Study of the Modulation Schemes in the Hybrid Three-Phase Multilevel Inverter

Abstract

-This work proposes and analyzes modulation strategies for a hybrid three-phase multilevel inverter, which employs two different topologies in a cascade connection, a three-phase Neutral Point Clamped (NPC) converter and single-phase half-bridge converters. Two different modulation schemes are proposed: the hybrid modulation and the space vector modulation. The both modulation schemes can synthesize five voltage levels in the output phase voltage at the hybrid three-phase multilevel inverter with symmetrical dc sources. The modulation schemes operate the three-phase NPC in low-switching frequency and the half-bridge converters in high-switching frequency. Thus, semiconductors with low conduction losses can be used for three-phase NPC, decreasing the semiconductor losses. The hybrid three-phase multilevel inverter structure and modulation schemes are explained in detail and verified by simulation and experimental results.