D. Multi-terminal HVDC system.
In this configuration there are more than two sets of converters like the bipolar version. In this case, converters
1 and 3 can operate as rectifiers while converter 2 operates as an inverter. Working in the other order, converter 2 can operate as a rectifier and converters 1 and 3 as inverters. By mechanically switching the connections of a given converter other combinations can be achieved. A multi-terminal CSC-HVDC system with 12-pulse converters per pole is shown in Fig. 6.
III. VSC-HVDC FUNDAMENTAL CONCEPTS
frequency.
1
0
-1
0
0
Fundamental
Time
Carrier
Reference
2π
A basic VSC-HVDC system comprises of two converter stations built with VSC topologies (Fig. 2). The simplest VSC topology is the conventional two-level three-phase bridge shown in Fig. 7.
Typically, many series connected IGBTs are used for each semiconductor shown (Fig. 7) in order to deliver a higher blocking voltage capability for the converter and therefore increase the DC bus voltage level of the HVDC system. It should be noted that an antiparallel diode is also