Scalable Solid State Transformers (SSTs) for DC railway substations

Inhalt:
DC railway substations may require different rated powers, input AC voltages and output DC voltages. Hence, current substation technology needs to be adapted to each application. To overcome this issue, the Solid State Transformer (SST) topology, which is inherently modular, can address the different applications with a single elementary power electronic building block (PEBB). In this paper, a methodology is proposed to define the optimal rated power and number of PEBBs. It results in a 94kW PEBB with a 3.6 kV intermediate DC bus which leads to an oversizing ratio regarding normal operation comprised between 3.38 and 5.7 and a number of PEBBs per MW comprised between 36 and 60. A topology of the PEBB with a reconfigurable secondary bridge to address both 750 V urban and 1.5 kV suburban applications is also proposed. The power losses are similar to those obtained with dedicated secondary inverters sized specifically for either urban or suburban applications.