Research On High Misalignment-tolerant Wireless Power Transfer System Based On Bipolar Coupling Magnetic Field Control

Without cables to connect the charging equipment to the vehicle,electric vehicle(EV)charged by wireless power transfer(WPT)is safer and more convenient.The wireless charging system of EV has been highly concerned.During static wireless charging of EV,misalignment between the primary and secondary coils is inevitable.Such misalignment may cause a rapid decrease in the coupling coefficient and transfer efficiency.Therefore,a critical issue for the static WPT system of the EV is to improve the coupler anti-misalignment performance.Firstly,the research background of WPT technology are introduced,and the contribution of domestic and foreign research institutions to the development of WPT technology as well as the current research of the anti-misalignment performance of WPT technology are elaborated.The composition of the WPT system and working principle are introduced.Based on the mutual inductance coupling model,the equivalent coupling coefficient of the multi-path power transfer coupler is deduced according to the single-path power transfer coupler,and the misalignment characteristics of unipolar coil and bipolar coil are analyzed by the variation case of coupling coefficient.Secondly,a transmitter based on bipolar double-layer quadrature DD(DQDD)coil is proposed.The winding scheme of the DQDD coil is given,and the excitation magnetic field distribution characteristics of the transmitter are analyzed.In addition,the model of the DQDD coil is established by Maxwell finite element simulation software,and the influence of the coil window width,the ferrite core size parameters and the coupling coefficient is given.According to this influence,the coil window width and the ferrite core size under the optimal coupling coefficient are selected.Finally,for EV applications with different load cases and power levels,magnetic field control strategies are proposed for the WPT system based on bipolar DQDD receiver and the WPT system based on bipolar overlapping DD(OLDD)receiver,respectively.For magnetic field control strategy of WPT system based on bipolar DQDD receiver.The equivalent circuit model of the WPT system with dual path LCC-S compensation network is constructed,and the parameter configuration for constant excitation current of primary coil and output voltage are deduced.Then,a magnetic-field control strategy and the coil positioning method are proposed.By calculating the coupling coefficient,the relationship between the coupling coefficient and the displacement of the transmitter and receiver is deduced.According to the position of the receiver,the magnetic field distribution of the transmitter is controlled to achieve the maximum coupling coefficient.An 1-k W experimental prototype is built to verify the effectiveness of the anti-misalignment performance improvement method.For magnetic field control strategy of WPT system based on bipolar OLDD receiver.The receiver is replaced by an OLDD coil,an LCC-S circuit based on dual inverter-single rectifier is constructed,and the parameter configuration for constant excitation current of transmitting coil are deduced.Then,a magnetic field control strategy that the maximum coupling coefficient as desired target is given.The enumeration method is used to match the optimal working mode to maximize the transfer efficiency of the WPT system.The anti-misalignment performance of the proposed WPT system is verified by experiments.