Medium Voltage DC, Challenges Related to the Building of Long Overhead Lines

Abstract

Particularly in Germany, but also in many other countries of the world, the electrical networks will change greatly in the future due to the integration of renewable energy generation. For a successful execution of this energy transition (German: Energiewende) the design and operation of the networks has to change in order to solve the new requirements of modern energy supply. Medium voltage direct current (MVDC) technology is an innovative solution to face some of these challenges. A new concept consisting in the down-scaling of a HVDC Modular Multilevel Converter (MMC) is presented. It combines the advantages from MMC such as low converter losses, fast active and reactive control and compact footprint to reduced acquisition costs. The technical implications of the construction of long distance medium voltage dc links are highlighted. Especially the losses in the DC line and the AC-Fault Ride Through capability are discussed.