May 23, 2007 — Siemens Power Transmission and Distribution (PTD) has launched a high-voltage direct current transmission (HVDC) system, based on a new generation of converters using voltage-sourced converter (VSC) technology. The “HVDC Plus” system is suitable for direct current links up to the 1,000 MW power range where line-commutated converters are still used exclusively today. In contrast to line-commutated converter technology, the HVDC Plus system operates with power semiconductors which have both turn-on and turn-off capability. As a result, the commutation processes in the converter are independent from the AC system voltage. Next to other applications the transmission system allows the low-loss transport of electrical energy from offshore wind farms to the coast and the economical and environmentally-friendly supply of power to oil platforms from the AC system on the mainland.
HVDC Plus makes use of all the advantages offered by self-commutated voltage-sourced converter technology. This includes grid access to very weak AC systems as well as supplying passive networks. Active and reactive power can be controlled independently. The capability of very rapid control and protection actions of the converter makes the system highly dynamic, which is necessary especially for AC faults and system disturbances. Also, the black-start capability function enables the HVDC system to restart a collapsed network.
HVDC Plus operates with an innovative multilevel converter concept, which offers in comparison to existing VSC solutions additional significant benefits. Amongst others these are low losses due to low switching frequencies, full modular design and therewith a straightforward scalability. In addition to the operation as back-to-back link and as cable transmission, HVDC Plus can also be used in combination with overhead lines.