Research On Finite Time Sliding Mode Control Algorithm For Underwater Vehicle

China has a vast sea area and abundant resources in the ocean.Since most of the marine resources are distributed underwater,it is necessary to conduct underwater operations in order to exploit these resources.However,human beings live on land and are difficult to reach in many areas underwater.Even professional divers have limited depth of dive,and long-term underwater operations will cause some degree of damage to their bodies.Remotely operated vehicle(ROV)can well replace human beings for underwater operations,and have been widely used in the exploration and exploitation of offshore oil and gas,underwater photography search and rescue,underwater scientific research and investigation,marine fishery and other fields.Therefore,it is necessary to study the motion control algorithm of the underwater vehicle.The main contents of this paper are as follows:(1)A fast finite-time disturbance observer(FDO)is designed to estimate the total uncertainty of the system in view of the complex working environment and the ubiquitous external disturbance of the underwater vehicle,as well as the model parameter uncertainties.The estimation error is faster than that of the traditional non-linear disturbance observer and can converge in a finite time.The observer estimates are then used to feed-forward compensate the nonsingular fast terminal sliding mode controller(NFTSMC)so that the track tracking error converges to zero in a limited time.The theory is strictly analyzed and verified,and its validity is verified by simulation examples.(2)Furthermore,a disturbance observer is designed for the external disturbance,and then a pre-determined performance controller is designed based on the barrier Lyapunov function combined with the non-singular fast integral terminal sliding mode(NFITSM)to make the trajectory tracking error of the underwater vehicle meet the pre-determined performance requirements and ensure in a finite time converge to zero.It is also analyzed and proved strictly in theory,and its validity is verified by simulation examples.(3)The hardware and software of the underwater vhicle physical system are designed,and a multi-functional autonomous underwater vehicle is developed.It can work in both cable mode and cable-free mode,and has high flexibility and autonomy.The control algorithm designed above is validated by the developed underwater vehicle.The results show that the proposed control algorithm has fast convergence and robustness.