Application of multilevel full bridge converters in HVDC multiterminal systems

The worldwide demand for flexible transmission grids leads to an increasing interest in high voltage direct current (HVDC)-voltage source converter systems resulting to the planning of radial and interconnected HVDC multiterminal grids. Since HVDC multiterminal systems have high requirements on control and protection, modular multilevel converter with full bridge (FB) submodules can be applied, preventing the handling of high fault current amplitudes. However, the feasibility of multiterminal HVDC systems utilising FB submodules has to be evaluated against the general background of selective fault handling and velocity of the fault clearing process. These necessary investigations are presented within this contribution, carried out by use of an appropriate simulation model in PSCAD tm / EMTDC tm . Thereby, requirements for protection concepts and protective devices for multiterminal systems can be further formulated. Three different variations of a protection concept have been investigated, which differ in the degree of communication structure between the converter stations and protective devices. These scenarios contain approaches with no communication, minimum communication and full communication.