Study On Single Phase Isolated High Efficiency AC/DC Converter

With the rapid development of information technology,cloud computing center construction,switching power supply technology and 5G business,the requirements of AC/DC converter efficiency and power density are higher and higher in medium and small power applications.The traditional AC/DC converter works in the hard switching mode,and the switching loss of the switching devices is large.At the same time,the heat sink and fan are added to the switching devices to increase the size of the power supply equipment.High frequency switching devices and soft switching mode are effective methods to achieve high efficiency and high power density of power supply equipment.In order to solve the shortcomings of traditional power supply devices,such as hard switching mode,high switching loss,low efficiency and large volume,this paper designs an AC/DC converter with full soft switching control based on GaN devices.The converter adopts two-stage circuit structure,and the front stage adopts totem pole bridgeless PFC as rectifier topology.The front stage rectifier converter works in soft switching mode by adjusting the control mode.The latter stage DC converter adopts LLC resonant converter,which is a hot spot topology in DC/DC converter field.Soft switching is realized by adjusting the switching frequency of the converter.Firstly,this paper analyzes the working mode and transient process of bridgeless PFC under TCM control mode,analyzes the realization method of soft switching of main switch under TCM control mode,and analyzes the working frequency characteristics of switch.According to the analysis results,the switch selection,input inductance design and output filter capacitor design are carried out.According to the theoretical analysis and design parameters,the control method is simulated in Simulink,and the simulation results show that in the input voltage range±The soft switching of the main switch can be realized within 20%,which verifies the correctness of the theoretical analysis.According to the design requirements,a half bridge LLC resonant converter is designed in the latter stage.The topology has the function of isolation while realizing the soft switching of switches.Through the analysis of circuit principle and harmonic network gain characteristics in a switching cycle,the resonant network parameters are designed according to the design requirements.The analysis shows that the synchronous rectification method proposed in this paper can realize the design of up to 250V synchronous rectification,which makes up for the blank of high voltage synchronous rectification scheme in the market.The resonant circuit is simulated by Simulink simulation software,and the simulation results verify the correctness of theoretical analysis and parameter design.Finally,the algorithm and signal detection circuit of two-stage power change digital controller TMS320F28027 are designed,and a 400W output experimental platform is built according to the hardware circuit design and software implementation scheme.The experimental results show that the design of GaN based all soft switching communication power supply device meets the design indicators,the overall efficiency is up to 96%at full load,and the power density is up to 3.3W/cm~3,which has high efficiency and power density.