Research On Constant Current And Constant Voltage Wireless Charging System Based On Changeable Resonant Circuit

With the proposal of the 14th Five-Year Plan,electric vehicles(EVs)have officially become a strategic emerging industry.At present,the power battery and its charging technology are important factors that limit the promotion of electric vehicles.Because of its safe power supply and strong environmental applicability,wireless power transmission(WPT)can eliminate the disadvantages of contact charging when applied to EV charging.However,the voltage of power battery varies widely in the charging process,as well as the equivalent impedance keeps rising.In order to ensure the safe and reliable charging process and slow down the battery loss and prolong the battery life,the charger usually adopts the output mode of constant current switching constant voltage to avoid constant current charging or constant voltage undercharging.This article starts from the conditions of constant input voltage and varying load,to realize the segmented CC-CV output of the converter by using open-loop control.And carry out the following research:Firstly,a loosely coupled transformer model is established.Based on the modeling and analysis of LCC-LCC and LCC-S compensation networks.And the output characteristics and energy efficiency characteristics of the two compensation networks are obtained by fundamental wave analysis.In addition,combine the two compensation networks based on the changeable resonant circut to obtain a hybrid compensation network,and the parameters of the compensation network are designed and optimized.This network has natural constant current or constant voltage output characteristics,which can realize the CC-CV output of the entire WPT system without introducing a closed-loop negative feedback link,and meets the requirements of input voltage and current zero phase(ZPA).Then,the hybrid compensation network is analyzed under abnormal conditions,such as secondary side missing,load open circuit,load short circuit and so on.The variation range of the current of the secondary receiving coil is given.When the current of the secondary receiving coil exceeds the normal value,the secondary compensation network is switched to protect the system,so as to gain time for the protection of the primary side shutdown and improve the reliability and safety of the system.Aiming at the circuit impact caused by the switching of variable structure mode,the switching sequence is optimized,and a control strategy to turn off the switch in stages through the current flow is proposed,which can enable the system to achieve smooth switching from constant current to constant voltage mode which can improve the stability and reliably of system operation.Finally,a 1.1kW experimental prototype is built with the main circuit and loosely coupled transformer of the system based on the hybrid compensation network.And the experimental results show that the system basically realizes CC-CV output in the range of load variation.During the switching process,the transient oscillation of the system is small,which verifies the rationality of the proposed control strategy.The voltage and current on the output side of the inverter are almost in the same phase.And the acquisition of ZPA characteristics is of great significance for improving efficiency and realizing soft switching.