Hybrid Virtual Coordinate-Driven CBPWM Strategy of Three-Level T-Type NPC Converters for Electric Aircraft Propulsion Applications

Green airborne transportation driven by the state-of-the-art turboelectric propulsion technology has received considerable attention from the aviation industry. To generate electrified thrust, three-level neutral-point-clamped (3L-NPC) converter-fed motor drives are one of the most promising candidates for the powertrain of future aircraft. However, the neutral-point (NP) potential ripple and deviation lead to harmonics and imperil the lifespan of semiconductors and capacitors. Besides, excessive power losses on the converter can limit propulsive power and shorten flight distance. To solve these issues, in this article, a new hybrid modulation strategy is proposed. With respect to the takeoff and climb featuring NP voltage drift-prone regions, carrier-based coordinate-driven modulation waves are exploited to enable virtual-space vectors. For operating points with high power factor, such as cruise, by reconstructing modulated signals, not only can the NP voltage balance be realized but also the switching loss is reduced using active discontinuous pulse trains. The less computational burden is attributed to implementations in the sextant-coordinate system. The effectiveness of the proposed algorithm is verified by simulation results from a Simulink/PLECS model and the experimental results are obtained from a 200 kVA silicon-carbide-based T-type 3L-NPC prototype with a variable output fundamental frequency.