SiC Modules Based Intermediate Frequency Isolated DC-DC Converter

With the rapid development of urban rail transit,the lightweight and high efficiency of auxiliary converters for urban rail vehicles has become a trend.High-voltage and high-power silicon carbide(SiC)devices have been gradually commercialized,and the power density and efficiency of auxiliary converters are expected to be further improved.Aiming at the core component of the intermediate frequency auxiliary converter,namely,the intermediate frequency isolated DC-DC converter,this thesis studies an input-series-output-parallel(ISOP)system composed of Boost converter + Full-Bridge LLC resonant converter cascade modules,and all SiC power devices are used to achieve the goal of higher efficiency and lighter weight.Firstly,the operating principles of the interleaved Boost converter and the Full-Bridge LLC resonant converter are analyzed.Based on the operating characteristics of the LLC resonant converter and the realization mechanism of soft switching,an optimization design method of the resonant parameters is proposed,which can make LLC resonant converters exhibit the characteristics of DC transformer(DCT)and realize soft switching in the full load range.Considering the power losses of the converter and the voltage stress of SiC MOSFET,the design method of the intermediate bus voltage is given.Then,based on the mechanism of the input voltage sharing and output current sharing for the ISOP system,it is deduced that input voltage sharing and output current sharing can be achieved through the intermediate DC bus voltage sharing.Based on the small-signal model of the interleaved Boost converter and the second-order simplified small-signal model of the Full-Bridge LLC resonant converter in DCT mode,the effects of mismatches in the individual moudle parameters on the voltage sharing of intermediate DC bus is studied.The results show that the mismatches in the individual moudle parameters has little influence on the intermediate DC bus voltage sharing,the ISOP system composed of Boost + DCT-LLC cascaded modules exhibits excellent ability of auto-balancing the input voltage and output current.And,the reliability and stability of the common-duty-ratio control strategy of the ISOP system are verified by simulation.Finally,the experimental prototype of auxiliary converter employing all SiC devices is developed to verify the theoretical analysis.The experimental results show that the ISOP system composed of Boost + DCT-LLC cascaded modules realizes the functions of electrical isolation and voltage regulation,and has good performance of input voltage sharing and output current sharing.At the same time,the intermediate frequency isolated DC-DC converter employing all SiC devices achieves the goals of higher efficiency and lighter weight.71 figures,13 tables,58 references.