Research On Trajectory Tracking Control Algorithm Of Unmanned Aerial Vehicles

Small quadrotor aircrafts have specific advantages like vertical takeoff/landing ability,low cost,autonomous flight,and onboard vision system in high definition.Therefore,they have wide applications in military and civil fields,such as aerial surveillance,search for survivors and power line inspection where the operation environments are dangerous.Quadrotor aircrafts are under-actuated,high coupled and nonlinear,and they will face external disturbances and system model uncertainties.Thus,the trajectory tracking control of quadrotors has been greatly investigated so far.This paper aims to design appropriate nonlinear controllers for quadrotors to achieve tracking control by using feedback control in time domain and Lyapunov stability analysis theory,in order to propose flight control laws such that the aircrafts can autonomously follow the desired trajectory in the presence of model uncertainties,external disturbances and control input saturation,given as follows:1)The dynamical motion equations can be obtained by the Lagrange-Euler formalism,Newton-Euler formalism and quaternion expression,to get the relation between four control inputs and six position/attitude variables.Then,for the sustained external disturbances and parameter uncertainties,we propose a novel hierarchical control strategy based on adaptive RBF neural networks and double-loop integral sliding mode control,to achieve translational and rotational tracking.Approximation ability of arbitrary functions ensured by RBFNNs helps compensate the external disturbances and parameter uncertainties,while double-loop integral sliding mode control simplifies the attitude control law design and eliminates the tracking errors.2)For the limitations of rotor speed,we propose an adaptive robust saturation control method.On the basis of adaptive controller,the emendatory tracking error prevents the system and adaption law from degradation or even instability;robust term gives aircrafts robustness to uncertain mass or inertia parameters.The system stability can be guaranteed by Lyapunov theory,and the controller can effectively eliminate the influence on stability caused by control input saturation.3)A formation control method is proposed for the multiple aircrafts expressed by quaternion.This controller is a simple feedback control method comprised of the relative position error between aircrafts and velocity error of single aircraft.It can achieve any formation flight of multiple aircrafts in short time and keep each aircraft following the desired speed.This paper uses Matlab/Simulink as the simulation platform,and builds the quadrotor dynamic models in this platform.The three aforementioned control strategies are validated by simulation,and simulation results are analyzed and summarized respectively.Simulation results show that the control methods presented in this paper can achieve the desired trajectory tracking for quadrotors,as well as the strong robustness to system uncertainties and control input saturation,which can provide effective theory foundation for practical control problem that quadrotors may encounter.