A T-Type Modular Multilevel Converter

This article proposes a novel modular multilevel converter (MMC) named “T-type MMC” (T-MMC) for reliable, controllable, and efficient performance in energy conversion applications. Circuitry configurations and control structures are presented with respect to fundamental and additional functions. The T-MMC topology consists of two solid-state power stages (Stage-I and Stage-II), which are coordinated for ac and dc fault tolerance and increased ac-side voltage synthesis. Energy storage elements can be integrated into the submodules. As a result, the T-MMC based energy storage system can not only increase system inertia but also maintain continuous power transmission during faults. A thyristor forced-commutation technique facilitates actively controlled utilization of symmetrical thyristors in the conduction path; thus, T-MMC normal-mode operation losses can be equivalent to those of the conventional half-bridge MMC. Simulation and experimentation demonstrate the performance of the T-MMC.