PWM Strategy for MW-Scale 'SiC+Si' ANPC Converter in Aircraft Propulsion Applications

In this article, an improved pulsewidth modulation (PWM) strategy is introduced for three-level active neutral point clamped converters based on a hybrid configuration of silicon carbide (SiC) mosfets and silicon (Si) insulated gate bipolar transistor (IGBTs). Compared with the conventional PWM strategies in the literature, this proposed PWM strategy enables the SiC switches only to interface with small commutation loops, thus the turn-off voltage overshoots caused by the parasitic loop inductance and high di/dt are much lower. Soft switching is achieved across all the IGBTs, and the switching losses of the converter only dissipate from the SiC mosfets, leading to high efficiency of the converter. Also, with this improved PWM strategy, the conduction loss at zero voltage output of this converter is reduced due to the turn-on of two parallel conduction paths. Furthermore, this proposed PWM strategy can protect the body diodes of the SiC mosfets from conducting large load current. All these advantages with the proposed PWM strategy are experimentally verified in a megawatt-scale three-phase three-level 'SiC+Si' hybrid active neutral point clamped inverter developed for electric aircraft propulsion applications.