An Accurate Accelerated Steady-State Model for High-Level Modular Multilevel Converters

Due to their salient features, modular multilevel converters (MMCs) are particularly suitable for a high-voltage direct current (HVDC) transmission system. Nevertheless, for an HVDC system, each phase of the MMC terminal may consist of several hundreds of submodules. This imposes a particular challenge in terms of steady-state simulation and modeling. Steady-state modeling is usually needed for determining the operating point for the MMC controller design and for predicting harmonics propagation in a power network. In this article, an efficient and accurate steady-state model for an MMC system with high-voltage levels is proposed. The model is based on a model reduction technique, namely residual-time restarting Krylov subspace method. As will be shown in this article, the proposed method is able to model various MMC systems. The results obtained from the proposed model are highly agreeable with those from PSCAD/EMTDC. Moreover, it will also be shown that the proposed method can drastically reduce the computation time for obtaining steady-state solutions.