Development of medium voltage solid-state fault isolation devices for ultra-fast protection of distribution systems

Three generations of medium voltage fault isolation devices (FID) for a power electronics based distribution system, the FREEDM System, are reported in this paper. In the Gen-I FID, three 6.5 kV silicon IGBTs are series connected to achieve 15 kV class distribution voltage blocking capability. Whereas in the Gen-II and the Gen-III FIDs, 15 kV Silicon Carbide (SiC) ETO devices are used. Since one single such device can meet the voltage withstand requirement, the operation losses as well as dimensions are significantly reduced. Future improvements in the Gen-III FID include the use of hybrid schemes and the development of symmetrical blocking high voltage SiC devices to further minimize the operation losses.