Topologically reduced multilevel converters using complementary unidirectional phase-legs

This paper presents a family of multilevel converters based on topological reductions of the three most well established multilevel converter structures, i.e. the cascaded H-bridge (CHB), neutral-point clamped (NPC), and flying-capacitor (FC) inverters. The topologically reduced arrangements are created by parallel-connections of pairs of complementary unidirectional phase-legs linked by a coupled-inductor. Depending on the choice of power semiconductor devices, these converters use the same amount of silicon as traditional converter structures, while also achieving a substantially improved output voltage harmonic performance. The paper presents a common framework for the topological reduction of H-Bridge and NPC converter phase-legs (similar to previously reported structures), and then proposes a new topologically reduced flying-capacitor (RFC) inverter phase-leg based on the same principles. The operation of this new RFC inverter is supported by simulation and experimental results.