Analysis of Average Neutral Point Current in 3-level NPC Converter under Generalized Unbalanced AC Input Condition

This paper presents a neutral point deviation compensating control algorithm applied to a 3-level NPC converter under generalized unbalanced ac input conditions. The neutral point deviation is analyzed with a focus on the current flowing out of or into the neutral point of the dc-link in 3-level NPC converter. The model of neutral point deviation and neutral current are also constructed. The positive and negative sequence components of the pole voltages and ac input currents are employed to accurately explain the behavior of 3-level NPC converter and its impact on neutral point deviation. This paper includes the harmonic characteristic of neutral point current under various imbalance AC operating conditions.