Planar Transformer Design And Optimization For Half Bridge LLC Resonant Converter

In the field of switching power supply system,the volume of transformer accounts for one fifth to one third of the whole power supply system,and the energy loss accounts for one third of the total loss of power supply system.Meanwhile,planar transformer has replaced the traditional winding transformer because of its good good heat dissipation,small leakage inductance,large current density,high power density and good parameter repeatability.Therefore,the design and optimization of planar transformer is particularly important for the high-efficiency and high-power density power supply system.However,in high frequency,the parasitic effect of the planar transformer becomes increasingly serious.Meanwhile,the high-frequency eddy current effect makes the magnetic loss and copper loss of transformer no longer equal.Thus,the traditional transformer design method is no longer suitable for the high-frequency planar transformer.It is of great significance to study the tradeoff design between planar transformer parasitic parameters,efficiency and power density at high frequency.Aiming at the application of high-frequency half-bridge LLC resonant converter and based on the finite element analysis software Maxwell,this thesis discusses the design method and concrete implementation of a high-efficiency and high-power density planar transformer.The thesis analyzes several key problems including leakage inductance calculation,parasitic capacitance calculation,winding aragement optimization and magnetic core optimization of planar transformer.The work of this thesis mainly includes:(1)the calculation method of parasitic capacitance of planar transformer is proposed.It obtains the more accurate value by calculating the current between the two layers of PCB windings;The calculation method of leakage inducatance of planar transformer is proposed.It gets the value by calculating the stored energy in the planar transformer.(2)The winding losses,leakage inductance and parasitic capacitance of planar transformers with different winding arrangements are compared,and the winding arrangements are optimized by adding shielding layers to obtain the optimal design with both parasitic parameters and losses.(3)The magnetic core design of planar transformer is optimized,and a compromise design method between power density and efficiency of planar transformer is proposed.It calculates and fits the relation between loss and core area through Matlab to obtain the optimal design between power density and efficiency.The design of this thesis is verified on 300V/12V and 300W half-bridge LLC resonant converters.The test results show that the peak efficiency of the planar transformer at 1MHz are 98.9%,its power density is178W/cm~3,the equivalent primary leakage inductance is 0.45μH,and the equivalent parasitic capacitance is 246pF,which meets the design requirements and is suitable for high power density and high efficiency power supply system.