Application of DC choppers in HVDC grids

This paper investigates the use and need for DC choppers in VSC HVDC grids. Sudden increases in the DC link voltage, caused by AC grid side voltage drops, can lead to potential damage of the DC equipment. Therefore, DC choppers are currently used in point-to-point links to keep the voltage within safe margins. Given that the HVDC grid topology is expected to change from point-to-point connected offshore wind farms to multi-terminal HVDC structures in the future, the potential of DC choppers in HVDC grids, is investigated. Simulations on a multi-terminal HVDC model are presented to show the performance of the system equipped with a DC chopper. The system influence of over-voltage protection using DC choppers in different grid topologies is examined. Investigations include the combination of DC choppers with DC voltage droop control. Concluding from simulations, DC choppers are a feasible measure to reach proper fault ride-through (FRT). However, the requirements for DC choppers in HVDC grids are comparatively low compared to point-to-point connections through the use of droop control.