Power Electronics is expected to become a major component in the field of the global electric power management, as it is already today within most of electric power applications like variable speed drives or other conventional user applications. From the end of the sixties, up to the beginning of the 21st century, high power electronic converters have been used more and more for many usages connected to the grid, from the reactive power compensation to the long distance transmission lines. More recent examples have shown a large potential of new flexible management systems like UPFC's, or other Flexible AC Transmission Systems.