight in Matlab environment.And transplanted into the flight system,the self-stabilized flight and altitude control flight experiments were carried out to verify the effectiveness of the designed control algorithm.