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NPC-H Bridge Multilevel Inverter using Third Harmonic Injection

Babitha T Abraham, Anish Benny

Multilevel inverters (MLI) plays vital role in the field of power electronics and being widely used in many industrial and commercial applications since it possess low electromagnetic interference and the efficiency is considerably high. Neutral point clamped, flying capacitor and cascaded H bridge multilevel inverter are the basic multilevel inverter topologies available. Even though the multilevel inverter plays a vital role, usage of more switches in the conventional configuration poses a limitation to its wide range application. The number of switching devices in the converter system can be reduced by adopting hybrid topology. The topology used here is a three phase seven level hybrid inverter consisting of three level cascaded H- Bridge (CHBMLI) and neutral point clamped multilevel inverter (NPCMLI). Asymmetric dc bus voltage ratio is employed to increase the number of levels of the entire system. The number of levels in line voltage could be increased to 13 levels by third harmonic injection. The main objective of this hybridised structure is to reduce the number of switches with the increase in number of levels. The performance of this hybrid structure with and without third harmonic injection is analyzed in this paper by simulation in MATLAB/SIMULINK. A prototype of single phase topology is also developed.