Capacitor Voltage Balance for the Neutral-Point- Clamped Converter using the Virtual Space Vector Concept With Optimized Spectral Performance

This paper presents a new pulsewidth modulation (PWM) for the complete control of the neutral-point voltage in the three-level three-phase neutral-point-clamped (NPC) direct current–alternating current (dc–ac) converter. The balancing of the neutral-point voltage is achieved over the full range of converter output voltages and for all load power factors with the minimum output voltage distortion at around the switching frequency. The simple phase duty-ratio expressions in $d\hbox{-}q\hbox{-}0$ coordinates that define this modulation are presented. The performance of this modulation approach and its benefits over other previously proposed solutions are verified through simulation and experiments.