Comprehensive Loss Evaluation of Neutral-Point-Clamped (NPC) and T-Type Three-Level Invertersbased on a Circuit Level Decoupling Modulation.

In this paper, an efficiency comparison ofneutral-point-clamped (NPC) inverters and bipolar switch NPC(T-Type) inverters is studied and the result shows that the T-Type inverter is more efficient at lower switching frequencies.Nevertheless, its efficiency suffers when the switching frequencyincreases due to high switching loss of the equipped high voltagepower switches. In order to reduce switching loss and herebyenhance efficiency, a newly proposed circuit-level decouplingmodulation (CLDM) scheme is applied for these two widely usedthree-phase three-level inverters, as well as their correspondingloss analyses are addressed. The switching loss reduction isevaluated comprehensively undervariant modulation indices andload power factors. The analysis results reveal that the CLDM isan alternative discontinuouspulse-width modulation (DPWM)approach for inverters with high switching frequencies in orderto achieve superior output voltage quality without loweringefficiency.