Research On Automotive Auxiliary DC-DC Based On High-efficiency Power Device

With the depletion of energy and the rise of the global temperature,electric vehicles have become one of the best ways to solve this problem,so electric vehicles have developed rapidly in recent years.Automotive auxiliary DC-DC converters,as bridges for high-voltage power batteries and 12 V batteries and low-voltage equipments in electric vehicles,has continuously improved its convertion efficiency and power density.Although increasing the switching frequency can increase the power density of the converter,traditional silicion devices limit their higher switching frequency due to their own characteristics.Highefficiency power devices—GaN and Si C have significant advantages in improving the power density of automotive auxiliary DC-DC converters due to their advantages such as small parasitic parameters,fast switching speed,and small switching loss.This article first introduces the structure,components,working principle of the power system and characteristics and topology structure of the auxiliary DC-DC converter on the electric vehicles.By comparing several common topologies,Buck + LLC is selected as the main circuit topology.GaN power devices are selected as the power switching devices of the automotive auxiliary DC-DC converters studied considering the development of wide bandgap semiconductor materials—GaN and Si C and the advantages over Si materials.The LLC resonant converter is the core component of the converter,so the topology and working principle of LLC resonant converter are analyzed in detail.Mathematic model based on fundamental harmonic analysis is established to analyze the influences of the quality factor Q and the inductance k on the DC gain,as well as the constraint conditions for the converter to achieve ZVS in the full load range.The high-frequency transformer design also directly affects the efficiency transmission of the converter.Therefore,the high-frequency transformer is designed according to the area product method(AP).Although GaN power devices have the advantages of fast switching speed,small onresistance,and small parasitic parameters,GaN power devices have the disadvantages of narrow gate turn-on voltage range and low gate threshold voltage.In high-frequency operation,the existence of parasitic parameters is not conducive to the design of the driving circuit.Therefore,the effects of high /,/,common mode current,and parasitic parameters on the driving circuit of GaN power devices are discussed in this article,and corresponding solutions are given.Finally,a automotive auxiliary DC-DC converter with a power of 1.5k W,an input voltage of 210 V ～ 480 V,an output voltage of 12 V,and a switching frequency of 100 k Hz is designed.Firstly,the correctness of the design parameters and the reliability of the driving circuit design of the GaN power device were verified by LTspice simulation software.Finally,the rationality and reliability of the design were verified by experiments.