Design And Optimization Of Mid-frequency Wireless Charging System For Electric Vehicle With Magnetic Resonance

Charging problem has an negative impact on the development of ElectricVehicle. Wireless charging for Electric Vehicle has become a hot research issue forits convenience, safety and space saving etc. This paper theoretically analyzes andsimulates the mainstream wireless charging system with magnetic resonance indetails. Different coil structure models are proposed, especially three-coil structureis first presented and validated by experiments in this paper. This paper has theintent of providing a design and analysis methodology for the innovative three-coilstructure systems.Firstly, with equivalent circuit model, this paper analyzes the chargingcharacteristics of different coil structures. Characteristic parameters such as powerand efficiency are deduced. Enlightened by the conventional two-coil and four-coilstructure, I proposed the three-coil structure in this paper. Comparison shows thatthree-coil structure is more robust to the load variation and has lower EMFcharacteristics compared to the two-coil and four-coil structure.Low power test bed consisting of software and hardware are set up forvalidation. Considering the rapid progress of the power electronics technology,mid-frequency(300kHz-3MHz) are adopted, which is a little higher than theconventional frequency range of wireless charging for Electric Vehicle. Class-Dinverter consisting of H-bridge FET driver and MOSFET can switch at frequency upto1MHz. Planar coils are closely wounded with Litz wire. Low-loss film capacitorsare adopted as the resonant capacitors. Four low forward voltage diodes consist thebridge rectifier. DSP F28035Controller designed can generate high-resolution PWM signal. Switching frequency can be adjusted and DC bus current of the inverter isdisplayed in the interface complied by Labview.Using low power test bed, combined with the theoretical analysis of efficiency,power, and coil misalignment, this paper performs the comparison experimentsbetween the two-coil structure and three-coil structure. Power and efficiency aremeasured by changing the load, transfer distance and misalignment conditionrespectively. The results of experiment show that the system set up in this paper canachieve the maximum efficiency of80%with50W at the distance of50mm(0.7times coil diameter). The efficiency can be improved more by increasing the powerlevel, because the loss portion of power electronics can be decreased.In summary, three-coil structure are more robust than the two-coil structurewhich means it can achieve higher efficiency within the load variation. Besides,under coil misalignment, the EMF can be reduced.