I. Introduction
Medium-frequency (MF) electronic transformers open up new possibilities for ac–ac and dc–dc conversion systems, characterized by high efficiency, small volume, low weight, and cost effective features. Thus, there is an obvious interest in developing this type of systems in various applications where space and weight restrictions are critical, like railway traction [1]– [8], offshore wind power [9], or electrical vehicles [10]–[12] . The railway electrical traction sector is currently the most important one, as MF transformers could be potentially used not only to replace on-board low-frequency (LF) bulky transformers in ac trains (50 or 16 2/3 Hz), but also as the key element of on-board dc–dc conversion systems. In this last application, transformer-based converters can be an interesting alternative to conventional topologies due to their high voltage transformation ratio and efficiency.