Method of neutral-point voltage balancing for a grid connected NPC inverter system with time-offset variant estimating

This paper proposes a neutral-point voltage balancing method for a grid-connected NPC inverter system. The proposed method is achieved by adding the time-offset to three phase turn-on times of switches. The proper time-offset is simply obtained through the proposed time-offset variant estimating. By using the proposed method, it is possible to balance the neutral-point voltage without additional hardware, complex calculation and analysis. Simulations are carried out to confirm the effectiveness of the proposed method.