Research On Flight Control Technology Of Quadrotor Unmanned Aerial Vehicle Under Indoor Environment

The quadrotor unmanned aerial vehicle(UAV) which is capable of vertical take-off and landing, hovering and flying in low speed can be categorized to the unmanned rotorcraft family. Compared to the conventional unmanned helicopter, the quadrotor owns unique advantages such as a more compact structure, simpler manipulation, more convenient maintenance and lower cost. Due to those characteristics and advantages, the quadrotor has been attracting more and more interest around the global academic community in recent years. The quadrotors are also widely used in military and civilian areas. Working on the design and implementation of the quadrotor flight control system and taking the indoor autonomous flight as the objective, this thesis focuses on the modeling of the quadrotor, attitude and heading reference system, disturbance observer based flight control methods, hardware design and software programming. The ground control station is also developed in this thesis. The main research contents are listed as follows:Firstly, the forces and torques acting on the quadrotor are analyzed in detail and then the twelve-state nonlinear dynamics are established based on the Newton-Euler principle. Some parameters involved in the dynamics including body inertias and rotor lift coefficient are determined through experiments. Meanwhile, the function of the rotor speed with PWM and input voltage is obtained. To further facilitate the engineering realization and controller design, the linear model expressed by transfer function is obtained using the small perturbation linearization technique.Secondly, the attitude and heading reference system(AHRS) is designed based on the quaternion extended Kalman filter(EKF) algorithm using low-cost micro-electro-mechanical-system sensors. To increase the AHRS estimation precision in face of disturbance acceleration, an improved disturbance acceleration compensated attitude and heading estimation method is proposed, and the proposed method is successfully implemented on a TMS320F28335 digital signal controller. The comparative experiments with the convential algorithm show that the proposed method has higher accuracy and can satisfy the requirement of the indoor flight control system.Thirdly, two kind of disturbance observer based flight control methods are designed to handle the internal and external disturbances. The cascaded sliding mode control method with a nonlinear disturbance observer is used to stabilize the quadrotor attitude, and the simulation results show that the system has good performances of attitude stabilization and external disturbance suppression. To enhance the disturbance observing accuracy of the traditional disturbance observer, a linear dual disturbance observer based quadrotor trajectory tracking control scheme is proposed. Followed by the stability proof of the closed-loop system, a Smith prediction compensator based PID position controller is derived. The simulation results validate the effectiveness of the linear dual disturbance observer based trajectory tracking control strategy.Following, hardware design and software implementation are completed for the quadrotor UAV indoor flight control system. In terms of hardware, the flight control main board which takes the TMS320F28335 as the master control chip is deeply investigated. Both schematic diagram and PCB are desinged for the flight control main board. In terms of software, a DSP/BIOS embedded real-time operating system based flight control software framework is built. Detailed designs for the primary function blocks in the software are finished. To fulfill the requirments of the flight control system, a ground control station(GCS) is also developed based on the MFC.Finally, the indoor flight tests for the quadrotor UAV including attitude and position control are conducted. The test results demonstrate that the designed quadrotor UAV flight control system is reasonable and effective.