Research On Attitude Control Technology Of Underwater Vehicle Based On CMGs

Since the CMG(control moment gyro)has been widely applied and greatly developed in the fields of aerospace related engineering control.It can provide a large torque with lower energy consumption,and can be distributedly installed to save more space.Therefore,the CMG is suitable for applying on the space-constrained underwater vehicles.Considering that underwater vehicles need to maintain a certain attitude for underwater operations,attitude control is an important subject in the field of underwater vehicle control.The underwater vehicles will be affected by the uncertain interference caused by the complex underwater environment and the perturbation of the inertia matrix caused by the load change.The mathematical expression of the control system is six-degree-of-freedom complex nonlinear equation.The aforementioned factors require that the controller should be robust.The related researches have been carried out in this paper on the attitude control of the research object in view of the problems above and summarized as follows:Firstly,the fixed coordinate system and the accompanying vehicle coordinate system are established,and the mathematical model of the under-actuated underwater vehicle based on CMGs is presented.The related definitions and theorems of the back-stepping method,the terminal sliding mode control technique and finite time stability are expounded.Considering the limited size of equipment for underwater vehicles and studying the overall configuration of CMGs,the CMGs minimum redundancy system consisting of more complex pyramid configurations is adopted.Several typical CMGs steering laws are studied,and the closed-loop control system is constructed.The hybrid control law used in this paper is compared with two typical CMGs steering laws.By analyzing the experimental results,it is verified that the hybrid CMGs steering law used in this paper is suitable for the under-actuated underwater vehicle model with the pyramid CMGs configuration.Secondly,based on the mathematical model in accordance Euler angles,by introducing Extended State Observer(ESO)and sliding mode control technology,a closed-loop control system is proposed.Specifically,considering the existence of un-modeled terms and external disturbances in the model,it is used as the compound perturbation of the system,and the second-order extended state observer is used for real-time estimation and compensation.This paper makes a reasonable hypothesis,introduces the back-stepping design idea into the controller design process,recursively to the overall sliding mode controller,and the asymptotic stability of the control system is proved.The simulation experiment is carried out by MATLAB.The analysis results show that the designed controller can accurately and effectively perform attitude tracking control for the controlled object.In the face of composite interference,it has strong robustness.The control system is simple and easy to be implemented,and provides a more effective control method for practical engineering applications.Finally,considering that the convergence speed of general control technology is uncontrollable,the terminal sliding mode control is introduced,which makes the controlled system achieve controllable limited convergence time,thus greatly enhancing the system's rapidity.In order to avoid the singular phenomenon and realize the attitude tracking control,this paper proposes a mathematical model of the error quaternion representation,and designs a terminal sliding mode controller based on FTCESO(Finite Time Convergent ESO),with the perturbation of the inertia array,and uncertain dynamic disturbances considered,Simulation experiments are carried out.According to the experimental results,it can be seen that the underwater vehicle can complete the attitude tracking control under the influence of the above factors,thus verifying the validity and correctness of the controller based on the finite time controller.Compared with the back-stepping sliding mode control system,the closed-loop control system has the advantage of controllable convergence time and good simulation results,which enhance the significance of this topic for practical engineering applications.