Optimization And Design Of Magnetically Coupled Wireless Charging System With Stable Output For Electric Vehicles

Different from the wired charging system,wireless charging system for electric vehicles(EVs)transmits electric energy through the transmitting device laid under the ground,and the device receives electric energy at the receiving end of the EVs chassis,thereby providing the electric energy to the on-board battery to achieve inductive charging.Therefore,there is no additional charging pile and cables connection,which is reduced the space occupied and the risk of electric shock.According to different application scenarios,wireless charging system for EVs is divided into static wireless charging(SWC)and dynamic wireless charging(DWC)system.For SWC system,the method of constant current(CC)first and then constant voltage(CV)is usually adopted,but the misalignment between coils and the changes of lithium battery internal resistance are difficult to maintain constant output.In addition,different compensation topologies will also affect the different output characteristics of the charging circuit,which cannot ensure the stable switching of CC mode and CV mode.Secondly,it is inevitable that there will be foreign objects between the transmission coils since the transmitting device is laid under road,which will affect the transmission of the charging system and too high temperature of system.For DWC system,EVs in motion can be charged,which pays more attention to the smoothness of system output,and when EV drives to the rail switching area,output drop phenomenon is happened due to the zero point of magnetic field.In order to solove the shortcomings of such wireless charging technology,SWC and DWC systems for EVs are studied and analyzed in this paper.The main research includes four aspects of CC and CV output circuit,coupling mechanism,foreign object detection(FOD)and dynamic output volatility.(1)The overall framework of wireless charging system for EVs is analyzed,and the expressions of the first-order compensation topology and the higher-order compensation topology are derived based on the equivalent circuit method.It is analyzed that the higher-order compensation topology of T-type equivalent structure can achieve CC and CV output with loadindependet.(2)LCC-LCL compensation topology is proposed for EVs wireless charging based on the high-order compensation topology of T-type equivalent structure,which could be achieved to CC output and CV output with load-independent that only changes the compensation capacitor to switch the resonant angular frequenc,and could also be adjusted the output power of WPT system by primary side LCC circuit.(3)The anti-misaligment ability and FOD function of wireless charging system are studied,and a Bipolar Symmetrical DD(BSDD)magnetic coupling coil structure is proposed,which adds a symmetrical DD compensation coil on the BP coil,and further improves the antimisalignment ability of the transmission coil in the longitudinal direction while maintaining its lateral offset ability.In addition,in oreder to realize FOD function of the transmission system according to whether the induced voltage difference between the added symmetrical DD compensation coils is zero,thus meeting the compatible realization of the coil offset tolerance and FOD function,and further improves the steale output capability of the system.(4)The models of long-orbit launch guide and short-orbit launch cascade guide are built,the short guide is improved to be staggered arrangement,then BSDD magnetic coupling coil structure is used as the receiver coils and LCC-LCL topology is combined as the dynamic charging circuit.Compared with the tiled short guide,the improved short-orbit launch guide can reduce the output fluctuation and drop of system,and also improve the smoothness of power output.