-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.
This work presents a novel hybrid three-phase multilevel inverter that employs a three-phase Neutral Point Clamped converter and single-phase Half-Bridge cells in a particular cascade connection. Its cascaded structure allows its application in medium-voltage applications with low voltage semiconductors. The inverter operation is analyzed and can lead to a 5, 7 or 9 level structure. A hybrid modulation scheme for the operation with five levels at the output phase voltage is proposed, which leads to unidirectional power flow in all dc sources and, thus, eases the implementation. The proposed structure and modulation scheme are analyzed and explained in details and simulation and experimental results are provided to verify the presented analysis.
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