Half and full-bridge modular multilevel converter models for simulations of full-scale HVDC links and multi-terminal DC grids

This paper presents an improved electromagnetic transient (EMT) simulation models for the half and full-bridge modular multilevel converters that can be used for full-scale simulation of multilevel high-voltage dc transmission systems, with hundreds of cells per arm. The presented models employ minimum software overhead within their electromagnetic transient parts to correctly represent modular multilevel converters (MMC) behaviour 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 2nd 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 behaviour of the MMC during normal, and ac and dc network faults.