After the occurrence of fault with sub-modules of modular multilevel converter(MMC)

the fault-phase voltage output capacity will be changed since the changed number of sub-modules of the fault bridge

which will make the system neutral point shift. For the fault-tolerant control problem following the sub-module fault of MMC

this paper proposes a fault-tolerant control strategy based on neutral point shift control(NPSC)to ensure the line-to-line voltage of the system symmetrical output. It controls the neutral point shift in the fault phase by correcting each phase modulation wave after the fault. It can complete the sub-module fault ride-through while reducing the complexity of the traditional neutral-offset control algorithm at the same time. The influence of MMC system operating characteristic under the NPSC fault-tolerant control is analyzed

and the distribution characteristics of fundamental frequency component and direct current component of bridge current are pointed out. Finally

simulation and experiment results verify the feasibility of the theoretical analysis and the proposed scheme. This work is supported by Application Technology Research and Engineering Demonstration Program of National Energy of China(No. NY20150302).