Design and Optimization of a High-Performance 3D-Stacked Flying Capacitor Multilevel Inverter for Electric Drivetrains

The development of future electric vehicles depends on high-performance power electronics. In aerospace applications, minimizing weight while maximizing efficiency is critical, whereas volumetric power density is a primary constraint in traction drives. This work presents the design process of a flying capacitor multilevel (FCML) inverter intended for lightweight, low-inductance electric machines. A detailed loss model is developed, accounting for the impact of flying capacitor voltage ripple, and is integrated with a volume estimation framework to enable multi-objective optimization across key design parameters. To validate the analysis, a 10-level GaN-based FCML inverter is designed. Featuring an innovative 3D-stacked layout, the hardware prototype achieves an unprecedented volumetric power density of 800 kW/L and a gravimetric power density of 250 kW/kg, along with a peak efficiency of 97.34 % and total harmonic distortion (THD) below 5 %.