Research On DC-DC Converter With High And Wide Range Voltage Input

In secondary power supply,DC-DC converters with high voltage input and low voltage output are required in many applications.Especially in recent years,electric vehicles are stepping into people’s daily life at a faster and faster speed.In addition,there are special rechargeable vehicle ships such as national defense and military industry.Based on this application background,the DC-DC converter suitable for high voltage and wide range input is studied in this paper.Firstly,the working principle of the half-bridge three-level LLC resonant converter with medium-high power,high voltage and wide input range was analyzed in different modulation modes,and its DC output gain was analyzed by the First Harmonic Approximation(FHA).In order to provide a theoretical basis for the control scheme,the small signal AC model of the converter in FM modulation mode was established by using Extended Describing Function Method(EDF),and the feedback compensation network was designed.The auxiliary power supply of half-bridge three-level LLC resonant converter adopted dual-switch flyback topology.The reason of bad cross-regulation of dual-switch flyback converter was analyzed,and the approximate calculation method of cross-regulation value of output voltages and load of dual-switch flyback converter was concluded.A typical dual-output converter was modeled and analyzed with AC small signal.The voltage difference of load cross-regulation was distributed to each side circuit according to the weighted coefficient by using the method of weighted voltage control,so as to reduce the maximum voltage regulation value of all branches on the side and optimize the cross-regulation rate of the converter.Finally,the simulation model was built to verify the superiority of hybrid modulation strategy and the correctness of small signal modeling method for half-bridge three-level LLC resonant converter.An experimental prototype of 15W dual-transistor flyback converter was built.Combining with the simulation model,the reason why the cross-regulation rate of the dual-switch flyback converter becomes worse is related to the input voltage amplitude,and the rationality of applying the weighted voltage control strategy to the dual-switch flyback topology was verified.