Research On Control Of Tilt Rotor Heavier Than Water Autonomous Underwater Vehicle

Human development is inseparable from the ocean,and tools for exploring the ocean are needed.The autonomous underwater vehicle(AUV)is an efficient ocean exploration tool that can automatically gather information and work in the water,and is therefore widely used.However,AUV rarely combines high speed,long cruise range,disturbance rejection and fixed point hover abilities.Therefore,this paper proposes a tilt rotor heavier than water(or negative buoyancy)AUV with no buoyancy material.Its weight in the water is greater than buoyancy,and it requires thrust or lift force generated by hydrofoil to maintain in the water.The control of the AUV is arranged into three modes: hover mode(including general hover mode and body tilt hover mode),transition mode and level cruise mode.The AUV suffers various internal and external disturbances,such as internal mechanism rotation,external turbulence,and various unmodeled dynamics,which affect the control accuracy and robustness.Therefore,according to the characteristics of each mode,the disturbance rejection controller is designed to achieve high precision and robustness.The main content and contribution of this thesis are as follows:(1)For the operation characteristics of the tilt rotor heavier than water AUV,the motion control is arranged into three sequential modes: hover mode,transition mode and level cruise mode,and two configurations are proposed: tri-tilt-rotor and quadtilt-rotor.The two configurations are analyzed.(2)For the uncertainty of hydrodynamic parameters of hovering mode,a nonlinear adaptive hovering attitude controller based on immersion and invariant methodology is proposed.The hovering mode is modeled,the attitude tracking error model is derived,and the unknown hydrodynamic parameter estimator and nonlinear attitude controller are designed.The stability of the system is theoretically proved.The experimental results show that the nonlinear controller based on immersion and invariant can improve the rigidity and response speed of the system and enhance the disturbance rejection ability of the system.(3)The attitude stabilization and tracking of the body tilt hover mode are studied.The body tilt hover mode has the characteristic of large angle maneuvering,and is disturbed by the surrounding flow field during the tilt process.Therefore,a quaternion dynamic attitude tracking model without singularity is established,and a disturbance observer based controller is proposed.The experimental results show that the nonlinear attitude controller based on the disturbance observer can accurately estimate the disturbance and improve the attitude tracking accuracy.(4)For the transition mode,a linear extended state observer with only one parameter is proposed to estimate the total internal and external disturbance.The attitude tracking controller is designed based on the back stepping method.The experimental results show that the single parameter linear extended state observer is easy to tune,it can accurately estimate the total disturbance,and improve the attitude control accuracy.(5)For the level cruise mode,the hydrofoil provides the lift and control force,therefore,the nonlinear model of the cruise mode is established,and the automatic linearization derivation program is programmed to derive the linear model based on small perturbation.The short and long period cycle characteristics of the longitudinal motion of the linearized model are analyzed,and the pitch angle controller is designed for the short period motion.(6)The problem of path following under disturbance is studied.Based on the geometric method,the kinematics equation of the line-of-sight(LOS)navigation law is derived.A side-slip angle estimator is proposed to compensate the disturbance of the ocean current.The stability of the system is analyzed.The simulation shows that the proposed nonlinear adaptive LOS has faster response speed compared with the integral LOS.