Design And Research Of Full Bridge Three Level DC/DC Converter

DC converters play an important role in the fields of new energy generation,DC transmission,and industrial equipment power supply.Due to the advantages of flexible modulation strategies,low voltage stress of a single switch tube,and low total harmonic distortion rate of the voltage waveform at the midpoint of the primary bridge arm,three-level structures have attracted much attention in the field of DC transmission.This article takes the full bridge three-level DC/DC converter as the research object,with the aim of ensuring the safe and stable operation of the converter.Firstly,the working principles of a full bridge three-level DC/DC converter in two-level mode and three-level mode were analyzed.To address the issue of duty cycle loss,a mathematical expression between duty cycle loss and converter system parameters is derived.At the same time,Fourier decomposition was performed on the midpoint voltage of the original bridge arm of the full bridge three-level DC/DC converter in three-level mode,and the duty cycle corresponding to the minimum total harmonic distortion rate was calculated.Then,based on Buck converter small signal modeling and duty cycle loss expression,a full bridge threelevel DC/DC converter small-signal modeling is established.Appropriate PI parameters are designed through Bode diagram,and the control effect of the double closed-loop control system is verified through simulation experiments.Secondly,the imbalance of the neutral point potential of the input side divider capacitor in a full bridge three-level DC/DC converter will lead to issues such as reduced converter efficiency,increased output voltage ripple,and transformer bias.In response to the issue of midpoint potential imbalance,this article adopts the method of pulse width compensation to adjust the power supply time of the divider capacitor,thereby achieving midpoint potential balance of the divider capacitor.The effectiveness of this voltage sharing strategy is verified through simulation experiments.Finally,the software and hardware design of the full bridge three-level DC/DC converter experimental platform was completed,and a clamp diode buffer circuit was added to the power circuit to suppress the voltage oscillation problem of the rectifier diode.By analyzing the voltage/current waveform of the FBTL DC/DC converter during stable operation,sudden load increase,and sudden load decrease,it is proven that the system can operate stably under complex working conditions.