Research On Design And Optimization Of On-road Charging Systems For Electric Vehicles

The development of electric vehicle(EV)is on the rise due to the problems of energy shortage and environment pollution.There is no doubt that convenient,safe and reliable charging mode is of significant importance and necessity to promote EV applications.Nevertheless,existing charging mode by electric cables has shown several constraints such as cumbersome facilities,complex operations,electric leakage and time-costing charging.Fortunately,wireless power transfer(WPT)technology provides an alternative for EV wireless charging.Transmitting coil installed on the road can transfer power to the receiving coil embedded under the chassis so that EV can be charged while driving and the driving range can be increased to a great extent.The EV on-road charging system,which consists of single transmitting coil and several receiving coils,is investigated in the paper.Key technologies,working performance optimization and power control strategies of the system are analyzed and the main contents are as follows;Based on the equivalent circuit theory,circuit models of high-frequency full bridge inverter,electromagnetic coupler and rectifier are built respectively,forming the foundation for system characteristic analyses.Design of the electromagnetic coupler for EV wireless charging is optimized from three aspects:wire types,coil structures and coupler topologies.In addition,soft-switching technology of the inverter which can be implemented in WPT systems is analyzed to reduce power loss.Major modules of the on-road charging system as well as system working principle are introduced.The circuit model of the EV on-road charging system is then constructed.Accordingly,the effects of load quantity and value on output power and power transfer efficiency are analyzed.Theoretical values of the optimal loads to achieve maximum output power and power transfer efficiency are deduced in a mathematical form respectively.Power control strategies are then taken into discussions in detail.Stable output power control strategy is proposed to deal with the power instability caused by load quantity variations.Efficient energy compensation strategy based on driving speed adjustment is used to resolve the problem of too low charging power.Emergent charging requirement control strategy is introduced to provide more power for individual EV.Double-transmitting coil structure and corresponding power control strategy are employed to avoid the phenomenon of charging power drop when receiving coil is in the middle of two adjacent transmitting coils.Experimental platform of the WPT system is finally set up,based on which theoretical analyses of system working performance and load characteristics are validated.