Unified High-Speed EMT Equivalent and Implementation Method of MMCs With Single-Port Submodules

This paper proposes a unified high-speed electromagnetic transient (EMT) equivalent and implementation method for modular multilevel converter (MMC) with arbitrary single-port submodule (SM) structures. The proposed method, interacts with the users by the incidence matrix, branch admittance matrix and the column vector of the current sources as input, then a nodal admittance matrix is automatically generated for each individual SM and the internal node information of the SMs are transferred to the interfacing nodes. Hence, the internal nodes are eliminated without obtaining the complicated analytical solutions, the reduced-order equivalent circuit of each SM is obtained and all the SMs within each arm are cascaded into one ultimate Thévenin equivalent. At the end of each time step, the EMT solver updates all the previously eliminated internal node information so that nothing is lost under steady and transient states. The proposed approach is validated by EMT models of an enhanced double half-bridge sub-module based MMC-HVdc system on power systems computer aided design (PSCAD)/EMTdc.