Research On Multilevel Flying Capacitor Bridgeless Pfc Converter Based On GaN Device

Switching-mode AC/DC converters are widely used in modern power supplies for computers,data centers and tele-communication equipment.Achieving Power Factor Correction(PFC)and high efficiency are the two most important requirements.in many cases,high power density is also an important indicator to measure the performance of converters.Both power efficiency and power density are greatly influenced by the power devices,the topology and the control used.GaN totem-pole bridgeless PFC converters have simple circuits and low conduction losses,and GaN devices have excellent performance such as zero reverse recovery loss,low switching losses,and drive losses,making it become the most efficient PFC converters available today.However,to maintain high efficiency,the converter’s hard switching frequency must be lower than 100 k Hz,which limits the reduction in converter volume and the increase in power density.This paper introduces a multi-level structure into the totem-pole bridgeless PFC,and proposes a five-level flying-capacitor bridgeless PFC converter that allows th use more cost-effective low-voltage GaN transistors.First,this article analyzes the topological structure and working principle of a five-level bridgeless PFC converter,compared with GaN totem pole bridgeless PFC converter,this topology has the advantages of lower device cost,reduced voltage stress and high effective switching frequency,Therefore,while maintaining high efficiency,the converter greatly reduces the volume of the main inductor and EMI filter inductor,thus improving the power density.Secondly,the five-level topology brings challenges to PFC control due to the increase of additional flying capacitance and the reduction of main inductance.In this paper,the small-signal modeling of the current loop and the voltage loop is used to analyze the effect of multilevel parameter changes on the dynamic performance of the system.At the same time,a part of feedforward control is introduced for the input current zero-crossing distortion caused by small inductors.The influence of feedforward control on system performance is analyzed,partial feedforward control eliminates the current phase shift caused by the inductor,and improves the distortion of the input current waveform;and the rationality and feasibility of the control strategy are verified by MATLAB simulation platform.Finally,according to the converter design requirements,the hardware circuit parameters and key circuits are designed,and a 1.6k W five-level flying-capacitor bridgeless PFC converter prototype is produced to verify the analysis and design.The experimental results show that the prototype has excellent performances such as high efficiency,high power factor and low input current THD.