Reasearch Of CLLLC DC Power Conversion On EV Charger

New energy vehicles have developed rapidly in China.The number of new energy vehicles has reached 2.61 million in 2018.According to estimates,the cumulative energy storage of electric vehicles reached 230 GWh,while China's electrochemical energy storage is only 4.3 GWh.New energy vehicle's energy storage is becoming more and more important.How to design high-character and reliable bidirectional charging machine is an important issue.This topic focuses on the design of bidirectional charging machine.This dissertation focuses on the CLLLC topology for theoretical analysis,simulation analysis and make prototype to carry out research.The theoretical study of CLLLC converter.The formula of voltage gain is derived through model analysis,different voltage gain characteristic curves are drawn.The voltage gain is influenced by different parameter is obtained.The specific resonant working model of the three regions in the converter is established,thus the working area of the converter is determined.By establishing the design method of the main circuit parameters about the resonant cavity,the transformer's ratio,resonant inductor and resonant capacitor are designed.The specific circuit parameters are simulated by b uilding the CLLLC circuit model in Saber software.The soft switch characteristics,resonant current,and zero current switch are verified and analyzed in the positive and reverse mode.These characteristics are consistent with theoretical analysis.By using the extended description function method,the large signal model and small signal model of the CLLLC converter are established.The transfer function about the output voltage against the input voltage and frequency is further derived.The compensation design of the loop is completed through PID regulation,the design of the loop is satisfied.Finally,the experimental platform is set up to complete the design,mainly including transformer,resonant inductor s,resonant capacitors,main circuit,driving circuit,sampling circuit and other hardware circuits.The circuit adopts PFM control.Through simulation and experiments,This CLLLC prototype has the advantages of good positive and reverse soft switching characteristics,good symmetry and high efficiency,which is consistent with theoretical analysis.