To improve the reliability of modular multilevel converter(MMC)

the submodule failure should be detected and located rapidly when fault occurs. The speed characteristics of fault diagnosis are analyzed during submodule failure in the MMC. A new rapid diagnostic method for fault is proposed. For fault detection

the improved model predictive method is used to detect the fault by comparing the difference between the predictive value and the measured value with the threshold value and then the failures are located rapidly by comparing the slopes of submodule voltage. The proposed method can locate multiple submodule failures without additional sensors and can easily be implemented with the use of a microprocessor. Finally

the proposed method has been validated by the results of an MMC simulation and experiment platform.