3.3KV, MEGAWATT LEVEL MODULAR MULTILEVEL INVERTER FOR HYBRID/FULL ELECTRIC AIRCRAFT

Abstract

Hybrid/Full electric aircraft (HEA/FEA) represents an attractive concept due to its potential to reduce CO2 emissions, decrease fossil-fuel consumption, enhance overall aircraft efficiency, and lower operational costs. As technology progresses towards hybrid/full electric aircraft, the development of high-performance motor drive systems becomes imperative. This necessity introduces new constraints, particularly in low-pressure environments. Designing for high-altitude applications requires careful consideration to prevent issues like partial discharge and power system failures in the air. Converters must exhibit ultra-high efficiency, high power density, and exceptional reliability. While wide band-gap devices, such as Silicon-carbide based Metal Oxide Silicon Field Effect Transistors (SiC-MOSFETs), offer improved switching and high-temperature performance over silicon counterparts, their integration into HEA/FEA applications remains challenging. The high switching speed of SiC-MOSFETs reduces switching losses and facilitates the design of high-density inverters. However, selecting suitable devices is critical for designing high-power-rated inverters. Moreover, the risk of partial discharge increases at high voltages in conditions of low air pressure, posing a threat to inverter longevity by compromising system insulation. This thesis evaluates three distinct inverter/converter topologies comprehensively to determine the optimal circuit topology for HEA/FEA applications. The study explores design strategies to ensure busbar integrity, preventing partial discharge without compromising parasitic control. Throughout the thesis, a three-phase megawatt-scale inverter and a 3.3 kV, 288 A power module are designed, fabricated, and tested to validate the proposed design strategies.