Research On The High-voltage Full-brick DC/DC Power Module

As the promotion of distributed power supply system,DC/DC module supplies are widely used in many fields.The demands for high-power-density,high efficiency and high reliability module power supply is continuous growing,so it's of great significance to do research on high-performance,high-voltage,full-brick DC/DC power module.This thesis focuses on full brick power module with 200~400VDC input voltage and 28 VDC ouput voltage.A two-stage topology composed of Buck and LLC-DCX is adopted in this paper.The pre-stage Buck converters the wide input voltage to stable bus voltage and LLC-DCX with matrix transformer form to reduce secondary conduction loss is utilized to realize electric isolation and voltage transformer function.In this paper the smaller package MCU UCD3138 is used to reduce the size of control circuits.First of all,a detailed operation principle of cascaded topology is analyzed.And the small-signal models are established to designe the loop compensation function for the cascaded topology.Then the characteristics of UCD3138 and hardware design of control circuit are introduced.Combined with the features of UCD3138,the concept of multi-threading is used in the software,and the control program design based on finite state machine is proposed.Secondly,a new control algorithm with higher control accuracy and fewer peripheral circuits is proposed based on detection of the SR body-doide conduction time.For the influence of the LLC-DCX resonant component parameters and load variations on the resonant frequency,the resonant frequency tracking control is realized based on the relationship of the pulse width of the primary and secondary switch drivers under different switching frequency and resonant frequency,which can make LLC-DCX achieve high efficiency at all times.Finally,the main circuits parameters of full-brick DC/DC power module including device selection,magnetic cmoponents design and LLC-DCX dead time optimization design is completed.And a 1000 W full-brick prototype is designed in this paper,the experimental results are provided to verify the analysis and proposed control strategies.The efficiency of prototype can reach 95% at 200 V input voltage.