Developmemnt Of Soft-switching DC-DC Converter With GaN Devices For Aviation High Voltage DC Power System

As the important part of aviation high-voltage dc power system,high-voltage dc-dc converters should have high power density and conversion efficiency.The use of GaN devices can increase the switching frequency and thus increase the power density of aviation high-voltage dc-dc converters.while achieving soft-switching for the GaN power devices can further improve the conversion efficiency.This thesis focuses on the soft-switching dc-dc converter with GaN power devices for aviation high-voltage dc power system.The characteristics of the current mainstream commercial high-voltage GaN power devices are presented and compared with Si MOSFETs,and the driver circuits and reverse conduction principles of the GaN power devices are presented.A boost converter with synchrounous rectifier is designed,and with which,the switching characteristics of GaN power devices operating under hard-switching and soft-switching conditions are tested.The experimental results show that the turn-on loss of the GaN power device is larger under hard-switching condition,and it is eliminated under soft-switching condition,leading to a high efficiency when operating at a very high switching frequency.The LLC resonant converter is a popular topology in medium-to-high power conversions thanks to the soft-switching of the power devices.The operating principle of the half-bridge LLC resonant converter is analyzed and the voltage conversion gain is derived.For achieving a high efficiency,the half-bridge LLC resonant converter is operated at fixed switching frequency and performs as a dc Transformer(DCX).A pre-regulator or a post-regulator is incorporated for regulating the output voltage.The configurations of the pre-regulator+DCX-LLC resonant converter and the DCX-LLC resonant converter+post-regulator are discussed,and the former is chosen as the aviation high-voltage dc-dc converters since it is suitable for the application with wide input voltage variation range.Two interleaved boost converters with synchronous rectifier is chosen as the pre-regulator for achieving soft-switching and reducing the input current ripple.With the aforementioned topologies,a 350-W prototype of soft-switching aviation high-voltage dc-dc converter operated at 500 k Hz is fabricated and tested in the lab.The experimental results are provided,and it is shown that all the power switches can achieve soft-switching,and the overall efficiency is high up to 94.64%.