Power Loss Assessment of Three-Level Neutral-Point-Clamped Inverter With DPWM Modulation

The three-level neutral-point-clamped (3L NPC) inverter is widely employed for the renewable energy application. To achieve lower life cycle cost, the efficiency of 3L NPC inverter is highlighted. Compared to the continuous PWM (CPWM) modulation, the discontinuous PWM (DPWM) modulation is preferred to reduce switching and conduction losses. Nevertheless, the power loss assessment of the DPWM modulation is a remaining challenge for the 3L NPC inverter. In this paper, the general mathematical model of the DPWM modulations is created to quantify the power loss of the 3L NPC inverter. The duty cycles of the power device are modeled for the unipolar and bipolar CPWM modulations, even for the DPWM modulations of the 3L NPC inverter. Moreover, the switching and conduction losses of the 3L NPC inverter are analyzed, considering different CPWM and DPWM modulations. The experimental test rig and switching trajectory are presented to observe the specific loss of the commercial 3L NPC power module. Besides, comprehensive comparisons of the power loss dependent on PWM modulation are demonstrated for the 3L NPC inverter. It is found that the theoretical predictions of the proposed model are consistent with the simulated results of the PLCES tool. Due to the optimal power loss, the DPWM1 is recommended for the 3L NPC inverter application. The methodologies and findings in this paper are also helpful for the 3L T-type NPC (TNPC) and active NPC (ANPC) inverter application.