DC-bus voltage balancing for three-level NPC inverter using deadbeat controller

A new DC-bus voltage balancing method using the deadbeat control concept for three-level neutral-point clamped power converters (3L-NPCs) is proposed and experimentally verified in this work. Within this paper, we firstly derived a model of the instant neutral point current, with which, the average model of the neutral point current is obtained. This average model allows us to calculate neutral point current within one sample interval. Based on a well-known model of the DC-bus voltage and the developed average neutral-point current model, a deadbeat controller dealing with the DC-bus balancing control is designed and incorporated into a space vector modulation (SVM) method, which allows to adjust the neutral-point current continuously. The novelty of the proposed method is that, a good DC-bus voltage balancing control can be assured, at a any load condition and any output voltage of the converter, while the normal functionality (phase voltage and current output) of a 3L-NPC remains, which have been proofed with both simulation and experimental data. The experimental data also shows that good dynamics of the dc-bus voltage adjusting and low neutral point voltage ripples can be achieved with such solution.