Forum 

Major milestones in the development of high voltage direct current (HVDC) technologies and concepts were achieved in 1950s. Thanks to the high power thyristor switches (1960-70s), the HVDC technologies reached a significant degree of maturity in 1980s. The classical HVDC uses thyristor-based current-sourced line-commutated converter (LCC) technology. The advent of power semiconductor switches in 1980-90s, with turn on-off capabilities especially the IGBTs and IGCTs, and the on-going progress in this field, have introduced the conventional (two-level) voltage-source converter (VSC) technology and its variety of configurations, multi-level and multi-module VSCs, also as viable converter technologies for power system applications. The DC system is experiencing significant degree of re-emergence due to its potential to either directly address, or to facilitate resolving a large number of existing and anticipated interconnected AC power system steady-state and dynamic issues. HVDC technology made possible to transfer bulk power over long distances. Research works could be conducted on, comparative evaluations, studies, and review of HVDC versus HVAC transmission systems, are presented. Applications, different schemes of HVDC systems can also be covered.