Modeling And Design Of High-power High-frequency Transformers For Energy Routers

High-power high-frequency transformers have a wide application background in the field of power conversion.As key components of energy routers,high-power high-frequency transformers perform functions such as electrical isolation and voltage conversion,their performance plays an important role in determining overall power transmission characteristics of the converter.The increase of frequency enhances the power density,but it also brings about challenges in loss control,insulation complexity and temperature rise,which increases the design difficulty of high-power high-frequency transformers.This paper conducts researches in fields shown below.Firstly,winding loss affects the efficiency and temperature rise of high-frequency transformer.This paper discusses the analytical loss calculation methods for foil and litz wire winding.After that,the accuracy of several analytical expression for litz wire is evaluated through finite element analysis.Tourkhani formula is found to possess the smallest error.At the same time,in order to minimize winding loss,the optimal thicknesses/diameter for the foil and litz wire winding is obtained in a fixed operating frequency.In terms of core loss calculation methods under arbitrary waveform excitation,this paper introduces the transient finite element method based on the core loss time-domain general model and a variety of semi-empirical algorithms based on Steinmetz equation.The core loss measurement under square wave excitation shows that the improved generalized Steinmetz equation(IGSE)is accurate enough to be used as a reference for high-power high-frequency transformer design.Secondly,leakage inductance is an important parameter in high-frequency transformer for its influence on power transmission performance and soft switching of converters.This paper presents a detailed model of leakage energy for litz wire,and proposes an accurate closed-form expression for calculating the leakage inductance in high-frequency transformer.The frequency effect of litz wire is taken into account and the filling factor is also considered.A global sensitivity analysis is performed to assess the influence of each parameter on the overall leakage inductance,which finds that adjusting the insulation distance between primary and secondary winding is the most effective method to changing the leakage inductance of high frequency transformer.Finally,two transformer prototypes are built to verify the accuracy of the proposed analytical expression in a wide frequency range.Finally,a 10 k Hz/200 k VA dry-type high-power high-frequency transformer prototype is developed.Design considerations such as constraints between temperature rise and flux density,leakage inductance and insulation,optimal winding selection,heat dissipation optimization are taken into consideration.The design scheme is introduced in detail and several experiments along with simulations are carried out,which shows that the high-power prototype has an efficiency of 99.87%,a power density of 1.54 k W/kg,a leakage inductance of 8.7μH and a maximum temperature rise of 69 K.Its overall performance reaches state-of-art.