Research On Efficiency Optimization Of Magnetic Coupling Resonant Wireless Power Transfer System For Electric Vehicles

With the rapid development of new energy vehicles,wireless charging technology for electric vehicles with the advantages of non-contact and flexible charging has also received widespread attention.However,the low transmission efficiency of the wireless charging system has become the most critical factor restricting the development of wireless charging,so this paper optimizes the coupling mechanism and control strategy of the wireless charging system to optimize the overall work efficiency of the system,so as to achieve the goal of improving the transmission efficiency of the wireless charging system of electric vehicles.Firstly,this paper analyzes and compares the characteristics of various wireless power transfer technologies,and selects the magnetically coupled resonant wireless power transfer system as the research object.At the same time,four basic compensation structures of magnetically coupled resonant wireless power charging system are introduced,and the influence of coupling coefficient and load on transmission efficiency of wireless charging system using series-string compensation structure is analyzed,which provides a theoretical basis for the optimization design below.Secondly,the magnetic circuit equivalent model of the coupling mechanism is analyzed,the expression of the coupling coefficient is derived,and the coupling coefficient is analyzed and optimized.In order to improve the coupling coefficient of the coupling mechanism,an optimization design method of asymmetric DD coil is used to obtain the relative optimal coil size under certain conditions.At the same time,the core design is optimized to improve the coupling coefficient,and the strip core is used instead of the flat core to reduce the weight of the system.In addition,in order to reduce the electromagnetic radiation that may be generated during the charging process,an aluminum plate is added to suppress electromagnetic radiation.The joint simulation of Maxwell and Simplorer field path is verified,and it is concluded that the optimized coupling mechanism has strong anti-offset ability and high transmission efficiency.Finally,aiming at the problem of reducing transmission efficiency due to the change of load and coupling coefficient during electric vehicle charging,a maximum efficiency tracking control strategy is proposed.The Buck-Boost converter in DCM is used for impedance matching,which solves the problem that traditional active impedance matching is limited by the load,and realizes the decoupling of load and transmission efficiency.Aiming at the problem that the coupling coefficient changes due to coil offset,a coupling coefficient identification method is proposed,and adaptive maximum efficiency tracking control can be realized by adjusting the duty cycle of the converter when the coupling coefficient changes.In order to realize the constant voltage output of the system,the phase-shifted voltage regulation control method is adopted,and compared with the DC-DC voltage regulation method,it is concluded that the phase-shifted voltage regulation is more suitable for the wireless power transfer system.By building a WPT system simulation model and simulating and analyzing the variable load and variable coupling coefficient,the results show that the control strategy can maintain the maximum efficiency of the system.