A new control strategy to balance neutral-point voltage in three-level NPC inverter

The three-level neutral-point-clamped (NPC) inverter has attracted significant interest for high power/voltage applications, due to its significant advantages. A drawback of NPC inverter is that it is prone to voltage drifts and low-frequency voltage ripples of the neutral-point. In this paper, a novel control strategy of neutral-point balancing under SVPWM-based switching strategy is proposed which can be generally applied for all NPC inverters. Different from the previous control strategies, the proposed strategy utilizes a proportional resonant (PR) controller, which not only can eliminate voltage drifts, but also can minimize low-frequency voltage ripples at the same time. The effectiveness of the approach is documented by experiments obtained from a grid-tie three-phase NPC inverter.