Coordinated Control Strategy of Fault Ride-through for DC Grid Based on Hybrid MMC

A DC grid based on a hybrid modular multilevel converter (MMC) effectively achieves large-scale renewable energy integration, multi-energy complementarity, and friendly grid connection. Aiming at the problem that the traditional DC fault ride-through (FRT) scheme will cause the interruption of power transmission in the whole network, a novel DC FRT coordinated control strategy is proposed in this paper, which can quickly interrupt the fault current and avoid the MMC exiting operation. Based on the analysis of fault current composition and key influencing factors, for fault line MMC (FLMMC), a negative voltage control strategy adaptive to the change of fault current is proposed, which can improve the current attenuation speed and ensure reliable fault isolation. For non-fault line MMC (NFLMMC), considering the overvoltage and overcurrent risks of FLMMC, the coordinated current-limiting control method and parameter selection principle of NFLMMC is proposed, where the current-limiting performance can be adaptive to the voltage change of DC bus, to realize the rapid recovery of DC power grid while restraining fault current. Finally, a four-terminal DC grid simulation model is built using the RTLAB OP5600 real-time digital simulation platform. The simulation results show that the coordinated control strategy proposed in this paper can quickly interrupt DC fault current, shorten DC grid recovery time, and improve system security and stability. © 2024 Power System Technology Press. All rights reserved.