Full bridge MMC converter controller for HVDC operation in normal and DC fault conditions

摘要

Three-channel controller of FB-MMC HVDC that enables four-quadrant operation on DC side and fault ride through on AC and DC sides without blocking IGBTs is proposed. Phasor modeling of FB MMC is studied to provide insight into independent AC and DC control. Three modulation indices are used: the conventional d-axis, q-axis AC-side modulation indices Md, Mq and a newly proposed DC modulation index Mdc. Dedicated control of arm sum voltages and DC current are proposed. The controller is thoroughly tested on EMTP/RV model. It is demonstrated that DC power can be independently controlled regardless of DC voltage (including negative DC voltage) and operation in all four quadrants is verified. The reactive power support to the AC system is provided at any values of positive, negative or zero DC voltage. Safe and continuous operation of FB-MMC without blocking IGBTs is verified. Additional control for extinguishing DC fault arc is also illustrated.