Research On Control Performance Of Coaxial Unmanned Helicopter Based On Finite Time Convergent Sliding Mode Observer

In recent years,coaxial helicopter has played an increasingly important role in military and civil fields.However,the development of coaxial unmanned helicopter in China is in its infancy.In the research and development,most of them are customized research and development for a certain scenario,and the control algorithm is seriously coupled with the parameters of the helicopter itself,with high upgrading and maintenance costs,which can not meet the needs of the future all-round and multi-functional market.In this study,based on the background of geophysical exploration platform,relying on the "development of heavy load intelligent geophysical exploration unmanned helicopter(863 plan)"(Project No.:2013aa063903),a new control algorithm is studied based on the observer technology of finite time convergence,aiming to improve the control performance of coaxial helicopter.The research content of this paper mainly includes:(1)In the aspect of modeling,the rigid body kinematics model of coaxial helicopter and the models of each component are established.Based on the blade element theory,the aerodynamic model of the rotor is established;based on the three-dimensional nonlinear Pitt Peters dynamic inflow theory,the induced velocity model of the upper and lower rotors is established by introducing interference factors,and finally the resultant force and moment model suitable for the design control algorithm is obtained.(2)In the algorithm design stage,the controller of position loop and attitude loop is designed based on the principle of backstepping control.Decoupling is based on the idea of time sequence separation.In order to realize the estimation of time-varying disturbance,a sliding mode observer which can converge in finite time is built by designing PI type auxiliary sliding mode surface to compensate the time-varying disturbance in real time.In the dynamic loop,after the input dynamic error passes through the proportional differential controller,the feedback linearization model is used to realize the closed-loop control from the output control force of the dynamic loop to the kinematic model of the rigid body.In the simulation stage,the performance of the controller is compared based on three common environmental disturbances(time-varying external disturbance,time-varying inertia parameters and sensor noise).The control group algorithm designed is:double loop PID control algorithm,traditional backstepping method,and sliding mode observer algorithm based on the approach rate.The performance of the terminal sliding mode observer based on finite time convergence is verified(3)Based on Caputo fractional calculus,the fractional terminal sliding mode observer is derived,and it is proved that the observer is asymptotically stable by Lyapunov stability theory.Then the fractional calculus operator is simulated by the oustaloup filter,and the observer Simulink model is built.The response errors of different orders are compared by the observer test module,and the order superior to the integer order is selected for the actual simulation.Finally,by combining with backstepping,the control algorithm based on fractional order observer is simulated in the case of only external disturbance,and compared with integer order(4)Based on the open source flight control,a four-rotor algorithm test platform is built.Through the secondary development of the source code,compilation and link,upload the compiled file to the flight control board,and complete the test flight through further debugging.