Zero-sequence voltage injection for narrow pulse compensation and neutral point potential balancing of NPC inverter

The narrow pulse problem is existed in high power application, especially with GTO using. The balancing problem of the DC-link capacitor voltage is inherent in the NPC (Neutral Point Converter) inverter. It is important to solve these two problems for the security operation. In this paper, a novel method is presented to solve the narrow pulse problem and neutral point potential balancing problem in NPC inverter at the same time. Zero sequence voltage is obtained by narrow pulse eliminating and neutral point potential imbalance, after that it is injecting into the modulation waves. The new waves is compared with carried wave to produce PWM without narrow pulse appearing to control NPC inverter, and the neutral point potential is controlled balanced at the same time.