Control of an eVTOL Series Hybrid Electric Propulsion System Using a Dual Rotor Generator

This paper proposes a series hybrid electric propulsion (SHEP) architecture for electric vertical takeoff and landing (eVTOL) aircraft based on a dual-rotor, nine-phase generator (DGe) interfaced with a nine-leg passive rectifier. The DGe integrates a permanent-magnet (PM) rotor that produces a fixed air-gap flux and a wound-field (WF) rotor that provides controllable excitation through a DC field current. Since passive rectification prevents reverse power flow and requires the generator voltage to remain compatible with the DC-link voltage, a wound-field excitation controller is developed to regulate the generator back-EMF in real time and maintain DC-link voltage stability under varying load conditions. A dynamic model of the DGe is established and used to derive the control law linking the WF excitation to the required rectified voltage. The nine-phase configuration reduces per-phase current stress and significantly lowers DC ripple compared to the three-phase case, enabling smaller DC-link capacitors and improving system robustness. The proposed architecture and control strategy are validated through simulations and experimental studies on a reduced-scale prototype, demonstrating effective DC-link voltage regulation and stable operation.