Virtual vector-based strategy with capacitor voltage balancing for three-level active neutral-point-clamped converters in electric propulsion applications

As the power level of aircraft electric propulsion systems increases, the three-level neutral-point-clamped (NPC) inverters are extensively utilized in turbofan drives and power transmission systems due to their exceptional characteristics. To balance the switching losses, the clamping diodes in the NPC inverters can be further replaced by active semiconductors such as MOSFETs, resulting in active neutral-point-clamped (ANPC) inverters. However, issue of neutral-point potential imbalance in ANPC inverters remains to be addressed. Therefore, a virtual vector-based modulation strategy with a neutral-point potential balancing function is proposed for the ANPC inverters. The proposed virtual vectors are coordinated with two adjacent conventional vectors to attain capacitor voltage equilibrium by controlling dwelling time. The effectiveness of the proposed capacitor voltage balancing strategy for ANPC inverters is validated through both simulation and experimental results.