Research And Design Of Bidirectional CLLLC Resonant Converter

The bidirectional isolated dc/dc converter can realize the bidirectional energy transmission between different DC voltages isolated from each other.It has the advantages of high efficiency and high power density,and is one of the core components of power supply system with energy storage link.In this paper,a 1k W bi-directional CLLLC resonant converter based on frequency modulation is designed based on the energy interaction between high voltage DC bus and low voltage energy storage battery.Firstly,the operational modes of the bidirectional CLLLC resonant converter are analyzed.The equivalent model of bidirectional CLLLC converter is established by using the first harmonic approximation.The voltage gain transfer function and the corresponding voltage gain frequency curve are obtained.The gain frequency characteristics of the converter are analyzed in detail.On this basis,the parameter design method of the bidirectional CLLLC resonant converter is given.The design of the converter includes the determination of the turns ratio of the transformer,the resonant components design based on ZVS condition.The parameters are verified by PSIM.Meanwhile,express the problem that the high current at the low voltage side causes the high loss of rectification,a kind of synchronous rectification strategy without sensor is adopted,that is,the switching time of the synchronous rectifier is judged by analyzing the voltage and current.This method improves the efficiency of converter without increasing the cost of hardware.In order to verify the correctness of the analysis,a 1k W bidirectional CLLLC converter with high voltage of 400 V and low voltage of 35V-50 V was manufactured in the laboratory.The power device was selected.high frequency transformer was designed and power switch drive circuit was designed.The experimental results show that the conversion efficiency is96% when the converter outputs 44 V during the 20 A constant current charging.The prototype experiment proves the feasibility and the correctness of the analysis of the working characteristics of the energy bidirectional flow in the bidirectional CLLLC resonant converter.Meanwhile,it is found that the stable output of 400 V is difficult to be realized under the conditions of input voltage of 50 V,under 50% load and input voltage of 44 V and under 20% load in discharge mode.Express the problem that the CLLLC converter is difficult to achieve low gain under light load,and other literatures mainly use the topology or hybrid modulation method of cascade post DC/DC converter to bring about complex control and high cost.The paper introduces new parameter design variables: inductance ratio h and capacitance ratio g,and solves the difficulty of realizing wide voltage range by parameter optimization design The new idea of the problem of high efficiency operation.The influence of h and g on the characteristics of the converter is discussed in detail.Based on this,the appropriate h value and g value are designed,and the resonance parameters of CLLLC resonant converter are further optimized.And through the experiment to verify.The results show that the converter can achieve low gain under light load.The working efficiency of the prototype is the highest under the condition of 50 V output voltage and full load,which is 95.1%.The feasibility of parameter optimization design is verified.