Development Of High Power Density And High Efficiency Power Module For Aerospace Based On GaN Devices

With the development of society and the increase of science technology,human demand for space exploration and scientific research has also increased.Electric propulsion technology with high specific impulse and high load has emerged at the historic moment.The Power Processing Unit(PPU)is responsible for converting the electric energy generated by the solar panel into the energy required by the electric thruster,and it is one of the most important components in the electric propulsion system.PPU has the characteristics of wide input and wide output voltage range,and has to meet the requirements of high efficiency and high power density.The input-output isolation is also needed.Therefore,the DCX-LLC resonant converter is selected and the two-stage architecture using preregulator + LLC is determined.After comparing common buck-boost converters,the DSBB converter is chosen.In order to achieve high efficiency and high power density,the DSBB converter is improved into an interleaved parallel FSBB converter.Finally,an interleaved parallel FSBB + LLC resonant converter is proposed as the solution for PPU.In order to improve the power density,the wide band gap GaN devices were used.This thesis introduced the principle and the classification of GaN devices.The turn-on and turn-off conditions for Cascode GaN transistor are given.According to the specific structure and parasitic parameters of Cascode GaN,the problems of divergent oscillation and failure to achieve ZVS are analysed.In addition,corresponding solutions are proposed and verified by simulation.In addition,the operating principle of the FSBB is analysed.This research uses a single carrier and dual modulation signals method to achieve smooth switching of two modes.Moreover,the operating principle of LLC resonant converter is analyzed.With the fundamental sinusoidal approximation approach,the voltage gain function and characteristics of the LLC resonant converter is derived.With reasonable parameter design,LLC resonant circuit works as DC Transformer.Based on the single module converter,a module parallel system with master-slave current sharing control is designed to increase the power level.In order to control output voltage,the control paramaters of the two-stage converter are designed.Moreover,regard of wide input and output voltage range,the failure of ZVS caused by excessive parasitic capacitance is analyzed.A method of decreasing four-element resonant period to reduce the effect of parasitic capacitance on ZVS is proposed.According to the theoretical analysis above,main circuit parameters are designed,devices are selected.Finally,a 1.2 kW power processing unit prototype and a two-module parallel system are fabricated and tested in the laboratory to verify the correctness of theoretical analysis.