Research On Two-stage DC/DC Converter With Wide Input And Wide Output Voltage Range For Aerospace Application

As an advanced space propulsion technology,the electric propulsion has many advantages such as high specific impulse and long life,widely applied in the fields of orbital transfer and deep space exploration.As an important part of the electric propulsion system,the Power Processing Unit(PPU)regulates the current generated by the solar panel,and supplies power to the electric propeller and other loads.The output voltage and output power determine the main performance of the thruster.This paper uses GaN transistor and develops a FSBB+LLC two-stage DC-DC converter.Firstly,for the requirements of wide input and wide output voltage range,high efficiency and high power density of aerospace power propulsion system anode power supply,this paper analyzes the working principle of the two-mode control strategy and dual modulation-single carrier control principle for two-switch Buck-Boost converter.In order to further reduce loss,a four-switch Buck-Boost converter is obtained by using the synchronous rectification technology.Secondly,this paper analyzes the two-mode control and soft-switching technology of the fourswitch Buck-Boost converter,and deduces the realization conditions of the soft-switch in detail.Then,we established small-signal models of the converter and adopted a voltage-current double closed-loop control strategy.Finally,the closed-loop parameter design is carried out to ensure the stability of the system in Buck and Boost mode.Then the paper analyzes the working principle of the LLC resonant converter operating in the DC Transformer(DCX)mode.Since the switching frequency is constant,it is beneficial to optimize the design of the resonant inductor and the transformer.And when the switching frequency is slightly lower than the resonant frequency,the ZVS of the primary side switching switch and the ZCS of the secondary side rectifier switch can be realized at the same time,so that the converter has high conversion efficiency.The simplified circuit of the converter is obtained by the fundamental component approximation method and the voltage gain function of the converter is derived.Finally,a prototype of a two-stage DC-DC converter with a switching frequency of 400 kHz and an output power of 600 W was built in the laboratory,using GaN transistor.And the experimental results were given,which verify the correctness of the above theoretical analysis.