Research On Small AUV Trajectory Tracking Control Method

As an important equipment for ocean exploration,Small AUV has high mobility,invisibility,and low cost.It is gradually being applied in practical engineering and will be widely used in underwater manned/unmanned cooperative operations in the future.Therefore,high requirements are put forward for the control performance and control accuracy of Small AUV.However,due to model uncertainties,unknown ocean current disturbances,and thruster saturations,the control precision of Small AUV cannot meet the requirements of increasingly complex tasks at present.Therefore,it is of great theoretical significance and application value to research the trajectory tracking control method of Small AUV with model uncertainties and unknown external disturbances.Based on the prescribed performance control,sliding mode control method,and observer technique,this paper researches the trajectory tracking control of Small AUV with model uncertainties,unknown external ocean current disturbances,unmeasured acceleration,and thrust input saturation.The main works are represented as follows:Aiming at the prescribed precision tracking control of Small AUV,a prescribed performance control scheme based on error constraint is introduced.Firstly,considering the unmeasured acceleration of Small AUV,an improved disturbance observer without acceleration input is designed to compensate model uncertainties and external disturbances.By combining the prescribed performance control method with the backstepping method,a prescribed performance control law based on the improved observer is designed.The trajectory tracking error and velocity error of Small AUV are constrained by the prescribed performance constraint boundary,so that the trajectory tracking error converges to the prescribed control precision,and the actual velocity can track the virtual velocity.The feasibility of the proposed control algorithm is proved by Lyapunov theory.Finally,the effectiveness of the proposed controller is verified by numerical simulations.Based on the above research,the improved disturbance observer is introduced to compensate the total uncertainties for the finite time tracking control of Small AUV.Considering the large fluctuation of observation error and control error in the initial phase,sliding mode control method is introduced to improve the robustness to parameter changes.By combining the non-singular terminal sliding mode control method with the prescribed performance control,a prescribed performance terminal sliding mode control method is proposed,which makes the Small AUV meet the requirements of finite time control while realizing the prescribed control precision.Furthermore,for the problem of Small AUV thrust saturation,a saturation compensation system is designed to compensate the input saturation,and an improved terminal sliding mode controller with prescribed performance is designed to enable the Small AUV to achieve finite time control in the case of input saturation,and the control accuracy meets the prescribed requirements.The feasibility is verified by Lyapunov method.Finally,the effectiveness of the prescribed performance terminal sliding mode controller is proved by the Small AUV numerical simulations.Aiming at the Small AUV finite time constrained control problem,the radial basis neural network method is introduced to approximate the model uncertainties of Small AUV by considering the different change rules between model uncertainties and external disturbances.Based on the transformed error model and neural network system,a disturbance observer based on neural network is designed to observe unknown ocean current disturbances.Then,to meet the requirements of finite time constrained control,a finite time performance function which can converge to the prescribed accuracy in finite time is designed to constrain the error.Combining the finite time performance function with the second order sliding mode control method,a Small AUV adaptive prescribed performance second order sliding mode control method is proposed.This control method can make the Small AUV tracking errors converge to the prescribed control precision in finite time,and overcome the chattering problem of sliding mode control.Lyapunov method is applied to prove the feasibility of the proposed control scheme.Finally,the effectiveness and robustness of the finite time prescribed performance second order sliding mode controller are verified by the Small AUV simulations results under different conditions.