DC Fault Ride-through Strategy for Modified Series Single Chain-link Modular Multilevel Converter

This paper presents a DC fault ride-through strategy for modified series single chain-link modular multilevel converter (MSSC-MMC). Although the Modular multilevel converter (MMC) has good application prospects in medium-voltage DC distribution networks, the series single chain-link modular multilevel converter (SSC-MMC) has more significant advantages in reducing the number of sub-modules (SMs), equipment costs, and volume. In DC distribution networks, DC short circuit fault is an important challenge that must be considered and addressed. The existing DC fault ride-through strategy based on modified MMC mainly includes blocking protection and voltage regulation operation. The blocking method can effectively control fault current, but restarting is more difficult. The voltage regulation operation strategy makes restarting easier, but the fault current will be relatively high. Due to the different topological structures between SSC-MMC and MMC, the above approach cannot be directly applied to SSCMMC-based systems. Therefore, a modified topology of SSCMMC and the corresponding DC fault ride-through strategy is proposed in this paper.