Modular Multilevel Converter-energy difference controller in rotating reference frame

This paper presents a control strategy capable of eliminating the mean value of the energy differences between the upper and lower arms in a three-phase Modular Multilevel Converter (MMC) in Park Coordinates for HVDC applications. This is achieved by controlling the active and reactive differential currents using a rotating reference frame at fundamental frequency in order to eliminate the zero sequence energy difference components by means of an inner and outer control loops. All feed-forward equations are demonstrated, with specific attention being paid to the cross-coupled terms.