Study Of Key Technologies Of GaN Based Very High Frequency Resonant Flyback Converter

Increasing the switching frequency of power converter is the most direct way to improve the power density,but the switching loss of traditional power converter in high frequency applications is too large.Very High Frequency（VHF）resonant converters can achieve soft switching,which greatly reduces switching losses.GaN devices have low conduction losses,fast switching speeds,and high upper frequency limits,which can further improve the efficiency and power density of the converter.Therefore,GaN based VHF resonant converter has become a research hotspot in the field of power supply.In this paper,the optimization and design of GaN based VHF resonant flyback converter are carried out,and the key technical problems such as the design method of converter parameters,the optimization of magnetic components and the improvement of controller are studied.Firstly,the parameter design methods of Class Φ₂ and class E VHF resonant flyback converters are studied.Flyback converter is mainly composed of inverter and rectifier.Different types of flyback topologies lie in the difference of inverter parts.For the Class Φ₂inverter,due to the secondary resonance network,the impedance of corresponding parameter design has high-order term.Therefore,the parameter design method of Class Φ₂ inverter is studied and deduced from the perspective of frequency domain.In contrast,the structure of Class E inverter is relatively simple,and the resonant components corresponding to the secondary resonant network are removed.Therefore,the parameter design method for Class E inverter is studied and deduced from the perspective of the time domain.For the rectifier part of the flyback converter,when the time-domain equation derivation method is used,more parameter assumptions are required and a unique solution cannot be obtained by numerical analysis,so the accuracy is low.In order to improve the design accuracy,the rectifier parameter design method based on numerical scanning method is studied.Finally,a prototype model is built in ltspcie and verified by experiments.Although the PCB air-core transformer has effectively improved the power density and efficiency of the VHF converter,it cannot be adjusted later after the structure is fixed.Therefore,the precise design method of the PCB air-core transformer is studied next.Based on the improved Wheeler formula to calibrate the initial value range of the transformer,the model of the transformer is built in the finite element simulation software,and the precise design of the air-core transformer is realized in combination with the design goals.In addition,a magnetic integration method is proposed,which directly integrates the resonant inductor of the rectifier in the form of leakage inductance in the air-core transformer to further reduce the number of magnetic components and increase the power density.When the switching frequency reaches more than tens of MHz,the realization of soft switching directly determines the stability and efficiency of the converter.Therefore,an ON/OFF control technology suitable for the realization of soft switching of VHF converters is studied.When the converter is in the ON state,the converter is in the best working state to achieve soft switching and the output voltage rises.When the converter is in the OFF state,the converter stops working and the output voltage drops.The ON/OFF control method completes the closed-loop control of the converter while ensuring the realization of the soft switching of the power transistor.Finally,the prototype of 10 MHz、10 W Class Φ₂ VHF resonant flyback converter and 30MHz、15 W Class E VHF resonant flyback converter are built respectively.The Class Φ₂ VHF resonant converter achieves the full load efficiency of 77.4%,and the Class E VHF resonant converter achieves the full load efficiency of 83.1%.The validity of the above theory is verified.