Research On Soft Switching Characteristics And Loss Equalization Method Of Dual Half Bridge ANPC-DAB Converter

With the continuous development of new energy generation technology and more and more DC loads such as electric vehicles are connected to the power grid,the research on DC distribution network becomes more and more important.DC transformer based on DC/DC converter plays an important role as the core equipment in DC power grid.Dual active bridge(Dual Active Bridge,DAB)converter has become one of the most suitable DC/DC converters for DC transformer due to its high power density,bidirectional flow of energy and fast control speed.In order to improve the withstand voltage capability of a single converter and optimize the loss distribution of the converter,a half bridge ANPC-DAB circuit is constructed based on the active neutral point clamped(active neutral point clamped,ANPC)three-level circuit.The soft switching characteristics of ANPC-DAB are analyzed in detail,and the loss equalization control method of ANPC-DAB is deeply studied.This paper first describes all the switching states of ANPC-DAB.By analyzing the influence of zero level switch state switching on the soft switching distribution,the conditions for all 12 switches to realize zero voltage switching(zero voltage switching,ZVS)are obtained.On this basis,a modulation method which can effectively improve the switch loss distribution is proposed.By establishing the loss estimation model of the converter,this paper analyzes the loss characteristics of ANPC-DAB for the proposed modulation algorithm,and compares the loss characteristics of ANPC-DAB with that of DNPC-DAB,and verifies the effectiveness of ANPC-DAB loss equalization algorithm.Then,in order to realize the high efficiency operation of ANPC-DAB converter,.In this paper,the working characteristics of ANPC-DAB with dual phase-shifting control are analyzed in detail.The expressions of transmission power and current stress in each power mode of ANPC-DAB are derived,and the soft switching characteristics of ANPC-DAB under dual phase-shifting are analyzed in detail.Thirdly,in order to further optimize the efficiency of ANPC-DAB converter,this paper studies the current stress optimization strategy of ANPC-DAB under dual phase shift modulation.Two kinds of soft switching modes are considered in the current stress optimization strategy: one is to make all switches work in ZVS state,the other is not forced to work in ZVS state.Combined with the loss analysis of ANPC-DAB converter,this paper proves the effectiveness of the two optimal control strategies.Finally,the ANPC-DAB experimental platform is built to verify and compare the loss equalization algorithm and current stress minimization control strategy.The experimental results show that the ANPC-DAB loss equalization modulation algorithm can significantly improve the loss distribution;in terms of efficiency,the current stress optimization of non-full-soft switching can achieve the highest efficiency in the full power range.Finally,it is proved that the proposed comprehensive optimization method which combines ANPC-DAB loss equalization method with current stress optimization of non full soft switching can make the converter realize the balanced distribution of loss when realizing efficient operation.The research results of this paper will provide a theoretical basis for the design of high efficiency and high power density DAB converter,and have a very important engineering significance for the application of DAB converter in DC transformer...