Design Of Planar Transformer Based On Three-level DAB Converter

Today,with the rapid development of electric vehicles,renewable energy generation and data centers,power converters has penetrated into every aspect of industrial development.Switching power supply technology plays a vital role in this,and with the development of the industry’s needs,nowadays,switching power converters are gradually developing rapidly in the direction of small size and weight and high power density.For isolated switching power converters,the transformer is an important component,which has always been assumed the role of voltage conversion,and at the same time occupies a large proportion of the volume and weight of the whole converter.Therefore,the miniaturization of switching power converters requires the planarization of their magnetic components.In this thesis,the planarized design of high-frequency transformers is investigated with a three-level Dual Active Bridge(DAB)converter.Also,this thesis uses the leakage inductance of the transformer instead of an individual power inductor in the circuit to enable the power transfer of the converter.The details of the full thesis are as follows:Firstly,the thesis describes in detail the circuit structure of the three-level DAB converter and analyzes its operating principle.Based on the specific waveforms of each operating mode of the converter,the inductor-current segmentation expressions are derived and used to obtain the power transfer characteristics in each switching cycle,and then the typical control strategy of the three-level DAB converter is presented.Finally,the circuit simulation of the three-level DAB converter is performed.Then,the equivalent circuit of the actual transformer is modeled,and its key distribution parameters and operating losses are analyzed and calculated.On this basis,the theoretical calculations and comparisons are performed for different planar winding layouts.The electromagnetic simulation of four typical winding arrangements was carried out using Maxwell 3D electromagnetic simulation software to extract the leakage inductance data.The simulation results match the theoretical calculation results,which provides design directions for the implementation of the actual transformer.Then,based on the actual technical parameters of the three-level DAB converter,a planar transformer is designed that focuses on the selection of the core,the design of the primary and secondary windings including the number of winding turns,the design of the copper cladding alignment structure,the width of the copper cladding,and so on.The designed transformer takes into account the arrangement of primary and secondary windings and the spacing,so that the leakage inductance of the transformer can meet the actual application requirements.Finally,the designed planar transformer is subjected to the electromagnetic simulation of the actual working conditions.The simulation of the magnetic line circuit and the magnetic potential distribution cloud can be found that the planar transformer can work normally without the magnetic saturation phenomenon.An experimental prototype of a three-level DAB converter with planar transformers is built,and an experimental prototype with conventional Leeds line transformers is built for comparison,and the design of hardware circuits and control software is introduced.Through experiments,the effectiveness of the planar transformer designed in this thesis is verified.From the experimental results,it can be seen that the efficiency of the planar transformer circuit is better than that of the conventional transformer circuit at low power operating conditions,while at high power operating conditions,the experimental efficiency is slightly lower than that of the conventional transformer circuit,and the thesis gives the results of the overall loss distribution of the system.Combined with the electromagnetic simulation analysis,the efficiency at high power range is slightly lower than that of the conventional transformer circuit,which is caused by the increased value of the flowing current after the power level is increased,and the skin effect on the secondary winding near the center column of the core leads to an obvious increase in winding losses.It is possible to stagger the windings of different layers in the winding design,which can reduce the front-to-back area between the windings,thus reducing the skin effect and proximity effect.Ultimately,the size of the converter with planar transformers is reduced by30% and the power density of the converter is greatly improved.