Research And Design Of Phase-shifted Full-bridge DC-DC Converter

At present,the development direction of switching power supplies are soft switching technology,digital control technology and new power devices.The phase-shifted full-bridge converter has the advantages of simple structure,simple control and easy implementation,and is widely used in the topology of the vehicle charger.In this paper,a full-bridge DC-DC converter with multi-mode control is designed by using low-loss and high-temperature resistance of silicon carbide devices,combined with soft switching technology and digital control technology.In order to improve the stability of the system without adding additional auxiliary circuits,the converter adopts PWM control under light load,which simplifies the design requirements of the radiator.The research object of this paper is the phase-shifting full-bridge dc-dc converter.Firstly,the soft switching technology,new switching devices represented by silicon carbide devices and digital control system are introduced.The appropriate circuit topology and control mode are selected according to the design index,and the basic working principle of ZVS full-bridge converter is described,and the control strategy of the system is given.Secondly,the hardware design of the main circuit is completed,including high-frequency transformer design,MOSFET and rectifier diode selection,resonant inductance design,resonant capacitor selection,output filter circuit design,etc.The PSIM power electronic simulation software is used to simulate the main circuit parameters of the design,and the waveform of voltage and current of the switching tube is analyzed to verify the rationality of the design.The small-signal models of the full-bridge converter in different modes are established and the stability of the system is analyzed.Finally,according to the switching characteristics of silicon carbide devices,a negative voltage drive circuit is designed.Based on TMS320F28335 digital controller,the digital PI controller and digital filter are realized,and the software design is completed.In the experiment,the prototype of the full-bridge DC-DC converter with input 400 V and output 48V/25 A was tested and the experimental results were analyzed.The experimental results show that the full-bridge DC-DC converter based on silicon carbide device design can realize bipolar and phase-shifting control modes.The phase shift control mode under heavy load conditions can realize ZVS soft switching and improve conversion efficiency;bipolar control is adopted at light load,which reduces current and improves system stability.