Research Of Magnetically-coupled Resonant Electric Vehicles Wireless Power Transfer System

With the popularization of Electric Vehicle(EV),battery charging becomes the main limiting factor for its development.The use of large-sized charging piles will take up much urban land in cities,and it will have a great impact on the power grid.EV charging has a new choice with the advent of Magnetic-coupled Resonant Wireless Power Transmission(MCR-WPT).At present,the domestic and foreign researchers had carried out research on the Magnetic-coupled Resonant Electric Vehicle Wireless Power Transfer technology,mainly for the design of coupled coil and circuit topology optimization,which obtained lots of results.However,there are still many problems to be solved,such as the optimization of coupled coil,and charging instability casued by coupled coil offset while EV parked.In this paper,the optimal design of coupled coil and the problem of charging instability were studied.First of all,this paper analyzed the mathematical model of the EV’s WPT system by magnetic coupled mode theory,and found out the influence factors of transmission efficiency.Four basic resonant compensation topologies of SS,SP,PS and PP were analyzed by circuit resonance theory,the SS topology was selected to be the optimal resonant topology for the topic.Then the type of high frequency inverter circuit was compared and the full bridge inverter was selected to be the most suitable type of high frequency power supply for MCR-WPT system.And the system model was simulated by PSIM.Then,the coupled coil was designed and optimized with Matlab and ANSYS tools,separately from four aspects: the shape of coil,quality factor Q,geometry parameters and the structure of magnetic core.In order to solve the problem that EV’s unstable charging caused by the shift of the energy receiving coil on EV’s stop charging,a solution based on the PLL oforiginal voltage and current fundmental wave was proposed to track the resonant frequency of system,so as to maintain the maximum transmission power under the condition of high transmission efficiency.Then the phenomenon of coil offset was simulated by ANSYS and the above solution was verified by PSIM.Finally,the coupled coil device was made and the experiments platform was built based on the theoretical analysis and simulation results.The system tested in the open loop and the closed loop respectively: The transmission power and charging efficiency when receiving coil shifted the optimal transmission distance(axial deviation);Transmission power and charging efficiency when receiving coil under different level offset.The experimental results showed that the system had a high transmission efficiency at the optimal distance,which proved the rationality of the coil design.At the same time,the system could maintain high transmission power and charging efficiency under frequency tracking,which proved the feasibility of PLL based on the original voltage and current fundmental wave phase.