Hybrid Active PWM Strategy With Dual-Mode Modulation Waves of Three-Level T-Type Converter for Aircraft Turboelectric Propulsion Systems

Turboelectric propulsion is emerging as an enabling technology for the future aviation industry, aiming to reduce its carbon footprint. To provide electrified thrust for aircraft, the converter-fed motor drive system is a promising solution for the energy conversion between an onboard dc distribution bus and a high-speed electric machine. However, the neutral-point potential fluctuation and even drifting can be an outstanding issue when employing three-level neutral-point-clamped (3L-NPC) topologies, which puts the converter output performance and the lifespan of capacitors at risk. To address these problems, in this article, a new hybrid active pulse-width-modulation (PWM) strategy is proposed for the studied airborne electric propulsion systems. With the versatile dual-mode modulation signals, not only can the proposed PWM algorithm keep capacitor voltages balanced at the entire range of operating points but also switching losses can be lowered with the help of discontinuous pulse trains during the cruise. Moreover, the computational burden rendered by a short switching cycle is reduced by the sextant coordinate-based analytical derivation. The effectiveness of the presented modulation technique are validated through simulation results from a Simulink/PLECS model and experimental results obtained from a 200 kVA silicon-carbide (SiC) based T-type 3L-NPC prototype with a variable output fundamental frequency.