NASA Electric Aircraft Testbed

The highest voltage used now is 540 (±270) volts, but distributing megawatt-scale power will require higher voltage to reduce current for smaller, lighter electric cables. One megawatt over 150 ft (46 m) need 900 kg at 540 V but would be reduced to 200 kg at 2,000 V DC. A near-term hybrid would need 1,000–3,000-volt and a fully turboelectric large aircraft 5,000–10,000-volt, like ship power systems but arcing occurs at much lower voltages at low pressures than at sea level.^[2]

While a battery power source would use a direct current distribution, a gas turbine power source would also allow alternating current which would need power converters, mainly inverters to convert DC to controlled, variable-frequency AC to regulate a motor speed and torque. Silicon carbide [SiC] and gallium nitride [GaN] switches can operate at higher frequencies with lower losses, increasing efficiency. GE is building a 2,400-volt DC, 1-megawatt inverter with SiC switches and its 1.7-kW MOSFETs power modules. The University of Illinois is building a 1,000 volts DC, 200-kW "flying capacitor" scalable to a 1-megawatt with GaN-based field-effect transistor switches. Both are liquid cooled and target 19 kW/kg at 99% efficiency, but Boeing is developing a cryogenically cooled 1-megawatt inverter for 26 kW/kg and 99.3% efficiency with off-the-shelf silicon semiconductors, and is currently fabricating a liquid-nitrogen-cooled 200-kW inverter before a 1-megawatt one.^[2]