Simulation And Calculation Of Multiphysical Field Of High-Frequency Transformer

The high power and high voltage DC/DC converter is the key equipment for realizing large-scale DC source interconnection,megawatt DC voltage transformation and DC power network.The high-frequency transformer based on magnetic coupling can achieve electrical isolation and voltage transformation on both sides of the high and low voltage of the DC/DC converter.Accurately estimating the copper losses and magnetic core losses of high-frequency transformers under non-sinusoidal voltage magnetization,and analyzing the temperature property in DC-DC converter under normal mode,are essential for the optimization design and dissipation design of the high-power high-frequency transformer.The transient electromagnetic field and temperature field control equations and boundary conditions are given in the calculation of electromagnetic,loss and temperature rise characteristics of high-frequency transformers.considering the non-sinusoidal excitation waveform of HFT in normal mode,the transient 3D magnetic field distribution of HFT is simulated based on Infolytica MagNet software.Utilizing the measured magnetization curve and core loss characteristics,losses of windings and core of the HFT are calculated.The obtained loss is applied in ThermNet to calculate the transient 3D temperature distribution.Two prototypes of 10kVA/5kHz nanocrystalline-based HFTs with shell and core type topologies are designed and manufactured.Using the above method,the magnetic field,loss,and temperature are calculated.The results show that,the deviation between the simulated and measured loss is within 15%.The maximum temperature rise of core and shell type prototypes under the natural cooling are 84 ℃ and 88 ℃,respectively.The heat dissipation characteristic of shell type topology is better than that of the core type.Using the COMSOL Multiphysics multi-physical field simulation software to simulate the temperature distribution of a 200kVA/10kHz large-capacity high-frequency transformer under natural convection and rated conditions,the steady state maximum temperature rise is 105℃,and the temperature rise is more serious.The heat dissipation design of the high-frequency transformer was studied,the heat resistance model of the heat dissipation plate was established,and the optimization design of the heat dissipation plate was carried out using the constant power heat dissipation model.First,the temperature simulation of the high-frequency transformer with heat sink under natural convection and empty load conditions is carried out,and the steady temperature measurement results of a prototype transformer with an empty load condition with heat sink are compared.The maximum temperature simulation and measurement values of the core are 54 0C and 58.6 0C,respectively,which verify the correctness of the model.The temperature distribution of the high-frequency transformer under forced air cooling and normal operating conditions was then simulated,as well as the overall wind speed in the tank.The maximum temperature appeared on the primary winding of the fluid outlet attachment,which was 62℃,below the maximum temperature limit.The correctness and rationality of the optimal design method and the selection method of fan type are verified.