Research On Nonlinear Control For A Quadrotor Unmanned Aerial Vehicle With A Suspended Load

As a typical type of multi-rotor unmanned aerial vehicle(UAV),quadrotor UAV iswidely used in various fields because of its special properties such as simple structure,vertical take-off and landing(VTOL),fixed-point hovering and low cost.One of the important applications of quadrotor UAV is that transporting the load depends on the movement of the quadrotor UAV which the load is directly suspended below.It's known that the quadrotor UAV itself is an underactuated nonlinear system.The introduction of the suspended load increases the degree of freedom for the whole system,and consequently the system is more underactuated and strongly coupled.In addition,the swing motion of suspended load will affect the stability of the quadrotor UAV.Therefore,the research on nonlinear control strategy for the quadrotor UAV with a suspended load has attracted the attention in recent years.This thesis mainly studies the adaptive control strategy of the quadrotor UAV with a suspended load and the online trajectory planning in real time for the quadrotor.Then the stability of the proposed control strategies are analyzed,and the validity and robustness of the proposed control law and the desired trajectory are verified on the full-autonomous flight testbed.The main achievements of this thesis are listed as follows:1.This thesis considers the two-dimensional quadrotor UAV with a suspended load under the constraints of underactuated feature and unknown system parameters,a nonlinear control strategy is designed based on the energy method,which achieves accurate position control of UAV as well as payload swing fast suppression during the flight.The stability of the closed-loop system,convergence of position error and payload swing suppression are proved by Lyapunov-based stability analysis method.Experimental results show that the proposed control strategy in this paper has better control performance.2.For the three-dimensional quadrotor UAV with a suspended load,this thesis designs an adaptive anti-swing controller with the unknown parameters including the air damping coefficients and load's mass.Evenmore,an online parameter's update law is proposed in this thesis,which can achieve the precise eatimation of load's mass.Then the stability of the closed-loop system is proved by Lyapunov method.Finally,four groups of comparative flight experiments show that the proposed controller has better control performance than LQR(Linear Quadratic Regulator)controller,and is robust to external swing disturbance and different load's mass.3.To achieve the quadrotor's position control and load's swing suppression meanwhile for a quadrotor UAV with a suspended load,this thesis accomplishes this objective by means of online trajectory planning for quadrotor's position,which combines two parts including a positioning target trajectory component and an anti-swing component.The former is to lead the quadrotor to the desired position,the latter is designed to eliminate the payload's swing motion.Then the stability of the closed-loop system is proved via Lyapunov based stability analysis.Finally,the numerical simulation and experimental results are performed to validate the stability and effectiveness of the proposed desired trajectory.