AC / DC decoupling control strategy for DC short circuit fault ride through of full bridge MMC

Abstract

Full Bridge Modular Multilevel Converter (FBMMC) is suitable for DC short-circuit fault ride-through in high voltage direct current (HVDC) transmission due to its characteristic of outputting negative level. This paper establishes a theoretical mathematical model for the DC component and AC component of the MMC bridge, and then proposes an AC-DC decoupling control strategy that can quickly achieve fault ride-through. This strategy separately controls the AC component and DC voltage of the bridge voltage by constructing an intermediate voltage, effectively avoiding the influence of DC faults on the AC component. The voltage fluctuation of the sub-module changes during the fault ride-through process. This paper derives its fluctuation characteristics from the perspective of energy fluctuations. Finally, a corresponding simulation was built in the RTLAB real-time simulation platform to verify the correctness and effectiveness of the strategy and the fluctuation of the fault process sub-module.