Direct and alternating currentHVDC converters
Direct current must first of all be rectified from alternating current. There are two different approaches to doing this: self-commutated (voltage-source (VSC)) and line-commutated (LCC) converters. LCC converters can transmit greater capacities but require a relatively large amount of reactive power and a stable grid. In addition, it is only possible to inverse the power by changing the voltage. With VSC converters, switching valves are installed that can be turned both on or off and a stable grid is not required. Their black-start capability makes them suitable for areas without stable grids such as offshore applications. Since the power is inverted by changing the current direction, VSC converters are in principle suitable for use in HVDC grids.