Power-dense multilevel inverter module using interleaved GaN-based phases for electric aircraft propulsion

Realizing the electrification of aircraft necessitates the development of inverters and rectifiers with ultra-high efficiency and specific power simultaneously. Unconventional topologies such as the flying capacitor multilevel (FCML) inverter hold great promise for achieving transformational reductions in inverter power loss and weight due to drastically smaller filters and compact hybrid energy transfer mechanism. After describing methods to overcome obstacles in ultra-efficient and lightweight converter design, this work presents an example of interleaved FCML inverter operation. The successful, balanced interleaved operation was demonstrated in the laboratory with a dual-interleaved, 9-level converter prototype at 1 kV input bus voltage and 9.7 kW output power. At 98.6% peak efficiency, this converter achieves a gravimetric power density of 17.3 kW/kg and a volumetric power density of 35.3 kW/L including the contributions of the heat sink. Interestingly, observations from loss modeling and hardware efficiency measurements revealed the large impact of second-order loss mechanisms, such as dynamic on-state resistance and junction temperature. Insights gained from this new understanding can be incorporated into future modeling for more thorough optimization of the converter design.