| Isolated DC/DC converters are widely used in the fields of vehicle power supply,data center power supply,electronic product adaptation power supply and other fields,because of their flexible topology,wide variety,and electrical isolation of input and output sides,can adapt to various power levels.As an important part of power converters,magnetic components are responsible for energy storage,filtering,power conversion and energy transmission,and their weight,volume and loss occupy a large proportion of the converter.With the increasing requirements of various industries on the volume and weight,power density,efficiency and other indicators of switching power supplies,the study on the planarization and integration of magnetic components is the key to promote the miniaturization and high-power-density of switching power supplies.In this dissertation,based on LLC resonant converter,the separation design of magnetic components and integrated design of resonant inductor and transformer were carried out respectively,with the goal of reducing the distribution parameters of magnetic components and the total loss and volume of the power supply system through the optimization of structural parameters of magnetic components to improve the efficiency and power density of the power supply system.(1)The working principle of LLC resonant converter was briefly introduced,the influence of important parameters on the operating characteristics of the converter was analyzed,based on which the key parameters of magnetic components were designed.Considering the problems of device stress,current sharing,transformer volume and so on,which are faced by the converter design in low-voltage and high-current output occasions,the transformer was considered to be split into several transformer units with smaller ratio,and the circuit topology of LLC resonant converter was adjusted.(2)In order to reduce the high frequency loss and distribution parameters of the inductor,the resonant inductor was optimized.Firstly,mathematical modeling and analysis were carried out for the loss composition of inductor.In order to reduce the loss of magnetic core,magnetic materials and magnetic core types were selected.Considering the influence of air gap on the loss of high frequency inductor,the characteristics of different air gap structures were analyzed,and the effect of winding transverse air gap avoidance,winding longitudinal air gap avoidance,and distributed air gap on reducing winding loss were studied.In view of the influence of distribution parameters on its operating characteristics,and the causes,calculation methods,influencing factors and optimization measures were studied.Whereby the optimized design of the inductor winding was proposed,and distribution parameters were extracted by Q3D Extractor software,and the optimized scheme was verified;and then,Maxwell 3D software was used for modeling and simulation of the design scheme.After analyzing the feasibility of the design scheme,a prototype was made.Finally,distribution parameters and thermal characteristics of the prototype were tested to prove the rationality of the design scheme.(3)The composition of the loss of center-tapped transformer was analyzed,and the causes of the high frequency passive loss and the measures to reduce the loss were emphatically introduced.Then the application of area product method in transformer design was given.The proximity effect was weakened by the staggered arrangement of primary and secondary windings.In view of the leakage inductance and distributed capacitance of the transformer,the influence on the working characteristics of the transformer itself and the main circuit,the causes,calculation methods,influencing factors and optimization measures were studied,the results showed that the staggered structure of the primary and secondary windings can reduce the leakage inductance and the distributed capacitance in the winding,but increase the distributed capacitance between the windings.In order to eliminate the contradiction,a shielding layer was added between the primary and secondary windings.Finally,the feasibility analysis of the transformer design scheme was carried out by electromagnetic simulation software,and the prototype was tested to prove the rationality of the design scheme.(4)The principles and analysis methods of magnetic integration technology were introduced,and three methods for magnetic integration of resonant inductors and transformers were proposed based on the topology of this paper.The integration was realized by using a pair of cores and two pairs of cores to achieve decoupling integration through the center column,and by dividing the resonant inductors equally to cancel the coupling effect to achieve integration.With the help of Maxwell 3D software,the three integration schemes were simulated and analyzed.After the evaluation,the prototypes of the two reasonable schemes were made.After the experimental test of the prototypes,the magnetic integration scheme with lower leakage inductance,lower temperature rises of magnetic core and winding and lower loss was finally selected. |
