Modular multilevel converters and HVDC/FACTS: A success story

The first modular multilevel converter for HVDC application went operational in 2010. The Trans Bay Cable project transfers 400 MW of electrical power from Pittsburg, CA to the city of San Francisco, via a subsea cable of 88 km. It clearly demonstrated that the advantages of this technology are not only of theoretical nature, but can also be achieved in practice: efficiency comparable to thyristor-based HVDC plants, very low space consumption due to the absence of filters and, most important for the customer, a very good reliability. In the meantime, Siemens was awarded several HVDC PLUS^® contracts reaching transmission capacities of up to 1000 MW. The same success could be achieved for Static VAR Compensators (SVC) based on the modular multilevel concept. Both products will certainly play a vital role in meeting the future challenges imposed upon the transmission grids, like integration of large amounts of renewable energy sources or increasing the power transmission capability of the existing grids.