Abstract: A method of removing a direct current component at an output terminal of an MMC converter according to the present invention includes a detection step of individually detecting charging voltages charged in capacitors of a plurality of sub-modules connected in series to each other in the MMC converter; outputting an average value of the individually detected charging voltages; delaying the outputted average value by a predetermined phase to output a phase-delayed average value; outputting the average value and the phase-delayed average value as a q-axis component voltage by using a predetermined dq conversion unit; calculating an error between the q-axis component voltage and a three-phase average voltage for the q-axis component voltage; and outputting, through a pre-determined first PI control unit, an offset voltage for reducing the error.

Abstract: A method of removing a direct current component at an output terminal of an MMC converter according to the present invention includes a detection step of individually detecting charging voltages charged in capacitors of a plurality of sub-modules connected in series to each other in the MMC converter; outputting an average value of the individually detected charging voltages; delaying the outputted average value by a predetermined phase to output a phase-delayed average value; outputting the average value and the phase-delayed average value as a q-axis component voltage by using a predetermined dq conversion unit; calculating an error between the q-axis component voltage and a three-phase average voltage for the q-axis component voltage; and outputting, through a pre-determined first PI control unit, an offset voltage for reducing the error.

Abstract: Proposed is a power supply device for a submodule controller of a modular multilevel converter (MMC) connected to a high voltage direct current (HVDC) system, which generates and supplies power through by hydraulic turbine generation using coolant flowing through a heat sink that cools a submodule. The power supply device includes a heat sink disposed inside the submodule of the MMC converter to cool the submodule using coolant; a pipe having an inlet configured to supply the coolant to the heat sink and an outlet configured to discharge the coolant to outside of the heat sink and configured to form a flow path to cause the coolant supplied through the inlet to flow to the heat sink; and a hydraulic turbine generator disposed at one side of the pipe to generate power by the coolant flowing through the pipe and supply the power to the submodule controller.