A new discontinuous PWM method of three-level inverter for neutral-point voltage ripple reduction

A new pulse width modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is proposed in this paper. A three-level NPC inverter is completely mature and very well established topology in high-power applications. However, the three-level NPC inverter has the inherent problem of neutral-point voltage unbalancing due to the split dc-link capacitors. This structure can cause the large neutral-point voltage ripple. Furthermore, output currents of the three-level NPC inverter can be distorted by the neutral-point voltage ripple. In this paper, a new DPWM method using two different offsets for the neutral-point ripple reduction is proposed and the effectiveness of the proposed DPWM method is verified by using the simulation.