Research On 350W 270V/28V High Power Density Converter

One of the latest trend in aircraft power supply is high voltage 270 VDC power supply.It is rather probable that using the power supply to power the digital electronic controller.Therefore it is the urgent demand for the current major and project that to carry out the research on high voltage 270 V DC/DC converter of high reliability,high efficiency and miniaturization.In order to achieve the purpose of high efficiency,high power density,high reliability,low cost and to have the ability to operate normally with large capacitance load,this paper adopts LLC resonant converter as the main stage and does a lot of jobs as followed.Firstly,based on the characteristic analysis of the half-bridge LLC resonant converter,the influence of symmetrical and unsymmetrical structure on the multiplexed-output half-bridge LLC resonant converter is analyzed.The condition that the power of asymmetrical output unit needs to be less than or equal to the power of the corresponding symmetrical output unit is obtained.Secondary,small signal model of the converter is built to design the compensating network based on frequency characteristic analyzing.Thirdly,in the case of converter start-up or with large capacitance,two current limiting methods are studied.One is switch-controlled inductance method.One is frequency raising parallel current loop method.The switching frequency required to limit average current is first proposed by equivalent impedance method and the switching frequency required to limit transient current is deduced by phase plane method.Fourthly,in the view of the fact that the traditional auxiliary power supply has some problems such as big volume,heavy weight,EMI noise and low reliability,this paper improved traditional self start-up circuit and a low-loss start-up circuit that can restart is designed.Fifthly,two types of loss of the converter is analyzed.One type is the loss relative to temperature,the other type is the loss having nothing to do with temperature.The theoretical value of the loss is calculated.The theoretical efficiency curve is calculated and the experimental efficiency curve is tested.Then,the optimization direction of the improvement of efficiency is pointed out and verified by theoretical calculation.At last,a 270VDC-28 VDC,rated power 350 W aviation converter prototype is designed.The efficiency is 94.81%,the power density is 2.3W/g and 65.1W/in3.