A zero‐current‐transition soft‐switching technique for T‐type NPC three‐level inverter

Abstract

Based on the commutation property of the T-type neutral point clamped (T-NPC) three-level inverter, a novel zero-current-transition (ZCT) soft-switching topology is proposed. The proposed topology employs only two auxiliary switches and one inductor and capacitor (LC) resonant tank on each phase leg. The commutation process of the soft-switching technique is analyzed. The results show that all switches on main leg and auxiliary leg can achieve soft commutation without changing pulse width modulation (PWM) strategy. The control family of T-NPC three-level ZCT soft-switching topology are analyzed respectively, and then the resonant tank and timing schemes of different modes are given. Using two auxiliary switches in resonance can produce greater resonance current due to the combination of external excitation sources, which is more conducive to realize the soft-switching commutation of the main switch. At last, a half bridge prototype of T-NPC three-level inverter is built. The influence of equivalent internal resistance of power switches, diode reverse recovery and stray inductance for soft commutation is analyzed. The advantages of ZCT soft-switching technology is verified.