Average value MMC model with accurate blocked state and cell charging/discharging dynamics

This paper proposes a simple and accurate average value model (AVM) of a high-power half-bridge MMC for electromagnetic-transient (EMT) studies. Least number of generic EMT blocks is used. Functioning as voltage source converter (VSC), the accuracy of a simplified MMC model would eventually be determined by its accuracy in reproducing the cell charging/discharging dynamics of the detailed models under all operating conditions. The validity of the proposed MMC average value model is verified against a detailed 1GW 21-level model in PSCAD. System dynamics and modelling accuracy of the AVM are tested with various operating conditions, including MMC startup, normal operation with power reversal, DC fault conditions, and MMC cell charging/discharging dynamics from AC and DC sides, with blocked or unblocked MMC status.