A comparative evaluation of HVDC ties using line commutated and modular multilevel converters

Traditional HVDC systems employ line commutated converters (LCCs) which are prone to commutation failures and feature significant harmonic distortion. Voltage source converter (VSC)-based HVDC systems have been employed to overcome these disadvantages, but their high switching frequency makes it difficult to scale to high power levels. Recently, a VSC topology named modular multilevel converter (MMC) has been introduced featuring higher power quality and reduced losses due to its modularity. Its application for HVDC transmission systems has already been studied in the literature and demonstrated in the field. In this paper, an HVDC tie based on back-to-back MMCs is realized, and a qualitative and quantitative comparative evaluation against its LCC-based counterpart is performed. The evaluation is grounded on a real case study, the Stegall HVDC tie, which provides power exchange between the western and eastern North American interconnections.