Research On Wide Gain Magnetic Integrated Three-Phase LLC Resonant Converter

In order to make LLC resonant converter suitable for wide gain range applications such as charging piles,a wide gain magnetic integrated three-phase LLC resonant converter is put forward.Based on this,the magnetic integration of three transformers in the converter is carried out to improve the power density.Firstly,the main circuit topology of wide gain LLC resonant converter is introduced,and the advantages of it are highlighted.Based on the principle of half bridge LLC resonant converter,the working process is introduced.The simplified working circuit and waveform are given.The working process of each stage is analyzed in detail.The revelant working mode of stage charging is given.Then,the fundamental equivalent model of the converter is established,the equivalent resistance and model of four modes are analyzed,and the gain is summarized.The influence of resonant parameter changes on each mode and the switching between modes is analyzed in detail,and the gain curves of the proposed converter are compared with the traditional three-phase LLC resonant converter which is symmetrically connected with Y-Y type.At the same time,the selection method of switching points between modes is given,and the switching conditions are designed.A parameter design method for wide gain applications is proposed,and the parameters are rationally designed.In order to solve the problem of the large volume of magnetic parts caused by the expansion of the phase number to three phases of the converter,a five-pillar structure is proposed to integrate three transformers.Firstly,according to the working mode of the circuit,the magnetic flux direction is analyzed,and then the magnetic circuit model is established,and the integrated transformer and independent transformer are designed.Using Ansys to simulate the transformer,the results show that the magnetic flux density distribution of the integrated transformer is uniform,which meets the design requirements.The prototype of the independent transformer and the five-pillar integrated transformer are made respectively.Finally,Psim simulation is performed according to the designed converter parameters.which verify the validity and the feasibility of wide gain topology.The experimental platform is built,and the wide gain range of 0.45～2.1 can be achieved by mode switching,and it works in the frequency band of 57 k Hz～150k Hz.The experimental results show that the converter can achieve a wide gain range in a narrow operating frequency band.By magnetic integration of the three-phase transformer,the volume of the transformer is reduced by 12%,which effectively increases the power density of the converter and improves the efficiency of the converter in mode 3.There are 64 figures,6 tables and 57 references in this paper.