Research On Three Phase LLC Resonant Converter Based On Magnetic Integration

With the increasing number of electric vehicles,the demand for charging piles based on high-power,high-efficiency,and high-power density DC / DC converters is increasing.The three-phase LLC resonant converter has good soft-switching characteristics as a DC /DC converter and is widely used in charging piles.In order to improve the applicability of three-phase LLC resonant converter in charging pile,a three-phase LLC resonant converter based on magnetic integration technology is proposed in this paper.By magnetic integration of three transformers and three resonant inductors in the converter,the efficiency and power density of the converter are further improved.The specific work is as follows:Firstly,the topology and working principle of the three-phase LLC resonant converter are introduced,and the nine working modes of the converter are introduced in detail by analyzing the on-off state of the switch tube.The relationship between the number of parallel phases of the LLC resonant converter and the output current ripple is described,and the influence of the connection mode of the converter on the current sharing when there is a difference in the resonant components,highlighting the superiority of the three-phase LLC resonant converter.Then,based on the fundamental wave analysis method,the equivalent model of the three-phase LLC resonant converter is derived.After analysis and calculation,the voltage gain formula and voltage gain curve of the converter are given,and the related factors affecting the voltage gain are analyzed in detail.At the same time,by analyzing the influence of the working frequency of the converter on the resonant network,the working range of the converter is determined,and the parameters of the three-phase LLC resonant converter are designed.Secondly,aiming at the problem that there are too many magnetic components in the traditional three-phase resonant converter,which is not conducive to the lightweight and portability of the converter,the magnetic integration technology is proposed to integrate the transformer and the resonant inductor in the converter.According to the working mode of the converter,the magnetic flux distribution in the magnetic core is analyzed.The results show that the magnetic integration technology can reduce the volume and weight of the magnetic core and reduce the loss of the magnetic core.Then,the magnetic circuit models of integrated transformer and integrated inductor are established respectively,and the magnetic core,winding diameter and air gap size of the two are designed.At the same time,their losses are analyzed.In order to verify the performance of the integrated transformer and the integrated inductor,ANSYS Maxwell software is used for simulation comparison.The results show that the magnetic flux distribution of the magnetic core after magnetic integration is more uniform and the overall magnetic flux density is lower than that of the discrete magnetic core.According to the design parameters,discrete and integrated transformers and resonant inductors are fabricated respectively.Finally,the three-phase LLC resonant converter is simulated,and the rationality of the parameter design is verified by analyzing the simulation results.According to the working voltage,working current and other parameters of the converter,the appropriate components are selected and the main circuit,sampling circuit and driving circuit are designed to complete the construction of the experimental platform.The prototypes using discrete magnetic components and integrated magnetic components were tested respectively,and the experimental waveforms were given.The results show that the efficiency of the converter based on the magnetic integrated structure is generally higher than that of the converter based on the discrete magnetic components in the whole load range,which further verifies the superiority of the magnetic integrated converter.