Research On High Efficiency High Density CHB Single-phase PFC With GaN Devices

For space-constrained applications such as electric vehicles,data centers,and aerospace,high-power density and high-efficiency are required for converters.In recent years,multilevel PFC with gallium nitride devices has shown great advantages in terms of power density and efficiency.In the design process of the traditional multilevel PFC converter,since the loss model of the GaN device is related to its voltage stress,efficiency optimization requires calculation of losses for GaN devices for different voltage levels.Therefore,as the number of levels increases,calculations of switching losses become more and more complicated.In order to derive the unified loss model of the multilevel converter and simplify the design method,this paper proposes the minimum loss model of the GaN device in the multilevel converter based on NFoM(NFoM=C_osser*R_dson).With this unified device loss model,the tedious process,which requires repeatedly replacing device parameters with different breakdown voltages into the loss model and comparing the calculation results,can be avoided.The best efficiency with the level number as the independent variable can be directly obtained.According to this model,this paper provides the design method of the number of levels and the switching frequency under a certain efficiency.According to this method,a 2kW cascaded H-bridge?CHB?PFC prototype was constructed,achieving over 99%efficiency and more than 1000 W/in³ power density.The volume of the electrolytic capacitor of the intermediate DC bus is optimized,on the basis of the number of levels selected according to high efficiency.The theoretical minimum value of the bus capacitor volume is given as well.The comparison between CHB and two-level scheme in the volume of the bus electrolytic capacitor is analyzed.Since the common schemes for general AC/DC applications are composed of two stages:the front-stage PFC and the second-stage isolated DC/DC,the multiple low-voltage DC bus problems caused by CHB multilevel PFC can be solved by using isolated DC/DC.In view of the two-stage application situation,this paper analyzes the stability of commonly used control scheme under the two connection modes of input series output parallel?ISOP?and input series output serial?ISOS?.This paper gives the modification control method in terms of unstable conditions.Simulation is conducted to verify the analysis.