Series-stacked and neutral point clamped multilevel converter topologies for MVDC transmission

Advances in semiconductor technology have extended the economical power range for direct current transmission for low power levels. Medium voltage direct current transmission lines transmit power without absorbing any reactive power, making it more attractive in terms of line voltage consistency and power stability. It can therefore be used to bridge greater distances with low voltage and low power. Breakeven distances between medium voltage alternating current and direct current lines are mainly determined by the cost of converter stations and therefore the technology and topology of static power conversion being used. Numerous multi-level converter topologies have been developed over recent years to address the industry demand for higher power and voltage levels. The paper covers feasibility studies as well as technical aspects on the two most feasible converter configurations, the series-stacked converter and neutral point clamped converter.