Research On High Step-down Ratio DC-DC Power Supply

With the continuous development of power electronics technology and the emergence of new high-voltage resistant power devices,high step-down ratio DC-DC power supplies have been widely used in military,medical,communications,etc..This article aims to design a DC-DC power supply with high step-down ratio for Drone power supply,and the DC-DC converter with high step-down ratio is studied.Firstly,LLC resonant converter is considered as the basic topology to be studied.Based on the fundamental wave analysis method and the time domain analysis method,the working principle and gain characteristics of the LLC resonant converter in the frequency conversion and phase shift control modes are analyzed,and the phase trajectory analysis method of the LLC resonant converter is introduced.Secondly,due to some simplification and errors in the fundamental harmonic approximation,a differential equation model based on numerical solution is used,in order to analyze the working principle of the LLC resonant converter more accurately,combined with the phase trajectory method.The resonance frequency operating point and below resonance frequency operating point are analyzed,and the accuracy and correctness of the differential equation model are verified by PSIM simulation.On this basis,the gain curve of the LLC resonant converter is revised to improve the analysis of the basic working principle.Afterwards,in order to achieve a high step-down ratio and high power conversion,several combined topologies of LLC resonant converters are analyzed and compared,the pros and cons of each topology and the difficulty of parameters design are evaluated.The best feasible solution is selected to achieve the design optimization and performance improvement of the high step-down ratio converter.On this basis,the parameter design of the converter is completed,at the same time,the design of the main circuit and the control circuit and the device selection are completed,and the simulation analysis is completed based on PSIM.Finally,a 8k W experimental prototype with input of 790 V,output of 48 V was built to verify the correctness of the theoretical analysis.