METHOD FOR REMOVING DIRECT CURRENT COMPONENT AT OUTPUT TERMINAL OF MMC CONVERTER

A method for removing a direct current component at an output terminal of an MMC converter according to an embodiment of the present invention comprises: a detection step of individually detecting charging voltages charged in capacitors of a plurality of sub-modules connected in series to each other in an MMC converter; a first output step of outputting an average value (Vdc_avg) of the individually detected charging voltages; a second output step of delaying the outputted average value (Vdc_avg) by a pre-determined phase to output a phase-delayed average value (Vdc_avg_θdelay); a third output step of outputting the average value (Vdc_avg) and the phase-delayed average value (Vdc_avg_θdelay) as a voltage (Vq_dc) of a q-axis component by using a pre-determined dq conversion unit; a calculation step of calculating an error between the voltage (Vq_dc) of the q-axis component and a 3-phase average voltage (Vq_dc_3φ_avg) for the voltage (Vq_dc) of q-axis component; and a fourth output step of outputting, through a pre-determined first proportional integration (PI) control unit, an offset voltage (Vref_dc_current) for reducing the error.