Design And Optimization Of Planar Transformer In LLC Resonant Converter

With the continuous development of unmanned aerial vehicle(UAV)technology,the power systems of UAV are required to be smaller volume,lighter weight,and higher power density to carry more loads.LLC resonant converter is widely used in UAV power system due to its advantages of good soft switching characteristics,high efficiency,and easy magnetic integration.As a key device in the LLC resonant converter,the transformer has great influence on the power density and performance of the power supply system.Compared with the traditional transformers,planar transformers have small size,good parameter consistency,flexible and diverse winding structures,and meet the development requirements of power supply systems,so they are widely used in LLC resonant converters.Aiming at the design requirements of UAV power system,based on the full bridge LLC resonant converter,the key issues that affect the performance and power density of the transformer such as the parasitic parameters,loss,parallel winding layout and magnetic integration method of the planar transformer are studied.Firstly,the calculation methods of the power loss,leakage inductance and distributed capacitance of planar transformer are analyzed.Four parallel winding layout methods are studied for double windings planar transformer and center-tapped planar transformer.The effects of different parallel winding layouts on transformer loss,leakage inductance,distributed capacitance in the windings,and distributed capacitance between the windings can be obtained through theory and simulation analysis.Finally,the best winding layout method is obtained.Secondly,the magnetic integration design method of matrix transformer is studied.By integrating the two separate cores of the matrix transformer into a single core,the core volume is reduced and the power density is increased.By analyzing the calculation method of the total winding loss of the matrix transformer,the optimal solution of the copper thickness of winding and the number of parallel windings is obtained.In addition,the parasitic parameters of the transformer were extracted by ANSYS Maxwell 3D simulation software,and the working conditions of the transformer in the circuit were simulated by Maxwell and Simplorer software.The loss distribution of the transformer was obtained and the design rationality of the transformer in terms of loss and parasitic parameters was verified by joint simulation.Finally,a 2k W LLC resonant converter experimental prototype with input DC 70V?100V,output DC 50 V was built,and its different working conditions were verified.