AC Crowbar Protection Scheme for Medium-Voltage Solid-State Transformers

Solid-State Transformers (SSTs) are gaining popularity in a number of applications to directly interface with the medium-voltage (MV) AC grid. As SSTs fundamentally consist of power electronic semiconductor devices, a key challenge is to design SST systems capable of withstanding the various overvoltage conditions observed on the MVAC grid such as lightning surges, switching surges and transient overvoltage conditions. This paper proposes a protection scheme that uses an AC crowbar in combination with existing MV overvoltage protection devices to offer robust protection to SSTs. The AC crowbar operation is analyzed in conjunction with MV breakers and surge protection equipment and design guidelines are presented for the case of a 13.8kV/1MVA grid-tied SST.