Achieving DC fault tolerance in modular
multilevel converters requires the use of a significant
number sub-modules which are capable of generating
a negative voltage. This results in an increase in the
number of IGBT devices in the current path, resulting
in an increase in conduction losses within the converter.
This paper introduces a thyristor augmented multilevel
structure called a Power-Group, offering both negative
voltage capability as well as a low conduction loss state,
which can be used to construct high efficiency DC fault
tolerant converters. When combined with the Alternate
Arm Converter topology the power-group concept has
been found to result in a converter topology that exhibits
very low power-losses, high quality AC and DC current
waveforms, while also achieving DC fault tolerance.