Design of a GaN-Based Interleaved Nine-Level Flying Capacitor Multilevel Inverter for Electric Aircraft Applications

Multilevel inverters such as the flying capacitor multilevel inverter (FCML) hold large potential benefit in applications where the size and weight of the inverter is constrained. This article presents the design and implementation of an inverter module that incorporates two individual nine-level FCML single-phase inverters in an interleaved design. Each inverter utilizes GaN field-effect transistors (FETs) switching at 100 kHz for an effective inductor ripple frequency of 800 kHz. The implementation features an innovative dual-sided integrated switching cell layout, which decreases the commutation loop inductance of the inverter and allows fast switching with minimal ringing, while also enabling efficient double-sided cooling. The switching cell layout is particularly well suited for high-voltage applications, as creepage and clearance requirements can be easier met compared to single-sided solutions. The effectiveness of the approach is demonstrated in a hardware inverter prototype intended for driving low-inductance electric machines for future electric aircrafts. The 1000 V _dc to 380 V _ac,rms , 6-kW prototype achieves a peak efficiency of 98.6% and a peak power density of 15 kW/kg.