Modular Multilevel Converters as active filters to mitigate low frequency current harmonics in converter fed grid applications

This paper describes a method to improve converter fed grid structures with Modular Multilevel Converters (MMC). In grids with decentralized energy production and bidirectional power flow, an increasing number of power electronic loads and sources make power quality an important issue to ensure grid stability. The MMC topology is highly suitable to meet the requirements of a low Total Harmonic Distortion (THD) and voltage stability due to its high quality output voltages. In combination with power line communication based on harmonic injection, MMCs compensate low frequency grid current harmonics and imbalances to improve the power quality. A standalone laboratoryscale converter-fed microgrid including low voltage MMCs shows the capability of the developed control algorithms.