Research On Control Strategy Of Bidirectional LLC Resonant Converter

In recent years,with the rapid development of electric vehicle technology and the increase of the total reserves of electric vehicles,V2 G technology has developed rapidly,realizing the rational allocation of energy through the energy interaction between electric vehicles and the power grid.Therefore,it is necessary to study the bidirectional DC/DC converter in two-stage bidirectional on-board charger.The complex working conditions of V2 G require bidirectional DC/DC converter to have the ability of wide gain adjustment range,but the LLC resonant full-bridge converter is difficult to achieve wide gain adjustment range and maintain good working performance under the traditional control mode.Therefore,based on LLC resonant full-bridge topology,this thesis proposes a hybrid control strategy that combines frequency conversion control and pulse width control,which can realize soft switching in a wide voltage range and improve the overall efficiency.Firstly,this thesis analyzes the operation mode of LLC resonant full-bridge converter under frequency conversion control and pulse width control,and establishes a mathematical model for the converter through fundamental wave analysis,and obtains the corresponding voltage gain characteristics.At the same time,aiming at the problem of low gain of LLC resonant full-bridge converter in reverse transmission,the reverse gain is improved by changing the turn-on sequence of the switch on the rectifier side,and the principle of reverse boost is briefly analyzed.Then,the fundamental wave analysis method is used to establish the mathematical model,and the corresponding DC voltage gain function is obtained.Then,according to the voltage gain characteristic curve obtained from the modeling,the hybrid control design is carried out,and the working principle of LLC resonant full-bridge converter under the proposed hybrid control mode is analyzed,and the parameters of LLC resonant structure are optimized,so that the LLC resonant full-bridge converter can maintain good dynamic and steady performance when the voltage variation range is wide.Based on the development of a prototype of LLC resonant full-bridge bidirectional DC/DC converter,the proposed hybrid control strategy is experimentally verified.The results show that the converter can operate efficiently in a wide voltage range under the control mode proposed in this paper,and has good reverse boost characteristics.