A fully variable electromagnetic valve system designed for hydrogen free-piston engines

Hydrogen-fueled free-piston engine generator (FPEG) is a promising range-extender for electric vehicles, offering high efficiency and zero-carbon emissions. However, its crankshaft-less architecture causes strong coupling between combustion, piston dynamics, and gas exchange, challenging valve control. To address this, we propose an integrated solution: a variable valve timing electromagnetic actuator, a hierarchical control strategy, and a hardware-in-the-loop (HIL) validation system. A moving-coil actuator is designed for millisecond response and high frequency gas exchange demands of FPEGs. The upper control layer uses Pareto-based multi-objective optimization to generate a valve timing map for coarse power regulation, while the lower layer applies iterative learning control (ILC) to adjust valve lift for fine power tracking. A HIL platform integrating a real-time FPEG model, ECU, and valve prototype validates the strategy. Results show steady-state error reduced to ±0.1 kW, significantly outperforming single valve timing control. By leveraging cycle-to-cycle learning, the ILC-based scheme outperforms conventional feedback control in both transient response and steady-state accuracy. This work provides effective power regulation for hydrogen FPEGs.