Fabrication Of High-frequency Low Loss Density Constant Flux Toroid Core

With the rapid development of modern power electronics industry,especially for the emergence of 5G communication technology and its further application in recent years,power electronics equipment urgently needs to overcome the challenges brought by the high power conversion,frequency and energy density working environment.The inductors,as the crucial components of power electronics equipment,play an important role in power electronics industry.Therefore,the degree of development of inductors directly determines the developing level of power electronics.At present,the distribution of magnetic flux density in commercial core is not uniform,and the inner side will be saturated ahead of outer side of the core,which affects the power conversion efficiency seriously.In this paper,a theoretical design and fabrication method of continuously variable multi-permeability(CVMP)toroid core based on gradient sintering process was proposed to solve the saturation problem.The main conclusions are as follows:Firstly,the single-permeability toroid core was fabricated by conventional sintering process using LSF50 Ni Zn Cu ferrite which could be operated at high frequency.The effects of sintering temperature on electrical-magnetic properties of toroid core was investigated.The results showed that the permeability(?)and saturation magnetic flux density(B_s)of the core improved with the increase of sintering temperature ranging from 850^oC to 1000^oC.The?and B_s are improved 173.44%and9.3%respectively when the core sintered at 1000^oC.However,the inductance versus DC-bias dropped significantly with the increase of sintering temperature,and the core loss density decreased firstly and then increased subsequently.Therefore,the effects of sintering temperature on electrical and magnetic properties are not consistent.This can be attributed to the increase of permeability,which leads to the premature saturation of the core,further degrading the electrical properties.It is determined that 950^oC was the optimum sintering temperature,which could simultaneously take into account the electrical and magnetic properties.Secondly,the Eu₂O₃ dopants on the properties of the core was investigated based on the optimum sintering temperature.The results showed that permeability was improved significantly(36.23%)and the core loss density was decreased doped with Eu₂O₃.The core loss density of the core could be decreased 86.01%measured at 1 MHz and 10 m T.It is because that the grain boundary resistivity was increased due to the doped Eu₂O₃ segregation in the ferrite grain boundary.Thus,the high frequency eddy current loss was decreased and further reduced the total loss of the core.Finally,the concept of CVMP toroid core based on LSF50 Ni Zn Cu ferrite was proposed.The design principle of CVMP toroid core was determined combined with theoretical calculation and Ansoft Maxwell simulation.And the fabrication of CVMP toroid core was realized at last by gradient sintering process.The CVMP toroid core and single-permeability toroid core was tested in a DC-DC converter.The results showed that the CVMP toroid core using gradient sintering had lower operating temperature,less heat and higher output efficiency than the single-permeability toroid core using conventional sintering process.