Research On CLLLC Resonant Converter Of Bidirectional On-Board Charger

With the advantages of zero emission,low noise and sustainable development,the electric vehicle industry has developed rapidly under the encouragement of national policies.In more and more occasions,on-board charger need to realize the reverse discharge of lithium batteries as an energy storage system based on the realization of traditional charging functions.This kind of on-board charger has a wide application space to realize the bidirectional power transmission.The on-board charger is generally composed of a front-stage PFC circuit and a post-stage DC/DC converter.In the bidirectional on-board charger,the research on the topology of the post-stage DC/DC converter has become the focus,which requires comprehensive consideration of the requirements of high efficiency,high reliability and high power density.After comparing various topological structures of bidirectional DC/DC converters,it is finally confirmed that the topology of bidirectional CLLLC resonant converter is used as DC/DC converter.The CLLLC resonant converter evolved from the LLC resonant converter.By adding an LC resonant circuit on the secondary side,it can realize bidirectional power transmission,and has the excellent characteristics of bidirectional buck-boost and soft switching.Firstly,this paper analyze the soft switching characteristics and losses of clllc resonant converter;then the working state of the converter in the sub-resonance region,resonance point,and super-resonance region is studied,and the steady-state model of the converter is established by using the first harmonic approximation method,and the influence of the parameters of the resonant network on the gain characteristic curve is studied;finally,the driving circuit of the converter and the working characteristics of the forward and reverse operation under the pulse frequency modulation are simulated and analyzed,and the complete design scheme of the converter system hardware circuit and digital control is given.According to the previous design,a 3.3kW experimental prototype is made and debugged.In forward operation,the input voltage is between 390 V and 410 V,and the output voltage is between 250 V and 420 V.The reverse operation is exactly the opposite of the input and output voltage in forward operation.The final experimental results show that the peak efficiency of the prototype in forward and reverse operation can reach 97.52% and97.73% respectively,and the full-load efficiency is greater than 96%.The experimental results verify the feasibility of the design method of the bidirectional CLLLC resonant converter proposed in this paper.