A smooth changeover method of the hybrid control strategy for five-level active NPC converter

Pulse-width-modulation (PWM) method is a crucial technique to construct multilevel converter. A hybrid PWM combining the merits of both space vector PWM (SVPWM) and selective harmonic elimination PWM (SHEPWM) is proposed for the five-level active neutral-point clamped converter. SVPWM can lead to high DC voltage utilization and low ripple current at low frequency band. SHEPWM can eliminate specific low-order harmonics at high frequency band. After implementing SHEPWM, the remaining high-order harmonics can be easily eliminated by the designed filter. Large vibration usually happens to the changeover of two modulation methods. A control strategy is proposed in this paper to implement the smooth changeover between SHEPWM and SVPWM at any time. The simulation and experimental results are provided to verify the effectiveness of this control strategy.