Motors and batteries get most of the attention, but the power electronics sitting between them -- inverters and motor controllers -- are just as much of a limiting factor on eVTOL performance, and a lot less discussed.
Modern silicon carbide (SiC) MOSFET-based inverters can now hit roughly 99 percent conversion efficiency at the 400-to-850-volt DC bus voltages typical of eVTOL powertrains -- a genuinely impressive figure, and one that's improved substantially as SiC has matured. Gallium nitride (GaN) devices are also gaining ground, particularly where high switching frequency and compact packaging matter more than raw voltage handling, though SiC currently remains the preferred choice for high-voltage traction systems like eVTOL propulsion.
The harder constraint isn't efficiency at this point -- it's power density. Achieving high efficiency at low mass and volume is difficult in a way that doesn't show up in an efficiency percentage: current DC-DC converter designs achieve roughly 20 kW per kilogram, well short of an industry target closer to 80 kW/kg. That gap matters because every kilogram of power electronics is a kilogram not available for batteries, payload, or structural margin -- and unlike a battery pack, an inverter can't be made lighter by simply improving one chemistry.
Power electronics decisions aren't made in isolation from motor architecture. Joby's approach -- large, dual-wound motors designed to hit a 10 to the negative 9 catastrophic failure rate -- requires inverter and controller electronics with matching redundancy, since a motor's fault tolerance is only as good as the electronics feeding it. That's the same logic covered in our motor topology piece: aviation-grade redundancy has to be engineered through the entire power path, not bolted onto one component.
Altitude adds a wrinkle that ground-vehicle power electronics don't have to deal with, too: high-voltage components have to be derated for altitude under Paschen's law, since air's insulating properties change with pressure -- a genuinely aviation-specific engineering constraint that doesn't show up in automotive inverter design at all.
Power electronics rarely make headlines, but they're a real, quantifiable limiting factor on how light and how efficient an eVTOL powertrain can get -- and the power-density gap between where the industry is (roughly 20 kW/kg) and where it needs to be (roughly 80 kW/kg) is arguably a bigger open engineering problem right now than battery chemistry.
What Makes eVTOL Motors Different Than EV Motors? -- IEEE Spectrum: https://spectrum.ieee.org/evtol-joby-jon-wagner-motors
STMicroelectronics silicon carbide power technology -- ST News: https://newsroom.st.com/media-center/press-item.html/c3283.html
How SiC and GaN Are Transforming EV Motor Controllers -- Knowledge Sourcing: https://www.knowledge-sourcing.com/resources/thought-articles/sic-and-gan-transforming-india-ev-motor-controller-industry
