Design of MVA-Class High Power Density Multilevel Inverters for Electric Aircraft Propulsion

Abstract

Electric aircraft propulsion (EAP) has been in the spotlight over the past decade, promising a more sustainable future. As onboard power demands of future propulsion systems surpass the megavolt-ampere (MVA) level and the voltage of onboard electric power systems rises dramatically, multilevel inverters have garnered increasing attention in the aviation industry for their superior performance. To fully unleash the potential of multilevel inverters in MVA-class EAP applications, further optimization of its performance, particularly in power density, is essential to achieving lighter, more efficient, and more cost-effective EAP motor drives. To establish context for the development of multilevel inverters in EAP applications, a detailed review is conducted. The current status is thoroughly elaborated by presenting existing examples of multilevel inverters designed for EAP systems, and future trends in the development of multilevel inverters are also analyzed. To identify the most competitive inverter topology for MVA-class EAP motor drives, a comparative study is performed on various topology candidates. Their performance is evaluated across multiple aspects, including power density, efficiency, power quality, reliability, and cost. Based on this analysis, the inverter topology with the best overall performance is selected for further development. Optimization strategies for multilevel inverter design are proposed at both the system and component levels. For power semiconductor devices, their arrangement and connections are analyzed to achieve an optimal layout that balances power density, commutation behavior, thermal performance, and manufacturability. To optimize the design of DC-link capacitors, a simplified voltage and current ripple estimation method is introduced, and the minimum required capacitance for the designed inverter is accurately predicted. Additionally, as a critical part fulfilling interconnections of components, a design methodology of laminated bus bars in MVA-class multilevel inverters is proposed. The designed bus bar achieves a globally optimized performance in terms of weight, stray inductance, insulation, as well as heat dissipation. Finally, the designed inverter is fabricated and validated with a series of tests. As a result of extensive optimizations, the designed inverter achieves a total weight of 17.6 kg and a gravimetric power density of over 56.8 kVA/kg, establishing a new benchmark for MVA-class EAP systems. Comprehensive testing at rated DC voltage and power levels confirms the inverter's electrical and thermal performance, demonstrating its capability for high-power, high-voltage operation in demanding aviation applications.