Research On Transmission Characteristics And Control Strategy Of Wireless Charging System For Electric Vehicles

With advantages of convenience,reliability,safety and high intelligence,wireless charging technology has a broad application prospect in the field of electric vehicle charging.And dynamic wireless charging can realize electric vehicle charging in the process of driving,which is beneficial to reduce the battery pack capacity,shorten the charging time and improve the driving range effectively of electric vehicles.In this paper,the fluctuation of the output voltage and power of the wireless charging system for electric vehicles in the process of coils misalignment is studied.Firstly,the topology and working principle of the wireless charging system for electric vehicles are analyzed.Aiming at the wireless charging system using LCC-S compensation topology,the output characteristic equation is deduced and the influence of parameters such as mutual inductance and load on output characteristics is studied.Results show that the output power of the system is positively correlated with mutual inductance,and its rising speed is gradually accelerated with the increase of mutual inductance.With the increase of mutual inductance,the efficiency increases rapidly at first and then decreases slowly.In addition,when the system works in the resonant state,there is a load resistance under optimal efficiency.Secondly,the working principle of the wireless charging system powered by segmented rail coils is analyzed.Based on LCC-S compensation topology,variable parameter models in the single coil power supply mode and dual-coil power supply mode are derived,as the theoretical support of studying the constant power output control strategy.In order to reduce the fluctuation of mutual inductance in the process of coils misalignment,the magnetic coupling coils of the wireless charging system are designed based on the influence of coil structures and parameters on the coupling performance.Moreover,the characteristic of coils misalignment in the process of dynamic wireless charging is studied.Thirdly,aiming at the fluctuation of mutual inductance in the process of coils misalignment,the effective coupling region is studied in different power supply modes of rail coils.The results show that the single coil and dual-coil switching power supply mode has advantages in reducing the fluctuation range of mutual inductance,improving the setting standard of mutual inductance threshold and saving costs.A switching method of rail coils,which takes the intersection point of adjacent effective coupling region as the position point of rail coils switching,is proposed.And the switching control sequence of the rail coils is analyzed.Based on the variable parameter models of the wireless charging system and the method of switching rail coils power supply mode,the principle of the output voltage stabilization is analyzed.Accordingly,the single coil and dual-coil switching power supply control strategy and input voltage regulating control strategy are put forward,which realizes continuous power supply of rail coils and maintains stable output power of the system.Finally,based on the wireless charging system using LCC-S compensation topology powered by segmented rail coils,a MATLAB/SIMULINK simulation model is built to verify the output characteristics of the system.Moreover,the control scheme is optimized.An experimental prototype of 500 W wireless charging system is established to carry out the single coil and dual-coil switching power supply experiment.Results show that the output voltage and power of the wireless charging system can maintain around 100 V and500W,and the maximum fluctuation is always less than 0.64% of the target output.In the whole process of coils misalignment,the efficiency is always more than 86.55%.In addition,by comparing with results of the single-coil switching power supply experiment and the constant voltage input experiment,it is verified that the single-coil and dual-coil switching power supply control strategy and the input voltage regulating control strategy are feasible to achieve the efficient,continuous and stable output goal of wireless charging system.