Full-Bridge Submodule Development of an MMC-Like Topology for ASDEX Upgrade Toroidal Field Coils Power Supply

Abstract

The modular multilevel converter (MMC) has become one of the most attractive converters for high-power applications such as high-voltage dc (HVDC) converters, but also fusion devices’ power supplies. This converter, thanks to the discrete-leveled output voltage and its identical submodules (SMs) by which it is composed, represents a promising alternative to replace the flywheel generator (FG) that actually provides electrical power to Axially Symmetric Divertor Experiment (ASDEX) Upgrade device’s toroidal field (TF) coils. Due to the pulsed dc operation of these coils and their high-power needs (up to 150 MW) for each experiment, a small-scale version of MMC is under development with some differences compared with conventional ones: SM’s capacitors have been replaced with supercapacitor (SC) modules to increase the amount of available stored energy, while SMs belonging to different “rows” are interconnected to simplify their control and increase the reliability of the converter. This article shows the development and the operation of a single IGBT full-bridge (FB) SM highlighting advantages of this configuration and challenges of a full-scale converter: a proper power stage filter has been designed to protect SCs from voltage spikes and high-frequency current content generated during IGBT switching events, while SM’s control has been realized, thanks to the EtherCAT protocol, which ensures synchronization in case of SMs’ parallel operation and reliability of the future full-scale converter.