Research On Analysis Method And Synchronous Rectification Strategy Of Bidirectional CLLC Resonant Converter

The target of carbon neutrality propels the development of electric vehicles(EVs)and new energy resources such as photovoltaic and wind power.In these applications,the bidirectional DC/DC converter plays a significant role,which is in charge of the energy bidirectional transmission.Thanks to the superiority of soft switching,the bidirectional CLLC resonant converter gains much attention.This thesis devotes to its topology analysis,design consideration,and synchronous rectification strategy.The motivation of this thesis is to clarify the characteristics of this converter and develop a set of parameter optimization of the resonant tank which can achieve high density and efficiency.The main contents are outlined as follows.First,the inherent relation between symmetrical and asymmetrical bidirectional CLLC resonant converters is explored.Through the equivalent transformations,it is found that the properties of symmetrical and asymmetrical bidirectional CLLC resonant converters are identical.Based on this finding,the quantitative relations of the resonant component parameters are derived.Then,taking the symmetrical one as an example,the basic principle is given.Besides,referring to the analysis approach of the conventional LLC resonant converter,this thesis exerts efforts to simplify the fundamental harmonic analysis(FHA)model of the bidirectional CLLC resonant converter.Using the simplified model and phasor diagram based analysis method,the voltage transfer gain and the necessary condition of zero voltage switching(ZVS)are investigated.In return,the converter performance is clarified,and the parameter design of the resonant tank becomes easy.Furthermore,a novel synchronous rectification strategy which combines the secondaryside current and the primary-side driver signals is proposed.Compared with the existing strategies,the proposed one only needs two current sensors,resulting in simplicity and lower cost.More importantly,it is suitable for all kinds of the bidirectional resonant converters.Moreover,the parameter design method of the resonant tank is presented.It is revealed that when the quality factor is large,the voltage transfer gain will inevitably become nonlinear,posing adverse effect on the closed-loop regulation.To address this issue,the constraints for monotonous voltage transfer gain are explored.Besides,based on the prototype parameters,the power loss of the converter is studied,to tell the converter efficiency.Finally,a simulation model of the bidirectional CLLC resonant converter is developed in PLECS,and a 10-k W prototype is built in the lab.The associated simulation and experimental results confirms the theoretical expectations.