Geometric Sliding Mode Attitude Control Of Quadrotor UAV And Its Application In Disturbance Attenuation

With the development of computer, sensor and actuator techniques, the quadrotor has become a hot research direction of micro unmanned aerial vehicle(UAV). As a rotorcraft, the quadrotor has the ability of vertical takeoff and landing(VTOL) and hovering flight. In order to adapt the objectives of micro UAV missions, quadrotor must performance a wide range flying and rapid maneuvering. Since quadrotor has a small inertia, it is more suscrptible to its nonlinear and a variety of external interference, thus the control algorithm is also required to have a high robustness. In this paper, the attitude control algorithm is studied for quadrotor, mainly including the following aspects:1. Kinematics and dynamics of quadrotor. In order to design globally stable attitude controller, we use the unit quaternion, instead of the traditional Euler angles, for representing the kinematics of quadrotor attitude. The Lie Group structure of unit quaternion that provides a basis for analysis and controller design from the viewpoint of differential geometry is given. According to Newton’s second law and blade element theory, the dynamics of quadrotor attitude is stated. The ultimate mathematical model of quadrotor attitude is determined for simulation and controller design after discussing the disturbances.2. Geometric sliding mode attitude controller(GSMAC) of quadrotor. A unit quaternion based sliding mode attitude controller is designed using sliding mode technology which has a natural robust of matching interference. Take advantage of backstepping method and inverse optimal theory, the stability and optimality of the GSMAC is proved constructively. In simulation experiments, GSMAC is compared to a unit quaternion based PD controller. The results show that GSMAC gain a faster convergence rate while satisfying the saturation constrain. The experiments on the experimental platform showed the algorithm is effect, and adjust the quadrotor attitude rapidly.3. Geometric sliding mode attitude observer(GSMAO) of quadrotor. It is an effective method to eliminate the requirement of full state measurement to use sliding mode observer. However, the unit quaternion is seemed as an algebra tool in traditional unit quaternion based sliding mode observer. There is a normalization process in the observer algorithm, thus the performance of convergence is reduced. The algorithm constructs feedback in the angular velocity space and the space of equivalent Lie algebra of unit quaternion space, respectively. It avoids not only the complexity of constructing feedback in unit quaternion space but also the process of mandatory rescaling which is seen to deteriorate the accuracy of the angular velocity estimates during sliding. The performance of GSMAO is compared with traditional quaternion based sliding mode observer in which multiplicative quaternion correction is used and the results show that GSMAO gains better tracking performance. Then GSMAO is realized on a test bed and the effectiveness of the observer algorithm is verified by experimental studies.4. Two-degree of freedom robust controller. Because the geometric sliding mode attitude controller of quadrotor is robust for only matched interference, a two degrees of freedom robust controller is designed with the structure of sliding mode controller / sliding mode disturbance observer(SMC/SMDO). The disturbed attitude system is extended to a third order system, and a geometric sliding mode disturbance observer is designed to estimate the disturbance torque acting on the quadrotor. A simulation with ideal curves is implemented, and the results show that the geometric sliding mode disturbance observer can track the applied external interference signals effectively. In the simulation of interference suppression, the GSMAC can not keep the system stable while large amplitude slow disturbance is introduced, but at the mean time two-degree of freedom robust controller can make the system stable.