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

In this paper, an efficiency comparison of neutral-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 frequency increases due to high switching loss of the equipped high voltage power switches. In order to reduce switching loss and hereby enhance efficiency, a newly proposed circuit-level decoupling modulation (CLDM) scheme is applied for these two widely used three-phase three-level inverters, as well as their corresponding loss analyses are addressed. The switching loss reduction is evaluated comprehensively under variant modulation indices and load power factors. The analysis results reveal that the CLDM is an alternative discontinuous pulse-width modulation (DPWM) approach for inverters with high switching frequencies in order to achieve superior output voltage quality without lowering efficiency.