Motion Control of a Hydrogen-Fueled Free-Piston Engine Generator Considering Cyclic Combustion Variations

A hydrogen-fueled free-piston engine generator (FPEG) with a mechanical-pressurized structure is adopted to enable the prototype to operate at high frequency while improving the combustion efficiency. However, in the actual experiment, the prototype cannot run stably due to the low output power and the large cyclic combustion variations of pure hydrogen. In order to solve this problem, firstly, the radius of the air-spring is parameterized to maintain the high operating frequency of the prototype while reducing the bidirectional current flow. Secondly, the current in the expansion stroke is adjusted multiple times based on the ideal displacement, not only based on the maximum pressure in the cylinder, to ensure that the prototype can maintain high dead center control accuracy under large cyclic combustion variations. Finally, the control strategy is tested by simulating the combustion variations through the modification of the combustion parameters in the mathematical model, and the simulation results show that the control accuracy of inner dead center (IDC) can be within 0.2 mm and outer dead center (ODC) within 0.5 mm under the heat engine condition of ODC 38 mm and IDC 1 mm, which has accumulated valuable experience for the next-generation prototype as well as for experiments.