Research On Load Characteristic Of The Electric Vehicle Wireless Charging System

Under the background of global fossil energy continuous depletion and deterioration of the environment, electric vehicles have a rapid development because of its environmental protection, energy saving and low carbon. Wireless power transmission (WPT) technology is a new way for EVs’ charging. Compared with conventional hard-wired charging system, wireless power transmission technology are safer, reliable, flexible and many other advantages, which enjoys promising market application.The goal of the paper is to get a high efficient and stable power supply of WPT system. Build an electric vehicle wireless charging system based on the research of the load characteristic of Lithium iron phosphate battery; and the prototype system achieves a high efficient charging of lithium battery. The main content in the paper can be summarized as follows:Firstly, summarizes the implementation of WPT technology; and expounds the current research situation of electric vehicle wireless charging technology at home and abroad. Some current problems are also pointed out.Secondly, the SS topology of transferring efficiency was established for the EVs wireless charging system with technology of magnetic coupled resonance which is based on the theory of mutual inductance. Meanwhile, optimized analysis was carried on for the parameters of coils. The results of different types of loads accessing were also analyzed.Thirdly, focusing on the time-varying parameters of load during the charging period of EV, a series of research and analysis were carried on about loads’ characteristics (including SOC, open-circuit voltage, external equivalent resistance) based on the lithium iron phosphate battery. The accurate model of battery was established based on the results of research. A control strategy of frequency tracking and compensation was proposed based on the changing load, and the strategy was proved by the simulation model.Lastly, a set of prototype EV’s wireless charging model was built with Li battery load. The high-frequency power supply was full bridge inverter structure, which can realize the function of frequency modulation and phase shifted. The chip CD4046 was employed to realize frequency tracking; BOOST-BUCK circuit can regulate the voltage which can make the power supply of Li battery stable. Wireless charging experiments were done to validate the optimized charging range and the output waveform of frequency variation validates the feasibility of the controlling method which is proposed in the paper.