Research On High Performance And Low Cost Flying Capacitor Multilevel Converter Based On GaN/Si Devices

With the extensive development of industrial,automotive and consumer electronics and the increasingly urgent requirements for energy conservation and emission reduction,people have a wide range of application requirements for power electronic converters with high efficiency,high power density and low cost.The performance of traditional silicon(Si)-based power devices in all aspects has approached the theoretical limit determined by its material properties,and it is difficult to meet the development needs of high power density and high efficiency power electronic converters.In recent years,third-generation semiconductors represented by gallium nitride(GaN)and silicon carbide(Si C)have played an important role in the efficient use of electrical energy.With its higher electron mobility and higher switching frequency than Si C,GaN has becom e the best choice for designing high power density and high efficiency converters.However,GaN devices are limited in their application at high er voltage levels and their commercial scale due to bottlenecks such as low voltage stress and high price.To th is end,this paper studies the hybrid application of Si-based devices and GaN devices,and combines GaN devices with multi-level technology,breaking through the application limitations and expensive bottlenecks of low-voltage GaN devices in medium and high voltage applications.The research work of this paper is mainly reflected in the following aspects.(1)Aiming at the bottleneck problem of hi gh price of all-GaN multi-level flying capacitor converters,a GaN/Si hybrid flying capacitor multi-level converter is proposed,and the topology principle and performance advantages of the proposed converter are analyzed in detail.and cost advantages.Th en,the electrical characteristics of the proposed converter are analyzed,and the AC side current ripple model and the flying capacitor voltage ripple model are established,which provides an important theoretical basis for the selection of inductance and flying capacitor in the later prototype of the converter.(2)Aiming at the problem that the natural balance time of the flying capacitor is too long,an active voltage balance control strategy of the flying capacitor is proposed.The principle of realizing the voltage balance of the flying capacitor by compensating the duty ratio is analyzed in detail,and the specific implementation scheme in the actual control is given.A variety of flying capacitor boost converter simulation circuits are built to conduct experiments.The simulation results show that the proposed control strategy can make t he voltage of each flying capacitor always follow the output voltage to change proportionally,and reach the target state at the same time as the output voltage.The dynamic balance of the flying capacitor voltage provides technical support for the later optimization of the operating performance of the GaN/Si hybrid multilevel converter.(3)Aiming at the single operation mode of the existing GaN/Si hybrid flying capacitor multilevel converter,the bidirect ional operation mode of the GaN/Si flying capacitor multilevel converter is proposed,which is divided into inverter mode and rectifier mode.Two operating modes.The operation principle and control strategy of each mode are analyzed in detail,and the sim ulation is built for experimental verification.The simulation results sho w that the proposed control strategy can make the converter work stably in two operating modes,and can well control the voltage balance of the flying capacitor.(4)A 3.3k W flying capacitor multilevel converter prototype based on GaN/Si devices was developed,and the inverter mode and rectifier mode were experimentally verified.The experimental results show that the con verter can work stably in two operating modes,which fully verifies the rationality of the converter prototype hardware circuit design and the feasibility of the control strategy.