A novel circuital model for power electronic transformer: Sizing and simulation

The rail traffic in Europe is increasing in frequency. As a result of this, all the countries are updating their power supply system involving the use of high-power static converters. Moreover, the high required power implies the use of medium voltage (MV) supply chains (i.e. 15-25 kV) while the traction drives are operated at voltages of some kV. In order to adapt the two voltage levels, an on board transformer is typically used. Anyway, this transformer is characterized by high size and weight and limits the performances of the vehicle. A solution to this issue can be represented by the use of a power electronic transformer (PET) that is constituted by a double stage converter with an interposed high frequency transformer. The use of a high frequency transformer instead of the traditional at industrial frequency allows the reduction of size and weight with consequent advantages for vehicle performances. The paper presents a focus on circuital model, design and dimensioning of a PET. In particular, a topology of the converters and the relative control strategy are proposed. Moreover, the problem of core sizing is analysed and some guidelines are given. Finally, for chosen values of power and switching frequency, the sizing is executed and results of numerical simulations are given.