Medium frequency transformers for solid-state-transformer applications — Design and experimental verification

Solid-state-transformer technology pushes the specifications of electric transformers in the high-power medium-frequency range. This combination results in larger-sized transformers operating at higher frequencies whereby parasitic phenomenon should be carefully accounted for. This paper presents an analytical description of the limiting factors and the connection between frequency/power rating and the available core and copper conductor technology on the power density and efficiency of medium-frequency transformers. Furthermore, two designed transformers for 166kW/20kHz based on two different core materials and cooling systems are presented. Extensive copper, core and cooling system loss measurements on one of these transformers are discussed in order to analyze the transformers' behavior from a practical point of view.