Simple Neutral-Point Voltage Control for Three-Level Inverters Using a Discontinuous Pulse Width Modulation

This paper proposes a neutral-point voltage balancing method for a three-level inverter that uses discontinuous pulse width modulation (DPWM). The performance of a three-level inverter system is affected by the neutral-point voltage unbalancing. Therefore, the voltages of series connected dc-link capacitors should be equal. Generally, the offset voltage is added to reference voltages in the conventional voltage balancing method. However, when using DPWM, the performance of conventional balancing method is limitary because turn-on and turn-off switching occurs at regular intervals. The proposed method is implemented by adjusting the discontinuous pulsewidth of positive and negative cycle. The proposed method maintains low switching losses and achieves the effective voltage balancing, without additional hardware and complex calculations. Simulation and experimental results confirm the feasibility and effectiveness of the proposed method.