Power electronic transformer is the key equipment used in smart grid

electric vehicle

military aviation

and other fields. With the continuous development of power electronic transformer with high voltage and large power

considering works have been focused on its related theory and key technology. Currently

some researches have been studied

such as low conversion efficiency

high current stress of switching device

and unbalanced voltage and electric power flow between the power modules. However

few types of research were carried out on the high-frequency transformer

which is the key component in the high voltage DC-DC converters in power electronic transformer. Particularly

there are still many key issues remained in the high-frequency transformer under the high voltage

high frequency

and high temperature. According to the research background of high voltage and large capacity power electronic transformer

this paper reviews the fundamental technique and key issues in the high-frequency transformer. Based on the research results of the majority of published works

the complex working conditions of high-frequency transformer used in power electronic transformer are introduced firstly. Then

the state of the art of the magnetic core

the winding

the insulation

and the heat dissipation are mainly discussed. Furthermore

the key issues related to the transformer components are proposed. Finally

the research status of the high-frequency transformer are concluded and prospects and suggestions for the future development of large power electronic transformer equipment.