The Alternate Arm Converter “Extended-Overlap” Mode: AC Faults

This article presents ac fault ride-through strategies for the “extended-overlap” operating mode of the alternate arm converter (AAC), which is a type of modular multilevel voltage source converter that has been proposed for HVdc transmission applications. The AAC offers several benefits over the half-bridge modular multilevel converter, such as requiring fewer submodules with a smaller capacitance and providing dc fault ride-through capability. Novel symmetrical and asymmetrical ac fault ride-through strategies are described and these strategies are experimentally validated by using a small scale prototype.