Research On Resonant Asymmetric Half-Bridge Flyback Converter Based On GaN Switching Device

With the rapid development of consumer electronics,power adapters based on traditional power devices and converter topologies can no longer meet higher power density requirements.To solve this problem,optimizing the design of existing power adapters from the two aspects of power devices and converter topology is necessary.Because the resonant asymmetric half-bridge flyback converter combines the wide input and output range of the flyback converter and the soft switching operation characteristics of the LLC resonant converter,it can improve the work efficiency of the adapter and optimize the electromagnetic radiation level after it is applied to the field of the power adapter.Combined with wide bandgap semiconductor GaN switching devices,the advantages of low switching losses and low parasitic capacitance further improve work efficiency and power density.To realize the soft switching operation of the resonant asymmetric half-bridge flyback converter,the switching mode of the converter and the generation conditions of the primary side switch tube ZVS and the secondary side rectifier tube ZCS are analyzed in detail.The mathematical model of the soft switching process is established,and the relational expression between the negative excitation current amplitude and the input bus voltage of the converter is solved,as well as the expression of the dead time and resonance parameters,to obtain the negative excitation current conditions and dead time conditions of the soft switch under the wide input voltage of the upper tube Q₁.In order to broaden the resonant asymmetric half-bridge flyback converter,the indirect hysteresis current control strategy is introduced to realize the independent control of the output voltage and negative excitation current amplitude of the converter in the soft switching range under wide input voltage.This control strategy simplifies the current inner loop control system into a first-order system,and only a simple type 2 compensator is needed to realize the control compensation of the voltage outer loop.In the design of the hardware parameters,the output voltage ripple modulation effect when the resonant parameter ratio is too small and the maximum operating duty cycle limitation when the k value is too large are investigated to provide a theoretical basis for the design of the resonant parameters.At the same time,the design of GaN switching circuit is studied in depth.By connecting additional ceramic capacitors in parallel to the drain-source terminals of the GaN switch,the rise of the drain-source voltage is slowed down,thus optimizing the operation of the indirect hysteresis loop current control strategy.Finally,an experimental prototype platform with an output power of 75W is built and experimentally verified for the above theoretical analysis.The experimental results show that the power density of the prototype is 1.74W/cm³,the maximum working efficiency is94.1%,and the full-load efficiency is 93.9%.