A Novel Snubber Circuit for MMC Submodule Using Gap-RC to Suppress Fast Transient Overvoltage

The modular multilevel converter (MMC) will be subjected to transient impacts, such as switch operation in gas-insulated switchgear and wall bushing flashover, resulting in MMC submodules' ports suffering from fast transient overvoltage (FTO), posing a threat to the safe operation of power devices. This letter proposed an FTO suppression method using gap-RC as an additional snubber circuit and provided a method for selecting RC parameters that can reduce the FTO peak to below the device breakdown voltage. Among them, the gap could avoid additional oscillation processes generated by RC during normal operation of the submodule. Finally, an equivalent experimental circuit for the FTO injection submodule port was designed to verify the effectiveness of gap-RC in suppressing FTO.