The Modular Multilevel Converter (MMC) represents the recent development among the diverse available topologies of VSC and is allegedly the most suitable solution for converters in HVDC transmissions. This paper presents an Average Value Model (AVM) of the MMC that still includes the characteristic internal dynamics that are non-existent in traditional 2-level VSCs. This AVM and its control are described and linearized in order to obtain a state-space model of the MMC that can easily be used as a subsystem for multi-terminal HVDC (MTDC) grids. A case study showing a 401-level MMC-based HVDC link simulated in the EMTP-RV software validates the proposed state-space representation of the MMC.