Efficiency Performance of 7-Level Multilevel Multiplexed and 3-level NPC Converters

Multilevel converters play a vital role in medium-voltage AC drive system and grid-connected system applications, as they provide a high conversion efficiency while substantially reducing total harmonic distortion (THD) in the output voltages and currents, thereby enhancing overall power quality and performance of the system. This thesis presentsa comprehensive study of the efficiency, power losses, and THD characteristics of the three-phase multiplexed multilevel converter in comparison with the conventional three-phase three-level neutral-point-clamped (NPC) converter. Simulation models are designed using MATLAB®Simulink (R2024b), leveraging its advanced electro-thermal semiconductor models to accurately compute conduction and switching losses for both topologies under various operating conditions. Although the three-level NPC converter offers advantages such as simpler topology, fewer semiconductor components, and lower implementation cost, it exhibits inferior output voltage quality due to higher THD and high dv/dt stress. In contrast, the multiplexed multilevel converter achieves superior power quality and reduced harmonic content. The simulation results validate the THD for NPC converter is 54% higher, at medium load 75% higher and at lower load 57% higher, power losses in semiconductors are for NPC converter are: 13% higher at higher load, 18% higher at medium load, 39% higher and efficiency metrics for both, three-phase three-level NPC converter and the three-phase multiplexed multilevel converter, enabling a detailed comparative evaluation of their performance.