Neutral-point potential balancing method for Z-source three-level NPC inverters

The effect of shoot-through process on the neutral-point current for Z-source three-level neutral point clamped (NPC) inverters was explored. Analysis results show that the insertion of shoot-through states does not disturb the neutral-point voltage balancing. Based on this, a voltage balancing strategy for carrier-based pulse-width modulation was developed. The proposed method completely removes the low-frequency voltage fluctuation that appears at the neutral point utilizing double-signal PWM (DSPWM) technique. However, DSPWM does not provide natural voltage balancing. Therefore, a feed-forward compensation loop, which correctly modified the shoot-through duty cycle, was introduced. This compensation strategy does not increase the number of semiconductor commutations, and hence not increase the switching losses. Simulation and experimental results were included for verifying the validity of the proposed control algorithm.