The use of averaged-value model of modular multilevel converter in DC grid

The paper investigates the applicability of averaged-value models (AVM) for modular multilevel converters (MMC) operating in a voltage sourced converter based high voltage dc (VSC-HVDC) grid. The AVM models are benchmarked by comparison with a detailed electromagnetic transient (EMT) model of the grid including a full-detail MMC model. Analysis results show that the AVM is only effective as long as the capacitors are large enough to maintain nearly constant voltage across each MMC sub-module (SM). The paper also shows that previously developed MMC averaged models are not able to accurately simulate the transients under dc fault conditions. The paper introduces topology changes to a previously proposed averaged model that results in much improved simulation for such conditions. The paper also shows that model can be used effectively to study HVDC grids with significant time savings.