Research On Three-phase Star-connected Bidirectional CLLC Resonant Converter

With the continuous development of electric vehicles and distributed power generation technologies,car chargers that can achieve bidirectional flow of energy have become one of the current technical development directions of the electric vehicle industry.The LLC resonant converter in the bidirectional DC-DC converter family,because of its excellent characteristics of natural soft switching,can better meet the technical requirements of high efficiency and low EMI of the bidirectional vehicle charger.However,the traditional LLC resonant converter does not have the ability to reverse boost,which limits the use of bidirectional car chargers.At the same time,a larger output current ripple requires the use of multiple filter capacitors at the output,which reduces the reliability and power density of the product.In view of the above problems,after a variety of topological comparisons,this paper selects a bidirectional CLLC resonant converter as the basic topology.Based on the traditional LLC resonant converter,this topology adds a resonant capacitor to the secondary side,thereby achieving bidirectional buck-boost under soft switching conditions.In order to reduce the output current ripple,this paper introduces the interleaved parallel technology into the bidirectional CLLC resonant converter,and proposes a three-phase star-connected bidirectional CLLC resonant converter.Thanks to the self-current sharing capability of the three-phase star connection,this topology achieves three-phase equalization of the total power on the basis of inheriting all the advantages of the bidirectional CLLC resonant converter,and the current stress of each phase switch tube is reduced to the original One third,effectively reducing the output current ripple.The specific content of the full text is as follows:First of all,this paper introduces the specific working process of single-phase CLLC resonant converter in detail,establishes the equivalent model of fundamental wave in forward and reverse operation,and draws steady-state gain curves under different Q values.Then,the forward and reverse DC gains of the converter are analyzed in detail,and the gain characteristics of high-frequency point gain less than 1in forward operation and greater than 1 in reverse operation are derived.Then,by analyzing the relationship between the interleaved parallel connection and the output ripple,and the effect of the resonance parameter difference on the output ripple,the three-phase star-connected interleaved parallel scheme was selected.Finally,the working process of the three-phase star-connected bidirectional CLLC resonant converter is introduced,and the parameters are calculated.Secondly,by analyzing the relationship between the proportional coefficient of the circuit and the DC gain,the coefficient value process is given,and then the resonance parameters and the resonance components of the main circuit are calculated and designed respectively.Then the design is developed around the control circuit,and the selection of the control chip and the hardware design of the sampling circuit and the driving circuit are completed one by one.Finally,according to the previously designed parameters,this paper builds a Simulink simulation and a 6.6KW experimental prototype.Both simulation and experimental results show that the three-phase star-connected bidirectional CLLC resonant converter can realize soft switching during forward and reverse operation,and has reverse boost capability,and the output current ripple is greatly reduced.