Design Of Vehicle-assisted DC-DC Converter For Electric Vehicle

In order to solve global problems such as energy shortage,excessive carbon dioxide emissions and air pollution,the boom of research,development and application of electric vehicles has arisen worldwide.The vehicle-mounted auxiliary power supply(vehicle-assisted DC-DC converter)is an indispensable component of the electric vehicle,and it takes power from the high-voltage power battery to the low-voltage battery to meet the power demand of the vehicle low-voltage equipment.In this paper,a 1.5kw car-assisted DC-DC converter prototype is developed based on the design of vehicle-assisted DC-DC converter.The power density level of existing products was investigated.The advantages and disadvantages of several common topologies were introduced.The Boost+LLC two-level topology,which is easy to optimize efficiency in a wide range of input voltage applications,was chosen to design the converter.According to the design indicators,the parameter design of the main components of the converter was carried out.In addition,in order to meet the output ripple requirements and improve the power density,a CLC-type output filter is designed in combination with circuit network analysis and practical applications.The Boost control circuit based on L4981A and the LLC control circuit based on L6599D are designed,and the Psim simulation model is built to verify it.A three-layer structure is designed.In order to improve the power density,an aluminum substrate is used as the power board,and the flow-through copper strip is added to increase the flow-through capability.The structure of the CLC filter is optimized.For the application scenarios of low-voltage and high-current output,a multi-layer copper-stacked transformer secondary winding structure is designed.The experimental waveform of the prototype is given to verify the feasibility of the scheme.In order to further optimize the efficiency,the loss of the converter is analyzed in detail.The loss is divided into static loss and dynamic loss are discussed.The conduction loss of the LLC converter is divided into two cases of operating in the under-resonant region and operating in the over-resonant region.In estimating the core loss,the effects of square wave excitation and DC offset are considered.In addition,other losses that cannot be ignored in actual operation are estimated and modeled.The effectiveness of the estimation model is illustrated by comparing the estimation results with the measured efficiency of the prototype.