High-voltage direct-current transmission : converters, systems and DC grids.

Abstract

DC transmission technology was used in many instances in very early power systems but modern HVDC transmission begins with the 1954 Sweden–Gotland installation. This system and all the other HVDCs commissioned until the mid-1970s were based on mercury arc valves. A significant technical advance came with the introduction of solid-state valves (thyristors), although they only support the line-commutated converter (LCC) concept. In the first decade of the twenty-first century there has been very rapid development of fundamentally new technologies and an increasing demand for HVDC technology. The introduction of voltage-source converters (VSCs) requires new valves, which use insulated-gate bipolar transistors (IGBTs) and also new protection and control approaches. The modular multilevel converters have eventually emerged as the most cost effective VSC converter concept, which practically eliminates filtering needs with HVDC and removes voltage limits with VSC valves.