Voltage-source converters (VSC) that use self-commutated valves have been used for such applications as electric motor drives. Recently with the development of switches with high voltage and current ratings, these converters have been considered for high-power transmission as well. This internship with Manitoba Hydro, Manitoba’s major energy utility, aims at developing accurate computer simulation models for DC transmission systems using voltage-source converters. Such models will then be used to design proper control strategies and structures in order to fully utilize their capability in transmitting power while ensuring stability and smooth operation.