Research On Control Strategy Of AUV Roll Stabilizing Near Surface

AUV (Autonomous Underwater Vehicle) working in complex sea environment attracts increasing attention due to strengthened awareness of ocean exploitation and ocean utilization. With developing of ocean science and engineering in recent years, people make more wide research on atmosphere near sea surface, sea climate, torpedo arrangement, underwater fault-removing and submarine fight. Consequently, it becomes a new trend of sea robot developing to study and design AUV working on or near sea surface.Motion attitude of AUV working near sea surface often changes obviously under the influence of ocean wave. Intense roll and pitch will have a very negative effect on normal working and even safety of AUV. Therefore, the methods to control AUV's attitude and reduce roll and pitch near sea surface are always needed eagerly. In addition, energy which is carried on AUV for submergence is usually limited, so it comes to be one of the most important issues in AUV research that how to finish specified tasks and aquire balanced AUV attitude with limited energy effectively. Attitude control and energy consumption issues have both the important theoretical and practical values in promoting intelligent levels of AUV.In allusion to the attitude control problem of AUV working near sea surface with low navigating speed, AUV motion model is firstly analyzed in this paper. Through numerical calculation of wave force and wave moment near sea surface, it is found that traditional fin stabilizer is hard to generate enough lift for counteracting wave disturbance when AUV is navigating with low speed. Consequently roll motion is very difficult to control effectively at the moment. Then a new pattern of fin stabilizer working is required to increase lift force in zero-speed or low-speed navigation.In order to solve the above problem, zero-speed fin stabilizer based on Weis-Fogh device is used to control roll attitude in this paper. Lift force generated on zero-speed fin stabilizer is analyzed by using potential theory and vortex action theory. Through relevant deduction, model of lift on zero-speed fin stabilizer is obtained. Because the problem discussed in this paper is attitude control of AUV with low navigating speed, it is necessary to consider additional effect of water flow on the lift while sea water flows through fin surface with relative flow speed.Considering uncertainty, nonlinearity and strong coupling of AUV motion model respectively, research emphasis in this paper focuses on applying corresponding advanced control strategy (e.g. variable structure control, active disturbances rejection control, Hoo control based on feedback linearization, decoupling control and general predictive control) in attitude controller design for solving problems induced by complexity of AUV motion model. Effectiveness of each control strategy in system design and modification is verified by simulation on attitude control system based on zero-speed fin stabilizer of AUV near sea surface.In order to optimize utilization of energy resource, a synthetical performance index is raised, which is based on roll stabilizing performance and energy consumption used for driving fin stabilizer. Through relevant deduction, optimal control law of zero-speed fin stabilizer is obtained. Simulation and numerical calculation results show theoretical significance and practical engineering value in the research of AUV attitude control based on energy optimization.