Neutral-point voltage control for a three-level DC-AC inverter using equivalent-input-disturbance approach

One problem with a single-voltage source, three-level inverter is the drafting of its neutral-point voltage. This may occur during transition or when unbalanced loads are connected to the inverter system. Variation of neutral-point voltage may greatly deteriorate the power quality. In this paper, we employ an equivalent-input-disturbance approach to deal with this problem. By adding an extra neutral leg, the control problem of neutralpoint voltage is converted to a disturbance rejection problem. This method suppresses the variation of the neutral-point voltage to a small level and reduces the capacity of capacitors. Simulation results show the effectiveness of the method.