The space vector PWM scheme for a novel three-level inverter with two parallel three-phase full-bridges

Three-level inverters are increasingly being used in high power middle voltage applications due to their superior performance compared to two-level inverters. However, The neutral point fluctuation problem associated with the traditional three-level inverter like neutral-point clamped inverter is difficult to deal with. This paper proposes a novel three-level topology which is constructed by two three-phase full-bridges with parallel dc input and isolated series ac output. Of this topology, the neutral point imbalance problem is totally avoided, the utilization ratio of dc voltage is twice that of the traditional three-level inverters, and the reliability is increased by switching to two-level mode when one bridge fault occurs. Based on the basic vectors and switching states of this novel inverter, a corresponding SVPWM scheme is developed, which is realized by categorizing switching sequence into five different cases in accordance with modulation index m. The optimized switching sequence reduced the number of switching occurrence when the reference vector changing between sectors as well as triangle areas. Finally, simulation results are provided.