Optimization Design And Analysis Of DAB-type DC Converter Considering The Loss Characteristics

With the complication of the power grid and the deficiency of the ability to accept new energy and the deficiency of two-way interaction ability and the deterioration of the power quality,it will be the tendency for smart grid to build energy internet which based on the flexible DC distribution network.Especially the AC&DC hybrid distribution network with a lot of the new "source","grid" and "charge" has become an important direction for future distribution network construction.As The key component of the distribution network equipment,the traditional transformer which realizes isolation,energy transfer and other basic functions by iron core.But its poor controllability and compatibility,which is far from meeting the requirements of the hybrid AC and DC distribution network in the future.Therefore,a highly controllable power electronic transformer becomes the coordinated control electricity distribution network.A high-frequency DC-DC converter module is implemented as a high-frequency power electronic transformer isolation,the key unit of energy transfer and transforming voltage levels has become a hot topic in the present research.Dual active bridge(DAB),which is the most widely used in high frequency DC converter,with modular symmetrical structure and bidirectional power flow capability,better controllability,soft-switch can be realized easily and other advantages,DAB can be directly used as the interface circuit between different voltage levels in DC distribution network,In this paper,the principle of power transmission and system loss of DAB-type DC converter has been analyzed in detail under single phase shifted control,and established the steady-state loss model.considering the mismatch between the high frequency transformer ratio and the input and output voltage variation caused by the system loss under the condition of the constant input and output voltage of the system.optimization design the actual ratio of high-frequency transformer to imporve the efficiency of the system.First of all,the topology and working principle of DAB-type DC converter are analyzed,The mathematical model of the current waveform and power transmission of the converter is established under the traditional phase shift control,a detailed analysis of the various stages of DAB in steady working condition,power generation principle and realization condition of reflux soft switch.The power back-flow problem and the realization condition of soft switching by traditional phase shifting are also studied.Then the principle of the loss of each part of the DAB-type converter system is analyzed,The calculation method of the loss of the system is derived,and various factors affecting the efficiency of the transformer are found out.The design flow of various parameters of the high frequency transformer and the selection method of material are given.For the establishment of the experimental system provides a theoretical basis.Finally,considering the loss of the system,an efficiency optimization method is proposed,the most advantages of the system in various operating conditions are found and the overall efficiency of the system is improved by adjusting the actual ratio of the high-frequency transformer under the condition of certain transmission power.The 10 kW dual-active bridge DC converter experimental device is built,which verifies the accuracy and feasibility of the proposed loss model and optimization method.