High voltage direct current (HVDC) transmission is widely recognized as profitable for long-distance bulk-power delivery, asynchronous interconnections, and long submarine cable crossings. New converter designs have broadened the potential range of HVDC transmission to include applications for underground, offshore, economic replacement of reliability-must-run generation, and voltage stabilization. The two basic converter technologies used in modern HVDC transmission systems include the conventional line-commutated current source converters (CSC) and self-commutated voltage source converters (VSC). The controllability of HVDC links offer firm transmission capacity without limitation due to network congestion or loop flow on parallel paths. An HVDC control system aims to ensure stable operation with reliable commutation in the presence of system disturbances and also to minimize system losses and converter reactive power consumption.
