Research On Parameter Optimization Design And Synchronous Rectification Based On CLLLC Resonant Converter

Bidirectional isolated DC-DC converters are widely used in new energy power generation,electric vehicle charging,aerospace power supply and other systems due to their high efficiency and high power density.CLLLC resonant converter,as a common topology of bidirectional isolated DC-DC converter,has excellent soft switching characteristics and a wide range of gains,and has been widely concerned by scholars.However,due to the large non-linearity of the CLLLC resonant converter,its parameter design is a difficult problem.For this problem,a parameter optimization design method is proposed to improve the parameter design of the converter;When the converter is running in forward and reverse directions,half of the switching tubes are always in the rectified state,and the rectification loss accounts for a large proportion of the total loss of the converter.To solve this problem,a CLLLC sensorless synchronous rectification method based on phase-shift angle feedforward is proposed to reduce the rectification loss and improve the converter efficiency.The main research work and innovation of this thesis are as follows:1)Aiming at the problem of the limited gain range of CLLLC resonant converter,the working principle of variable frequency control and fixed frequency control of CLLLC resonant converter is analyzed,and a hybrid control based on variable frequency and fixed frequency is proposed to extend the gain of the converter.The hysteresis interval is set at the control switching point to prevent the converter from frequently switching the control mode near the switching point.2)Aiming at the difficult parameter design of CLLLC resonant converter,the influence of the parasitic capacitance of the switch tube on the soft switching range is analyzed,and the resonant parameters are adjusted by the transformer equivalent calculation model to make the actual characteristics of the converter closer to the theoretical characteristics.The parameter design of the device proposes a parameter optimization design method.3)Aiming at the problem that the rectification loss of the CLLLC resonant converter accounts for a large proportion of the total loss,this thesis proposes a CLLLC sensorless synchronous rectification control method based on phase-shift angle feedforward,which can achieve effective synchronization without increasing hardware costs to improve the efficiency of the converter.4)A 5k W experimental platform was built,and the correctness and effectiveness of the parameter optimization design method and synchronous rectification method were verified through the experimental platform.