A simple control method for neutral-point voltage oscillation reduction of three-level Neutral-Point-Clamped inverter

Three-level Neutral-Point-Clamped inverter has inherent problem which is the neutral-point voltage fluctuation caused by the neutral-point current that flows into or out from the neutral-point. Even though the neutral point voltage is balanced with certain method, the oscillation of neutral point voltage is still remains due to the output phase current. If total capacitance of DC-link capacitor is smaller, the amplitude of oscillation is larger. In this paper, three-level neutral-point-clamped inverter system is analysed by the small-signal modeling and the control method reducing the oscillation of the neutral-point voltage is proposed. By the proposed method, the amplitude of the neutral-point voltage oscillation is reduced to almost zero. The validity of the proposed method is verified by the simulation and the experiment.