Multi-mode Synchronized PWM Schemes for three-level NPC Inverter

The synchronous space vector pulse width modulation (SSVPWM) strategy for neutral-point-clamped three-level inverter is studied in this paper. Firstly, the composition principle of synchronous symmetric switching sequence is studied. Then, the switching sequences corresponding to each pulse number P are determined by reasonable partition of the space vector plane. After that, the harmonic characteristics of the selected three kinds of switching sequences are compared and analyzed. Finally, a three-level multi-mode SSVPWM is proposed for the high-power traction drive system with low switching frequency. Additionally, the switching rules between different modulation modes are analyzed. Simulation and experimental results verify the correctness and feasibility of the multi-mode modulation strategy.