Detection and isolation of multiple faults in a modular multilevel converter based on a sliding mode observer

This paper proposes a technique able to detect and isolate multiple open-circuit faults of power switches in an MMC. Based on a sliding mode observer (SMO), the basic idea of this FDI method is to compare the observed states with the measured states. The fault occurrence is detected when the difference between the observed and measured arm current is larger than a threshold value; while a cell is identified as faulty if the difference between the observed and measured capacitor voltage is larger than a threshold value. The implementation is simple and requires no additional sensors. Simulation results demonstrate that open-circuit faults occurring simultaneously on four different cells in an MMC can be detected and isolated within 200ms.