Research On X-rudder UUV Energy-saving Path Following Method

With human exploration and development of the ocean,Unmanned Underwater Vehicles(UUV)have become one of the most important engineering equipment in the process of developing the ocean.The highly nonlinear and strong coupling characteristics of the underactuated UUV,as well as the complex and changeable factors of the marine environment,bring great difficulties and challenges to the design of the UUV's motion controller.The X-rudder UUV,a special under-actuated UUV,has gradually attracted the attention of researchers.Although the X-rudder has the advantages of redundancy and high rudder efficiency,it adds difficulty to the design of the control allocation.The demands of UUVs performing long endurance and large-scale operations is increasing day by day,and the urgency for improving UUV endurance is also increasing.For UUVs in service,the cost of changing the design to increase the endurance is huge,so it is more engineering practical to reduce the system energy consumption and increase the endurance from the perspective of control.From the perspective of energy saving,this paper conducts research on X rudder UUV path following and control allocation,mainly in the following aspects:(1)The coordinate system required for the research is established,various external forces acting on the UUV are analyzed based on the Dynamics Theory,and the equations of the UUV's six-degree-of-freedom motion are given.According to the theory of ocean waves,a model of the force of ocean waves on UUV is established.From the perspective of overcoming sailing resistance and rudder mechanism,the energy consumption model is analyzed and established,and the concept of energy consumption index is proposed.According to the simulation experience results,the influence of pitch angle and rudder angle on energy consumption is analyzed and summarized,which provide a theoretical basis for the subsequent energy-saving design of the controller.(2)The under-actuated UUV path following method is studied.Inspired by PID control,the traditional line-of-sight guidance method is improved,and the path switching during the straight-line tracking process can easily lead to system overshoot and controller output saturation.A smooth switching strategy is designed,which is verified by the heading control and comb-scan simulation test.The logic and feasibility of the algorithm are verified by field experiments.Aiming at the under-actuated UUV path following problem in the presence of ocean currents and the differential explosion problem in traditional backstepping,a nonlinear finite-time path following controller is designed based on the filter backstepping and supertwisting observer.The controller's global stability is proved based on the Lyapunov stability theory.Simulation experiments show that UUV can track the desired path faster and has better robustness in the presence of interference than traditional backstepping methods.(3)The UUV energy-saving tracking control method is studied.Consider energy saving in the UUV path following control,design an energy-saving path following controller,and conduct research from the two aspects of optimal tracking speed and near surface interference filtering.In the case of ocean current interference,the guidance law is designed based on the line-of-sight method(LOS),and the best energy-saving tracking speed is designed to ensure that the best energy consumption state is maintained during the tracking process.According to the UUV's attitude and ocean current information and the energy consumption information of its own equipments,the track speed of optimal energy consumption is calculated.Simulation experiences are performed to verify.In order to further save energy,considering the interference of ocean currents,a wave filter is designed to solve the problem of high-frequency output of the controller caused by the interference of high-frequency ocean waves when the UUV is sailing near surface,and the low-frequency movement of the UUV is measured from the noisy output.Based on the passivity theory and the Lyapunov stability theory,the global stability of the designed filter is proved.Simulation experiments are used to verify the effectiveness of the designed method.(4)The X rudder UUV energy-saving control allocation method is studied.The concept of reachable set is introduced,and the X rudder UUV control allocation method is designed based on reachable set.Restrict the calculated virtual control moment according to the reachable set in the high-level controller,so that the control moment calculated by the control allocation is kept in the reachable set.The relationship between energy consumption and the number of executive rudders is analyzed,and the relationship between the number of different executive rudders involved in control allocation and energy consumption is studied.The results show that the more executive rudders participate,the lower the energy consumption of the executive agencies.In order to solve the saturation that easily occurs in the control allocation,a control allocation method considering the state of the actuator is designed.The simulation results show that after considering the redistribution,the unsaturated rudder angle is reused,and the UUV's attitude control effect is significantly improved.In order to quantify and evaluate the energy consumption of the actuator after the control allocation,the X rudder UUV energy-saving evaluation index is designed considering the navigation performance and the dynamic characteristics of the rudder.Finally,the effectiveness and energy-saving performance of the designed control distribution method is verified by designing a near surface tracking simulation test under low-level sea conditions.(5)The fault-tolerant control of X rudder UUV is studied.The UUV fault-tolerant control system based on double redundancy is designed to improve the fault-tolerant capability and reliability of the UUV control system,and reliability analysis is carried out.The fault-tolerant performance of the X rudder UUV is analyzed and verified from the theoretical level.In order to solve the problem that the high-level controller may cause the system to be unable to track the target or lose stability when the X rudder UUV fails,a sliding mode fault-tolerant controller is designed based on the adaptive theory,and the stability of the method is proved based on the Lyapunov stability theory.Further,considering the rudder failure,the rudder failure is divided into two types of failures: stuck rudder and failure.Based on the reconstruction theory,the faulttolerant control distributor is designed.The simulation experiment verifies the effectiveness of the designed method.