Benefits of HVDC for reducing the risk of cascading outages and large blackouts in AC/DC hybrid grid

Because of their controllability, HVDC (High Voltage Direct Current) links can be applied for controlling power flow on parallel AC transmission paths, and then the DC power can be automatically adapted to protect the AC lines from being overloaded and thereby prevents large cascading line outages in the grid, possibly leading to large blackouts. However, in the literature, many works have studied the impact of HVDC on the power system stability, but very few in the area of its impact on the system security. The idea of increasing the power transfer in the HVDC link to decrease the loading of the parallel AC lines to ensure system security is proposed and can be found in the literature, but with out any detailed description of the procedure. The main purpose of this paper is to clarify and discuss in detail the advantages provided by the HVDC links to limit cascading outage during severe contingencies. The effectiveness of the HVDC link to reduce the risk of cascading outages is assessed under various disturbances by detail simulation.