Reduced Dynamic Model of a Modular Multilevel Converter in PowerFactory

Modular Multi-level Converters (MMC) have emerged as the preferred technology for High Voltage DC transmission installations. The inclusion of these converters, characterized by complex control schemes, in large AC grids may cause AC/DC interactions that need to be fully investigated. The evaluation to what extent the MMC dynamics interact with the dynamics of a transmission network is of primary importance. It becomes critical for the grid operators, which usually rely on more traditional VSC topologies (two-level), to use such models when studying AC/DC interactions. This paper presents the development of a MMC reduced dynamic model (RDM) in PowerFactory that will facilitate the analysis of large AC systems incorporating MMC based VSC HVDC links. The MMC control scheme is designed following an alternative strategy which considers the energy balancing and the storage capability of the converter. The system is arranged as a point-to-point link, its operations are validated against a detailed equivalent circuit based model in PSCAD/EMTDC. A close match between the original system and the benchmark confirms the validity of the MMC RDM proposed.