A Design Of Isolated DC/DC Converter For Fuel-cell

In recent years,with the rapid development of new e nergy automotive industry,the use of on-board power products is becoming more and more common.According to market research and development,the new energy automobile industry hopes that DC/DC converter(DC-DC converter)can work efficiently and steadily under the working conditions adapting to the wide range of input voltage changes because of its special application environment and load conditions.At the same time,the requirements of stability,efficiency,weight,volume and cost of the whole system fo r DC/DC converter are very strict.Therefore,it is very important to study high efficiency,wide input and wide output voltage DC/DC converters.Based on the 30 KW fuel cell bus project,a high efficiency,wide input and wide output voltage isolated DC/DC converter is studied in detail in this paper.Firstly,the output characteristics of fuel cell are studied,and the detailed requirements and design difficulties of fuel cell power supply and common power supply are analyzed.At the same time,through mar ket research,the shortcomings of non-isolation and low-power and low-voltage full-power output of existing products are summarized.Finally,the technical specifications of DC/DC converter for fuel cell are extracted.In order to realize high voltage isol ation,full bridge LLC resonant topology is adopted.The advantages and disadvantages of three different working conditions are summarized through theoretical analysis and simulation.At the same time,the common full bridge LLC resonant topology frequency conversion control has the problems of wide frequency transition and low efficiency when the voltage input is in a wide range.A fixed frequency control solution is proposed and its working principle is described in detail.In order to improve the service life of fuel cell,two optimal design schemes for Boost circuit and the problems caused by the two schemes are presented.Based on the advantages of the two schemes,multi-boost is proposed to further reduce the input current ripple.Finally,taking the traversing frequency,phase margin and gain margin as the parameters,the loop compensation parameters of the system are designed reasonably,and the output response characteristics of different load switching are verified by simulation to verify the ration ality of the parameters and the stability of the system.Under the guidance of theoretical analysis and simulation verification,an experimental platform is built to test the voltage and current waveforms and soft switching waveforms of the converter.The experimental results show that the product has high conversion efficiency and good working characteristics in a wide input voltage range.