Besides the recognized advantages over conventional VSCs, one of the remarkable features of the MMC is the ability to store energy in the distributed sub-modules. As a solution to the DC voltage restoration problem, we propose a novel strategy that makes use of the energy storage capability of the MMC to bring the voltage in the HVDC lines back to its rated value. This implies a disconnection of the concerned MMC from its correspondent AC grid, in order to control the lines energization. By employing this method, the total time from the fault occurrence to the power restoring is around 1 sec. The proposed strategy allows to accelerate the time to restore the power while avoiding the use of DC discharging resistors and DC pre-insertion closing resistors. An insulation recovery check can be also performed smoothly.
Patent appl. FR3065590 PCT/EP2018/059849