Research On GaN Based Single Stage Isolated Bi-directional AC-DC Converter

Compared with silicon-based devices,the characteristics of low gate charge and low on-resistance caused by the high critical electric field of GaN are the main factors for achieving high efficiency and high power-density.This makes GaN widely concerned in high-frequency applications below 650 V such as photovoltaics and electric vehicles.Aiming at the single-stage isolated bidirectional AC-DC converter topology which can be used in OBC systems,this article researches GaN and its key technologies applied in the structure.Aiming at the cascade system composed of single-phase totem pole PFC and bidirectional converter,an isolated single-stage bidirectional AC-DC converter is proposed through bridge arm multiplexing,which reduces the number of switches.The intermediate bus voltage is converted according to the absolute value of the sine wave,and the bus does not need a large electrolytic capacitor to stabilize the voltage,which realizes a single-stage energy conversion and is beneficial to improve the power density of the converter.The modulation scheme,working mode,and output power characteristics of the integrated converter are studied.Combining the modulation scheme,the current time-domain expression of the converter at each time and the power transmission characteristics in each mode are derived,and the soft switching(ZVS)condition of the converter is analyzed,and deduced the control parameters needed to achieve the widest range of soft switching.Based on the optimized control parameters and closed-loop control objectives,an open-loop PFC closed-loop control scheme without inductor current detection is proposed,which reduces the cost and control complexity of the converter to a certain extent.Then,the main components and experimental prototype design were carried out,and the switches parameter selection,inductance,leakage inductance design,transformer design,rectified bus capacitor design,DC side bus capacitor design was completed,and the Altium Designer 3D equipment technology was used to build based on the modular GaN half-bridge test prototype.Finally,the characteristics of the proposed topology are verified,and the forward power transmission characteristics of the converter are mainly verified.And from the perspectives of GaN drive scheme design,layout optimization,reverse conduction voltage drop suppression,and heat dissipation treatment,the key technologies in GaN applications are studied.