Design Of Planar Magnetic Integrated Transformer For High Frequency LLC Converter

Switching power supplies are widely used in various power electronic equipment fields.The development requirements of high efficiency,high power density,and high reliability determine the future development trends of switching devices,circuit topology,control technology,and magnetic components.The high-frequency LLC resonant converter has the characteristics of high efficiency and high reliability,and the magnetic element is the main factor that limits its volume and height.The design of the planar magnetic integrated transformer,using theoretical analysis and Maxwell 3D high-frequency electromagnetic field modeling and simulation methods,were carried out from the following three aspects:(1)Analysis and design of planar magnetic integrated transformer.First,the working principle of LLC resonant converter topology was analyzed,and the design method of high-frequency planar transformer was given.Secondly,the design scheme of the planar transformer was completed,and the rationality of the design method was verified through modeling and simulation.Then,through the comparison of the characteristics of various magnetic integration schemes,the two methods of side column decoupling integration and magnetic core combination integration were selected for theoretical design and modeling simulation,and it was determined that the magnetic core combination integration has easy inductance adjustment,low loss and the advantage of small leakage inductance on the secondary side,and that was further verified by the prototype test.Finally,the planar transformer grouping scheme was studied,and the research showed that the transformer grouping scheme has the effect of improving the space utilization ratio of the converter.(2)Optimized design of loss of planar magnetic integrated transformer.First,the core loss and winding loss were analyzed,and the theoretical model of winding loss was established using Maxwell’s equations.Secondly,this paper calculated and analyzed the winding loss of the one-dimensional transformer model under different winding structures,and through the high frequency electromagnetic field simulation analysis and comparison,it was determined that the parallel winding symmetrical staggered arrangement method can effectively reduce the winding high frequency loss.Finally,the influence of the air gap position on the transformer flux distribution and winding loss was studied,and the structure of the distributed air gap was optimized through modelingand simulation,which provides a reference direction for the design of the air gap structure of the planar transformer.(3)Analysis and optimization of distributed parameters of planar magnetic integrated transformers.First,this paper analyzed the distribution parameters of the magnetic integrated transformer and their influence on the LLC converter.Secondly,this paper used the magnetic field energy method to carry out theoretical calculation and analysis of the transformer leakage inductance,and through modeling and simulation to study the effect of the magnetic integration method,winding arrangement and the winding’s own structure on the leakage inductance,it was determined that the magnetic core combined magnetic integration,the transformer structure in which the primary winding is arranged in a single layer and the parallel windings are symmetrically staggered has a small secondary leakage inductance.Finally,the electric field energy method and the plate capacitance equivalent method were used to calculate and analyze the distributed capacitance of the planar transformer under different winding structures.The distributed capacitance between the side windings has been designed for the shielding layer.