| The energy supply method of autonomous underwater vehicles has always been an important factor restricting its development.Compared with conductor contact wet plug charging,the bidirectional wireless power transmission system not only has the advantages of simple operation,no contact sparks,leakage,and intelligence,but also can realize two-way flow of energy in the underwater environment.It enables the equipment equipped with the system to obtain energy through wireless charging and provide emergency energy to other equipment through wireless discharge,making the device a mobile power source.It improves the adaptability and reliability of underwater equipment.The application of bidirectional wireless power transmission technology in seawater environment is still immature.Unlike the wireless energy transmission in the air,the coupler coils are liable to cause relative rotation or even misalignment due to water flow disturbances in seawater.And the influence of the electrical characteristics of seawater medium on the coil impedance is still the most important issue in current research.In this paper,a bidirectional wireless power transmission system is designed for autonomous underwater vehicles.The main research contents include the influence of seawater media on the parameters of bidirectional wireless power transmission systems,the design and analysis of electromagnetic couplers,the analysis of eddy current loss,and the impact of battery terminal voltage changes on the system during charging and discharging.This article describes the working principle of a bidirectional wireless power transmission system.Considering the electrical characteristics of the seawater medium,it is equivalent to an impedance model composed of resistance and inductance.The influence of seawater medium on the impedance parameters of the coil of the bidirectional wireless power transmission system is analyzed.Based on this,the transmission power and efficiency formulas of the bidirectional wireless power transmission system in seawater are derived.The relationship curve between output power and primary and secondary inductance,frequency,and coupling coefficient,and the relationship between efficiency and primary and secondary inductance,frequency,and coupling coefficient are plotted using MATLAB programming,and analyzed the relationship between them.Finally,the control flow of the bidirectional wireless power transmission system is givenAiming at the problems of relative rotation and even misalignment of the electromagnetic coupler coil caused by factors such as water flow disturbance,this paper uses a cylindrical electromagnetic coupler for energy transmission.The cylindrical coil can mechanically offset the effect of relative rotation.The magnetic field distribution of the cylindrical coil was analyzed by ANSYS Maxwell three-dimensional modeling.According to the magnetic field distribution of the cylindrical coil,the magnetic field is divided into a self-coupling region and a mutual coupling region,and a magnetic circuit model of the cylindrical electromagnetic coupler is established,and then an expression of a coupling coefficient is given to pave the way for the coil design theory.The anti-offset characteristics of cylindrical coils are studied,and it is found that the coils have good resistance regardless of the axial or radial offset of the coil alignment.Especially when the coil alignment is shifted radially,the transmission efficiency of the system increases because the coupling coefficient does not decrease but rises.The eddy current loss generated by the system in seawater is studied,the expression of eddy current loss in seawater is derived,and the relationship between eddy current loss and excitation current and frequency is calculated.The relationship between the magnitude of the eddy current loss and the ratio of the eddy current loss to the total output power is obtained through simulation analysisThe charging and discharging principle of lithium battery is briefly introduced Considering the change of the terminal voltage of the battery during the charging and discharging process,the ratio of the terminal voltage of the primary and secondary battery packs is defined as the voltage gain,and the expression of the effect of the voltage gain change on the system output power and efficiency is derived.The change curves of system output power and efficiency with voltage gain are plotted by MATLAB software programming.Simulink is used for modeling and simulation to prove the correctness of this theoryIn order to verify the correctness of the theoretical analysis and simulation,an experimental platform for a bidirectional wireless power transmission system of an autonomous underwater vehicle is set up,a cylindrical electromagnetic coupler is wound,and a two-way energy transmission test is performed in a simulated seawater environment.The feasibility of bidirectional flow of system energy in seawater is discussed.In addition,the anti-offset characteristics of the cylindrical electromagnetic coupler are researched.In the experiment,the working conditions of the system were simulated when the coil alignment occurred radial offset,axial offset and simultaneous radial and axial offset.The anti-offset characteristic of the cylindrical coil is verified,which is consistent with the theoretical and simulation results. |
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