Research And Design Of High Frequency Bidirectional DC/DC Converter Based On GaN HEMT

Power electronic semiconductor devices,as the core of electrical energy conversion and transmission,play a vital role in new energy generation,electric vehicles,and power supplies for electrical and electronic equipment.Traditional silicon-based MOSFET devices are approaching the physical limit,while wide bandgap semiconductor devices have many advantages such as high frequency and high efficiency,high temperature resistance,and radiation resistance.GaN HEMTs have been widely used in power supply systems such as fast charging sources,LIDAR,and consumer electronics.But GaN HEMT device structure and drive requirements are diverse,the threshold voltage is low and the switching frequency is high,easy to introduce bridge arm crosstalk straight-through risk,and voltage and current oscillation problems,while the turnon loss is large,dynamic onresistance fluctuations will lead to efficiency degradation and other problems,so we need to optimize the drive design,improve the switching characteristics test,the use of soft switching to reduce switching losses.At present,commercial high-voltage GaN HEMTs can be divided into monolithic enhancement type and Cascode type from device structure,among which monolithic enhancement type includes Schottky gate type and pGaN ohmic contact gate type.Unlike the voltage drive characteristics of Si,SiC MOSFETs and other GaN HEMTs,the pGaN ohmic contact gate type GaN HEMT device studied in this paper has a unique structure and needs to be driven by a current source,so the previous voltage drive scheme is no longer applicable.In this regard,the main research contents of this thesis are:(1)From the analysis of the structure of high-voltage 600V/650V GaN HEMT devices,the structural characteristics and driving requirements of each GaN HEMT device are explained in depth,focusing on the device structure of pGaN ohmic contact gate type GaN HEMT,the suppression of dynamic on-resistance fluctuations and the optimization of the current driving design scheme.(2)Two GaN HEMT drivers are designed,and then the switching characteristics and driving effects of the high-voltage GaN HEMT are tested by doublepulse experiments,the test platform and PCB layout wiring are optimized,and the comparison experiments with 650V SiC MOSFETs verify the advantages of faster turn-on speed and smaller turn-on loss of the improved current-driven GaN HEMT.(3)Finally,two quasi-resonant synchronous rectifier Buck/Boost converters based on SiC MOSFET and GaN HEMT are designed to achieve CRM operation by increasing the inductor current pulsation and capturing the inductor current past zero point,constructing ZVS and ZCS soft switches,while greatly reducing the switching instantaneous voltage and current oscillations.In addition,synchronous rectification reduces the through-state loss and improves the conversion efficiency to around 90%.Based on the characteristics of GaN HEMT device structure,the optimized current driver can meet the driving requirements of pGaN ohmic contact gate type GaN HEMT and achieve nanosecond switching,while the negative voltage shutdown GaN HEMT can effectively suppress the risk of half-bridge crosstalk misconduct and avoid half-bridge direct short circuit.And from the device's double pulse test can be seen,compared to SiC MOSFET,GaN HEMT switching speed is faster,optimize PCB layout wiring to minimize parasitic parameters,can reduce power loop oscillation.The high-frequency bidirectional synchronous rectifier Buck/Boost converter operating in CRM mode can realize ZVS turn-on and ZCS turn-off continuity tube,effectively reducing the reverse conduction loss and switching loss,and efficiently transferring the power conversion to the load side.