A novel embedded voltage-clamped circuit for multilevel modular converters submodule to suppress very fast transient overvoltage

The submodule in multilevel modular converters experiences a very fast transient overvoltage (VFTO) during switch operation of gas-insulated switchgear, which also results in overvoltage on power devices, such as thyristors and insulated gate bipolar transistors (IGBTs). This work presents an embedded circuit that utilises a gap in conjunction with a metal oxide varistor (MOV) to control the voltage of the surge arrester and prevent false triggers during the transient phase when the IGBT is turned off. The mechanism of VFTO is analysed. Moreover, the design idea is suggested and the gap-MOV circuit is constructed. Ultimately, experiments are conducted to validate the effectiveness of the suggested gap-MOV in suppressing overvoltage.