An Effective Average Value Model for Modular Multilevel Converters under Startup Process

The detailed physics model of the modular multilevel converters (MMCs) consumes excessive computational resources because of massive submodules (SMs). To deal with this problem, several simplified modeling methods have been proposed. However, the startup process modeling techniques attract little attention. In this paper, two common startup processes of MMC are analyzed, including the ac-side and dc-side pre-charge. Firstly, a charging index is defined to represent the charging state of the arm capacitors. Based on the charging index, the ordinary differential equations of MMC under startup process are derived. Furthermore, an average value model (AVM) of MMC is proposed based on the ordinary differential equations. The proposed model is compared and validated by the IGBT-based MMC model in PSCAD/EMTDC.