Design Of Llc Resonant Converter With Input Series Output Parallel Structure

DC/DC converter is an indispensable link in the field of new energy and electric vehicle.The LLC resonant converter has many advantages,such as high efficiency,high power density and low EMI noise.It has been widely used in various bi-directional DC/DC transform occasions.In order to meet the application requirements of input high voltage and output high current DC conversion,input series output parallel structure based on LLC resonant converter is proposed.The thesis paper is a detailed study of this topology.The AC equivalent model of LLC resonant converter with input series output parallel structure is established in the thesis.The relationship between DC voltage gain and normalized frequency is analyzed.And the influence of quality factor and equivalent load on voltage gain is analyzed respectively.A simulation model is built in MATLAB to verify its working process and soft switching.Because the circuit parameters of each module in the ISOP structure can not be exactly the same,the current sharing analysis is needed.After adding the flying capacitor,the voltage can be effectively balanced.But there is a spike current in the energy transfer process.Therefore,a double loop control method is proposed.First,the small signal model of a simplified single LLC resonant converter is used to derive the small signal model of the ISOP structure,and the transfer function of the control to the input voltage and output voltage is calculated.According to the control block diagram,the decoupling between two loop controls is proved.Specific parameters are substituted into the corresponding compensation network.The shortcomings of LLC resonant converter in light load state is studied,and the working process of intermittent mode is analyzed.The loss calculation method of the circuit system under this control mode is also proposed.By comparing and analyzing the advantages and disadvantages of different control strategies in burst mode,the corresponding improvement methods are proposed and verified by simulation.According to the characteristics and requirements of the work,the experimental prototype of the 1k W converter is built to test and analyze the forward and reverse operation.The soft start and load cutting experiments are carried out at the same time.Under the condition of light load,the control of burst mode is realized.