Dead-time effect and a neutral point voltage control for a single-phase NPC converter

Single phase neutral point clamped (NPC) converters are increasingly applied in high speed railway traction drive systems as they allow the use of lower voltage devices in higher voltage applications, provide reduced output voltage THD and can develop low common mode voltage. To solve the imbalance problem of neutral point voltage, dead-time effect for neutral point voltage is described in this paper in detail, and a novel method of controlling the neutral point voltage by adjusting dead-time indirectly is proposed. Compared with the neutral point voltage control method by adjusting dead-time directly, the novel control method draws a lower harmonic sinusoidal line current with high power factor. To verify the proposed operation strategy, performance characteristics are provided by the computer simulation.