Design Of Autonomous Underwater Vehicle Wireless Charging System Based On Bipolar Coupling Magnetic Field

The Autonomous Underwater Vehicle(AUV),as an important equipment for ocean exploration,plays an irreplaceable role in ocean resource development,marine homeland security inspection and other aeras.However,the limited endurance and restricted cruising range have become the bottlenecks in the generalization of AUV.Underwater wireless charging technology is expected to become an important means to enlarge AUV's cruising range,since it has no short-circuit risk and no need for precise alignment.Thus,in this article,a wireless charging system for AUV is designed from four aspects respectively,which are magnetic coupler,resonant compensation network and power conversion circuit,power closed-loop control system,as well as prototype implementation.As a result of the special cases where there's limited space and the arc outward appearance of AUV,a magnetic coupler based on bipolar coupling magnetic field is proposed and optimized.Firstly,the magnetic coupler is optimized according to the magnetic field distribution characteristics.Then the influence rule of the geometric parameters on the performance of the magnetic coupler is obtained based on the parameter scanning method,and parameter design of the magnetic coupler is acquired according to the system's misalignment tolerance and output voltage requirements.Finally,the actual magnetic coupler is built and tested under alignment and misalignment conditions.The results in the simulation and experiment show that the designed magnetic coupler has advantages of small volume,strong coupling capability,low sensitivity to misalignment and good convergence effect of magnetic field.In order to improve the stability and reliability of power transfer in underwater wireless charging systems,the compensation network and power conversion circuit are analyzed and designed.The LCL-S compensation network is chosen for the special environment of seawater,and by studying its transmission mechanism,the method to improve transmission capacity is obtained.The working mode of the inverter based on phase shift control is analyzed,and the control law of conduction angle to output voltage RMS and THD is obtained.The output voltage and current models of rectifier circuit with capacitive filter are obtained based on the fundamental mode analysis method.By integrating all the modules of the wireless power supply network,the mathematical description of the output voltage of the wireless power supply network is acquired,and the design method of parameters is further put forward.The simulation circuit is built by PSpice to test the working state of the system under alignment,single-dimensional and multi-dimensional misalignment.The results confirm the effectiveness of the design method and the stability of the circuit mentioned above.Aiming at the wide variations of the load impedance during the charging processes of the lithium battery,the closed-loop power controller is designed and optimized.The lithium battery charging model is established to analyze the law of impedance variations in the processes of the lithium battery charging.Based on the constant voltage source characteristic of the secondary side output,the Buck circuit is used to realize the power control and impedance matching.The accurate mathematical description of the coupling efficiency is established through the analysis of the efficiency distribution of the wireless charging system.The scheme of system efficiency optimization design is formulated by means of impedance transformation capability of Buck circuit.By designing the system power closed-loop control strategy,the power control system is founded.The experimental results of the closed-loop power controller show that the normal constant current and constant voltage charging of the lithium battery can be realized,and the maximum charging power is 600 W with the efficiency of 97%.In an attempt to verify the feasibility of the proposed scheme,a 600 W wireless charging system prototype test platform is built.Some problems in hardware circuit design are studied,such as the design of switch drive circuit and printed circuit board.The variable load and misaligned open-closed-loop tests are carried out on the wireless power supply network.The test indicate that the designed wireless charging system can achieve normal charging function within the specified misalignment range and the maximum charging power is 600 W,the maximum efficiency of the whole system is 90.6%.The system efficiency of 350 W power segment and above in the charging process is higher than 88%,and the coupling efficiency is higher than 97%.In conclusion,the design meets the requirements.