This document describes the implementation and validation of a three-phase average value model (AVM) of a voltage source converter high voltage direct current (VSC-HVDC) system using Modelica. The VSC-HVDC model is composed of controlled voltage and current sources that approximate the internal behavior of a modular multilevel converter. Each component of the model, including controls, is implemented and validated separately against an EMTP-RV reference model. System-level validation is also performed by connecting the VSC-HVDC model to a two-node power system and simulating the transfer of 1000MW active power while controlling voltage. The results show good agreement with EMTP-RV. A key benefit of the Modelica implementation