A power electronic traction transformer for a medium voltage DC electric railway system

Power Electronic Traction Transformers (PETT) are a trend in railway traction because of higher power density and efficiency. A PETT system achieves this by having Medium Frequency Transformers (MFT) in their converter modules as galvanic isolation. The latest PETT systems use Wide Band Gap (WBG) semiconductors to further increase system efficiency. All state-of-the-art PETT systems are developed for the Medium Voltage (MV) AC Railway Electrification Systems (RES). This work however, proposes a PETT system for a novel MV DC RES. In another article, we already studied, evaluated and presented different state of the art PETT topologies to choose an optimal one for this application. The paper will present simulation results for an 8-module Input Series Output Parallel (ISOP) MVDC PETT system capable of 1.2MW of total power. The converter topology used in the modules is Dual Active Bridge (DAB). In this paper, a decoupling method is also deduced for 8 modules to control each module separately. Results show how modules with different initial capacitor voltage are self-balancing and stabilizing at the same input voltage value. The results and theoretical notions obtained in this project will lay the foundation of a novel smart MVDC RES.