Research On Efficient Control Method For Synchronous Rectification Of LLC Resonant Converter

With the development of new infrastructure,data centers have been deeply and widely used in my country.But at the same time,the huge energy consumption of the data center has brought a huge burden to the environment,so how to reduce its energy consumption and improve the energy conversion efficiency has become a top priority.The soft switching characteristics and magnetic integration technology of LLC resonant converters meet the requirements for energy consumption and power density in the DC/DC power supply link of data centers.In order to further improve the energy conversion efficiency of highfrequency LLC resonant converters,this paper focuses on the synchronous rectification control of high-frequency LLC resonant converters.This thesis firstly introduces the topology structure and working mechanism of LLC resonant converter.The system is mathematically modeled by the fundamental analysis method（FHA）and its voltage gain curve is deduced.By analyzing the conditions for realizing ZVS,the dead time is optimized.In order to improve the overall efficiency of the system,the synchronous rectification control strategy is selected for the secondary side rectifier circuit,and the synchronous rectification scheme based on the drain-source voltage is selected through comparison and analysis.In this thesis,a synchronous rectification control scheme with phase compensation of drain-source voltage is designed,so that the on-duty ratio of the switch tube after compensation is close to the actual on-duty ratio.Considering the switch-off delay problem in the actual circuit,the proportional coefficient m is introduced to adjust the compensation network to avoid overcompensation of the system,and the influence of parameter changes in the circuit on the duty cycle of the synchronous rectification drive signal is analyzed.Aiming at the characteristics of inaccurate output voltage and poor dynamic response of the traditional drain-source voltage clamp circuit,this thesis adopts a new clamp circuit topology that utilizes the conduction characteristics of MOS transistors.The clamped voltage in this topology can well follow the actual voltage and the output voltage oscillation is small.In this thesis,by optimizing the winding structure of the planar transformer,the parasitic parameters of the planar transformer are reduced,and the influence of the parasitic parameters of the planar transformer on the system performance is weakened.Finally,according to the design index of the target prototype,the resonant network parameter design,planar transformer design and auxiliary circuit parameter design of LLC resonant converter are carried out.Finally,the synchronous rectification control strategy is verified by simulation and hardware circuit experiments.