A new T-type NPC-based submodule for modular multilevel cascaded converters

This paper presents a novel 4-Level T-Type Neutral-Point-Clamped (4LT²-NPC) submodule for modular multilevel cascaded converter (MMCC) family. Using the proposed modules in the cascaded converters is advantageous in reducing the number of submodules, thus reducing the dimensions of the converter. It is also shown; this new solution can contribute not only in reduction of converter submodules, but can also offer additional controllability in controlling the converter and overcome the typical NPC multilevel submodule drawback of dc capacitor voltage balancing limitation. The switching states and capacitor balancing of the new submodule are analyzed and a balancing scheme is introduced. The operation of the proposed submodule in MMCC is validated by simulation results.