Modeling And Event-triggered Control Of Quadrotor Suspension System

Quadrotor aircrafts have been widely used in recent years for air transport tasks,such as mine detection,cargo transport in dangerous environments or delivery of loads in areas inaccessible to vehicles,because it has strong vertical takeoff and landing ability and strong maneuverability.The rope suspension payload transport is an important way for the quadrotor to accomplish the transportation task,which maintains the flexibility of the quadrotor and makes the connection between the quadrotor and the payload more flexible.To solve the problem of payload’s swing and communication resource saving in the quadrotor suspension system under external interference,this paper establishes the mathematical model of quadrotor suspended system with variable cable length at unequal speed,and designs a compound control scheme.The main work is as follows:(1)This paper considers the modeling of the quadrotor suspension system when the cable length varies at non-constant velocity.Compared with the traditional modeling method,the separation modeling method is adopted to establish the quadrotor and suspension payload system respectively by using Newton-Euler equation,which is convenient for the observer and controller design.The modeling method in this paper avoids more derivation calculation and makes the modeling process more simple.The non-constant speed change of the rope length can effectively reduce the swing of the payload and improve the stability of the quadrotor,so that the cargoes can be loaded and unloaded more quickly and efficiently.(2)The tension of the quadrotor is regarded as the disturbance of the quadrotor system by the payload,and the expanded state observer is designed to observe the tension of the rope.Then,the observer of the pendulum angle is obtained through the dynamic equation of the payload and the static equation of the pendulum angle.Compared with the motion capture systems and camera measurement swing angle systems,the scheme is simple in design,it does not limit the application scenarios,and can still be used in complex terrain outdoors.(3)The adaptive sliding mode controller with strong robustness and anti-interference ability is designed to make the attitude angle convergence,and the hyperbolic tangent function is used to eliminate system buffeting.the anti-swing feedforward controller further inhibits the payload’s swing.The scheme can effectively restrain the payload’s swing,and the tracking error of the reference trajectory of the quadrotor is within an acceptable range.(4)The event-triggered strategies of fixed threshold,dynamic threshold and switching threshold are designed respectively to reduce the communication between the quadrotor flight control and the ground station.The measurement error of fixed threshold is limited by fixed value.The relative threshold strategy can ensure that when the amplitude of the control signal is large,the threshold value is also large,so as to obtain a long update interval.However,the measurement error of the control signal is too large.When the controller approaches zero,the system can be controlled more precisely and the system performance can be better.Switching threshold policy balances system tracking error and execution interval by combining the two event triggering policies.(5)To verify the compound control scheme designed in this paper,the quadrotor suspension system model was built in MATLAB/SIMULINK,and the observer observation pendulum angle,feedforward controller to suppress payload’s swing,adaptive sliding mode controller to enhance system robustness and event-triggered strategy to reduce traffic in flight control were simulated and analyzed.