A Fault Tolerant Control Strategy for the Delta-Connected Cascaded Converter

As the increased reliability requirement, the fault tolerant operation as the bridge-cell failures is an important issue for the modular multilevel cascaded converter (MMCC). This paper proposes an effective fault tolerant strategy for the delta-connected cascaded converter. During the occurrence of the bridge-cell fails, the proposed open-delta operation enables the converter continuous operation and maintains the dc capacitor voltages balanced. This fault tolerant technique does not require extra hardware circuit installation. Laboratory tested results are given to validate the proposed control approach.