Study on neutral-point potential control for the NPC three-level converter

The neutral-point potential control is very difficult for the NPC three-level converter. This paper proposes an accurate model of the NPC three-level converter with parametric perturbation. The developed model mathematically describes that the basic reason for the neutral-point potential drift is the unbalanced distribution of active power caused by parametric perturbation. By injecting zero-sequence voltage, the neutral-point potential balancing control can be realized based on the active power exchange between the two DC-side capacitors. Take the D-STATCOM[1] based on NPC three-level converter as example[1], the effectiveness and performance of this model and control strategy are verified by simulation and has been tested on a practical installation and operation of ±400 KVAR, 1.14-kV equipment in coal mine power supply system.