Abstract: Lightweight, energy-dense, high-efficiency, hybrid power systems for electric aircraft including a prime mover internal combustion engine or gas turbine coupled to a self-cooling polyphase axial-flux dual-Halbach-array motor/alternator where the number of phases Nphase is greater than or equal to three. The motor/alternator is connected to a regenerative power converter drive also having Nphase phases, which, in turn, is connected to a DC power bus, a battery, a battery management system, and a system controller. In some embodiments, the motor/alternator and regenerative power converter drive have a neutral connection.