A Loss Redistribution Technique for the Power Devices in the NPC Converter by PWM Zero-Sequence Injection

The neutral-point-clamped (NPC) converter suffers from uneven power loss distribution among semiconductor devices under the conventional modulation technique, which degrades its reliability. In this article, a zero-sequence voltage injection technique is proposed to address this issue. Its effectiveness of power loss redistribution is not restricted by operation conditions, and no extra devices are required. Its performance in reducing the power loss of the most stressed device in the NPC converter is verified by simulation and experiment tests under different power factors. A compatible active neutral-point voltage control strategy is designed and validated by laboratory tests. The output current quality and common-mode voltage are discussed as well.