Research Of High Efficiency DC/DC Converter

With the increasingly tense of energy consumption, efficiency becomes the most important issue for DC/DC converters in normal application. Lots of research work has been done to improve the converter efficiency. New topologies, soft switching and synchronous rectifier technology have been continuously raised.In this thesis, the state of the art of low power isolated DC/DC converter is reviewed. For 500W power rating, four promising DC/DC topologies are studied, including LLC resonant converter, ZVS phase-shift full-bridge converter, Boost-Half Bridge converter and Boost-LLC converter. According to the loss breakdown result, LLC resonant converter and Boost-LLC converter are preferred and selected to carry out further theoretical and experimental research.For LLC resonant converter, full range of soft switching can be realized inherently, thus high efficient is achieved. With the step-up characteristic, it can easily meet the wide input voltage requirement for DC/DC converter. In this paper, the pricinple of LLC resonant converter is deeply studied. An efficiency optimized design method and procedure are proposed. The impact of resonant parameter on synchronous rectification is also studied. A 400V input, 24V-20A output prototype is built and 96.9% high efficiency is obtained at full load.As two-stage converter, Boost-LLC converter gets high performance by making full use of its intrinsic properties. By optimized design, the efficiency boosted up in LLC stage can make up the efficiency brought down by Boost stage, so that an overall high efficiency can be achieved. The operating principle of Boost-LLC converter is introduced and an optimized design method is proposed. A 390V input, 24V-20A output prototype is built to verify its advantage and 97.2% total efficiency is achieved at full load, which is higher than single-stage LLC resonant converter.