Research Of Three-Level CLLC Resonant DC/DC Converter Based On SiC MOSFETs

At present,the bidirectional DC/DC converter is mainly applied to DC application scenario such as DC microgrid,electric vehicle,and uninterruptible power supply,and can be used as an important component of solid state transformers used in DC distribution networks in the future.The bidirectional DC/DC converter with excellent working performance and high efficiency has broad application prospects.This paper first expounds the research background,significance and current status of the research.Then introduces the reason for selecting the three-level CLLC resonant topology,taking into account the actual needs of the project and the complexity of theoretical analysis.Then,by using the fundamental analysis method to simplify the analysis of the converter,characteristics of the converter are intuitively obtained,which indicates the influence of resonant components.Next,the input impedance characteristics of the converter are analyzed,and the frequency range which can meet the conditions of soft switching is obtained.The analysis of the short-circuit output impedance and the no-load output impedance is then conducted.Finally,we get the ZVS/ZCS curve of the converter over the entire frequency range and under different load conditions,as well as the frequency range at which both the soft switching and boosting converter efficiency can be achieved.Secondly,the design and optimization of the parameters of each component in the three-level CLLC resonant DC/DC converter are studied.The design method of high-frequency transformer and resonant inductor is introduced in detail.The detailed process of designing the parameters of each component in the three-level CLLC resonant DC/DC converter is given.In addition,the above-mentioned design result is optimized to ensure that the converter can realize soft switching from light load to full load under both forward and reverse operating conditions,and has a good load dynamic adjustment performance.Finally,the simulation model and the physical platform based on SiC MOSFETs device are built strictly according to the proposed parameter design method.The simulation results and experimental results show that the converter has good steady state and transient response characteristics,whether it is working in forward or reverse operating modes.