Design And Optimization Of High Frequency High Efficiency High Power Density Planar Transformers

With the rapid construction of data centers around the world,their large amount of energy consumption has become a problem that cannot be ignored.In recent years,the performance of wide-bandgap semiconductor devices continues to improve;the study of soft switching topologies is gradually used in commercial products.As a result,the switching frequency can be increased to reduce the size of the passive components,thereby increase the power density of the converter and provide a fresh approach to the development of next-generation data center power architecture.In this paper,we will discuss in detail how to improve the power density of converters based on gallium nitride(GaN)devices and LLC resonant circuit topologies.At first,this paper introduces the principle of LLC resonant converter,analyzes the advantages of its soft switching operating characteristics.The voltage gain characteristics are deduced to determine the operating state suitable for the converter designed in this paper.On the basis of the simulated,all components of the converter are selected and the losses of each part of the converter are calculated in detail to determine the high frequency transformer design target.Next,this paper discusses the problems faced in the design of high frequency planar transformers.Skin effect,proximity effect and fringing effect on winding losses are analyzed in detail,and corresponding design principles are proposed.Different winding layout lead to different AC parallel via hole number and different terminal structure.The optimal winding layout was selected.On this basis,the traditional planar transformer is optimized and designed to obtain the optimal structure.In view of the deficiencies of the traditional planar transformer,this paper proposes three different transformer structures to increase efficiency and power density,which are fractional-turn planar transformer,matrix planar transformers and integrated matrix planar transformer.The principles of each transformer structure are introduced,and detailed optimized design for each structure is developed.A general comparison is made to select the best solution for the converter designed in this paper.At the same time,a universal design process for high frequency planar transformers has been developed.Finally,a 1-MHz 400V/12V 500W LLC converter with GaN devices using the proposed planar transformer structure is demonstrated.The prototype achieves a peak efficiency of96.8%and full load efficiency of 95.9%with a power density of 327W/in~3,verifies the feasibility of the universal design process for high frequency planar transformers.