CONTROL OF MMC DURING FAULT

A method of controlling a Modular Multilevel Converter (MMC) during a fault in a power grid to which the MMC is connected is disclosed. The MMC includes a plurality of phases, each including at least one phase leg. Each phase leg includes a plurality of series connected converter cells. The method includes determining that a fault has occurred in the power grid, the fault including a reduced voltage in the power grid. The method also includes, for each phase leg of the MMC, reducing the DC voltage of the phase leg by a predetermined amount from a nominal DC voltage to a reduced DC voltage, the DC voltage being the sum of all respective voltages over an energy storage of each cell of the phase leg. The method also includes determining that the fault has been cleared, whereby the voltage in the power grid is returned to nominal. The method also includes for each of the phase legs of the MMC, increasing the DC voltage back to the nominal DC voltage.