Research On Dual Active Bridge DCX Converter Based On UI Core Magnetic Integrated Transformer

Due to the advantages of high frequency,high efficiency,high power density,bidirectional energy flow and simple symmetrical circuit structure,dual active bridge(DAB)converter is widely used as the intermediate stage of solid state transformer(SST),which is mainly used for voltage conversion and electrical isolation.Under simple single phase shift(SPS)control,DAB converter usually works in DC transformer(DCX)mode with relatively fixed voltage conversion gain.Due to the voltage fluctuation under SPS modulation,DAB converter is prone to the loss of light load soft switching.Therefore,this paper considers using transformer excitation inductance to inject excitation current to help broaden the full load soft switching.However,compared with the traditional double active bridge converter,the auxiliary widening method adds an inductance.Therefore,on this basis,this paper further proposes a magnetic integrated transformer structure based on the standard UI core,which integrates the leakage inductance and excitation inductance into the transformer,reduces the number of magnetic components and reduces the volume of the magnetic components of the converter.The main research work and innovations include:1)Aiming at the loss of light load soft switching under SPS modulation,the injection of excitation current is considered to assist in realizing zero voltage switching(ZVS)in the full load range of the switches.By analyzing the working mode,soft switching conditions and transmission power characteristics of DAB converter with excitation inductance;The results show that compared with the traditional double active bridge converter,the circuit structure based on excitation inductance widens the ZVS region of the full load range.At the same time,on this basis,the parameters of magnetic components of DAB converter are designed preliminarily.2)A magnetic integrated transformer structure based on standard UI core is proposed,which integrates the leakage inductance and excitation inductance of DAB converter.This paper analyzes the advantages and disadvantages of the traditional EI core integration scheme,and through the magnetic circuit analysis and deduction,combined with its magnetic circuit model,proposes to use the UI core to integrate the leakage inductance and excitation inductance of the transformer.Finally,taking the DAB converter based on the excitation inductance of the transformer as the carrier,the magnetic integration parameters of its magnetic components are designed.The structure has the following advantages: a)reduce the number of magnetic components,reduce the volume of the converter system and improve the power density;b)Using 6-layer PCB to make magnetic integrated planar transformer has less layers and reduces the cost of multilayer PCB;c)There is no need for special customization of the magnetic core,and the standard UI magnetic core is easy to obtain.3)Based on PCB winding magnetic integrated planar transformer,an experimental prototype of dual active bridge DCX converter with rated360 V input and 360 V / 800 W output is designed.The experimental results show that the proposed magnetic integration scheme can effectively realize the integration of magnetic components of the converter,and can realize the steady-state operation and full load range ZVS of the converter.