A Novel Modulation Strategy With Unconditional Neutral Point Voltage Balance and Three Switching Actions in One Switching Cycle for Neutral Point Clamped Three-Level Converter

The carrier-based pulsewidth modulation (CBPWM) and virtual space vector pulsewidth modulation (VSVPWM) for neutral point clamped three-level converter are reviewed briefly in this paper. A novel modulation strategy is proposed to maintain unconditional neutral point voltage balance under the full range of power factor and modulation index. The proposed PWM strategy is featured with three switching actions in one switching cycle, which is named 3SNPBPWM hereafter. In 3SNPBPWM, one phase is clamped to a certain level without switching action, and the other two phases have one and two switching actions in one switching cycle (SC), respectively. Moreover, a neutral point voltage recovery algorithm for 3SNPBPWM is also proposed. The performance of 3SNPBPWM is analyzed and compared with CBPWM and VSVPWM in terms of switching loss, waveform quality, and ability of neutral point voltage recovery. Finally, the feasibility and superiority of 3SNPBPWM are verified by experiment.