Research On Bidirectional CLLLC Resonant Converter

The bidirectional DC/DC converter is an interface converter between different systems or in the same system,which can realize electrical isolation,wide buck-boost ratio and control energy bidirectional flow,and its application is more and more extensive.In the context of vigorously promoting the concept of green and efficient,it is very important to improve the efficiency and power density of the bidirectional DC/DC converter.This paper combines the characteristics of bidirectional DC/DC application scenarios and the advantages and disadvantages of bidirectional DC/DC converter topology,and chooses to study the bidirectional CLLLC resonant converter.Firstly,the forward and reverse working principle of the converter is analyzed.The fundamental frequency analysis method is used to study the resonant frequency,gain characteristics and impedance characteristics of the converter.It is found that the symmetry of the resonance parameters can not only ensure the consistency of the forward and reverse characteristics of the converter,but also enable the converter to inherit the gain characteristics,impedance characteristics and soft switching characteristics of the LLC resonant converter in the full load range on the forward and reverse directions.The converter has good parameter tolerance when the resonance parameters are symmetrical to ensure the consistency of the forward and reverse characteristics of the converter.Secondly,the constraints of the design of the resonant parameters of the converter are analyzed.From the perspective of gain,frequency modulation range and efficiency,the limiting conditions of the designing the magnetizing inductance,the conditions for the zero-voltage turn-on of the switching tube and the influence of the normalized important parameters on the converter design are analyzed.Starting from the full load maximum gain point of the converter,the light load minimum gain point and the soft switch implementation conditions in the full load range,a complete resonance parameter design scheme is proposed.Based on this,the selection of each component in the experimental converter is completed.Finally,the converter is simulated and experimentally verified to complete the forward and reverse working principle,gain requirement,soft switching characteristics and verification of symmetry and tolerance under full load and light load.The soft start strategy of the converter is studied.Three different soft start methods are proposed and the feasibility of these methods is verified by simulation and experiment.