Theory to practical implementation of full-bridge modular multilevel converter for HVDC applications

Modular multilevel converter (MMC) has become a prominent converter topology used in HVDC transmission systems over the past decade. The efficiency, size and system performance are the main factors of the HVDC converter stations which directly affect the converter performance end-cost. Replacing conventional half-bridge (HB) cells by full-bridge (FB) cells in the MMC arms offers new features such as the dc fault blocking capability for grid-connected voltage source converters (VSC) at the cost of higher number of devices and conduction losses. However, practical implementation of FB MMC has not been fully discussed so far. In this paper, the implementation challenges of FB MMC is addressed in both steady-state and dynamic operation modes of a point-to-point HVDC link. The work is supported with the analysis of design arguments for a realistic converter station.