Research On Two-stage AC/DC Converter Based On GaN Device

The strategic development goals of carbon peak and carbon neutrality have placed new demands on the green and low-carbon transformation of energy.Therefore,the demand for high power density AC/DC converters with high efficiency is increasing.Aiming at the deficiencies of the existing two-stage converter,a digital-controlled two-stage AC / DC converter based on Ga N device is developed.The front stage adopts bridgeless totem pole PFC and the second stage adopts half bridge LLC.The converter has the advantages of high frequency,high efficiency and soft switching operation.Firstly,the mode analysis and mathematical modeling of the synchronous rectification BTP PFC converter based on Ga N device are carried out,and the modulation mode establishment and control system design are completed.The design of main circuit is completed based on the converter parameters.The PFC circuit and its control system are simulated and verified based on Simulink platform.Secondly,based on the mode analysis and fundamental wave analysis,the working principle and circuit gain characteristics of LLC resonant converter are studied,and the control system design based on PFM is completed.To solve the problem of impulse current during circuit startup,an improved hybrid mode soft-start control strategy combining PWM and PFM is presented.The gain adjustment range of LLC circuit is improved by using burst control strategy.With the introduction of synchronous rectification,the device loss of rectifier network is reduced.Based on the converter parameters,the main circuit design and its simulation is completed.Thirdly,the EMI filter circuit,soft start circuit,drive circuit and sampling circuit are designed.A filter algorithm combining SOGI with IIR filter is presented,which ensures the accuracy and immunity of sampling.Based on STM32F407 controller,the control system design of two-stage AC/DC converter is completed.Finally,a 200 W converter with 93.4% full load efficiency is built and experimental analysis is carried which verifies the design correctness of the two-stage AC/DC converter and its control strategy.