A New PWM Scheme for Loss Balancing and Neutral-Point Voltage Balancing in Three-Level Active NPC Converter

Three-level neutral point clamped voltage source converter (NPC VSC) is widely used in high-power high-voltage applications. The main drawbacks of NPC VSC are the unequal loss distribution among the semiconductors and the fluctuation in the neutral point voltage. Compared with NPC converter, active NPC (ANPC) converter enable more commutations and thus improve the loss distribution among semiconductor devices, the output power rating is increased. However the fluctuation in the neutral point voltage of ANPC may destroy the loss balancing and increase the voltage stress across the power devices. A novel PWM scheme that includes loss balancing and NP voltage balancing over the full range of converter output voltage and for all load power factors is proposed in this paper. The performance of this modulation approach and its benefits are verified through simulation and experiments.