A Novel Snubber Circuit for MMC Submodule Using Gap-<i>RC</i> to Suppress Fast Transient Overvoltage
Hong Shen, Xiangyu Zhang, Lei Qi, Sheng Zhang
Abstract
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- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> as an additional snubber circuit and provided a method for selecting <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> parameters that can reduce the FTO peak to below the device breakdown voltage. Among them, the gap could avoid additional oscillation processes generated by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> 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- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> in suppressing FTO.