Neutral-Point Deviation Control for Three-Phase T-Type NPC Rectifiers With Fewer Voltage Sensors

In three-phase three-level neutral point clamped (NPC) converter, keeping neutral-point (NP) voltage balance is essential for stable operation. The common balance methods typically need two voltage sensors to sample the voltages of two split capacitors, which are not conducive to reducing cost and improving reliability. This article proposes a method of obtaining the sign of the voltage difference by only using one voltage sensor. By discussing the relationship between voltage difference, voltage and current error phase angle, it is concluded that the sign of unbalanced voltage can be obtained by calculating the error of the current vector and analyzing its phase angle. As a result, the NP voltage can be balanced with a single voltage sensor. Finally, the feasibility of this method is verified through experimental results on a three-phase three-level T-type NPC rectifier.