Neutral-Point Voltage Regulation of Three-Level Neutral-Point Clamped Converter for LVDC Power Distribution Application

A three-level neutral clamp (NPC) converter is a promising candidate for constructing a low-voltage DC (LVDC) power distribution system with a bipolar DC bus structure since it can provide a unipolar high-voltage DC output and bipolar low-voltage DC outputs. However, it has a severe neutral-point (NP) voltage imbalance with the load deviation between the bipolar low-voltage DC outputs. This paper proposes a neutral-point (NP) voltage regulation method for the three-level NPC converter in the LVDC power distribution system application. The proposed method injects DC and AC signals into the PWM reference to mitigate both AC and DC components of the NP voltage error. Therefore, the three-level NPC converter can improve the power quality of the low voltage DC outputs under the load unbalance condition. The proposed method has been verified using a 400-kW three-phase three-level NPC converter prototype.