Half- and Full-Bridge Modular Multilevel Converter Models for Simulations of Full-Scale HVDC Links and Multiterminal DC Grids

This paper presents an improved electromagnetic transient (EMT) simulation model for the half- and full-bridge modular multilevel converters (MMCs) that can be used for full-scale simulation of multilevel high-voltage dc (HVDC) transmission systems, with hundreds of cells per arm. The presented models employ minimum software overhead within their EMT parts to correctly represent MMCs behavior during dc network faults when converter switching devices are blocked. The validity and scalabilities of the presented models are demonstrated using open-loop simulations of the half-and full-bridge MMCs, and closed-loop simulation of a full-scale HVDC link, with 201 cells per arm that equipped with basic HVDC controllers, including that for suppression of the second harmonic currents in the converter arms. The results obtained from both demonstrations have shown that the presented models are able to accurately simulate the typical behavior of the MMC during normal, and ac and dc network faults.