General analysis on imbalanced voltage of DC capacitors in NPC three-level inverter

As Neutral-Point-Clamped topology has been widely studied and applied in three-level inverter, owing to its simple structure and low cost, balance of DC capacitors´ voltage is one of the key issues involving operation safety and output performance in this topology type. With detailedly discussing causes and impacts of imbalance of neutral-point level in NPC three-level inverter, a comprehensive analysis is conducted on the imbalance characteristics. A tight connection is revealed through the analyzing process, as voltage fluctuation of the DC capacitor and the union combined with both modulation index and power factor. Strong guidance for circuit design and control scheme of the NPC type inverter could be given according to research results in this paper. Simulation results on the model built in Matlab verify the analysis results above.