Research On Fast Charging Control Strategy Of DC Charging Pile Resonant Converter

New energy electric vehicles solve the problems of energy shortage and pollution emissions;however,its development has been restricted dramatically by the slow development of electric vehicle charging technology in today’s fast-paced life.Conventional low-current constant-current charging will result in a long charging time.In order to reduce the charging time,DC electric current is usually used to charge electric vehicles.However,in the process of constant high current charging,polarization will occur due to gas evolution,which will cause great damage to the life of the lithium battery.In view of the above problems,it is of great significance to design a fast,efficient,and lossless lithium battery fast charging control system.In this paper,a high-power three-level LLC resonant circuit is used as the main circuit topology.Based on Maas’ s three laws,a variable pulse width positive pulse charging control method is designed.It has many advantages like fast charging speed,high efficiency,and no battery polarization.It meets the demand for non-destructive fast charging of electric vehicles.The specific research contents are as follows:Firstly,it analyzes the main content of the three laws of Mas,and analyzes the polarization phenomenon caused by the gas generated during the charging process of the battery and the method of eliminating the polarization phenomenon.Through the traditional constant current,constant voltage,three-stage charging method and the analysis of the impact of conventional fast charging methods on battery charging,combined with the requirements of fast charging,proposes a control method of variable pulse width positive pulse charging.From the theoretical analysis,it can be known that while this method accelerates the charging speed,it can control the suppression of the polarization phenomenon through the charging stop time and the changing charging time.Secondly,the control system of the DC/DC converter at the post-stage of the DC charging pile during fast charging was studied.According to the designed charging method,the half-bridge three-level LLC resonant converter is selected as the main circuit topology.This topology has the advantages of low voltage stress on the primary side switch tube,wide output power range,and small ripple current to meet high power.Requirements.In order to solve the problem of small voltage adjustable range when the resonant converter adopts frequency modulation control,a hybrid control strategy combining frequency conversion and phase shift is adopted,and the three-level converter under frequency conversion and phase shift control is modeled separately and used fundamental wave analysis method for characteristic analysis.In order to realize the stable output of constant current and constant voltage,a current and voltage double closed-loop controller is designed.Thirdly,a charging system model composed of a controller module,a phase shift angle processing module,a pulse module,a voltage outer loop and current inner loop module,and a PI controller was built in Matlab-Simulink to charge the proposed fast charging.The method is combined with PI algorithm for simulation,and the simulation results are compared with the constant current charging method to verify the correctness and effectiveness of the proposed positive pulse charging method with variable pulse width and a three-level resonant converter as the main circuit topology.Finally,the experimental platform of the three-level resonant converter was developed,the selection of the main circuit device,the calculation of the parameters and the design of the hardware circuit and software are given.Using TMS320F28335 DSP and host computer to achieve battery charge management,DSP and host computer through the serial port for data exchange.And designed for its hardware circuit and software.