take better advantage of the high level of synergy of the LH2 as a fuel and as a cryogenic cooling medium for superconducting power conversion. Figures 10 and 11 depict two different turbo electric architectures with batteries as an energy buffer. The first one (Figure 10) is composed of modular series-connected propulsors. This concept can be proposed to achieve highvoltage transmission and thus save overall weight. The series-connected propulsors also have the benefit of floating ground for each propulsor, yielding low voltage across the insulation to achieve better reliability. Alternatively, the propulsors could be connected in parallel instead, as in Figure 11. LH2 Tank Boiler Cryogenic Cooling Circuit Inverter H2 dc + - B4 T2 H2 Turbine + - G2 Inverter H2 Turbine B3 + - dc B2 T1 LH2 Tank H2 Boiler + - G1 Cryogenic Cooling Circuit LH2 as a Key Enabler for Lightweight Electric Propulsion All-electric aviation will always be technically possible by replacing conventional propulsors with classical electric motors. However, they have an intrinsically high weight and size, which is a major technological barrier. In fact, today's electric machinery in the multimegawatt range is roughly 50-100× too heavy to be used in future electric propulsion systems in large aircraft segments. By means of intensive cooling and lightweight design efforts, the weight could be reduced by a factor of 10 when compared to conventional designs. This is not sufficient in the large segments of aviation, where ultra-efficient lightweight Converter dc Inverter dc dc Converter dc P4 Inverter dc M4 Inverter dc M3 Inverter M2 dc Converter dc P3 dc Converter P2 dc dc dc P1 B1 M1 H2: Hydrogen Figure 10. Hydrogen turbo electric propulsion for four propellers in series configuration assisted with batteries as a buffer. M: motor; P: propellor; B: battery; G: generator. LH2 Tank Boiler Inverter Cryogenic Cooling Circuit Inverter H2 dc P4 dc Inverter T2 H2 Turbine dc P3 G2 Converter Inverter H2 Turbine dc dc T1 LH2 Tank Boiler B1 Inverter M3 dc P2 + - H2 M4 Inverter dc M2 dc G1 Cryogenic Cooling Circuit P1 M1 H2: Hydrogen Figure 11. Hydrogen turbo electric propulsion for four propellers in parallel configuration assisted with batteries as a buffer. 100 I E E E E l e c t r i f i cati o n M agaz ine / MARCH 2021