The Study And Design Of Wide Input Range Isolated DC-DC Converter

With the development of the defense and the industry,the demand for standardized DC-DC module is increasing.How to achieve high efficiency and high power density of power modules under high voltage/wide input,low voltage/high current output operating conditions is the main design challenge of current power module.The review of literature show that the main the acture employed in the power module can be divided into two types:single-stage and two-stage.The single-stage structure has the advantages of simple control,low cost,high power density.However,it is difficult to meet the requirements of maintaining high efficiency over a wide input voltage range.The two-stage converter is composed of a voltage-regulated converter and an efficiency-optimized isolated converter.It has the better dynamic performance and the higher output voltage accuracy.However the two-stage converter has more passive components.It is difficult to achieve high power density.Aiming at the design specifications,after evaluating the traditional converter,the single-stage two-phase interleaved half-bridge isolated DC-DC converter is proposed in this thesis.The proposed solution can reduce the input current,output voltage ripple and improve the power capacity of the converter.Furthermore,the full-bridge synchronous rectification is employed,which can greatly reduce the conduction loss of secondary side.After that,this thesis foucs on how to achieves the high efficiency and high power density of the power module with high voltage/wide input and low voltage/high current output.Firstly,the paper introduces the operation principle of the proposed interleaved parallel half bridge DC-DC converter and designs the parameters of the power stage.Based on this,the loss analysis of the converter is finished,which provides a theoretical basis for the efficiency optimization of the converter.At the same time,the influence of leakage inductance for the transformer in the practical application is discussed,and the simulation verification is carried out,which provides theoretical guidance for the design of the active clamp circuit.Then,aiming at the spike and oscillation issue for the secondary synchronous rectifier,a novel active clamp circuit is proposed after compraing traditional active clamp circuits.Its operation principle is introduced in detail and the implementation of its control circuit is given.On this basis,the parameters of the proposed active clamp circuit are designed.The simulation comparison illustrates the effectiveness of the propode active clamp circuit.Next,according to the requirements of the current sharing between the multiple power modules in parallel,the operation characteristics of the power module in parallel are analyzed.After comparing and analyzing the the commonly used current sharing methods,a current sharing control strategy is proposed based on automatic current-sharing approach.According to the control block diagram of the current sharing strategy,the hardwre current sharing circuit is designed.Finally,full-brick power modules with wide input voltage of 200-400V and output of28V/1200W were built.The experimental results show that the active clamp circuit can effectively elimilates the spike and oscillation of the synchronous rectifier and improve the reliability of the circuit.The measured results show the efficiency is above 94.5%at the rated input voltage and full load output,and in the full input voltage range,the efficiency can be maintained above 93%.The power density is about 217.39W/in~3.Under eight module power supplies in parallel condition,the current sharing error is less than 8%.